The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 08-14-2007, 09:23 PM   #1
swb70
Registered User
 
Join Date: Sep 2003
Location: Commerce Texas
Posts: 36
Brake Problem

I have a 1970 chevy pickup and the rear brakes lockup on me when I hit them.
I have to bleed them off to release them. Was told that the problem may be the porportional(spelling wrong) valve. I have never had to replace one of these but guess the can go bad. All the brakes were rebuilt about 5 yrs ago.
Shoes, wheel cylinders, hoses, master cylinder. Could this be the problem. Already tried to buy one at local auto parts and was told that this was a dealer part. Any help will be appreciated.. Thanks Ben
swb70 is offline   Reply With Quote
Old 08-14-2007, 10:14 PM   #2
cdowns
Senior Member
 
cdowns's Avatar
 
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
Re: Brake Problem

well the first thing to do is to take the drums off and look for obvious problems like excess rust on backing plates adjuster stuck wheelcylinders leaking shoes worn out grooves in the drums rust on the braking surface of the drums broken or weak springs axel seals leaking etc
__________________
71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane

MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF

DONT BELIEVE EVERYTHING YOU THINK

TAKE MY ADVISE;I DON'T USE IT ANYWAY
cdowns is offline   Reply With Quote
Old 08-14-2007, 11:07 PM   #3
68gmsee
Active Member
 
68gmsee's Avatar
 
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
Re: Brake Problem

I had a similar problem that I fought for about a week on one of my drum brakes. Replaced brakes, springs, redid the drums, new brake cylinder kits, etc...

I finally decided to check the lines. On mine the problem was the rubber line above the axle where the metal line attaches to the rubber line and then to the frame. It had swelled/collapsed internally.

Here's how it worked. When you depress the pedal, there's a high hydraulic pressure forcing the fluid through. But when the pedal is released, spring tension forces the fluid back to the master cylinder. This was not enough to force the fluid back through the swelled rubber lines.

This also happens on the front rubber lines. So if you find one that's bad, you need to replace all of them..

Hopes this helps.
68gmsee is offline   Reply With Quote
Old 08-15-2007, 10:35 PM   #4
swb70
Registered User
 
Join Date: Sep 2003
Location: Commerce Texas
Posts: 36
Re: Brake Problem

Thanks cdowns and 68gmsee. I did rebuild all break parts about 5 yrs ago
except for the flex line near the rearend. Will try that. Thanks again.
swb70 is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 09:05 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com