Home » Public Forums » GMCnet » [GMCnet] Subject: Re: Brake problem, badly need suggestions
| [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350589] |
Mon, 09 December 2019 16:48  |
THOMAS R WHITTON
Messages: 47
Registered: September 2016
Karma: -1
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Appreciate your suggestions. I'm at my wits end.
Earlier this year the brakes on our GMC faded badly on a panic stop. I avoided a catastrophe and, in an effort to remedy the situation, I decided to install the Hydro-Boost system. It's now installed but something isn't right. I'm not sure at this point if the problem is the Hydro-Boost system or the normal brake system, beyond the Hydro-Boost. (For those not familiar, Hydro-Boost simply replaces the vacuum booster with a hydraulic ram. Everything else in the braking system remains the same. Hydro-Boost provides more pressure to the master cylinder, which should be providing much better braking.) The coach should stop almost like a new van but, unfortunately, it doesn't. I've cancelled three trips trying to get this problem resolved but the brakes still are not safe for a trip.
The problems I'm having:
Inadequate braking capability in normal driving situationssuch as traffic lights, slowing for traffic, etc.
Brakes are capable of good stopping in hard braking or panicsituations with maximum pedal effort but the brake light comes on.
Limited gradual braking with light to medium pedal effort (too much effort in normal stop and go traffic).
Excessive pedal effort to brake normally.
What's been done and added:
Rebuilt Hydro Boost unit originally from nineties Astro Van.
Custom mounting flange.
Custom rear clevis.
Custom mounting on brake pedal cylinder.
Power steering cooler from donor Ford vehicle.
New hoses to and from power steering pump, Hydro Boostunit, power steering unit and cooler.
Rebuilt original calipers from donor GMC motorhome.
New front brake hoses.
New front stainless-steel brake lines from master cylinderto distribution valve.
New distribution valve.
New master cylinder.
New power steering fluid reservoir.
New power steering pump.
Four new rear wheel cylinders.
Four new brake drums.
Front P30 calipers were replaced with restored original calipers with yellow sticky pads.
Good performance friction rear brake shoes were reinstalled.
System has been thoroughly pressure bled on all six wheels multipletimes.
Tom Whitton
26 foot updated GMC
Paducah, KY
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350592 is a reply to message #350589] |
Mon, 09 December 2019 17:23  |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Tom,
Is this a Bob Stone setup? If so I would suggest that you talk with him.
He is so close to you. He is real knowledge about the system. He
unfortunately does not use the internet. Have you checked the brake
pressure at the front and rear.
This is the one that I bought and use for testing.
<
https://www.ebay.com/itm/Leed-Brakes-BPG001-Brake-Pressure-Gauge-Kit-0-3000-psi-1-8-NPT-Thread-Includes/113986345531?hash=item1a8a1d9a3b:g:EV0AAOSw7qR d2rmM
>
J.R. Wright
GMC Great Laker
GMCGL Tech Editor
GMC Eastern States
GMCMHI
TZE Zone Restorations
78 Buskirk Custom 29.5' Stretch
75 Avion (Under going Frame up Restoration)
On Mon, Dec 9, 2019 at 3:49 PM THOMAS R WHITTON via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Appreciate your suggestions. I'm at my wits end.
> Earlier this year the brakes on our GMC faded badly on a panic stop. I
> avoided a catastrophe and, in an effort to remedy the situation, I decided
> to install the Hydro-Boost system. It's now installed but something isn't
> right. I'm not sure at this point if the problem is the Hydro-Boost system
> or the normal brake system, beyond the Hydro-Boost. (For those not
> familiar, Hydro-Boost simply replaces the vacuum booster with a hydraulic
> ram. Everything else in the braking system remains the same. Hydro-Boost
> provides more pressure to the master cylinder, which should be providing
> much better braking.) The coach should stop almost like a new van but,
> unfortunately, it doesn't. I've cancelled three trips trying to get this
> problem resolved but the brakes still are not safe for a trip.
>
> The problems I'm having:
> Inadequate braking capability in normal driving situationssuch as traffic
> lights, slowing for traffic, etc.
> Brakes are capable of good stopping in hard braking or panicsituations
> with maximum pedal effort but the brake light comes on.
>
> Limited gradual braking with light to medium pedal effort (too much effort
> in normal stop and go traffic).
>
> Excessive pedal effort to brake normally.
>
>
>
>
> What's been done and added:
> Rebuilt Hydro Boost unit originally from nineties Astro Van.
> Custom mounting flange.
>
> Custom rear clevis.
>
> Custom mounting on brake pedal cylinder.
>
> Power steering cooler from donor Ford vehicle.
