Home » Public Forums » GMCnet » disk brake upgrade
| disk brake upgrade [message #234770] |
Wed, 01 January 2014 20:51  |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
Karma: -1
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got a question on disk brake systems...looking at the TSM system for the back axles...saw a write up on doing the upgrade with cadillac parts...which way is the best?
Tom Geiger
76 Eleganza II
KCMO
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| Re: disk brake upgrade [message #234772 is a reply to message #234770] |
Wed, 01 January 2014 21:18  |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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I don't get it...what is the real problem with the 4 drum brakes on the rear of these vehicles? I don't get enough action from the rear brakes on mine, and I've adjusted them up and bled the system, but still don't seem to be getting much rear brake action and the pedal is low. I don't have the bucks to convert to a new disc setup, so finding used Cadillac parts might be an option. Where was that write up about them?
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] disk brake upgrade [message #234776 is a reply to message #234770] |
Wed, 01 January 2014 22:18 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Tom,
Somewhere I've got the parts list posted for conversion to Cadillac rear
discs. When I did it in about 2004, it cost me almost as much as Manny
charges today for the reaction arm system INCLUDING disc brakes and true
track. No way I can advise anyone to go the Cad. route. Especially since
I later found that the Cad backing plates were really not as good as the
aftermarket caliper mounts (TSM, Applied, and others). So I changed to
those -- in the 7" spacing variety and the 5-1/2" later version. None of
those can hold a candle price-wise or performance-wise to the reaction arm
system. Don't waste your money on anything less.
JMHO
Ken "Tried Most of the Options" H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
On Wed, Jan 1, 2014 at 9:51 PM, tom geiger wrote:
>
>
> got a question on disk brake systems...looking at the TSM system for the
> back axles...saw a write up on doing the upgrade with cadillac
> parts...which way is the best?
>
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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: disk brake upgrade [message #234793 is a reply to message #234770] |
Thu, 02 January 2014 07:24 |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
Karma: -1
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My hope is to improve the braking system to be able to travel through mountain regions with a tow and not get myself into a brake fade problem. With that said I'm not to hip and spending a ton of money doing it. I've spent plently enough on this motorhome already. I'm hoping to get to that solution without breaking the bank over it.
Tom Geiger
76 Eleganza II
KCMO
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| Re: disk brake upgrade [message #234799 is a reply to message #234795] |
Thu, 02 January 2014 09:50 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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I agree with what Matt said. If you are going to tow - trailer or towd - it should have brakes. I stop better with the big trailer with double axles and electric brakes than no trailer at all.
Neil
76 Eleganza now sold
Los Angeles
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| Re: [GMCnet] disk brake upgrade [message #234825 is a reply to message #234793] |
Thu, 02 January 2014 16:37 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Well, I'm on the same page. I havv e the 'reactiion arm', past scooter experience, plus what the users have to say, lead me to believe that's about all I need for my uses. The disks aren't subject to fade, but once you lock the wheel, doesn't matter much how. I expect the floated brakes will raise the speed at which it locks substantially. I don't see the cost/benefit for rear discs. I don't do many mountains.
--johnny
23' transmode norris
________________________________
From: tom geiger <tgeiger@burnsmcd.com>
To: gmclist@temp.gmcnet.org
Sent: Thursday, January 2, 2014 8:24 AM
Subject: Re: [GMCnet] disk brake upgrade
My hope is to improve the braking system to be able to travel through mountain regions with a tow and not get myself into a brake fade problem. With that said I'm not to hip and spending a ton of money doing it. I've spent plently enough on this motorhome already. I'm hoping to get to that solution without breaking the bank over it.
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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: disk brake upgrade [message #234864 is a reply to message #234793] |
Thu, 02 January 2014 21:18 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| tgeiger wrote on Thu, 02 January 2014 06:24 |
My hope is to improve the braking system to be able to travel through mountain regions with a tow and not get myself into a brake fade problem. With that said I'm not to hip and spending a ton of money doing it. I've spent plently enough on this motorhome already. I'm hoping to get to that solution without breaking the bank over it.
|
I'm not against any of the brake upgrades, but you sound like you have been infected with forum paranoia  A stock brake system if it is set up correctly will let you travel safely anywhere in this country without even thinking about it. There' a natural tendency here for people to immediately look at alternatives if a stock system isn't performing. People here are innovative and love to dabble in ways to improve the coach. But that's not for everyone. I run stock brakes in the mountains here and have never experienced fade nor in-ability to stop. GM designed a safe and well performing coach in the 70's and if maintained and adjusted correctly, will perform well to current standards. The problem is that most people here bought old coaches and have never experienced one that is in or close to design intent. If you buy a frapped out coach, you get what you paid for. Given all that, there's nothing wrong with stopping quicker or accelerating faster--that's always the chalenge and fun part, but your wallet can suffer dramatically. If you follow car magazines or Autoweek on TV you will see that modern cars will stop from 60mph anywhere from about 125 ft down to 110 feet. Those that stop in 110 feet will say that anything else is dangerous--that's hype and great for enthusiasts but not practical for normal people.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] disk brake upgrade [message #234900 is a reply to message #234864] |
Fri, 03 January 2014 05:48 |
scott cowden
Messages: 170
Registered: February 2004
Karma: 0
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> The problem is that most people here bought old coaches and have never experienced one that is in or close to design intent.
