****NOW HEAR THIS! Dunaruna, please report to the bridge!

[Boomyal]

Ya'll might recall the episode with my son's '87 Pontiac Sunbird rear brakes. When you apply the brakes, especially after sitting, the rear shoes grab so hard they actually chirp the tires or worse.<br /><br />The first thing that I did was to remove the drums, check for fluid leaks, (none) reinstall the drums and adjust the shoes. This made no difference.<br /><br />Then I figured that the internal proportioners, that are part of the mastercylinder, had failed. There is one proportioner valve per rear wheel. So, I replaced the master cylinder. Still no improvement.<br /><br />So now I am scratching my head. We put new shoes on the vehicle a while back but did not replace the springs. I'm sure that they are original. We never really drove the car before putting the shoes on it because we had the body and engine repair to do immediately after obtaining the car. However for some time after installing the new shoes, this problem did not exist. <br /><br />The car is now 19 years old with 114k on it. Could the springs be so weak that when you moderately apply the brake, the shoes are just sucked into the drums??? )They sure did not seam weak when we reinstalled them.)<br /><br />Could we have put the springs on wrong? or perhaps failed to put the short shoe on the leading position?

 

[qaztwo]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

used to have an old buick century that would do that after siting for a while. the rear drums would rust up and first time you hit the breaks lock up. Normally would only happen when going slow.

 

[Reel Poor]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Boom the proportioning vale is not in the master cylinder, that is a residual check valve. The proportioning valve is located in the combination valve. This is the aluminum block looking thing under the master cylinder where all the lines connect before going to the individual wheels. You need to change the combination valve.<br /><br /> Combination Valve

 

[steamboatwilly]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

What Reel Poor said...The proportion-valves purpose is,if front or rear line busts or lose pressure,the valve closes THAT section off,then you still have brakes on the opposite end.I believe your p-v is stuck or bad.If stuck,Sometimes you can take the line loose,apply pressure(some way)and unstick it.Sometimes a new one has to be set.Hope this helps.

 

[Reel Poor]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

James.....That is the job of the pressure differential valve. This valve moniters pressure between front and rear brake systen. It is the valve that activates the switch that will illuminate the light on dash to indicate hydraulic system fault.<br /><br />The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes. If equal braking pressure were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain amount of the pressure through to the rear wheels so that the front wheels apply more braking force. Not to be confused with the metering valve which is required on vehicles with front disc and rear drum brakes.

 

[Boomyal]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Reel Poor, in typical GM fashion, especially for their throw away cars, the master cylinder provides all functions. This is a dual cylinder with lines from all four wheels that screw into the M/C. The front half of the M/C has one line to the front disc and one regulated port to the rear drum. The rear portion of the M/C duplicates that except to the remaining front and rear wheels. There is no combination valve as you pictured and as I have seen in other applications.<br /><br />This is why I feel that something else is going on that does not meet the eye

 

[Dunaruna]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Any chance of a picture of one side with the drum removed? I'd like to see the shoe configuration.

 

[Boomyal]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Originally posted by Dunaruna:<br /> Any chance of a picture of one side with the drum removed? I'd like to see the shoe configuration.

I'll take one and post it Aldo. It probably will not happen before this weekend though. Keep an eye out for this post to be bumped. It will probably fade into the background by this weekend.<br /><br />Nice to see you. Haven't crossed paths in a while.

 

[jlshields]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Boomyal, my '96 F150 did the rear brake grab thing after sitting for a few days...especially in damp weather. Mechanic friend advised that dampness would soften the brake shoe composition somewhat and make them grab. Replaced rear shoes and no more grabbing.<br />John

 

[rwise]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Boomyal, sounds like you have already checked this, but the Buick I had would do the rear brake grab if they were out of adjustment. The adjusters did not work correctly and with time would get loose and bind, slide to a stop!<br />Good luck with it,,,,

 

[Boomyal]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Originally posted by jlshields:<br /> Boomyal, my '96 F150 did the rear brake grab thing after sitting for a few days...especially in damp weather. Mechanic friend advised that dampness would soften the brake shoe composition somewhat and make them grab. Replaced rear shoes and no more grabbing.<br />John

JL, I assume you replaced them with shoes of a different material. I'll call the supplier of the brake shoes and see if he might think that to be the issue.<br /><br />Rwise, I did adjust them right after the problem showed up.