>
> New hoses to and from power steering pump, Hydro Boostunit, power steering
> unit and cooler.
>
> Rebuilt original calipers from donor GMC motorhome.
>
> New front brake hoses.
>
> New front stainless-steel brake lines from master cylinderto distribution
> valve.
>
> New distribution valve.
>
> New master cylinder.
>
> New power steering fluid reservoir.
>
> New power steering pump.
>
> Four new rear wheel cylinders.
>
> Four new brake drums.
>
> Front P30 calipers were replaced with restored original calipers with
> yellow sticky pads.
>
> Good performance friction rear brake shoes were reinstalled.
>
> System has been thoroughly pressure bled on all six wheels multipletimes.
>
>
>
>
> Tom Whitton
>
> 26 foot updated GMC
>
> Paducah, KY
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Brake problem, badly need suggestions [message #350593 is a reply to message #350591] |
Mon, 09 December 2019 17:39 |
Mike Kelley
Messages: 467
Registered: February 2017
Karma: -2
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Senior Member |
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Tom W.:
I concur w/ J R - call Bob Stone - He is the Hydro boost expert and a good guy - just give him time to understand what all you have done and then to explain his thoughts!
Mike/The Corvair a holic
P S - I have his phone number if you need it!
Sent from my iPhone
> On Dec 9, 2019, at 5:29 PM, Matt Colie via Gmclist wrote:
>
> Tom,
>
> It sure looks like you have covered everything, and I have never done any work on a Hydroboost. What I can imagine is that the servo valve in the
> booster is not set up properly, not unlike when the pushrod in a sensitized booster is the wrong length. I say all this, but I do not know how to
> check or change it with a Hydroboost. I can tell you that I had to help out a sensitized booster install that had almost no brakes at all.
>
> I hope some that knows more comes along soon.
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350596 is a reply to message #350589] |
Mon, 09 December 2019 19:36 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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Seems to me what makes the brake light come on is differential pressure
between brake circuits. If the brake light comes on only on hard braking, I
suspect air in the system somewhere. Given how hard it was for me to bleed
my system, I don’t doubt the difficulty for even experienced mechanics to
get all the air out.
I recall hearing KenH tell the story of bleeding every flare joint, on
Bobby Moore’s insistence.
Rick “who spent two days bleeding about two gallons through the system
before being (somewhat) satisfied” Denney
On Mon, Dec 9, 2019 at 5:49 PM THOMAS R WHITTON via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Appreciate your suggestions. I'm at my wits end.
> Earlier this year the brakes on our GMC faded badly on a panic stop. I
> avoided a catastrophe and, in an effort to remedy the situation, I decided
> to install the Hydro-Boost system. It's now installed but something isn't
> right. I'm not sure at this point if the problem is the Hydro-Boost system
> or the normal brake system, beyond the Hydro-Boost. (For those not
> familiar, Hydro-Boost simply replaces the vacuum booster with a hydraulic
> ram. Everything else in the braking system remains the same. Hydro-Boost
> provides more pressure to the master cylinder, which should be providing
> much better braking.) The coach should stop almost like a new van but,
> unfortunately, it doesn't. I've cancelled three trips trying to get this
> problem resolved but the brakes still are not safe for a trip.
>
> The problems I'm having:
> Inadequate braking capability in normal driving situationssuch as traffic
> lights, slowing for traffic, etc.
> Brakes are capable of good stopping in hard braking or panicsituations
> with maximum pedal effort but the brake light comes on.
>
> Limited gradual braking with light to medium pedal effort (too much effort
> in normal stop and go traffic).
>
> Excessive pedal effort to brake normally.
>
>
>
>
> What's been done and added:
> Rebuilt Hydro Boost unit originally from nineties Astro Van.
> Custom mounting flange.
>
> Custom rear clevis.
>
> Custom mounting on brake pedal cylinder.
>
> Power steering cooler from donor Ford vehicle.
>
> New hoses to and from power steering pump, Hydro Boostunit, power steering
> unit and cooler.
>
> Rebuilt original calipers from donor GMC motorhome.
>
> New front brake hoses.
>
> New front stainless-steel brake lines from master cylinderto distribution
> valve.
>
> New distribution valve.
>
> New master cylinder.
>
> New power steering fluid reservoir.
>
> New power steering pump.
>
> Four new rear wheel cylinders.
>
> Four new brake drums.
>
> Front P30 calipers were replaced with restored original calipers with
> yellow sticky pads.
>
> Good performance friction rear brake shoes were reinstalled.
>
> System has been thoroughly pressure bled on all six wheels multipletimes.
