Home » Public Forums » GMCnet » [GMCnet] Brake pads, and the 1 ton.
| [GMCnet] Brake pads, and the 1 ton. [message #332265] |
Fri, 18 May 2018 10:58  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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How much bigger is the 1 ton brake pad then the stock GM pads? A common upgrade has Been the 80 MM GM caliper. We bought our first GMC in 2003. At every GMCMI event since. The talk has been that the original brakes left something to be desired. My thought was that. How did GM get the GMC out to the public with brakes that lacked performance in the area of braking. The problem has been how self adjusting rear drum brakes function. To self adjust properly. You have to have brisk braking in reverse. We never do that. Thus the adjuster can't do the job. So for 13 years. I jacked up the rear axles once a year to adjust the rear brakes manually. I tow all the time in the range of 17,to 24,000 GVW. Live in the flat Midwest. Been very happy with the braking of all 6 wheels. Even when we have been out West. But. To get the best braking from the original braking system. YOU MUST adjust those rear brakes once a year. Two years ago. I decided to reduce my adjusting by 50%. I installed Disc on the front rear axle only. Braking is improved. Have Quad bags with the rear disc. No reaction arm, or true track. Haven't experienced rear/rear lockup. Adjust the rears properly. Or add the rear disc first. Before trying to add more braking to the front. The front is already doing the most. Bob Dunahugh
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332267 is a reply to message #332265] |
Fri, 18 May 2018 11:57  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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I didn't notice that my coach stopped any better with the new 1 ton front end over the 80 mm calipers using performance friction pads on each . I used the police car pads on the 80mm setup . I don't ,remember the new 1 ton pads having more area just a different shape. I do believe the larger rotors will have less fad however. The original pads were asbestos I believe and they stopped pretty good compared to a lot of pads made today. My toad was a Toyota pu.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332274 is a reply to message #332265] |
Fri, 18 May 2018 15:39 |
Richard Denney
Messages: 920
Registered: April 2010
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Nothing wrong with drum brakes in normal applications. It's true that 1.)
the drums become bell-shaped and lose contact surface when they overheat,
2.) the application of braking force is non-linear making it hard to
modulate to prevent lockup on the back in the rare extreme case, and 3.)
the brakes don't ventilate well and are thus more prone to fading. The
latter is made worse by the lack of carbon metallic friction materials, and
the traditional composite materials off-gas when they get really hot, which
lubricates the brake (not in a good way). These are relative subtleties in
routine driving, but may make a difference in a long, steep downhill with a
stop at the bottom (we don't do many repeated hard braking applications as
is common in racing). I agree with everything else you wrote about drums. I
check my rear brake adjustment routinely, but it's always been okay--I do
have to back up in my driveway, though, so I get to exercise the adjusters
on every trip. Drum brakes are fiddly, though, and require disassembly to
check wear. I'm looking forward to rear disks.
Improving braking starts with the fronts--here I disagree a little with
what you wrote. Adding lots of braking capability to the rear without
balancing it at the front might result in the rears locking up before the
fronts do in a panic stop, which is Not Good. Excessive front brakes might
make them lock up earlier with respect to the rears, but that has a
relatively small effect in the panic situation compared with locking up the
rears too soon. And that's the issue with the servo action of the rear
drums--their response is non-linear while the front response is linear, so
it's hard to manage the balance between front and rear on a hard stop.
There is nothing wrong with the front disks at all--they were state of the
art in the early 70's. Using carbon-metallic pads makes them better. But
mine required high pedal effort. I might have used a sensitized booster,
which would address the pedal effort at low braking applications, but at
ultimate braking on impending lockup, the sensitized booster doesn't make
any difference. But what does make a difference is diameter. Rotor diameter
makes a linear difference in braking--a 15% increase in rotor diameter
multiplies the braking force from a given clamping force by 15%. So, 15%
better stopping force for the same pedal pressure, or 15% lower pedal
effort for the same stopping force. The bigger piston helps as much, but
the one-ton kit also has an 80mm piston. So, the pedal effort at lockup
will be lower with larger rotors, and with larger caliper pistons. Larger
both is additive. (I would add that the GMC motorhome had about the same
braking setup up as my '75 GMC pickup, despite being twice as heavy--the
pole-vaulting that unloads the rearmost wheels undermines the advantage of
six brakes).
Of course, tires do the braking, and brakes just dissipate the heat. If we
can lock up the front tires, our brakes are doing all they can in a single
panic stop. I'm not sure how many of us could lock up the fronts on our
coaches, though. (I hope your heavy towd has its own brakes, by the way.)
