Home » Public Forums » GMCnet » Re: [GMCnet] disk brake upgrade
| Re: [GMCnet] disk brake upgrade [message #234816] |
Thu, 02 January 2014 14:43  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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> Engine braking is the way to control descent.
I try not to argue with Matt because he's far more experienced
than virtually anybody here. But, I've had extensive discussions
with Manny on this topic. Manny is, as far as I can tell,
the world's expert on GMC motorhome transmissions.
Engine braking is fine in a light vehicle, but not, apparently,
in a GMC. It's just too heavy, and you will immediately
start burning up your transmission clutch plates.
Having always been taught to use engine braking,
I tried arguing all sorts of "what if" scenarios, but
the bottom line in all cases was: don't do it in a GMC
(unless it's an emergency).
To paraphrase Manny: use the brakes, that's what they're for,
and they're much cheaper and easier to fix than the tranny.
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] disk brake upgrade [message #234819 is a reply to message #234816] |
Thu, 02 January 2014 15:21  |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Yeah, it may well be that is the place where GM's engineering falls short.
5 years as a school bus driver makes me very unhappy at the idea of using
the brakes to hold a speed, rather than the motor, and the brakes only to
change my speed.
But Manny knows rather a lot about this application.
On Thu, Jan 2, 2014 at 12:43 PM, KB <kab7@sonic.net> wrote:
> > Engine braking is the way to control descent.
>
> I try not to argue with Matt because he's far more experienced
> than virtually anybody here. But, I've had extensive discussions
> with Manny on this topic. Manny is, as far as I can tell,
> the world's expert on GMC motorhome transmissions.
>
> Engine braking is fine in a light vehicle, but not, apparently,
> in a GMC. It's just too heavy, and you will immediately
> start burning up your transmission clutch plates.
>
> Having always been taught to use engine braking,
> I tried arguing all sorts of "what if" scenarios, but
> the bottom line in all cases was: don't do it in a GMC
> (unless it's an emergency).
>
> To paraphrase Manny: use the brakes, that's what they're for,
> and they're much cheaper and easier to fix than the tranny.
>
> Karen
> 1973 23'
> 1975 26'
>
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Plato seems wrong to me today.
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| Re: [GMCnet] disk brake upgrade [message #234820 is a reply to message #234819] |
Thu, 02 January 2014 15:36 |
appie
Messages: 902
Registered: April 2013
Location: denmark
Karma: 2
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ronald
your bus was that with automatic transmission?
We are used to using enginebreak in Europe, but that is with manual gearboxes
There is no problem there of course
Appie
eleganza 76 "Olga" now sadly sold
6 wheel discbrake
Quadrabags
Springfield stage 2 462 olds
Manny tranny
( pictures at http://www.gmcmhphotos.com/photos/g6489-olga.html
Fulltiming in Europe july 2014 til july 2016
Denmark
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| Re: [GMCnet] disk brake upgrade [message #234821 is a reply to message #234820] |
Thu, 02 January 2014 15:51 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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I drove both, no distinction was made in the training regarding hill
descents (though a fun place to double clutch your downshifts!). 4 speed
auto, manual with and without syncromesh. All straight 6 (vertical NA and
turbo 4 stroke, horizontal two stroke supercharged and turbo supercharged).
I think a chopped and channeled Crown school bus (those are the ones that
don't have a flat panel (aside from the glass) on them, fully rounded front
and back, curved sides and top) would look very cool.
http://www.flickr.com/groups/crownschoolbus/ Unique art deco look, Gillig
look like a cheap knock off.
On Thu, Jan 2, 2014 at 1:36 PM, lenze middelberg <lenze@middelberg.dk>wrote:
>
>
> ronald
>
> your bus was that with automatic transmission?
> We are used to using enginebreak in Europe, but that is with manual
> gearboxes
> There is no problem there of course
> --
> Appie
> eleganza 76 "Olga" ( pictures at
> http://www.gmcmhphotos.com/photos/g6489-olga.html and
> https://picasaweb.google.com/101021920836990233644/GMCMHOlga02)
> Volvo v70
> Denmark
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--
Plato seems wrong to me today.
