Rear brake bleeding struggles

74 k20. I'm new to these things aside from dirt bikes and quads.

I don't know if the rear brakes were working before but the pedal was mushy. I bled the front brakes fine (ish).

When I went to bleed the rear left the vacuum wasn't pulling any fluid at all. The bleeder screw was cleaned out before trying. So I tried the old pedal pump method and that seemed to work.

I was afraid I messed up the proportioning valve but I'm assuming that this was not the case if the rear left was working.

It still seems odd that it worked pumping but not vacuuming. No biggie. Got a few bubbles out and topped off the reservoir.

On to the right side rear. Cleaned out the bleeder screw (brake cleaner, small wire). Note: neither side leaked fluid with the bleeder screw removed. Maybe that's normal for rear brakes.

The vacuum wasn't pulling anything so I tried the pedal and nothing was going to that drum at all from the pedal.

I have the proportioning valve that has the little reset button for the front (I believe).

Any thoughts of how I should diagnose this? It almost seems like that line from the split on the axle is clogged because I could pump fluid through the rear left. That said the brakes on the rear are not working at all.

Also when pumping the brakes we do this with the motor off. I'm assuming that's correct.

Maybe the rubber part of the line is collapsing when applying the vacuum, and a seized right rear wheel cylinder?

Normmus said:

Maybe the rubber part of the line is collapsing when applying the vacuum, and a seized right rear wheel cylinder?

Click to expand...

That would explain the vacuum failure.

If it was seized, wouldn't brake fluid still come out of the bleed screw?

Bleeding brakes is something I've failed at with motorcycles/quads/mountain bikes and now trucks . The nice thing with this truck is I really don't even have to remove the tire to bleed it. It's pretty easy to access from the back.

If you had to clean out the bleeder screw, and no fluid came out of them, the wheel cylinders are shot.
Good news is , if the bleeders came out, you should be able to get the brake lines loose without much issue.

yes it should, but the steel line could be blocked between the flex hose and wheel cylinder

Im goin with wheel cylinder too.
Also.
As well as
In addition to

They got that deal in the valve what goes to one side if it's bad so the rest still works?

Here's your clue, Blue.

Gravity bleeding can't not work...
Somethin ain't right.

*edit"
Pintle! That's what that slidey deal is called.

Have you tried this yet get a friend or family member have them sit in the drivers seat open up one bleeder on either right or left your choice open up the bleeder and have who ever slowly push the pedal down with the pedal down close the bleeder then have them let the pedal up then do the same procedure until there is fluid from that side wheel cylinder if you get fluid close the bleeder then do the same on the other side. If you get fluid from both sides fill up the master open up both bleeders and see if fluid gravity bleeds from both sides. If so cap the master and bleed all of them one last time to remove any left over air. If only one side has fluid than there is a problem from the tee at the rear to that wheel. If neither of the rear gravity bleeds than there's a problem with the master. Hope this helps

Jimmyperf400 said:

Have you tried this yet get a friend or family member have them sit in the drivers seat open up one bleeder on either right or left your choice open up the bleeder and have who ever slowly push the pedal down with the pedal down close the bleeder then have them let the pedal up then do the same procedure until there is fluid from that side wheel cylinder if you get fluid close the bleeder then do the same on the other side. If you get fluid from both sides fill up the master open up both bleeders and see if fluid gravity bleeds from both sides. If so cap the master and bleed all of them one last time to remove any left over air. If only one side has fluid than there is a problem from the tee at the rear to that wheel. If neither of the rear gravity bleeds than there's a problem with the master. Hope this helps

Click to expand...

We did do this. The rear left bled fine. The rear right did not.

It seems like the line or the caliper is blocking any fluid from coming out. I guess I should pull the line out of the caliper and see if the fluid can get that far.

Chris64 said:

We did do this. The rear left bled fine. The rear right did not.

It seems like the line or the caliper is blocking any fluid from coming out. I guess I should pull the line out of the caliper and see if the fluid can get that far.

Click to expand...

Confused, you have disk brakes in the rear on that truck? Or did you mean wheel cylinder?
You haven’t expounded on the basic condition or believed age of the brake components, but my assumptions was they are OLD. If that’s the case, any/all could be an issue and any/all components could/should be replaced.

Grit dog said:

Confused, you have disk brakes in the rear on that truck? Or did you mean wheel cylinder?
You haven’t expounded on the basic condition or believed age of the brake components, but my assumptions was they are OLD. If that’s the case, any/all could be an issue and any/all components could/should be replaced.

Click to expand...

You're correct - I meant cylinder.

I'm watching videos on replacing the cylinder now. I guess that's in my future. Time to buy some new tools (spindle nut socket?).

Chris64 said:

You're correct - I meant cylinder.

I'm watching videos on replacing the cylinder now. I guess that's in my future. Time to buy some new tools (spindle nut socket?).

Click to expand...

Hopefully you have the type of rear end that lets the drums just come off when you take the wheel off. I have the full float 14 bolt and removing the drums will involve pulling the axle shaft out of the center section. Needless to say I'm not at all looking forward to THAT when the time comes.....

Chris64 said:

You're correct - I meant cylinder.

I'm watching videos on replacing the cylinder now. I guess that's in my future. Time to buy some new tools (spindle nut socket?).

Click to expand...

Yup, if you can’t force any fluid thru the wheel cylinder then it’s time to take it apart. If you suspect it’s been (decades) since rear brakes have been apart, probably in for wheel cylinders, pads if they ever leaked or if worn, spring kit and adjusters at a minimum. E brake cable(s) replace flex hose at the diff, axle seals while it’s apart. Assuming the drums are good or can be turned.
If you plan on keeping the truck a long time, drum brake work on a full floating axle is a bit of a process, so best to do it once and do it right, imo.

Part of the reason I’m thankful our 86 K20 is a semi floater and that the brakes had been redone completely, front and rear. Was a lot of value in that in my opinion when we bought it.

YakkoWarner said:

Hopefully you have the type of rear end that lets the drums just come off when you take the wheel off. I have the full float 14 bolt and removing the drums will involve pulling the axle shaft out of the center section. Needless to say I'm not at all looking forward to THAT when the time comes.....

Click to expand...

That 14 bolt process is what I'm watching. Mine is the 10 bolt so maybe it's not quite so exhaustive

You have a k20? 1974 would be a full float 14 bolt. 12/10 bolts came in half tons.

Inboard rotors/drums are not as convenient as if they were outboard, but not really a big deal overall.

Buy the correct socket for the axle/spindle nuts.

If drum needs to be removed to be changed or turned, it will require pounding all the lug studs out and reinstalling them (personally I’d replace them).

Technically, on a drum brake full floater, you don’t even have to take the wheel off to pull the hub/drum, if you were only needing to change a wheel cylinder and no work needed on drum itself. Pull axle shaft (make sure you have enough room to slide the shaft out), spindle nut(s) off and slide assembly off.

Not something most do on smaller trucks, but class 8 and medium duty’s that pretty normal to pull the hub, drum, wheels as an assembly.

Other than that they are not really any different than any other self adjusting drum brake setup.

Also, I’d replace the rubber soft lines, if they have not been replaced in your ownership or a known date of if/when they were replaced. One of those fairly cheap parts that get overlooked and can cause plenty of headaches.

If and when you go back together with the hub....DO NOT drag the seal over the threads on the housing........you will be taking it back apart to fix the differential oil leak that's ruining your new parts inside the drum!!!