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Brake issues 98

bison

bison

Well-Known Member
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Location
Near Peace River-Alberta
I need to haul a load of bison to the butcher but I have trouble getting my truck to stop. I can push the brake pedal to the floor when braking hard.Been like that for a long time but it won't do towing 15000 lbs
Replaced rear drums and shoes last year, replaced front pads today although the old ones had plenty life in them(rotors and calipers are OK)
Front wheels will skid on the gravel,ABS kicks in as supposed to,.. rear wheels keep turning
Rear shoes adjusted and I bled the brakes all around for good measure. no result.
PS pump full and working fine.Brake booster appears OK
No leaks in the brake system

What gives?
 
There was a member here that pointed out different wheel cylinder bore diameters making a notable difference in braking power. Not sure of the whys or hows of that particular circumstance. Just a thought.

A whole list of things can add up. Hoses, less than optimum brake shoe compound, lack of trailer brakes.. Etc.
 
3500GMC said:
There was a member here that pointed out different wheel cylinder bore diameters making a notable difference in braking power. Not sure of the whys or hows of that particular circumstance. Just a thought.

A whole list of things can add up. Hoses, less than optimum brake shoe compound, lack of trailer brakes.. Etc.
Click to expand...
None of the above applies to the problem at hand,..truck's brakes are stock and well adjusted,.. trailer brakes are electric.

Pedal is not supposed to bottom out ,..they don't feel spongy.

Proportioning valve??
Were is it located and how to reset.
 
bison said:
I need to haul a load of bison to the butcher but I have trouble getting my truck to stop. I can push the brake pedal to the floor when braking hard.Been like that for a long time but it won't do towing 15000 lbs
Replaced rear drums and shoes last year, replaced front pads today although the old ones had plenty life in them(rotors and calipers are OK)
Front wheels will skid on the gravel,ABS kicks in as supposed to,.. rear wheels keep turning
Rear shoes adjusted and I bled the brakes all around for good measure. no result.
PS pump full and working fine.Brake booster appears OK
No leaks in the brake system

What gives?
Click to expand...

Burning oil said:
Air in the lines? Try bleeding I bet it improves.
Click to expand...

;)
 
Master cylinder is more probable from the pedal to floor description, except the good front braking and poor rear braking makes me suspect it. Could be a waste of $ but when it comes to brakes I don't pinch pennies.

The proportioning valve is the rectangular aluminum looking block that both the front and rear lines feed into and out of. Most but not all have a small circular button looking piece on the side of it. No adjusting, just replace. I dont own pickup anymore, by the '01 burb it is on driver side frame rail. Follow brake lines out from master.
Flush all fluid while your at it, moisture is a killer.
 
Simple and cheap first, Simon. Humour me. I forgot about the old valves.

I bet your pro portioning valve is locked out (segmented sustem). It can happen when you get a leak, blown line, or just excessive travel in the rears. There is a toggle that locks out front or back in brake loss conditions. Ie - when the back line blows, the toggle flips to the back and shuts off the fluid so the fronts still work. Needs to be reset.

Set up your rears so they're close, have the wife step on the brakes hard and while she does, crack the front lines at the valve so the toggle flips back to the middle. If you overdo it, the fronts will lock out.

No cost, it won't hurt to try.
 
There is no toggle on the proportioning valve on these trucks I don't think. The proportioning valve is bolted onto the side of the ABS pump, and is a completely sealed unit. There IS a possibility you have air in the ABS unit which is impossible to bleed out without a scanner that can can talk to the ABS and initiate a system bleed(run the ABS through a system test and bleed it internally). It sounds more like a bad master cylinder to me, but it could be the proportioning valve or a sticking isolation valve inside the ABS pump. If the isolation valve sticks, all of your fluid pressure will simply go into the ABS accumulator piston instead of making it to the wheel cylinders.
 
THEFERMANATOR said:
There is no toggle on the proportioning valve on these trucks. The proportioning valve is bolted onto the side of the ABS pump, and is a completely sealed unit with no toggle in it that is resettable.
Click to expand...

Thanks for the correction, Ferm. I remember having to do that to an old truck I had, didn't know if it had stayed the same into the future models. I suggested it because it didn't cost anything to try.

Sorry for the dumb suggestion, Simon.
 
I bought a subscription on Alldata and it confirmed pretty much what Ferm said.
The literatuur pretty much points to the master cyl bypassing internally.
I have a spare out of a 95 sitting on the shelf,..hope it is the same as the 98.
As for air i can't see how it could have gotten in cause i never had the fluid system open or a low fluid tank level and i never found any when i bled it yesterday.

Don't worry Jim, Your first suggestion on the master appears to be dead on,..you can't be right all the time.;)
 
One way of cycling the ABS to bleed it that has worked for me is several lockups on a big patch of snow or in a pasture full of wet grass when there's no snow.
 
I went through my whole brake system which was basicly replace everything. The only thing I didn't replace was the MC cause I was sick of spending money. The pedal still went to the floor pretty easy and replacing MC was the final cure. I thought I could get away without replacing it cause it was only thing that didn't leak. The truck stopped well on the highway loaded with full mechanic tool chest and carpentry tools. The only thing I'm gonna upgrade is rubber lines for dot stainless hoses soon.
 
Update,
I changed the master cyl out and bled the system all around, still no rear brakes.
Pedal is hard when stepped on with engine off but i can step it just about to the floor when stepped on hard with engine running.
I checked my other 3 trucks and they all act the same so it must be normal.

I decided to take the rear drums off and have a looky see.
Shoes were greased op badly from leaking axle seals on both sides so that was why no braking.
I replaced shoes drums and hub seals less than 5 k ago but had to replace the hub seals(apparently wrong size with the kit ) again within a week of install with OEM seals due to oil dripping from the drums , i never figured them gonna leak again that soon.
hub bearing are ok and were adjusted properly( no hub play)Seals look perfect the OD and ID are correct for the application , Axle stub seal mating surface is perfect(no grooving or burrs) seal lip rides were it is supposed to be. Axle breather cap hose and hose end leading into the axle housing are wide open

Why would they leak??????

I picked up another set of seals which are supposed to be for the newer models but they fit the bill so to speak( It is seal that presses in the hub like normal but it a rides on a integrated collar, the collar is a tight push fit on the axle stub(not a speedy sleeve)
Hopefully it does the trick.
 
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