Will your brakes lock up your tires ?

[gator2511]

My brakes work just fine for normal or easy stops. Today I had to make a fast stop from about 55 mph for a traffic light and much to my surprise I had my foot all the way in it and it just barely stopped in time. In fact I had to back up some to let traffic pass. Any other vehicle I have owned would have locked up the tires long before this. Is this typical brake performance for these trucks? Every thing appears to be in good shape so I'm curious. Its a stock 72 4wd brake system and all the parts look correct. Tires are 32x11.5x15.

[zeeklu]

I have a 67 K10 with 33x12.5x15 tires and a 72 disk brake front axle. Mine will lock the tires in a extreme panic stop. I would check my back brake adjustment first and see what that does. I have also heard of the front brake hoses deteorating internally and causing poor performance but I don't know how true that is. Chris

[Boise69]

Originally Posted by zeeklu

I have a 67 K10 with 33x12.5x15 tires and a 72 disk brake front axle. Mine will lock the tires in a extreme panic stop. I would check my back brake adjustment first and see what that does. I have also heard of the front brake hoses deteorating internally and causing poor performance but I don't know how true that is. Chris

I have drums in the front and i can lock them up with the lightest of pressure on the dryest of days, scares the hell out of me > i hate front drum brakes.

[gator2511]

Mine won't lock up for nothin. I just looked at the rear adjustment last month and it was fine. My 64 Vette had drum brakes and it would lock em up fast. This truck feels like the ABS on my new truck.

[Huck]

You may need to rebleed the system and hold in the front pin on the proportioning valve when you do this---use a clamp or some other type device. Once this is done, you should be able to lock them up.

[pimperout]

i got drums all they way around and i can lock em up no problem they arnt new or anything they are old and rusty work good tho

[Robert1970C20rstbukt]

On mine they will, especially on a dirt road! Still has the original front/rear drum system. Front tires are 235/85/16, rears are 33/12.50/16.5.

[72 CustomCamper]

My 72 C-20 would lock em up in a heartbeat...

[bad_turbo]

my 1 ton won't stop to save my life!

[truckdude239]

my 71 c-10 has disc in front and drums in back it will lcok them up in a heart beat

[gator2511]

Originally Posted by Huck

You may need to rebleed the system and hold in the front pin on the proportioning valve when you do this---use a clamp or some other type device. Once this is done, you should be able to lock them up.

O.K. What does the little pin on the prop valve do? (maybe I need to convert the front brakes to drum) J/K

[68C15]

either your pads and rotors are glazed or your hoses are going bad. they can flake apart inside and act as a check valve under extreme fluid pressure. its also passible the booster or MC isnt up to par. its hard to say without seeing it in person.
BTW, lock up is undesirable. it means that you are not stopping, instead you are sliding.

[DMX84]

Originally Posted by Huck

You may need to rebleed the system and hold in the front pin on the proportioning valve when you do this---use a clamp or some other type device. Once this is done, you should be able to lock them up.

I would like more info on this please, any links?

[gator2511]

Originally Posted by 68C15

either your pads and rotors are glazed or your hoses are going bad. they can flake apart inside and act as a check valve under extreme fluid pressure. its also passible the booster or MC isnt up to par. its hard to say without seeing it in person.
BTW, lock up is undesirable. it means that you are not stopping, instead you are sliding.

I understand what you are saying about sliding but thats the only reference point I could think of. My point is that it doesn't stop anywhere as good as it should. Right now its the opposite of sliding.

[gator2511]

I just took a quick look at the prop valve and the pin on the radiator end of the valve is all the way in. It does not stick out of the valve at all. Correct me if I'm wrong but in that case the valve won't work and its just acting like a junction block. I need to pull it out and see whats hanging it it. What say guys? More info: I was looking at a brake website and they showed a prop valve like the one I have. Its brass and does not have the pin sticking out. It comes in a 50/50 and 70/30 configuration. The 50/50 is for all drum brakes. They look alike as far as I can tell so I might have the wrong one.

[JAKES 68GMC]

Well, my GMC will stop good, really good for drums, but the brakes won't lock up. I've tried going 35mph in 3rd on a dirt road, and then slammed on the brakes. It slid, but when you let off the brake pedal, the brakes worked fine and let the truck keep rolling.

[Musclerodz]

If you have a power booster, I would check that first along with the vaccum line for it.

Mike

[gator2511]

Originally Posted by Musclerodz

If you have a power booster, I would check that first along with the vaccum line for it.

Mike

I pulled the vaccum line off the booster and the engine ran rough, plugged it back in and it smoothed out. I'm gonna have to pull the drums and check out the shoes I guess. Maybe I'll get started tomorrow if the rain holds off. Normal stops from 45 on down don't require a lot of pedal effort, just the hard stops which leads me to believe its something wrong in the drums or the prop. valve.

[blacktruck]

the manual brakes for my '72 will lock the rears up if i slam on them, and do it pretty easy. what is the "normal" amount of pedal travel for these trucks?

[JAKES 68GMC]

If you just touch my gas pedal the truck will slow down. When I push the pedal as hard as I can, it's nowhere near the floor.

[gator2511]

Now my brakes lock up the tires! I was looking at at the rear brake linings through the little inspection and adjust hole in the drums and couldn't see the linings that well. When I pulled the drums the shoes were paper thin. I replaced the rear shoes, changed the prop valve with the right one and bled the air out of the system. I have plenty of brakes now. The right side drum came off pretty easily but the left was a bear. I finally rented a puller from the local shop and tightened it down real tight. I turned to pick up a hammer to tap it when it came off with a very loud BANG! I felt the concussion hit my chest and my ears started ringing and I got a headache. Now I'm not a delicate guy but I never had a drum come off like that! Everything was fine but its hard to understand how they can stick like that. Oh yeah, I had the shoes backed way off so that was not the problem.

[jake60]

Originally Posted by gator2511

Now I'm not a delicate guy but I never had a drum come off like that! Everything was fine but its hard to understand how they can stick like that. Oh yeah, I had the shoes backed way off so that was not the problem.

Take a file and enlarge the large hole in the outside of the drum a little. The drum can hang up on the axle and make removal difficult on a 1/2 ton.

[gator2511]

Thats a good idea Jake60. Thanks for the tip. Its just hard to imagine that drum could be so hard to get off. Once it was off I could just slip it on and off with ease. I had a BIG puller on it.