mushy brakes: stumped

[baldredhead]

hi

so as part of the front axle rebuild dealio i swapped in 4runner calipers and 1" mastercylinder.

prior to the rebuild, the brakes were squishy, eventually pumping up and even stopping fairly well on the first press, just almost to the floor.

i'm pretty sure all the air bubbles are gone, pumped quite a bit of brake fluid through the whole system including the LSPV and all 4 wheel cylinders/calipers.

so, if you'll all allow that the bubbles are gone for a minute: where else do i look?

is this a possible brake booster issue?

thanks
-bryan

 

[WristPin]

The calipers you installed, are the bleeder screws on top?
If you install calipers on the wrong sides, the bleeders will be at the bottom.

 

[baldredhead]

yep, bleeders are on top

 

[Toadhopper]

If the calipers and M/C are new and bled properly.....and no fluid is leaking, there isn't much else except the rear cylinders the booster and the soft lines.
Air in the lines is the most likely reason though. Are you pretty familar with the bleeding procedure?
There is a booster check procedure on a thread you could search for.
It has something to do with pressing the pedal down as you start the engine and checking for pedal drop.
Is the squishiness the sams as before you did the parts swap?

 

[WristPin]

to isolate problems,
pinch off the all 3 brake hoses.
pushing on the pedal should feel hard. if not, problems are behind the pincher.
as you push on the pedal, and have someone remove a pincher. ifthe effect is negative, you have further isolated the problem....

 

[agent orange]

I had a hell of a time getting a firm pedal after i swapped my caliper and MC. I would start with making sure the master cylinder is bled properly, i had some issues that stemmed from bubbles in the MC. Heres a link to a good thread about bleeding the MC https://forum.ih8mud.com/showthread.php?t=74063&highlight=bleeding+master+cylinder. Once youre sure about that, bleed the all 4 corners and the lspv a couple times. If its not better then, check the other stuff. Make sure your ebrake is adjusted right, other wise your drums might be out of adjustment and the excess travel back there is causing the problems. Do you have a residual pressure valve in the system?

 

[Cruiserdrew]

I was going to mention the bench bleed of the MC. I've always done that with a new MC and I've never had mushy brakes. Not sure if that will be the answer, but when you get right down to it-there has to be air in the system somewhere.

 

[baldredhead]

i use a pressure bleeder, motivepower bleeder style.

didn't bench bleed the master cylinder, so i think i'll start with one of the mastercylinder bleed methods.

the parking brake does need some adjustment too, i guess it's finally time to diagnose those problems.

squshiness is about the same as before the parts swap, and there is no residual valve in the system. i haven't seen mention of that being needed unless you get a MC from a rear disk brake truck and use it on a drum rear vehicle

pinching brake lines makes me a little uneasy, i replaced all the soft lines. will pinching damage them at all? they are NOT stainless.

thanks all, at least i have a few things to chase now

 

[Toadhopper]

I will second (or third) the MC bleeding. It can be done pretty easily after its been installed. Wrap up the hardlines in a rag to keep fluid from getting all over and crack the lines open to get the air out. If you cant find a thread in it post up and i'll go into more detail.
Toad

 

[Man Jerk]

Adjust your rear brakes. I'd bet that is the problem.

 

[baldredhead]

the rear brakes were indeed the problem. i didn't bleed anything

i had a helper yank on the lever while the wheel and drum were off to confirm that everyting was functioning on both sides. then just kept pulling and letting the lever down with wheels and drums back on. eventually the parking brake started working, pressure came up in the brake pedal immediately and now i have brakes again. WHOOOOOT

lesson learned, again: start with the basics

 

[sundaypunch]

the rear brakes were indeed the problem. i didn't bleed anything

i had a helper yank on the lever while the wheel and drum were off to confirm that everyting was functioning on both sides. then just kept pulling and letting the lever down with wheels and drums back on. eventually the parking brake started working, pressure came up in the brake pedal immediately and now i have brakes again. WHOOOOOT

lesson learned, again: start with the basics

I replaced my calipers and have the same mushy brake problem. I'm using speed bleeders and have gone around 3 times and am pretty sure there is no air in the system. I'm thinking I might have the same issue w/ my rear brakes.

Just so I understand, did you just keep working the parking brake lever up and down to get it to start working? I'm not sure why that would help firm up the brakes?

Thanks

 

[agent orange]

The parking brake has a little lever thats supposed the turn the star wheel in the drum to tighten them, but i just rebuilt my drums and pretty much decided that they dont do s***. You need to go get a brake spoon and turn the little toothed wheel thats visible through the slot in the backing plate to tighten them. Turn it clockwise to tighen the shoes. Id pull the drum and take a minute to familiarize yourself with how to tighten/loosen everything, it took me a while to figure out just how to loosen them with the drum on, save yourself the aggravation and pull the drum and familiarize yourself with the inner workings. Get some M8x1.25 bolts, they thread into little holes on the drum and pop it right off.

 

[sundaypunch]

Thanks for the info. I finally figured out that my parking brake doesn't adjust anything either. It actuates the lever outside the drum but doesn't turn the wheel. I ended up manually tightening the rears and it made my pedal way better. It took a while to figure out how to release the adjusting lever from the wheel but I was able to with a small screwdriver. I can see how the curved tool would make it easier.

 

[baldredhead]

if your rear brakes don't auto adjust, it's possible something has rusted together. when i rebuilt the rears, i checked/lubed everything and now the parking brake works just fine. i highly recomend figuring out why your parking brake isn't auto adjusting the rear drums, the mechanism is really simple once you stare at it a little.

sundaypunch, yes all i did was pull and release the brake lever in the cab till things firmed up. it took a few dozen pulls before it started working.

 

[sundaypunch]

I highly recomend figuring out why your parking brake isn't auto adjusting the rear drums, the mechanism is really simple once you stare at it a little.

Yeah, that's on "the list". It's a long list

Just finished a knuckle rebuild and front calipers / lines. Time for a breather. The exhaust leak is next....

 

[baldredhead]

the rear brakes should take about 1/5 the time, if that, compared to the front axle. suck it up lazyass