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| Re: [GMCnet] disk brake upgrade [message #234824 is a reply to message #234816] |
Thu, 02 January 2014 16:35 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Karen,
Hmmmmm, I have talked to Manny about this too and I came away with a different conclusion which was that it was OK to use Super to
engine brake but NOT to pull it down into Super at too high a speed which, IIRC, was 40mph.
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: KB
> Engine braking is the way to control descent.
I try not to argue with Matt because he's far more experienced
than virtually anybody here. But, I've had extensive discussions
with Manny on this topic. Manny is, as far as I can tell,
the world's expert on GMC motorhome transmissions.
Engine braking is fine in a light vehicle, but not, apparently,
in a GMC. It's just too heavy, and you will immediately
start burning up your transmission clutch plates.
Having always been taught to use engine braking,
I tried arguing all sorts of "what if" scenarios, but
the bottom line in all cases was: don't do it in a GMC
(unless it's an emergency).
To paraphrase Manny: use the brakes, that's what they're for,
and they're much cheaper and easier to fix than the tranny.
Karen
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] disk brake upgrade [message #234826 is a reply to message #234824] |
Thu, 02 January 2014 16:37 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Senior Member |
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That makes my brain much happier to hear, yeah, use the brakes to adjust
your speed, and then the engine to maintain it, and slow to a non crazy
speed before downshifting the transmission.
On Thu, Jan 2, 2014 at 2:37 PM, Robert Mueller <robmueller@iinet.net.au>wrote:
> Karen,
>
> Hmmmmm, I have talked to Manny about this too and I came away with a
> different conclusion which was that it was OK to use Super to
> engine brake but NOT to pull it down into Super at too high a speed which,
> IIRC, was 40mph.
>
> Regards,
> Rob M.
> Sydney, Australia
>
>
> -----Original Message-----
> From: KB
>
> > Engine braking is the way to control descent.
>
> I try not to argue with Matt because he's far more experienced
> than virtually anybody here. But, I've had extensive discussions
> with Manny on this topic. Manny is, as far as I can tell,
> the world's expert on GMC motorhome transmissions.
>
> Engine braking is fine in a light vehicle, but not, apparently,
> in a GMC. It's just too heavy, and you will immediately
> start burning up your transmission clutch plates.
>
> Having always been taught to use engine braking,
> I tried arguing all sorts of "what if" scenarios, but
> the bottom line in all cases was: don't do it in a GMC
> (unless it's an emergency).
>
> To paraphrase Manny: use the brakes, that's what they're for,
> and they're much cheaper and easier to fix than the tranny.
>
> Karen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Plato seems wrong to me today.
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1973 26' GM outfitted
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| Re: [GMCnet] disk brake upgrade [message #234828 is a reply to message #234816] |
Thu, 02 January 2014 16:48 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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I has learnt something, thankyew!
--johnny
________________________________
From: KB <kab7@sonic.net>
To: gmclist@temp.gmcnet.org
Sent: Thursday, January 2, 2014 3:43 PM
Subject: Re: [GMCnet] disk brake upgrade
> Engine braking is the way to control descent.
I try not to argue with Matt because he's far more experienced
than virtually anybody here. But, I've had extensive discussions
with Manny on this topic. Manny is, as far as I can tell,
the world's expert on GMC motorhome transmissions.
Engine braking is fine in a light vehicle, but not, apparently,
in a GMC. It's just too heavy, and you will immediately
start burning up your transmission clutch plates.
Having always been taught to use engine braking,
I tried arguing all sorts of "what if" scenarios, but
the bottom line in all cases was: don't do it in a GMC
(unless it's an emergency).
To paraphrase Manny: use the brakes, that's what they're for,
and they're much cheaper and easier to fix than the tranny.
Karen
1973 23'
1975 26'
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] disk brake upgrade [message #234832 is a reply to message #234828] |
Thu, 02 January 2014 17:25 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Planned stops or slowing with knowledge of the terrain is one thing. Panic
stops where one needs to approach "wheel lockup " to avoid running into
something or someone is another kettle of fish. When disc brakes first were
fitted to motor cycles, I would marvel at the front tire just carrying a
ring of smoke as it stopped without actual wheel lockup. Talk about stop.
Giant stride forward from the old four leading shoe brakes that they
replaced. If you could even manage to get to that point (smoke ring), you
just add in a touch more cable effort and you were on your butt so quick,
it was hard to tell what happened. Same thing applies on GMC disc systems.