Bob;
I think you hit the nail on the head there. I'd chime in and say that many owners through no fault of their own lack a complete understanding of how the brake system really operates and this results in a lot of uncertainty and confusion.
Other than updating to Jim B's modern flex lines, my system is bone stock and works well enough that I have little interest in major mods.
I have boiled the fluid once down a really long twisty constant-brake-needed downhill while towing 3,000 towed with no brake assist. To my mind, it was an extreme event scary as it was at the time.
When I read many of the troubling accounts here, one of the things often on my mind is 'proportioning valve' which, once poor wheel cylinders and shoe adjustment are addressed, should be the next thing checked but almost never is.
If you've had a problem with rear brakes like a blown line or a boil over event the very next thing i'd recommend checking is the prop valve as if it's moved due to a pressure difference front to rear, the system will never work properly until the thing is re-centered/reset. After 40 years, these puppies tend to be gummed up and often can't be reset without manual intervention or replacement.
GMC's have a good but basic brake system. All the parts have to be in good operating condition for it to perform well, though.
Just my humble red-neck spin on it or a very chilly Friday morning. -25 here in Halifax today.
Scott
'74 x-Glacier
Normally in Newmarket ON
Sent from my iPad
On 2014-01-02, at 11:18 PM, "Bob de Kruyff" <NEXT2POOL@AOL.COM> wrote:
> ctly, will perform well to current standards. If you buy a frapped out coach, you get what you paid for. Given all that, there's nothing wrong with stopping quicker or accelerating faster--that's always the chalenge a
> nd fun part, but your wallet can suffer dramatically. If you follow car magazines or Autoweek on TV you will see that modern cars will stop from 60mph anywhere from about 125 ft down to 110 feet. Those that stop in 110 feet will say that anything else is dangerous--that's hype and great for enthusiasts but not practical for normal people.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
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| Re: [GMCnet] disk brake upgrade [message #234904 is a reply to message #234900] |
Fri, 03 January 2014 06:47 |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
Karma: 7
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| scott cowden wrote on Fri, 03 January 2014 05:48 |
> The problem is that most people here bought old coaches and have never experienced one that is in or close to design intent.
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This. The Birch's brakes were so bad we almost rear ended a new honda on the test drive - I towed it straight to the shop where we replaced the flex lines and MC/Booster. Better, but still not right. Then we replaced the proportion valve and on the first test of the brakes was able to do a complete inventory of the coach as everything not fastened down flew forward and came to rest in the cockpit.
Now, the rest of my system did not need work. If the whole system is shot it may make sense to "go whole hog" on a new 6 wheel disc system.
Do what makes you happy. For me it was a new ss exhaust shipped from the other side of the country when a $100 bill at the local exhaust shop would have probably fixed it... 
"Forum paranoia". I like it. I have indulged in it myself.
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
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| Re: disk brake upgrade [message #234905 is a reply to message #234770] |
Fri, 03 January 2014 07:13 |
tgeiger
Messages: 518
Registered: February 2006
Location: kansas city
Karma: -1
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Senior Member |
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Thanks for all the input guys. I'm not one that want's to skimp on saftey items and am concerned about some plans coming this year to travel through some mountain regions. With that said I am hoping I place my money into this motorhome the best places it can be...I'm always wanting to make the sensible improvments. If I can have the existing system checked for it's best performance then I will do that. I've got a good mechanic that can address this. Appreciate the information from all and I will consult more over this issue that will hopefully give me a good plan to assure safe travels. Thanks all!! Your the best!
