Engine/Transmission (1994 - 1998) Rear Brake Grab

[grtescpa]

Hello,

I had posted this problem a few months ago. My rear brakes grab when I first pull out in the morning and only when the temp is above 45 deg. This grab goes away after a few miles of stop and go driving. I had been told that I might have an oil seal leak that is making its way to my beake linnings. Well during that warm spell in January I pulled the drums off. There was no sign of an oil leak anywhere. I just received this quater's issue of the TDR and read the article "EGR severe brakes" on pg 53. I don't do any towing but the proportional valve was mentioned in the article. Rear brakes will lock if to much of the braking load is tranfererd to the rear wheels. I plan to change this valve so if anyone has had this problem, I will repost my results. Thank you TDR for the great articles!

 

[The patriot]

Mine did the same thing for 80K miles. My seals are fine.

I dont know why it does this. There are a few theories, but who knows for sure.

Eric

 

[sam peterson]

save your money---Its not the valve. The problem is most likely moisture sensitive lining. That prop valve doesn't know whether your brakes are cold or hot. If it was bad it would do it all the time. ----Sam

 

[DieselB59]

Here in Jersey, we're getting this Seattle-like constant mist-rain, which causes the brakes to flash rust over a full day of work and my first few stops on the way home make the truck feel like it's got Brembo four piston calipers on all four corners. Perfectly normal.

 

[The patriot]

I should also ad, I'm only a few miles from the ocean. I didnt think this would matter?

I've noticed that if I let the rear brakes go out of adjustment, it dont grab as hard.

I jacked it up last week and adjusted the rears, grab is back with a vengence!!

Eric

 

[grtescpa]

RE: Brake grab

Thanks Sam and all for their input. Sam, what do you sujest I do about this problem? Just one more thing about the brake shoes, This problem did not start until 40k of use. I did replace them with raybestos linnings and the grab was still there.

 

[sam peterson]

grtescpa-----with the ban on asbestos a few years back friction material reacts differently than it used to. some of the new car dealers have been plagued with the problem for several years. if the grab is only for the first few stops when they are cold you can live with it or change the shoes untill you find a brand that is not moisture sensitive. from past experience we have found that the higher quality linings seem to be the worst. because the rear brakes don't wear out very fast on the rams we are currently using the wagner quardian brand of shoe. we haven't had problems with these. the least amount of problems is with the shoes that we reline in our own shop. the bendix economy grade also hasn't given any problems. ----Sam

 

[WadePatton]

Who still got grabbers?

Disclaimer--I'm in a rush and this is the first thing that popped up on topic sorta. Please be kind and re-direct me to threads that might help, thanks.



Our 98 has too much pressure going to the rear. I'm familiar with the cold brake thing, this is not it. Feels like 70/30 with 70 going to the rear.



I shut off the pressure to the rears. Made the truck drive much nicer--but has accelerated wear on the front--duh.



No amount of twiddling helped. Previous owner had manual bias valve installed--didn't help.



New plan of attack is to allow pressure to the rears again, but inject air into rear lines. May be mushy, but it'll be better than the way it is.

 

[Nate]

I ziptied that valve so it's all the way open. Other the rear brakes locking up if I really stomp on the brakes, it's the same as before.

 

[JGK]

My grabbies makes me crabby!

My rear brakes are pretty grabby sometimes, and not just when cold. Drives me nuts - to the point of considering swapping for an '01 axle with discs.



In the mean time, one mod that's been on the list but I haven't gotten to yet was to put an adjuster on the rod between the axle and the proportioning valve. My plan is to cut a section out and weld in a turnbuckle. I've found a screen door adjusting brace from the hardware store has the right diameter rod and the right price.



Consider that option.



-Jay

 

[Matthug]

Yup mine does the same thing just about everytime in rains or on a really humid day. This makes sense now hearing about the moisture. Very grabby and easily locked up for about half a dozen stops and then it goes away. What I learned to do is just accelereate with my foot on the brake for just a few seconds and it will be fine. Make sure you're doing atleast ~25 MPH before getting on the brakes or else they could lock up!

My bro has an 02', I told him on several occasions that I would swap rears with him free of charge but he never seems to go for it.

 

[gwizpro]

Rears brake grabbing got to a point where they almost launched me thru windshield on easy apply of brakes. Midas had replaced the pads about 2 months earlier, and every thing was okay. Then the grabbing started. Talked to few gents and came up with replacing the drums. Did so and everything fine again for a few weeks, then grabbing starts again. Replaced the pads with organics and grabbing stopped and has not occured for over 6 months now. Talked with some more people and our conclusion is that the drums were bad and NON organic pads should not be used. Of course this is not conclusive to all trucks but it was on mine.

 

[WadePatton]

I removed the "rigged" shutoff to the rears. Grabbed like hell again. Aired up the lines. Sponge pedal, then grab. So now I'm putting in a cleaner shutoff setup.



NO juice to the rears. Have plenty of front pad and the truck brakes Sooooo much better that way. Maybe it is the linings. I'll go see what the LPH has to offer. GAWD I hate fooling with the 1908-designed bendix brakes.



Will report.



Dammit man. Have new adjuster assemblies. Theory there is that old adjuster springs/clips worn and allowing over tightening. Which fits with my experience of loosening the shoes and having good brakes for two days--until they re-over-adjust. New friction material too.



Back in a couple of hours.

 

[WadePatton]

report and rant.

Oh, my apologies. Seems that there are three major variations on the brake design I lumped together as "Bendix". Seems there are Bendix, Delco-Moraine, and Wagner editions of the basic piston, two-shoe, auto-adjuster, drum brakes.



I still say they're dinosaurs. Heck, my cheapest bicycle has cable-actuated mechanical disc brakes (Avid). They are extremely simple and effective.



SO, back to the point. New friction material (Carquest-xxxx) and adjuster hardware. So far very good. We'll really find out when Wifey gets back from the beach and the linings and drums have had a chance to bed in.



Yesterday, after a few bits of cussing and griping, I found that a strap wrapped around the shoes helps hold them in place. Don't know why it took me so long to try this--but then I try not to fool with drum brakes much.



More ado about nothing---My first ride with rear discs was a 1973 911, and BOY was I disappointed when I pulled them off and found miniature drum brakes inside the rotors for parking/emergency brakes.



If I were designing braking for automobiles, there'd be four hydraulic discs at the wheels and a mechanical disc on the rear drive line.