Pedal feel is way different with discs than it is with drums. But braking
effect is more precise, after they (and the driver) are well broken in,
especially with the reaction arm. The difference is sliding the wheels and
hitting something, vs getting the coach stopped without any damage except
perhaps a change of underwear. I know, drive it like a truck, you say. Not
always possible in intense traffic.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Jan 2, 2014 2:48 PM, "Johnny Bridges" <jhbridges@ymail.com> wrote:
> I has learnt something, thankyew!
>
> --johnny
>
>
>
> ________________________________
> From: KB <kab7@sonic.net>
> To: gmclist@temp.gmcnet.org
> Sent: Thursday, January 2, 2014 3:43 PM
> Subject: Re: [GMCnet] disk brake upgrade
>
>
> > Engine braking is the way to control descent.
>
> I try not to argue with Matt because he's far more experienced
> than virtually anybody here. But, I've had extensive discussions
> with Manny on this topic. Manny is, as far as I can tell,
> the world's expert on GMC motorhome transmissions.
>
> Engine braking is fine in a light vehicle, but not, apparently,
> in a GMC. It's just too heavy, and you will immediately
> start burning up your transmission clutch plates.
>
> Having always been taught to use engine braking,
> I tried arguing all sorts of "what if" scenarios, but
> the bottom line in all cases was: don't do it in a GMC
> (unless it's an emergency).
>
> To paraphrase Manny: use the brakes, that's what they're for,
> and they're much cheaper and easier to fix than the tranny.
>
> Karen
> 1973 23'
> 1975 26'
>
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] disk brake upgrade [message #234833 is a reply to message #234816] |
Thu, 02 January 2014 17:48 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Karen,
Manny gave me the same lecture when he was here. Quite a change for me --
I've used the transmissions of every vehicle I've driven since the first
MG-TD in '54. I VERY rarely touch the brakes, even on the steepest grades
in the country. When I do, it's because the transmission and engine
braking can't do the job so I have to intermittenlty brake to well below
the target speed.
Manny finally said the cut of the gears is the ultimate culprit.
No question about one thing: Brake pads are cheaper than transmission
overhauls.
I'll probably have trouble breaking my 60 year habit, but if I do, I'll
continue to sync engine speed and road speed before down shifting. :-)
Ken H.
On Thu, Jan 2, 2014 at 3:43 PM, KB <kab7@sonic.net> wrote:
> > Engine braking is the way to control descent.
>
> I try not to argue with Matt because he's far more experienced
> than virtually anybody here. But, I've had extensive discussions
> with Manny on this topic. Manny is, as far as I can tell,
> the world's expert on GMC motorhome transmissions.
>
> Engine braking is fine in a light vehicle, but not, apparently,
> in a GMC. It's just too heavy, and you will immediately
> start burning up your transmission clutch plates.
>
> Having always been taught to use engine braking,
> I tried arguing all sorts of "what if" scenarios, but
> the bottom line in all cases was: don't do it in a GMC
> (unless it's an emergency).
>
> To paraphrase Manny: use the brakes, that's what they're for,
> and they're much cheaper and easier to fix than the tranny.
>
> Karen
> 1973 23'
> 1975 26'
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] disk brake upgrade [message #234836 is a reply to message #234824] |
Thu, 02 January 2014 18:36 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| Robert Mueller wrote on Thu, 02 January 2014 14:35 |
Karen,
Hmmmmm, I have talked to Manny about this too and I came away with a different conclusion which was that it was OK to use Super to
engine brake but NOT to pull it down into Super at too high a speed which, IIRC, was 40mph.
Regards,
Rob M.
Sydney, Australia
|
My daddy always taught me to downshift. He had manual transmissions.
I make at least one trip East each year, and pulled into S for most descents. I do the Grapevine in CA once or twice a year. Oregon coast once a year. I had a stock or rebuilt transmission failure.
Manny, put in one of his MannyTrannys. A few months later and it sometimes was in Drive but would shift unexpectedly into second when not pulling just floating. The odd part was that if you let off the gas it idled. I called it Second-freewheel. The book says "no transmission braking". It got so it was in Second-Freewheel more than Drive ratio. Manny was puzzled and pulled it apart and found wear symptoms that surprised him. When the second rebuilt Manny Tranny slipped into Second-freewheel while in Drive Manny could not believe it. He jerked it out and found the same issues. I was feeling like a chump at this point, causing all this trouble. I was getting pretty good at doing the jacking work from the top.