>
>
>
>
> Tom Whitton
>
> 26 foot updated GMC
>
> Paducah, KY
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350597 is a reply to message #350596] |
Mon, 09 December 2019 20:04 |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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The symptoms of the light coming on suggests air in the system somewhere. The M/C to Hydroboost rod distance needs to be correct-some even suggest a little pre load is acceptable or even preferred. Too much will definitely over heat the PS fluid though so one must be careful here. Without having the actual pressures at the wheels you are just guessing though. The P30 MC will require additional pedal pressure for sure but I didn't decipher weather you have one or not. Did you get a redone bell crank with the correct geometry for the booster? If not you will have an issue because the pedal ratio won't be correct and your pedal effort will be out of wack. Checking the PS pump pressure may be in the cards also. As stated earlier, Bob Sone is a good guy who will be more than willing to help if he can-give him a call.
Good luck,you'll get there. Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350600 is a reply to message #350597] |
Tue, 10 December 2019 08:13 |
GMC.LES
Messages: 505
Registered: April 2014
Karma: -2
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Senior Member |
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Have the rear brake shoes been re-arched to match the new drums?
If the shoes don’t Closely match the drum dia, the shoes will flex. This can cause the poor braking issue and brake light problem you are experiencing.
Les Burt
Montreal
'75 Eleganza 26'
> On Dec 9, 2019, at 9:18 PM, Hal StClair via Gmclist wrote:
>
> The symptoms of the light coming on suggests air in the system somewhere. The M/C to Hydroboost rod distance needs to be correct-some even suggest a
> little pre load is acceptable or even preferred. Too much will definitely over heat the PS fluid though so one must be careful here. Without having
> the actual pressures at the wheels you are just guessing though. The P30 MC will require additional pedal pressure for sure but I didn't decipher
> weather you have one or not. Did you get a redone bell crank with the correct geometry for the booster? If not you will have an issue because the
> pedal ratio won't be correct and your pedal effort will be out of wack. Checking the PS pump pressure may be in the cards also. As stated earlier, Bob
> Sone is a good guy who will be more than willing to help if he can-give him a call.
> Good luck,you'll get there. Hal
> --
> 1977 Royale 101348,
>
> 1977 Royale 101586, Diesel powered,
>
> 1975 Eleganza II, 101230,
>
> 1974 Eagle Bus 45',w/slideout,
>
> Rio Rancho, NM
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350608 is a reply to message #350589] |
Tue, 10 December 2019 16:25 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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If you have good PS pressure I would look at combination valve Did you replace the valve with a Chinese PV2? They have smaller ports and several defect modes, one of which blocks fluid pressure. I had my dealer friend, at Bob Stones suggestion, buy up the last GM 1257177 /ACD 172-1350 valves. You can get them from Bob or from Highwaystars.net. There you will see the PV2 that everyone seems to sell and the genuine GM NOS part and the difference in price. There is a reason.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Tue, 10 December 2019 16:39] Report message to a moderator |
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350692 is a reply to message #350589] |
Sat, 14 December 2019 16:47 |
6cuda6
Messages: 975
Registered: June 2019
Karma: -6
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Senior Member |
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Not knowing exactly how you selected the parts you have i'm just going to toss this out there from what your describing.....sounds to me like your master cylinder bore displacemrnt is to small...the light coming on, to me suggests fluid volume issue and the lack of application pressure at the low pedal pressure sounds like master cylinder piston diameters are too small so your not moving enough fluid for effective braking on light apply.
Ive seen it the other way as well....master to big and brakes locking up at the slightest pedal application.
Just my opinion of course.....lol.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350693 is a reply to message #350690] |
Sat, 14 December 2019 16:46 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Not sure that locked-up brakes are very effective. Best to absorb the heat
energy from the friction lining through the drums or rotors, converting
inertia into heat, instead of wearing flat spots on tires with the pavement.
I have read some engineering data on braking forces that claimed the
most effective braking was achieved by converting inertia into heat via the
rotors or drums. Engineers seldom have reasons to outright lie about their
data, unlike statisticians who make their living spinning it. But, you may
have a different set of data than I do.
I have been working on brakes since I was about 14, and I will be 80
in May. These coaches will really have you scratching your head, with
different master cylinders, distribution valves, etc. we find on them. Then
throw power boosters from hydraulic systems instead of vacuum boosters, and
all bets are off. Just change one thing at a time until you achieve results.