Tom Geiger
76 Eleganza II
KCMO
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| Re: disk brake upgrade [message #234915 is a reply to message #234770] |
Fri, 03 January 2014 09:13 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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Murphy's Law really got me this fall. A lot of details built up to this so I will skip to the Master cylinder part. So...I put in a new 34mm master to more closely match some other up grades I did on the brake system. I went through five....count them FIVE MC's that failed at the work bench. Four of them would not bench bleed properly and one in the middle of those four that did bleed out OK, leaked out the back seal. I've been doing this sort of thing since I was 14yrs old, taught auto-mechanics for several years, had a business out of my garage, and worked as a second job as a mechanic for a lot of years and never encountered something like this. I began to doubt my own skills. Even took two of the MC's back to the parts store and had them do the bench bleed where it failed for them. What I finally came to the conclusion was is that each MC that was ordered, came from one of the other chain stores in the system. They did not have in stock, so they got it from another in the chain somewhere in the country. Each time it was a MC that was the last one they had on the shelf. The 34mm MC is not a mover...apparently they do not sell many of them any more, so they were all MC's that had been sitting on the shelf for several (or more) years. My guess is that the seals/cups, over time seized to the metal bore. When I poured brake fluid in to bench bleed them, the seals failed on the first push breaking away from the bore. In every case where this happened, it was the front seal that failed, so that the front portion of the MC would not hold pressure...leaked down. After 5 of them, I borrowed a old used "OEM" MC from a friend. It still had brake fluid in the reservoirs, all be it muddy. I bench bled it with about a quart of brake fluid until it came out clear, installed it and now have great brakes...drove it 2100mi to California.
Sometimes I wish Murphy would just take a vacation...
Larry
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: [GMCnet] disk brake upgrade [message #234970 is a reply to message #234864] |
Fri, 03 January 2014 19:27 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Bob,
My sentiments EXACTLY!
I find it hilarious when individuals come on here forty years after the GMC was designed and make statements like "the brakes,
suspension, steering, etc. weren't designed properly." I will agree that the design may not have been optimized and compromises were
made for cost / selling price reasons.
A lot of people here seem to forget the people that designed the GMC were PROFESSIONAL engineers who specialized in a specific
discipline such as suspension, brakes, steering, engine, transmission, etc.
While the people the come up with the upgrades are clever, they are seat of the pants engineers. PLEASE don't think I'm criticizing
them for that or there's anything wrong with what they've come up with but I doubt that any of the aftermarket parts available were
engineered and tested to the extent and manner as the OEM systems.
There are a couple of things that baffle me regarding the design:
1) Why GMC didn't set the front track at the same width as the rear track. I understand they made new axles for the GMC so I don't
understand why they didn't move the upper and lower control arm mounting points outwards to align the front and rear wheels.
2) Why GMC set up the ride height higher in the front than the rear. People have stated it was done to achieve greater caster. They
could have adjusted the relationship between the upper and lower control arms to get as much camber as they wanted.
Regards,
Rob M.
-----Original Message-----
From: Bob de Kruyff
I'm not against any of the brake upgrades, but you sound like you have been infected with forum paranoia :) A stock brake system if
it is set up correctly will let you travel safely anywhere in this country without even thinking about it. There' a natural tendency
here for people to immediately look at alternatives if a stock system isn't performing. People here are innovative and love to
dabble in ways to improve the coach. But that's not for everyone. I run stock brakes in the mountains here and have never
experienced fade nor in-ability to stop. GM designed a safe and well performing coach in the 70's and if maintained and adjusted
correctly, will perform well to current standards. The problem is that most people here bought old coaches and have never
experienced one that is in or close to design intent. If you buy a frapped out coach, you get what you paid for. Given all that,
there's nothing wrong with stopping quicker or accelerating faster--that's always the challenge and fun part, but your wallet can
suffer dramatically. If you follow car magazines or Autoweek on TV you will see that modern cars will stop from 60mph anywhere from
about 125 ft down to 110 feet. Those that stop in 110 feet will say that anything else is dangerous--that's hype and great for
enthusiasts but not practical for normal people.
--
Bob de Kruyff
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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 #235007 is a reply to message #234970] |
Fri, 03 January 2014 22:42 |
Ronald Pottol
Messages: 505
Registered: September 2012
Location: Redwood City, California
Karma: -2
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Senior Member |
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Well, there are always compromises. The reaction arm set up is much like
the paralever rear suspension many BMW motorcycles, which showed up more
than a decade after the GMC. The could have built it, but it may not have
occurred to them, or it would have cost too much money.
The Ford Explorers with the exploding tires were because when Ford was
almost ready to begin production, they realized it was too roll over prone,
but the parts were all ready being made (I believe, could be wrong about
that, but it was very late in the design process), to fix the roll over,
they reduced the tire inflation (only 18psi!) and dropped the load to 900
pounds. Yes, a couple of fat people, and you are over weight, or loose just
a little air from your tire.... I'd assume it was the same sort of bean
counter who speced tired that couldn't handle the speeds of 1960s muscle
cars striking again.
I'd bet that some or all of those issues boiled down to not realizing the
implications until it was too late to fix cheaply, and deciding to live
with it.
