![]() |
Register or Log In To remove these advertisements. |
|
|
![]() |
|
Thread Tools | Display Modes |
|
![]() |
#1 |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Rear wheel panic stop lockup
Twice now I have had to hit the brakes hard once in the rain and once on dry a road. This truck is C10 with a chevy parts front disc conversion that I did not do. I pulled the rear drums off and discovered what I think is wrong. The front shoe is the long shoe and from what I gather that one should be on the back, not the front. Is that true? And could that be causing the rear to lock up during a hard stop?
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
![]() |
![]() |
![]() |
#2 |
Registered User
Join Date: Jul 2022
Location: Rockford, Mi
Posts: 70
|
Re: Rear wheel panic stop lockup
Yes, long show on the rear.
As for the rears locking up, the brake proportioning valve maybe adjusted wrong with too much bias on the rear. If it's not an adjustable valve you can get one. |
![]() |
![]() |
![]() |
#3 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
Since I didn't do this conversion I have no idea what parts they used. This is just one of the many things this guy did wrong on this truck. I have adjustable PVs on my Z and AMX. I am going to convert to 4 wheel discs so I will be getting all different stuff and probably add a adjustable PV.
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
#4 |
Senior Member
![]() Join Date: Dec 1999
Location: TX
Posts: 1,569
|
Re: Rear wheel panic stop lockup
I have a truck that I did the conversion on and have the same problem. Actually, the truck had the same problem before disc conversion.
Adjustable valve is the sure way to fix it. Put my adjustable only in the rear line. I have another truck with the Wilwood proportioning valve that has the adjustment built in. I think it only dials down the rear brakes, not adjust the proportion. |
![]() |
![]() |
![]() |
#5 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
Along with the rear disc kit I am also installing a Corvette disc/disc MS and a disc/disc PV. With all that I might not need the adjustable PV, we'll see.
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
#6 |
Registered User
Join Date: Jun 2013
Location: Somewhere
Posts: 3,073
|
Re: Rear wheel panic stop lockup
The rear of a pickup is light with no load so the rears lock up. With a full load they tend not do so. That's by design on old trucks. Another thing is that when the rears lock you can still steer.
Unless someone is worried about brake fade in the rear, disks are a cosmetic upgrade. |
![]() |
![]() |
![]() |
#7 | |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,104
|
Re: Rear wheel panic stop lockup
Quote:
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
|
![]() |
![]() |
![]() |
#8 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
#9 | |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,385
|
Re: Rear wheel panic stop lockup
Quote:
__________________
~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
|
![]() |
![]() |
![]() |
#10 |
Special Order
![]() ![]() Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,859
|
Re: Rear wheel panic stop lockup
Yeah, I don't get excited about putting rear discs on. The proper way brakes are supposed to operate says disc brakes on the rear are not needed. It's not only to save money that automakers went to front disc but not rear. The front pads should need replacement at least 2 to 1 with rear shoes or disc pads. My experience has been closer to 5:1. Usually when I do rear brakes it's due to a leaking axle seal or wheel cylinder. Many prefer discs to drum because they see disc brakes as easier to work on/change pads. I get that, and they look cool if you can see them. I may do rear discs some day, just because. But this problem is all about proportioning. These trucks running empty need a greater bias to the front
* One reason I may do discs on my K2500 is if I can't find new drum brake parts in the future. Also, on a 4wd a consideration is not retaining debris after running through deep mud and water
__________________
"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ |
![]() |
![]() |
![]() |
#11 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
#12 |
Special Order
![]() ![]() Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,859
|
Re: Rear wheel panic stop lockup
We're thinking the same. I wouldn't tell anyone it's not a good idea. I may end up doing my shortbed that way. Just saying I don't get worked up over needing them. My project started with a freshly done no part spared rolling chassis with 4/6 drop from an abandoned project being parted out. My brakes will be good for a while (once it gets driven). My '72 4wd, I think, needs the same thing as yours. I did new brakes/bearings/seals on it and have had two scares with brakes. It's off the road with another problem and I want to address the brakes once I get back on it. Not driving it until I do. Actually, mine has the opposite problem. Seems like I only have front or rears barely grab. Seems like a proportioning issue or other line pressure problem
__________________
"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 03-12-2023 at 09:07 PM. |
![]() |
![]() |
![]() |
#13 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
#14 |
Registered User
Join Date: Apr 2010
Location: So Cal
Posts: 1,437
|
Re: Rear wheel panic stop lockup
This photo is of a Toyota LSPV (load sensing proportion valve). I've only seem reference or pictures of them on '80-'90s import trucks.
ABS brakes have negated the need for proportion valves, even on trucks. The arm swings up/down with the axle and adjusts the valve. The arm is actually fairly flexible and they even call it a spring. The arm flexes to delay response to bumps in the road.
__________________
'67 GMC 2500, 292, 4spd, AC |
![]() |
![]() |
![]() |
#15 |
Andy
Join Date: Feb 2009
Location: Cleveland, GA
Posts: 224
|
Re: Rear wheel panic stop lockup
I had issues with mine locking up and one of the things that I did that helped greatly was sanding the very edge of the brake shoe material on the top and bottom to get that sharp corner off. One of my old mechanic friends told me to try it and what a difference it made in my truck.
__________________
1967 Camaro SS 406|522hp/514ft lbs|M20 Muncie|3.73s|Posi 1969 CST/10 383|Aisin AR5 5 speed 1972 K5 350|Turbo 350 4x4 2005 Duramax 2500HD 4x4 |
![]() |
![]() |
![]() |
#16 | |
Registered User
![]() Join Date: Jan 2016
Location: Sugar Hill GA
Posts: 368
|
Re: Rear wheel panic stop lockup
Quote:
__________________
1967 C10 Step side 1970 AMX 390 1977 Datsun 280Z highly modified with '95 LT1 power |
|
![]() |
![]() |
![]() |
Bookmarks |
|
|