 

[crazy charlie]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

I owned a Jeep Cherokee that did that every morning after it rained.After a while I got used to starting out of my driveway with the brake on and my other foot on the gas.I did this for about a block and that was the only way to prevent it from "grabbing".That grabbing was quite a shock when you were not expecting it.

 

[jlshields]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Boomyal, the brand I used to replace the shoes on the F150 were Raybestos but I don't know the composition. The ones that grabbed were OEM.<br />John

 

[SS MAYFLOAT]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Hey Boom, have you checked to make sure that the emergency brake cable isn't binding causing one side to be on a tad bit? I know on automatics that the e-brake cable usually siezes up from not getting used often. If it was applied at some time, it may have never completely released. Just a thought that might be part of the problem. Good Luck!

 

[DaleT]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

I had a Mustang years ago that had a similar problem. Turned out to be the spring sets and adjusters, although funtioning they were worn to a point that when the brakes were apllied they, the rear brakes, would either not work at all or lock up. After conuslting a mechanic friend of mine he suggested to change the spring sets and adjusters with every rear brake job. That being said our roads are not kind to brake components, salt and such, so this may not be the issues with yours. <br /><br />One other thing to check, was a problem on my Cherokee, the parking brake assembly inside the drum may not be seated properly or bent and thus binding on the other pieces of the brakes.

 

[Boomyal]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Originally posted by SS Mayfloat:<br /> Hey Boom, have you checked to make sure that the emergency brake cable isn't binding causing one side to be on a tad bit? I know on automatics that the e-brake cable usually siezes up from not getting used often. If it was applied at some time, it may have never completely released. Just a thought that might be part of the problem. Good Luck!

Well, SSM, a while ago I did adjust the E brake cable at the yoke. I don't think that this is a matter of one brake tighter than the other. <br /><br />I just went out and drove it again, one day later. Immediately, from just a slow roll, the brakes grabbed so hard the rear suspension bottomed out.<br /><br />I then put it in reverse and backed up for a while with the brakes applied. I then took off forward, periodically applying the breaks with some force and they did not grab.<br /><br />Sounds to me like it might be the shoes themselves. We have no lack of moisture here in the PNW but this condition had existed even in the summer months.

 

[dolluper]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Got any grooves in the backing plates where the shoes ride,the shoes will stay there until pressure builds {takes millasecond} and bingo like lockup,if so grindem smooth or add material if they are to deep {coat hanger cheap way melt it in then grind level}

 

[kenimpzoom]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Can the drums be out of true?<br />Any chance the rear brake flex hoses are soft and swelling?<br /><br />I would replace the springs cause they are cheap.<br /><br />Ken

 

[Boomyal]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Aldo, I hoped that revised title would get your attention. <br /><br />I have 6 good brake pictures that I think would be best sent via email. I would send them two at a time so as not to overload your dial up.<br /><br />If that works for you, email me at jjat at comcast dot net and I will send the pics.<br /><br />Thanks,<br />JB

 

[Reel Poor]

Re: ****NOW HEAR THIS! Dunaruna, please report to the bridge!

Hey Boom <br /><br />Been looking on the All Data and found a "common problem" list of brake grab on the rear drum brakes. Common problems listed are;<br />Shoes installed improperly; ie. primary and secondary shoes reversed, both primary shoes on one side and both secondary shoes one the other side.<br />.Wrong shoe size or type<br />.Loose or broken linings<br />.Brake shoe adjustment to tight or to loose<br />.Sticking wheel cylinders<br />.Weak or broken return springs<br />.Brake linings contaminated with brake fluid or grease<br />.Incorect fit of shoe to brake drum or backing plate<br /><br />I also found in a bulletin that the banjo fitting on the front calipers (where the line is bolted to the caliper) is prone to blockage. Thay claim that the hole in the bolt is small and can become restricted. If this is so it could also cause an agressive rear brake condition.<br /><br />I realize you are aware of these problems that are listed in the common list. But nothing really stood out on the All Data. The bulletin was the only thng that was uncommon. And honestly I got my doubts on that. Could be though. Just another thought, are the front brake hoses in good condition?<br /><br />If you'd like, I'd be glad to look at your pics. I can compare them to whats on the All Data.