Ron
On Fri, Jan 3, 2014 at 5:27 PM, Robert Mueller <robmueller@iinet.net.au>wrote:
> Bob,
>
> My sentiments EXACTLY!
>
> I find it hilarious when individuals come on here forty years after the
> GMC was designed and make statements like "the brakes,
> suspension, steering, etc. weren't designed properly." I will agree that
> the design may not have been optimized and compromises were
> made for cost / selling price reasons.
>
> A lot of people here seem to forget the people that designed the GMC were
> PROFESSIONAL engineers who specialized in a specific
> discipline such as suspension, brakes, steering, engine, transmission, etc.
>
> While the people the come up with the upgrades are clever, they are seat
> of the pants engineers. PLEASE don't think I'm criticizing
> them for that or there's anything wrong with what they've come up with but
> I doubt that any of the aftermarket parts available were
> engineered and tested to the extent and manner as the OEM systems.
>
> There are a couple of things that baffle me regarding the design:
>
> 1) Why GMC didn't set the front track at the same width as the rear track.
> I understand they made new axles for the GMC so I don't
> understand why they didn't move the upper and lower control arm mounting
> points outwards to align the front and rear wheels.
>
> 2) Why GMC set up the ride height higher in the front than the rear.
> People have stated it was done to achieve greater caster. They
> could have adjusted the relationship between the upper and lower control
> arms to get as much camber as they wanted.
>
> Regards,
> Rob M.
>
>
> -----Original Message-----
> From: Bob de Kruyff
>
> I'm not against any of the brake upgrades, but you sound like you have
> been infected with forum paranoia :) A stock brake system if
> it is set up correctly will let you travel safely anywhere in this country
> without even thinking about it. There' a natural tendency
> here for people to immediately look at alternatives if a stock system
> isn't performing. People here are innovative and love to
> dabble in ways to improve the coach. But that's not for everyone. I run
> stock brakes in the mountains here and have never
> experienced fade nor in-ability to stop. GM designed a safe and well
> performing coach in the 70's and if maintained and adjusted
> correctly, will perform well to current standards. The problem is that
> most people here bought old coaches and have never
> experienced one that is in or close to design intent. If you buy a frapped
> out coach, you get what you paid for. Given all that,
> there's nothing wrong with stopping quicker or accelerating faster--that's
> always the challenge and fun part, but your wallet can
> suffer dramatically. If you follow car magazines or Autoweek on TV you
> will see that modern cars will stop from 60mph anywhere from
> about 125 ft down to 110 feet. Those that stop in 110 feet will say that
> anything else is dangerous--that's hype and great for
> enthusiasts but not practical for normal people.
> --
> Bob de Kruyff
>
> _______________________________________________
> 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 #235010 is a reply to message #234970] |
Fri, 03 January 2014 23:06 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
|
|
""Bob,
My sentiments EXACTLY!
I find it hilarious when individuals come on here forty years after the GMC was designed and make statements like "the brakes,
suspension, steering, etc. weren't designed properly." I will agree that the design may not have been optimized and compromises were
made for cost / selling price reasons.
A lot of people here seem to forget the people that designed the GMC were PROFESSIONAL engineers who specialized in a specific
discipline such as suspension, brakes, steering, engine, transmission, etc.
While the people the come up with the upgrades are clever, they are seat of the pants engineers. PLEASE don't think I'm criticizing
them for that or there's anything wrong with what they've come up with but I doubt that any of the aftermarket parts available were
engineered and tested to the extent and manner as the OEM systems.
There are a couple of things that baffle me regarding the design:
1) Why GMC didn't set the front track at the same width as the rear track. I understand they made new axles for the GMC so I don't
understand why they didn't move the upper and lower control arm mounting points outwards to align the front and rear wheels.
2) Why GMC set up the ride height higher in the front than the rear. People have stated it was done to achieve greater caster. They
could have adjusted the relationship between the upper and lower control arms to get as much camber as they wanted.""
Rob, I can only guess at some of those questions since I wasn't on the GMC team. However, I can give opinions since I was involved in similar programs. The track difference was a bit underestimated and we did the same thing on some of our cars at the time--namely the Chevy Nova. We met with a lot of negative resistance and claims of crab tracking that finally we had to fix. As far as the ride heights, we usually set front heights based on clearance of the engine oil pan to ground at full jounce and let the rear follow. I hate to say it but the engineers that were assigned to the motorhome project were rejects from major truck programs. It's one of those inflamatory realities that happens when management expects the mainstream organizations to contribute to so called special projects. I recall when I was told to give up 110 engineers to the new Saturn project. I gave them my worst engineers. In the end, most of them did quite well with a new challenge. You need to realize that any engineers on the medium duty truck group were not the sharpest knives in the drawer to begin with even before reassignment to the motorhome project.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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