At this point we had the talk. Yes, I was a big shifter down. No, not jerking it in, but rather using the brake and a then planned easing it into S for a hill. But yes, then running down in S for the steep hills. Manny said, "Stop doing that. You have 6 wheel disk brakes, right? Use them."
I did and struggled up Monarch pass in S and glided down the other side in Drive. Coming back, no S down hills. Trans is working fine.
Manny is a great guy and would probably replace the trans until his strength failed, but I heard him. The transmissionwas never designed to try to hold 12K lbs. back on a hill. He talked all about thrust and bevel and showed me parts from his bins but I remember, "Stop doing that".
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] disk brake upgrade [message #234847 is a reply to message #234836] |
Thu, 02 January 2014 19:37 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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George,
Manny told me he also had a talk with you about DFCO. Now that REALLY
seems extreme!
At least for a while, I'm going to stop using it, but my discussion with
Doc Frohmader make me think that probably was NOT a contributor to my valve
problem.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
On Thu, Jan 2, 2014 at 7:36 PM, George Beckman <gbeckman@pggp.com> wrote:
>
> ...
> At this point we had the talk. Yes, I was a big shifter down. No, not
> jerking it in, but rather using the brake and a then planned easing it into
> S for a hill. But yes, then running down in S for the steep hills. Manny
> said, "Stop doing that. You have 6 wheel disk brakes, right? Use them."
>
> I did and struggled up Monarch pass in S and glided down the other side in
> Drive. Coming back, no S down hills. Trans is working fine.
>
> Manny is a great guy and would probably replace the trans until his
> strength failed, but I heard him. The transmissionwas never designed to try
> to hold 12K lbs. back on a hill. He talked all about thrust and bevel and
> showed me parts from his bins but I remember, "Stop doing that".
>
...
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] disk brake upgrade [message #234856 is a reply to message #234816] |
Thu, 02 January 2014 20:43 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| KB wrote on Thu, 02 January 2014 13:43 |
> Engine braking is the way to control descent.
I try not to argue with Matt because he's far more experienced
than virtually anybody here. But, I've had extensive discussions
with Manny on this topic. Manny is, as far as I can tell,
the world's expert on GMC motorhome transmissions.
Engine braking is fine in a light vehicle, but not, apparently,
in a GMC. It's just too heavy, and you will immediately
start burning up your transmission clutch plates.
Having always been taught to use engine braking,
I tried arguing all sorts of "what if" scenarios, but
the bottom line in all cases was: don't do it in a GMC
(unless it's an emergency).
To paraphrase Manny: use the brakes, that's what they're for,
and they're much cheaper and easier to fix than the tranny.
Karen
1973 23'
1975 26'
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I use engine braking extensively along with moderate braking when needed. It hasn't caused a problem for me over the last 20 years.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] disk brake upgrade [message #234860 is a reply to message #234826] |
Thu, 02 January 2014 20:53 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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""That makes my brain much happier to hear, yeah, use the brakes to adjust
your speed, and then the engine to maintain it, and slow to a non crazy
speed before downshifting the transmission.""
Unless the trans has been modified, it won't go into any gear it doesn't want to regardless of the the shift lever position. It won't downshift too soon nor upshift too late. You can pull it into low at 80 and it will downshift when it is ready--normaly the regulated max shift points. In the mountains here, I routinely leave it in low and it will shift all the way into 3rd and all the way back down to 1st when it gets to an appropriate shift point. This has always been the logic for GM Hydramatic transmissions in order to prevent damage. High engine RPM's don't hurt a thing because generally the loads are lower.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] disk brake upgrade [message #234861 is a reply to message #234836] |
Thu, 02 January 2014 20:57 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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When I had the second gear freewheel symptom in the THM 400 in my 69 Firebird, I was told that it was a failure of the rear pump. Could not let off the throttle in drive until 80 mph or it would drop into second gear and freewheel. Above 80 it would stay in drive and give engine braking.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] disk brake upgrade [message #234863 is a reply to message #234847] |
Thu, 02 January 2014 21:10 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| Ken Henderson wrote on Thu, 02 January 2014 17:37 |
George,
Manny told me he also had a talk with you about DFCO. Now that REALLY
seems extreme!
|
I don't think DFCO (Deceleration Fuel CutOff) causes much difference in the drag on the driveline. The thing causing drag is the extreme resistance (vacuum) at the throttle plates. When either the Quadrajet or throttlebody leaks a tiny, "idle's worth" of fuel through it does not make much power. In fact, because only one in several hundred strokes might actually fire properly, it may make for more jerking on the driveline, than a steady draw.