But heat is where the larger rotor also helps--it's a larger swept area and
dissipates more heat for a given clamping force. This may not be relevant
for one mild or moderate stop, or even for one panic stop. But repeated
applications going down the mountain builds up heat, and heat is the cause
of brake fade. Over the years of reading GMCnet, brake fade and marginal
brakes some up about as often as do front bearing woes, it seems to me, but
the consequences can be worse.
The stock brakes work fine--that's what I've used for 15 years until last
August. Pedal effort was high--the Redhead wasn't that happy with the pedal
effort--but that wasn't that unusual in the early 70's. Performance was
great compared to the competition of the day, which might well have used
drums all four corners on a poorly suspended truck chassis. But I've driven
modern motorhomes, too--we rented Winnebago Class C motorhomes during two
trips around Alaska over the last decade--and their brakes required less
effort.
Rick "whose braking foot has drawn its own conclusions" Denney
On Fri, May 18, 2018 at 11:58 AM, Bob Dunahugh wrote:
> How much bigger is the 1 ton brake pad then the stock GM pads? A common
> upgrade has Been the 80 MM GM caliper. We bought our first GMC in 2003. At
> every GMCMI event since. The talk has been that the original brakes left
> something to be desired. My thought was that. How did GM get the GMC out
> to the public with brakes that lacked performance in the area of braking.
> The problem has been how self adjusting rear drum brakes function. To
> self adjust properly. You have to have brisk braking in reverse. We never
> do that. Thus the adjuster can't do the job. So for 13 years. I jacked up
> the rear axles once a year to adjust the rear brakes manually. I tow all
> the time in the range of 17,to 24,000 GVW. Live in the flat Midwest. Been
> very happy with the braking of all 6 wheels. Even when we have been out
> West. But. To get the best braking from the original braking system. YOU
> MUST adjust those rear brakes once a year. Two years ago. I decided to
> reduce my adjusting by 50%. I installed Disc on the front rear axle only.
> Braking is improved. Have Quad bags with the rear disc. No reaction arm,
> or true track. Haven't experienced rear/rear lockup. Adjust the rears
> properly. Or add the rear disc first. Before trying to add more braking to
> the front. The front is already doing the most. Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
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--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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| Re: [GMCnet] Ideas on how you can improve your brakes. And keeping the cost down. [message #332282 is a reply to message #332273] |
Fri, 18 May 2018 18:48 |
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Tom Lins
Messages: 372
Registered: February 2004
Location: St Augustine, FL
Karma: 1
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BobDunahugh wrote on Fri, 18 May 2018 14:56
Subject line didn't cover the meat of my last E-mail. A common upgrade has Been the 80 MM GM caliper. We bought our first GMC in 2003. At every GMCMI event since. The talk has been that the original brakes left something to be desired. My thought was that. How did GM get the GMC out to the public with brakes that lacked performance in the area of braking. The problem has been how self adjusting rear drum brakes function. To self adjust properly. You have to have brisk braking in reverse. We never do that. Thus the adjuster can't do the job. So for 13 years. I jacked up the rear axles once a year to adjust the rear brakes manually. I tow all the time in the range of 17,to 24,000 GVW. Live in the flat Midwest. Been very happy with the braking of all 6 wheels. Even when we have been out West. But. To get the best braking from the original braking system. YOU MUST adjust those rear brakes once a year. Two years ago. I decided to reduce my adjusting by 50%. I installed Disc on the front rear axle only. Braking is improved. Have Quad bags with the rear disc. No reaction arm, or true track. Haven't experienced rear/rear lockup. Adjust the rears properly. Or add the rear disc first. Before trying to add more braking to the front. The front is already doing the most. Bob Dunahugh
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Bob
What are you towing that weighs 6k to 13k?
And what is your final drive ratio?
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
YOUTUBE Channel: GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332285 is a reply to message #332277] |
Fri, 18 May 2018 20:12 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Fred,
FYI
http://www.gmcmhphotos.com/photos/combination-valve/p59582-combination-valve.html
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Fred
Sent: Friday, May 18, 2018 5:09 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Brake pads, and the 1 ton.
that is interesting.. did the brake compensator remain stock or was it modified like the ones for the four, rear wheel disc
conversions?
did it require any other special components to make it work? like some type of proportioning valving to give more or less to the
drums than the
discs?