Jim Hupy
Salem, Oregon
On Sat, Dec 14, 2019, 2:25 PM Eelko Byker via Gmclist <
gmclist@list.gmcnet.org> wrote:
> what are the problems with the china brass pv2 valve an internet search
> comes up with a leaking valve no information about a performance problem I
> to
> am not happy with my brakes with all new parts spent more time bleeding
> the brakes than I have ever done on any other vehicle in my life as a
> mechanic
> I do not have a light that comes on pedal feels like it hits solid after
> initial application good brakes at low speed not so good at highway speed
> can not lock up any wheels at any speed made a panic application when a
> car cut me off was able to lock up the surge brakes on the tow dolly but
> nothing on the coach at about 35 mph will a new old stock help Eelko
> Byker 1976 Eleganza
>
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350699 is a reply to message #350697] |
Sat, 14 December 2019 18:52 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Get a pressure gage and put it at the wheels and see what it reads.
Make sure the brake surfaces are not glazed .
Glazed surface does not develop much coefficient if friction.
Our shop spend considerable time on brakes so it is not straight forward.
On Sat, Dec 14, 2019 at 4:27 PM Richard Denney via Gmclist <
gmclist@list.gmcnet.org> wrote:
> I have six disk brakes including big one-ton-kit calipers up front and a
> stock master cylinder. It has enough capacity to avoid a pressure mismatch,
> though it uses a lot of pedal to get to maximum stopping capability.
>
> But any air can cause a pressure mismatch on full application. With air in
> a line, the pressure will build more slowly in that circuit with pedal
> travel.
>
> Rick “thinking that brake light is the first problem to diagnose” Denney
>
>
> On Sat, Dec 14, 2019 at 5:48 PM tonka6cuda6--- via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> Not knowing exactly how you selected the parts you have i'm just going to
>> toss this out there from what your describing.....sounds to me like your
>> master cylinder bore displacemrnt is to small...the light coming on, to
> me
>> suggests fluid volume issue and the lack of application pressure at the
> low
>> pedal pressure sounds like master cylinder piston diameters are too small
>> so your not moving enough fluid for effective braking on light apply.
>>
>> Ive seen it the other way as well....master to big and brakes locking up
>> at the slightest pedal application.
>>
>> Just my opinion of course.....lol.
>> --
>> Rich Mondor,
>>
>> Brockville, ON
>>
>> 77 Hughes 2600
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> --
> '73 X-Glacier 230 "Jaws"
> Northern Virginia
> Offlist email: rick at rickdenney dot com
> _______________________________________________
> GMCnet mailing list
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>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350707 is a reply to message #350592] |
Sun, 15 December 2019 12:25 |
THOMAS R WHITTON
Messages: 47
Registered: September 2016
Karma: -1
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Member |
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Thanks for all the suggestions to resolve my poor braking. I've held off on doing anything for three reasons. First, I had to have my heart shocked in an attempt to resolve an electrical problem, causing an irregular beat. (That was an out-patient procedure, which only worked for about three days so I guess they will try it again.) Second, I wanted to wait until you guys had a chance to provide your suggestions. Third, my floor jack blew a seal when I tried to raise the coach to remove the wheels for the umpteenth time.
I'm going to use my bottle jack today to get the coach up on blocks to get started again. In order to resolve the slight "shoe-drum" point contact issue with the rear brakes, I'm going to replace all the rear shoes. (The four drums are brand new but the shoes I've been using for the tests were very slightly worn, emphasize "very".) How far I get today on this, I'm not sure but I'll at least get started. My thought is I may be getting point contact until the pressure from hard braking takes hold. New shoes for four wheels total $46, peanuts compared to what I've spent so far. Next, I'll use my Jim Hupy pressure bleeder for again for only God knows how many times. I cant imagine there is any air in the system but, of course, I'm not always right.
I'm slow under the best of circumstances so all the above will probably take two or three days. After that, unless I receive other suggestions, my plan is to put it all back together and try another road test. By all means, if you have other suggestions, please let me know as soon as you can before everything is still apart.
Thanks to everyone,
Tom Whitton26 foot updated GMCPaducah, KY
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350708 is a reply to message #350707] |
Sun, 15 December 2019 12:46 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Tom, in bleeding the rear Brakes sometimes I've had to raise the bogies to get the bleeders higher than the line. Meaning with wheels off and frame blocked up, I have jacked the boogies up after dumping air on bags. Seems to help on some coaches with air bubbles in line even using a pressure or vacuum bleeder.
THOMAS R WHITTON wrote on Sun, 15 December 2019 13:25Thanks for all the suggestions to resolve my poor braking. I've held off on doing anything for three reasons. First, I had to have my heart shocked in an attempt to resolve an electrical problem, causing an irregular beat. (That was an out-patient procedure, which only worked for about three days so I guess they will try it again.) Second, I wanted to wait until you guys had a chance to provide your suggestions. Third, my floor jack blew a seal when I tried to raise the coach to remove the wheels for the umpteenth time.
