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cory, GMC Technician
Category: GM
Satisfied Customers: 160
Experience:  14 years of gm experience ase master tech with advance engine performance
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1993 GMC: My drum brakes are over adjusting..2WD..V6..000 miles

Resolved Question:

My drum brakes are over adjusting. I have a 1993 GMC pickup truck 2WD with a V6. It has 158,000 miles on it. The rear drum brake on the driver side is over adjusting causing the brakes to lock up, hence no reverse, the trucks horsepower cannot even power through it. Anyhow, I recently had the brake cylinders replaced and started having the problem then, I dont know if that means anything, or if its a coincidence. Also my oil pressure seems high when I 1st start my truck, sometimes near 100 PSI, and its burning oil, lots of blue smoke when starting, not while driving. oil pressure normalizes after a few minutes. i know the two dont correspond, but if your nice enough an answer would be great =]
Submitted: 8 years ago.
Category: GM
Expert:  cory replied 8 years ago.
Hello there let me see if I can help with your problems here. Let first adress the braking issue. We first need to see if the problem is mechanical or hydrolic. First remove the wheel on the affected side. Look on the backside of the backing plate on top you will notice a bleeder screw on top should be either and 8mm or 10 mm, when the brake is locked up loosen the bleeder and see if any pressurized fluid comes out and the if brake frees up. If it does not then more than likely it mechanical. Next check the emergency brake cable is not hung up or overtightened the adjuster , this is on the drivers side near the gas tank in front of the leaf spring loosen it and see if the drum frees up. if it doen't look on the back side of the brake backing plate near the bottom and see if there is a oval opening with a small cover over it. If there is remove the cover and look inside the hole and you will see what looks like a small gear take a flatblade screwdriver and turn it till the drum frees up. remove drum and inspect to see if the adjuster lever is sitting the ajuster gear, this prevents it from turning when it is not suposed to. If you're not shure what your looking at use the other side for a reference. Next lets take a look at the oil pressure issue. I used to see this alot, the reason the oil pressure guage maxes out at times is because there is an intermittent open in the circuit since the guage works somtimes Its reasonably safe to assume the oil pressure sensor is starting to fail. This is very inexpensive part and pretty easy to replace. You will need to buy a special socket that you can pick up at probably at the same parts store you buy the sensor (napa or checker usually have tools right as you walk in on the wall) . This socket is also very inexpensive. The sensor it located on the back of your engine on top next to the distributer . And lastly the smoke on initial start up was also a very common problem (fixed hunderds of them). The reason for the smoke is the valve seals, gm did not put umbrella seals on the exhaust valves in those years, and when the valve guides wear it allows oil to travel down onto valve and gets burnt by the hot exhaust gasses. To repair this issue you will have to replace all of your valve seals. This is not a terribly expesive repair, but i do recomend this be done either by a profesional or someone with some expeience, because it can damage your engine if done improperly.
Customer: replied 8 years ago.
i know when the brakes lock up i can adjust the adjuster and it helps. but the brakes are real spongy and it makes the brake light come one. a week later it goes back to locking on me. i know that metal piece is touching the adjuster gear, but im not sure if its slipping being that i cannot see it while backing up

how much about for a valve job do you think? and is it something i should worry about?
Expert:  cory replied 8 years ago.
Wow thats unusual. When the the brakes are spongy means the shoes are too loose. But I've never seen them adjust up that fast. The adjuster rod has kind of a sharpened edge that sits against the teeth of the adjuster gear that holds it in place until it adjusts, which is done when the you pump the brakes in reverse. If the gear is held in that way then I wonder the the wheel cylider is getting stuck out. Or if the shoes and springs are not installed properly. You can use the other side as a refrence. Also I noticed that you said the wheel cylinder had been replaced. Were they leaking make sure that no brake fluid got on the shoes. They should be clean and dry. On the valve seals this is going to depend on where you take it. I would guess $400 to $600 epends on the labor rate. (The job is four hours and parts are usualy under $100) Honestly I've seen people never do this repair and the vehicle continues to run fine, you just have to replace your spark plugs more often.
Customer: replied 8 years ago.
okay, well ill leave the valves alone. thankyou...

i know the brakes are going to start locking up when they start to wrok "correctly" if you know what i mean. Braking becomes more responsive and the vehicle is easier to stop. thats when i adjust them, because i know if i dont ill be stuck in my driveway =O. and i only need to do the driver side. after i adjust them they become spongy again. Brake fluid is fine, and the brakes are clean. after replacing the cylinders we used 2 cans of brake cleaner on each wheel
Expert:  cory replied 8 years ago.

I suspect the brakes on that side are not assembled correctly. The shoes should be arranged so that the long shoe in the rear you can see this by looking at the lining on the shoe. The adjuster lever and adjuster gear should be on the same side as the ebrake lever which is on the back side of the shoe. There should be a rod that is straight with fork on each end one end is wider with a spring on it this should be just below the wheel cylinder with spring end pointed at the ebrake lever.

Customer: replied 8 years ago.
okay, ill see what my mechanic can do... but im curious. is there a way to stop them from self adjusting. in the old days we did it ourselves. i miss those days, simplicity!
Expert:  cory replied 8 years ago.
Well not really. The only thing I can think of is to install the adjuster gear in backwards away from lever and adjust the shoes till they just touch the drum and install the drum. But then you wont be able to get to the gear from the back of backing plate.
Customer: replied 8 years ago.
i hope im not bothering you, but im curious. what about the springy thing that touches the gear. could that be the issue, and can i remove that to "fix" it?
Expert:  cory replied 8 years ago.
No the retainer rod that attaches to the anchor at the top attaches to the adjuster lever and the spring that holds the shoe in attaches to the ratainer rod. so the shoe would not retun and drag on the drum. Also your not bothering me I'm happy to help wish I could show rather than tell you. Well any way if i have helped you if you could click on the accept button, or if you need more help let me know I'll be checking in periodically all day
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