Matt Colie? Ideas.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] disk brake upgrade [message #234871 is a reply to message #234863] |
Thu, 02 January 2014 21:35 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| George Beckman wrote on Thu, 02 January 2014 20:10 |
| Ken Henderson wrote on Thu, 02 January 2014 17:37 |
George,
Manny told me he also had a talk with you about DFCO. Now that REALLY
seems extreme!
|
I don't think DFCO (Deceleration Fuel CutOff) causes much difference in the drag on the driveline. The thing causing drag is the extreme resistance (vacuum) at the throttle plates. When either the Quadrajet or throttlebody leaks a tiny, "idle's worth" of fuel through it does not make much power. In fact, because only one in several hundred strokes might actually fire properly, it may make for more jerking on the driveline, than a steady draw.
Matt Colie? Ideas.
|
If you have a semi modern car, it most likely has fuel cutoff on decel. It is very noticeable when it shuts off fuel. In fact the decel is so noticeable that owners complain about it untill they understand what is going on. This has been standard fare for about 20 years.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] disk brake upgrade [message #234889 is a reply to message #234871] |
Fri, 03 January 2014 00:38 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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We have data that plainly show that the Cad type rear disc are superior to
the TSM.
Al Branscom presented the data as well at Bransom onvention.
The size of the calipers are dramatic.
When we came up with the rear disc kit in 1997, I reviewed all of the kits
and non kits and settled on the Cad design as Bobby Moore, and others in
the Mid West showed us the bennifits of that unit.
Our Disc/Disc Reaction arm will out perform any other Reaction arm system.
The big problem is our price.
we cannot match the number of kits we manfacture of Manney T.
He has shown us ways to o mching and other tings to lower the cost, but we
still have the High cost units in our inventory.
Manny has lot of savy when it comes to do it on a budget.
On Thu, Jan 2, 2014 at 7:35 PM, Bob de Kruyff <NEXT2POOL@aol.com> wrote:
>
>
> George Beckman wrote on Thu, 02 January 2014 20:10
> > Ken Henderson wrote on Thu, 02 January 2014 17:37
> > > George,
> > >
> > > Manny told me he also had a talk with you about DFCO. Now that REALLY
> > > seems extreme!
> >
> >
> > I don't think DFCO (Deceleration Fuel CutOff) causes much difference in
> the drag on the driveline. The thing causing drag is the extreme resistance
> (vacuum) at the throttle plates. When either the Quadrajet or throttlebody
> leaks a tiny, "idle's worth" of fuel through it does not make much power.
> In fact, because only one in several hundred strokes might actually fire
> properly, it may make for more jerking on the driveline, than a steady draw.
> >
> > Matt Colie? Ideas.
>
> If you have a semi modern car, it most likely has fuel cutoff on decel. It
> is very noticeable when it shuts off fuel. In fact the decel is so
> noticeable that owners complain about it untill they understand what is
> going on. This has been standard fare for about 20 years.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
> _______________________________________________
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>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
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jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] disk brake upgrade [message #234891 is a reply to message #234847] |
Fri, 03 January 2014 01:18 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
|
Senior Member |
|
|
| Ken Henderson wrote on Thu, 02 January 2014 17:37 |
George,
Manny told me he also had a talk with you about DFCO. Now that REALLY
seems extreme!
|
I should add one more point to the DFCO and Second gear on down hill runs.
Yes, Manny and I did discuss DFCO but what really got his attention was when I mentioned I had a 2.73 Final Drive.
This means the trans pump is almost at idle when you let off the gas at anything under 55 MPH. I put in a 3.21 at his suggestion.
