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1 ton 4 wheel disc disk brake issues

M

Mudstud

1/2 ton status
Joined
May 29, 2001
Posts
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Location
Memphis, TN
Where to start? I read and read and read the search results for brake issues now I'm just gonna ask for help. This is on a 76 K5- I did the 14 bolt disc swap while the truck was 3/4 ton. Used all factory brake stuff, just put on 3/4 ton calipers and rotors on the back. Never had good brakes during that time- Drove it very little. Fronts seems to grab while the rears did little grabbing. Now I just put the 60 up front, I also gutted the factory prop vavle (front and rear half of it). Plumbed in a Wildwood adjustable prop valve in the rear line only. I had a leak in the rear half of the factory prop valve so I just by passed it completly. So now I have the fronts running into a gutted factory valve to give me 100% pressure there and an adjustible prop valve in the rear, mounted right off the mc. I made a low pressure power bleeder. Hooked it up to the mc and opened the rear bleeders, nothing! I never worked the peddle while it was under pressure. Gave it a few more pumps and then the fluid started gushing outta the mc cover I adapted for the power bleeder. I tried gravity bleeding the system for about 2 hours last night and could not get fluid out of the rear calipers. Without the power bleeder hooked up, if I mashed the peddle some would squirt out but couldn't get it to constantly flow likeit should being gravity bled. Any words of wisdom for me? All my brake lines are SS. :confused:
 
what master ? if dana 60 front might need the bigger master. and also possible back half of master is bad. and wont flow to rears. try a mighty vac on the bleaders to pull fluid down to the rears.


and there is a thread in hear on a better master for 4wd setup last few weeks.
 
You might need to start with the front brakes. Whichever end the master cylinder is providing pressure for first should get bled first to get you going. I think your problems began when the porportioning valve was gutted. Its probably making it a bit harder to bleed. Finish it up the old fashioned way of working your way in from the wheel furthest away from the MC.
 
I just converted mine to 4whl disc. 'Didn't bother with the combination valve at ALL (just used an adjustable proportioning valve on the rear)

Assuming your "gutted" combination valve eliminated both the proportioning and the metering features; all that should leave is the imbalance switch. Maybe you should just bypass it to see if this is where the restriction is.

If it's not combo valve that leaves an issue with the master cylinder itself. (you did install the the adj pro valve in the correct direction, right?)
 
Dick brakes require more fluid that drum brakes. I would say you need to upgrade your master.
 
The problem of hardly any brakes in the back showed up when I first put the 14 bolt in with drum brakes. The brake light would stay on mostly. Swapped to 4 wheel disc like I said with nothing modified in the factory brake system except the rear calipers and braking was worse. I basically wanted to replicate what seems to work for the majority of people on CK5- plumb the front of the mc directly to the front calipers (100% flow thru) and plumb in an adjustable valve for the rears to adjust them according to the fronts. Tonight I'm gonna 'truck bleed' as opposed to 'bench bleed' the mc and see what the results are of that. If I get tons of air out then I'll manually bleed the sytem (without fooling with the lil button thing on the factory valve) If it still doesn't work then I will but either the 78 Firebird mc that is set up for disc or get the largest bore 1 ton chevy mc. Does this sound like a good plan? Could use my home made power bleeder to push fluid into the bleeders back up to the mc.

Yes I have the adjustable prop valve installed correctly- IN from MC and OUT to the brakes.

Thanks for all who chimed in. I need to get this fixed so I can drive the dang thing up to a friends to have him set up the 14 bolt 5.13 gears. Gotta big ride in Gray Rock coming up in a couple weeks.
 
I second taking the stock combo valve out of the system. That you aren't getting fluid to even dribble out of the rears makes me think that the combo valve's shuttle pin has been moved.

If you get to the point where the pedal is mushy and no amount of bleeding helps, then start looking into the m/c.
 
The stock prop valve IS out of the sytem for the rear brakes. Currently, only the fronts are plumbed through it. I have the adjustable Wildwood prop valve in the line to the rears. It is screwed wide open. My guess is I've got an air bubble in the rear half of the mc. Once its out then maybe it'll flow right on through. Tonights bleed session should reveal something.
Thanks again. I'll post up the results.
 
info on the stock valve. it is already 100% flow in fronts just splits it. and the rear is restricted. just buy a t fitting and install it for the front. what master do you have ? 1/2 ton or 3/4 ton. friend has 1/2 ton with 3/4 ton axles and drum rear. i think his brakes suck. 3/4 pedel travel before real brake use.


dont forget the 1 ton masters dont normaly fit the 1/2 and 3/4 boosters.
 
Ya, if you were getting a brake warning (idiot) light from the begining then I'll bet your MC was crapping-out. I got a big 1-ton MC (late model with factory disc brakes). It bolted on fine to my hydrabooster.
 
D- Dan you gotta 89 Jimmy 1 ton. I wonder if the later model 1 ton factory 4 wheel disc MC would still bolt right up to my old 76 booster? I like the idea of using a later model factory 4 wheel disc MC. Do you have a part number for the one you used or an appication it's used on? Your rigs brakes feel and work good? If you think it'll bolt up and you like your brakes I'll buy that one and hopefully all problems will go away.

Thanks.

BTW- Did the 'truck bleed' (bench bleeding on the truck) thing last night and got some air outta the front and rear reservoirs. Attempted to push the fluid up through the rear caliper up to the MC but wasn't sure if that would screw up the wildwood adj prop valv so stopped after a few pumps and then mainually bleed them. Got lots of air outta the rears and the front. Still spongy but the truck stops. Trying to decide which MC I should get now- early model 1 ton disc/drum OR D_Dan's suggestion, late model 1 ton disc/disc OR the 69 corvette disc/disc. Gotta call and verify bore size on the corvette one.
 
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I am currently using a MC for the stock application that my hydroboost came from - a 1981 diesel with disc/drum setup. The brake pedal has a great feel, much better than when I ran a vacuum booster and a 3/4 ton MC.
 
I don't really know if it will bolt up to your booster. I use a hydrabooster not a (vacume) diaphragm.

I wish I did have the part number. The master cylinder came off a wreck and it had already been pretty gutted by the time I got there. It is a Bendix unit don't remember seeing any numbers. All cast including the reseviors (which are equal size fr & rr). Yes it feels good; strong but not overly sensitive.
 
All right. I went with the 77 K30 mc. "T" ed the front lines and straight plumbed it to the rears with the Wildwood adj valve in the rear line. The brakes work awsome now. The real trick was the bleeding proceedure. With the new mc installed we truck bleed it- (bled it on the truck, not in the vise- used half the peddle travel to do this and worked the peddle slowly down AND up, beating on the mc often to dislodge bubbles.) With a full mc we began bleeding in typical order (rr,lr,rf,lf) Didn't pump pump pump/hold the brakes. Boz42 cracked the bleeder then told me to push the peddel moderatly, at half way down I said 'half' and he closed it while I continued pushing thru the half way point. I would let the peddle raise up slowly. He's giving the whole brake sytem a few good raps with a wrench to dislodge the bubbles. Then do it again. Had to go around to each wheel a couple times but it was worth it. With the truck off the peddle felt great. As soon as I started it it felt very soft but as soon as I rolled forard and hit them they stiffened up and were great. Still gotta dial in the rears better cuz they lock up a lil to soon. The fronts and rears will lock up now. Yea! :D
 
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