I'm going to use my bottle jack today to get the coach up on blocks to get started again. In order to resolve the slight "shoe-drum" point contact issue with the rear brakes, I'm going to replace all the rear shoes. (The four drums are brand new but the shoes I've been using for the tests were very slightly worn, emphasize "very".) How far I get today on this, I'm not sure but I'll at least get started. My thought is I may be getting point contact until the pressure from hard braking takes hold. New shoes for four wheels total $46, peanuts compared to what I've spent so far. Next, I'll use my Jim Hupy pressure bleeder for again for only God knows how many times. I cant imagine there is any air in the system but, of course, I'm not always right.
I'm slow under the best of circumstances so all the above will probably take two or three days. After that, unless I receive other suggestions, my plan is to put it all back together and try another road test. By all means, if you have other suggestions, please let me know as soon as you can before everything is still apart.
Thanks to everyone,
Tom Whitton26 foot updated GMCPaducah, KY
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C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350709 is a reply to message #350707] |
Sun, 15 December 2019 12:45 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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If you use "experienced" linings, be sure that you rough up the shoes or
pads with 60 grit. "WEAR A RESPIRATOR". If the drums or rotors are slick,
rough them up as well. I use the most aggressive linings I can find, and
break them in with hard use. Currently, I have 80 mm calipers with yellow
sticky pad linings on the front, coupled with metallic riveted linings on
the rear with mis-matched wheel cylinder diameters. I had occasion last
weekend to test them extensively with a drive up Interstate 5 through
Portland, Oregon, Olympia, Fort Lewis/Mchord, Tacoma, Seattle, Everett,
Washington. 6 major cities, a lot of stop n' go with a few panic stops
thrown in. Brakes work very well. I like the combination.
Jim Hupy
Salem, Oregon
On Sun, Dec 15, 2019, 10:26 AM THOMAS R WHITTON via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Thanks for all the suggestions to resolve my poor braking. I've held off
> on doing anything for three reasons. First, I had to have my heart shocked
> in an attempt to resolve an electrical problem, causing an irregular beat.
> (That was an out-patient procedure, which only worked for about three days
> so I guess they will try it again.) Second, I wanted to wait until you
> guys had a chance to provide your suggestions. Third, my floor jack blew a
> seal when I tried to raise the coach to remove the wheels for the umpteenth
> time.
> I'm going to use my bottle jack today to get the coach up on blocks to get
> started again. In order to resolve the slight "shoe-drum" point contact
> issue with the rear brakes, I'm going to replace all the rear shoes. (The
> four drums are brand new but the shoes I've been using for the tests were
> very slightly worn, emphasize "very".) How far I get today on this, I'm
> not sure but I'll at least get started. My thought is I may be getting
> point contact until the pressure from hard braking takes hold. New shoes
> for four wheels total $46, peanuts compared to what I've spent so far.
> Next, I'll use my Jim Hupy pressure bleeder for again for only God knows
> how many times. I cant imagine there is any air in the system but, of
> course, I'm not always right.
> I'm slow under the best of circumstances so all the above will probably
> take two or three days. After that, unless I receive other suggestions, my
> plan is to put it all back together and try another road test. By all
> means, if you have other suggestions, please let me know as soon as you can
> before everything is still apart.
> Thanks to everyone,
> Tom Whitton26 foot updated GMCPaducah, KY
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| Re: [GMCnet] Subject: Re: Brake problem, badly need suggestions [message #350736 is a reply to message #350735] |
Mon, 16 December 2019 12:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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At least 70% of the stopping effort is by the front brakes. The bigger
caliper pistons provide more of that. Barring changing to larger diameter
rotors, it is a good upgrade without any downside. Even when I convert
coaches to all discs, or reaction arm systems, I am very much inclined to
use the original master cylinder and modify the distribution valve to
remove the delay feature to the rear brakes. I am NOT A FAN of the P-30
master cylinder or that brass distribution valve. Lots of debate here.
Jim Hupy
Salem, Oregon
On Mon, Dec 16, 2019, 10:27 AM THOMAS R WHITTON via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Jim, why are you using 80mm calipers? I removed my 80mm calipers and went
> back to the originals as part of this current brake work. I used the still
> good (maybe 75% plus) yellow sticky pads, which I understand work with both
> the originals and the 80mm.
> Do you think going back to the 80mm calipers with new pads would have any
> benefit or not? If so, this would be a good time to do it.
> Tom Whitton26 foot updated GMCPaducah, KY
>
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