Frozen Brakes on '77 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MNiceGuy · 07-30-2012, 01:57 PM

The front brakes are engaged hard on my '77 Scottsdale...to the point I can barely move the truck without starting to break the rear tires loose. Here's what I know so far:

- No power assist
- Front disc / rear drum
- Brake lines (hard and soft) are original to the truck
- Brake dummy light lit on the dash
- Lots and lots of pedal travel. There is some resistance but I can push it to the floor
- No leaks anywhere that I can spot

I've read that I can reset the prop valve which may fix the conditions that are lighting the dummy light but I feel there may be more to it. I've also been told the soft lines may be collapsing from the negative pressure and not letting the fluid back out of the caliper. Is that possible? Where else should I be looking? Could it be a bad/faulty prop valve?

Thanks!

MNiceGuy · 07-31-2012, 02:38 PM

Here's a little update:

I took off one of the front wheels and tried to push the piston back in the caliper. It was absolutely not moving...period. I then cracked the bleeder and after a spurt of fluid came out I was able to push the piston back.

It seems that fluid is getting trapped between somewhere and the caliper to the extent it's able to hold its pressure. Where should I be looking next?

crazy longhorn · 07-31-2012, 08:52 PM

Quote:

Originally Posted by MNiceGuy

Here's a little update:

I took off one of the front wheels and tried to push the piston back in the caliper. It was absolutely not moving...period. I then cracked the bleeder and after a spurt of fluid came out I was able to push the piston back.

It seems that fluid is getting trapped between somewhere and the caliper to the extent it's able to hold its pressure. Where should I be looking next?

Collapsted brake hoses (internally). You have the pressure with the master, to push the fluid into the calipers, but the hoses arent letting it back out. ....crazyL

**N2TRUX** · 08-01-2012, 10:57 AM

Quote:

Originally Posted by crazy longhorn

Collapsted brake hoses (internally). You have the pressure with the master, to push the fluid into the calipers, but the hoses arent letting it back out. ....crazyL

That sounds like what you have going on. Even if its not the problem, replacing those original hoses isn't a bad idea.

andrewmp6 · 08-02-2012, 01:50 AM

And while your at it replace all the brake fluid too.Brake fluid gets old or gets water in it will cause you to have soft or spongy brakes.

crazy longhorn · 08-03-2012, 12:48 AM

A couple more thoughts, on the peddle travel....if the rear shoes are badly worn or out of adjustment, you will have a lot of peddle travel. The other thought is a bad master cyl...(if you pump on the brake,will it tighten the travel up,then float to the floor?) 1 more ?, is it manual brake, or does it have a booster , thats not working? crazyL

AusTruck · 08-03-2012, 10:29 AM

I had a very similar problem with the front brakes on my 78 G-20 Van. Driver's side front brake was locked up. Just replaced the flexible hose and everything was ok. Seems when the hoses get old, they become like a one-way valve. They let pressure past them, but won't relieve the pressure and the caliper stays applied.

At least on my old van, it was a pretty easy fix.

MNiceGuy · 08-04-2012, 12:11 AM

Thanks guys for the info!

I think I finally found the culprit or at least a major factor in why the brakes just aren't what they should be. After pulling the driver's side drum off to inspect everything it was clear something had gone wrong. Everything under the drum was coated in black grime. It didn't take a very thorough inspection to find that the wheel cylinder on that wheel was leaking fluid from both ends.

This truck has a lot of sentimental value to me (it was my dad's) so I didn't mind just investing in a complete brake system overhaul. I happen to know the brake system has never been touched so it seemed like it was time

Docs fitty6 · 08-04-2012, 01:28 AM

I'd like to add one more item to look at in this type situation.
When doing custom work, a pushrod off the brake pedal to master cylinder/booster length is critical. If it's a bit too long it will create a problem exactly as you described. It continues to keep pressure on the lines since it does not return completely.
Typically though, this is a problem that occurs when de-bugging a new ride after a build or brake swap.

07-30-2012, 01:57 PM	#1
MNiceGuy Registered User Join Date: Apr 2012 Location: Minneapolis, MN Posts: 25	Frozen Brakes on '77 The front brakes are engaged hard on my '77 Scottsdale...to the point I can barely move the truck without starting to break the rear tires loose. Here's what I know so far: - No power assist - Front disc / rear drum - Brake lines (hard and soft) are original to the truck - Brake dummy light lit on the dash - Lots and lots of pedal travel. There is some resistance but I can push it to the floor - No leaks anywhere that I can spot I've read that I can reset the prop valve which may fix the conditions that are lighting the dummy light but I feel there may be more to it. I've also been told the soft lines may be collapsing from the negative pressure and not letting the fluid back out of the caliper. Is that possible? Where else should I be looking? Could it be a bad/faulty prop valve? Thanks!

07-31-2012, 02:38 PM	#2
MNiceGuy Registered User Join Date: Apr 2012 Location: Minneapolis, MN Posts: 25	Re: Frozen Brakes on '77 Here's a little update: I took off one of the front wheels and tried to push the piston back in the caliper. It was absolutely not moving...period. I then cracked the bleeder and after a spurt of fluid came out I was able to push the piston back. It seems that fluid is getting trapped between somewhere and the caliper to the extent it's able to hold its pressure. Where should I be looking next?

08-02-2012, 01:50 AM	#5
andrewmp6 Registered User Join Date: Jan 2009 Location: Louisville,Ky Posts: 5,811	Re: Frozen Brakes on '77 And while your at it replace all the brake fluid too.Brake fluid gets old or gets water in it will cause you to have soft or spongy brakes.

08-03-2012, 12:48 AM	#6
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	Re: Frozen Brakes on '77 A couple more thoughts, on the peddle travel....if the rear shoes are badly worn or out of adjustment, you will have a lot of peddle travel. The other thought is a bad master cyl...(if you pump on the brake,will it tighten the travel up,then float to the floor?) 1 more ?, is it manual brake, or does it have a booster , thats not working? crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

08-03-2012, 10:29 AM	#7
AusTruck Registered User Join Date: Dec 2009 Location: Austin, Texas Posts: 90	Re: Frozen Brakes on '77 I had a very similar problem with the front brakes on my 78 G-20 Van. Driver's side front brake was locked up. Just replaced the flexible hose and everything was ok. Seems when the hoses get old, they become like a one-way valve. They let pressure past them, but won't relieve the pressure and the caliper stays applied. At least on my old van, it was a pretty easy fix.

08-04-2012, 12:11 AM	#8
MNiceGuy Registered User Join Date: Apr 2012 Location: Minneapolis, MN Posts: 25	Re: Frozen Brakes on '77 Thanks guys for the info! I think I finally found the culprit or at least a major factor in why the brakes just aren't what they should be. After pulling the driver's side drum off to inspect everything it was clear something had gone wrong. Everything under the drum was coated in black grime. It didn't take a very thorough inspection to find that the wheel cylinder on that wheel was leaking fluid from both ends. This truck has a lot of sentimental value to me (it was my dad's) so I didn't mind just investing in a complete brake system overhaul. I happen to know the brake system has never been touched so it seemed like it was time

08-04-2012, 01:28 AM	#9
Docs fitty6 Registered User Join Date: Aug 2012 Location: Shelton WA Posts: 37	Re: Frozen Brakes on '77 I'd like to add one more item to look at in this type situation. When doing custom work, a pushrod off the brake pedal to master cylinder/booster length is critical. If it's a bit too long it will create a problem exactly as you described. It continues to keep pressure on the lines since it does not return completely. Typically though, this is a problem that occurs when de-bugging a new ride after a build or brake swap.



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