So, the 2.73 maybe was a bad as everyone said, but I loved it. Power curve smower curve. The GMC was a cruiser. Quiet. I could climb hills at 55 in second without getting over 3K RPMs. and I never thought it was that sluggish. And, I broke Gene's 8 to 10 MPG by getting 10.7 at the pumps with a carefully calibrated speedometer on a 5200 mile trip through Oregon coast, Washington, Montana, Canada, Dakotas, Iowa and then a fast trip back to CA on 80.
Not too bad other than needing a new transmission when I got back. Grrr.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] disk brake upgrade [message #234912 is a reply to message #234891] |
Fri, 03 January 2014 08:58 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
George,
The 2.73 issue is interesting. My discussion with Doc Frohmader last week
got into gear ratios. His contention is that, at least with the
high-torque Cad 500, one should run a LOW ratio. He suggests the 2.73 or
lower (says the cars used 2.41). Claims the exhausts gases will be cooler
because more of the energy from the combustion is extracted in developing
power rather than being dumped out the exhaust valve.
I haven't researched nor tried to rationalize that proposition yet; just
reporting his position. I do know several people who run 2.73's and are
happy. I've got some & may try one, especially since I'm probably through
with any mountain over 1000' high.
Ken H.
On Fri, Jan 3, 2014 at 2:18 AM, George Beckman <gbeckman@pggp.com> wrote:
>
>
> Ken Henderson wrote on Thu, 02 January 2014 17:37
> > George,
> >
> > Manny told me he also had a talk with you about DFCO. Now that REALLY
> > seems extreme!
>
>
> I should add one more point to the DFCO and Second gear on down hill runs.
>
> Yes, Manny and I did discuss DFCO but what really got his attention was
> when I mentioned I had a 2.73 Final Drive.
>
> This means the trans pump is almost at idle when you let off the gas at
> anything under 55 MPH. I put in a 3.21 at his suggestion.
>
> So, the 2.73 maybe was a bad as everyone said, but I loved it. Power curve
> smower curve. The GMC was a cruiser. Quiet. I could climb hills at 55 in
> second without getting over 3K RPMs. and I never thought it was that
> sluggish. And, I broke Gene's 8 to 10 MPG by getting 10.7 at the pumps with
> a carefully calibrated speedometer on a 5200 mile trip through Oregon
> coast, Washington, Montana, Canada, Dakotas, Iowa and then a fast trip back
> to CA on 80.
>
> Not too bad other than needing a new transmission when I got back. Grrr.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] disk brake upgrade [message #234939 is a reply to message #234856] |
Fri, 03 January 2014 12:38 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
|
Senior Member |
|
|
Ok, Here I am...
No, I would not argue with Manny either, but I fear we are looking at two different situations.
First to answer some questions:
No DFCO should not make any difference in the engine's ability to retard.
Yes, brake shoes are less expensive to replace than clutches, but the even thought the transmission was not designed to 12K vehicle, it still should (notice he said should) not be slipping clutches with the engine turning (and running the pump). Provided you are at a road speed that is acceptable for that gear. This is why you should not try to retard by just heaving on the level.
While brake shoes and pads may be less expensive to service, Those of use that still have drum brakes have to include the thought that your brakes are heat limited. If you are not up to the "retard then roll" routine, and you allow the rear brake to fade into oblivion, that may become the least of you problems.
George's low numerical final drive problem is exactly why I would never do that or the chain ratio modification. Both of those put more torque thought the transmission components.
If you try to engage a lower gear while over speed as judged by the transmission governor, it will slip clutches until it is down to the speed it likes. This can smoke a clutch. That is true whether it is automatic or a mishandled manual.
(Little aside... road course motorcycles have oil bath clutches and an unloading mechanism to keep the rear wheel from effectively "locking-up" if the rider downshifts too early in a corner.)
A thought issue here (born out by a motoring test I did with a 460 several decades ago). The BMEP (Brake Mean Effective Pressure - how hard the combustion pushed the piston as an average down the stroke) of any engine like ours is going to be in the 70~100 psi range in a normal WOT condition. (Yes, peak my be in the 300~500 range, but it doesn't last long.) Compare that to the 15psi you could get in a closed throttle over-run condition.
While I don't doubt that Manny has seen some burned up clutches, I have to wonder if all the relevant data was collected. There is an awful lot that goes on inside of any automatic transmission and I am firmly convinced that nobody ever knew all of it until one could use a laptop it interrogate the computer that controls it and is supposed to know what is going on.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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