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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] Ideas on how you can improve your brakes. And keeping the cost down. [message #332292 is a reply to message #332273] |
Sat, 19 May 2018 09:16 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Tom. I tow Linda's handicap Chevy Uplander lift van at 5,000+ on a dolly. Or my 24 ft enclosed trailer with a shop, and Yenko to road race track events around the country coast to coast. The Royales are the heaviest GMC's. It's a pure stock GMC except for a 3:70 FD, and a Howell EFI with spark control on the 403. Just climbed out of Albuquerque NM,heading East. With Linda's van. 60 at the bottom. 50 at the top. Trans never shifted down. No more then half throttle. I'll never have a GMC without a 3;70, or 4:10 FD again. Towing or not. Bob Dunahugh 78 Royale
________________________________
From: Bob Dunahugh
Sent: Friday, May 18, 2018 1:56 PM
To: gmclist@list.gmcnet.org
Subject: Ideas on how you can improve your brakes. And keeping the cost down.
Subject line didn't cover the meat of my last E-mail. A common upgrade has Been the 80 MM GM caliper. We bought our first GMC in 2003. At every GMCMI event since. The talk has been that the original brakes left something to be desired. My thought was that. How did GM get the GMC out to the public with brakes that lacked performance in the area of braking. The problem has been how self adjusting rear drum brakes function. To self adjust properly. You have to have brisk braking in reverse. We never do that. Thus the adjuster can't do the job. So for 13 years. I jacked up the rear axles once a year to adjust the rear brakes manually. I tow all the time in the range of 17,to 24,000 GVW. Live in the flat Midwest. Been very happy with the braking of all 6 wheels. Even when we have been out West. But. To get the best braking from the original braking system. YOU MUST adjust those rear brakes once a year. Two years ago. I decided to reduce my adjusting by 50%. I installed Disc on the front rear axle only. Braking is improved. Have Quad bags with the rear disc. No reaction arm, or true track. Haven't experienced rear/rear lockup. Adjust the rears properly. Or add the rear disc first. Before trying to add more braking to the front. The front is already doing the most. Bob Dunahugh
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332295 is a reply to message #332293] |
Sat, 19 May 2018 09:46 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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If you drive a large domestic pickup, van, or box van in heavy traffic,
then you are already aware of the braking characteristics of heavy vehicles
with forward weight bias. GMC coaches are similar, but, throw front wheel
drive into the mix, and they become quirky.
Someone once told me when I was learning how to fly R/C model
airplanes, "Always fly 9 dumb thumbs high". That way, you can make 8 wrong
moves and still recover without crashing.
If you apply that to following distances in traffic with a GMC, it
should help with collision avoidance.
Of course, better brakes won't hurt in any case. Best bang for the
buck that I have noticed is larger rotors in front, like the ones in the 1
ton kit, and Reaction Arm brakes in the rear. Drum vs disc in the rear?
Both do the job. I lean a bit towards the discs, because of the ease of
service, and high visibility for wear components. But that is me. The drums
have better parking brake systems, IF THEY ARE MAINTAINED PROPERLY. Most
are not.
Jim Hupy
Salem, Or
78 GMC Royale 403
On May 19, 2018 7:21 AM, "Pete Smith" wrote:
"My thought was that. How did GM get the GMC out to the public with brakes
that lacked performance in the area of braking."
Brakes are far superior on modern vehicles.....even with the huge advantage
in having ABS. Even if our coaches stopped as well as they did new,
almost everything else on the road can stop much quicker.
Mine stops pretty well but I need to leave myself room.
--
Cary, NC
1978 Center Kitchen Royale.
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332301 is a reply to message #332298] |
Sat, 19 May 2018 10:50 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Some do, some don't. I find that the original master cylinder gives better
"feel" than the replacement p-30 does. If the distribution valve is faulty,
replace it.
Jim Hupy
On Sat, May 19, 2018, 8:42 AM Fred wrote:
> GMC2000 wrote on Fri, 18 May 2018 17:08
>> BobDunahugh wrote on Fri, 18 May 2018 10:58
>>> Two years ago. I decided to reduce my adjusting by 50%. I installed
> Disc on the front rear axle only. Braking is improved.
>>
>>
>> that is interesting.. did the brake compensator remain stock or was it
> modified like the ones for the four, rear wheel disc conversions?
>>
>> did it require any other special components to make it work? like some
> type of proportioning valving to give more or less to the drums than the
>> discs?
>
>
> my questions about mixing disc and drums on the rear remains. was the
> fluid system unchanged when adding only one disc per side on the rear or
> does it
> also need modification?
>
>
>
>
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| Re: [GMCnet] Brake pads, and the 1 ton. [message #332303 is a reply to message #332298] |
Sat, 19 May 2018 11:35 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Fred,
When I installed all disc brakes, I modified the combination valve:
http://www.gmcmhphotos.com/photos/g3510-deciphering-the-combination-valve.html
A lot of people have replaced the OEM valve with one designed for all disc
brakes.
At GMCMI Tucson, Dave Lenzi made a point of the fact that it really doesn't
matter whether you replace a PROPERLY FUNCTIONING combination valve.
That's because the only function of that valve affecting brake performance
is the metering valve. That valve merely keeps the rear brakes from
applying until there's approximately 135 psi to the front brakes. That
pressure is, for disc brakes, so insignificantly low that even a gentle
stop will engage the rear brakes also VERY soon after the front brakes.
So, your choice as to what to do about the combination valve. But DO be
sure that whatever you use is functional; it CAN disable one system or the
other.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, Troy-Bilt APU, etc., etc., etc.
www.gmcwipersetc.com
On Sat, May 19, 2018 at 11:42 AM Fred wrote:
> ...
>
> my questions about mixing disc and drums on the rear remains. was the
> fluid system unchanged when adding only one disc per side on the rear or
> does it
>
> also need modification?
>
>
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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] Brake pads, and the 1 ton. [message #332307 is a reply to message #332306] |
Sat, 19 May 2018 13:26 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Fred,
I seriously doubt that you'll ever be able to tell the difference
regardless of which method you choose. 135 psi imposed by the metering
hardly has any effect on disc brakes except to move the pads lightly into
contact with the rotors. And if you disable that function, as I did, all
you're REALLY doing is disabling a potential trouble spot, IMHO. The
important functions of the combination valve are to: 1. Isolate a failed
system from the remaining system in the case of a leak. and 2. To notify
the driver by illuminating the BRAKE warning light on the dash -- which is,
itself, sort of a joke -- the driver WILL know something about the brakes
has failed! The light doesn't tell him more than that.
As for "proportioning", our combination valve does not include that
function. Including that function, which really tries to balance front and
rear braking dynamically, would require far more testing than anyone's
likely to devote to a GMC in order to determine the correct relative line
pressures.
Reaction arms really have nothing to do with it except that an adjustable
proportioning valve is one (rather unsatisfactory) way some of us
considered for relieving the rear-most brakes of flat-spotting BEFORE we
had reaction arms. Regardless of what you do to any rear brakes on a GMC,
you DO want the reaction arms, IMHO.
Don't complicate things more than necessary.
Ken H.
On Sat, May 19, 2018 at 1:27 PM Fred wrote:
> Ken Henderson wrote on Sat, 19 May 2018 11:35
>> A lot of people have replaced the OEM valve with one designed for all
> disc
>> brakes.
>
>
> yes, I had just read about this the other day. so what if one adds only
> one disc brake on each side of the rear? Bob indicates he uses the OEM valve
> but he has reaction arm system also.
>
> if one were to upgrade to only one pair of rear disc brakes and leave the
> rear drum as it is, and without a reaction arm mod., would they want to use
> a modified or a non modified valve?
>
> or would it be even better to put another valve separating the rear discs
> and the rear drums?
>
>
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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] Brake pads, and the 1 ton. [message #332310 is a reply to message #332306] |
Sat, 19 May 2018 15:03 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Fred,
Double Trouble has 80mm calipers and OEM disks on the front wheels, 80mm calipers and Caddy disks on the middle wheels, OEM drum
brakes on the rear wheels, and a brass combination valve like this one:
http://www.gmcmhphotos.com/photos/combination-valve/p59582-combination-valve.html
It stops quite well.
I have all the same parts to into the Avion in Australia and the Kingsley in the USA.
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Fred
Sent: Saturday, May 19, 2018 12:27 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Brake pads, and the 1 ton.
Ken Henderson wrote on Sat, 19 May 2018 11:35
> A lot of people have replaced the OEM valve with one designed for all disc
> brakes.
yes, I had just read about this the other day. so what if one adds only one disc brake on each side of the rear? Bob indicates he
uses the OEM valve
but he has reaction arm system also.
if one were to upgrade to only one pair of rear disc brakes and leave the rear drum as it is, and without a reaction arm mod., would
they want to use
a modified or a non modified valve?
or would it be even better to put another valve separating the rear discs and the rear drums?
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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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