Brake System Issue after Knuckle Rebuild.

[Crash_AB]

Hey All,

I recently completed a knuckle rebuild on the passenger side, and after buttoning everything up, everything seems to be working fine – except for the minor issue of having a complete lack of brakes [minor issue].

They pressure up a bit when I pump them, but never to a firm pedal, and this quickly fades till the pedal has nothing to it and can be pushed right to the floor – maybe 10 seconds?. I had a pair of small vise-grips pinching the rubber closed while doing the knuckle. I can’t see any leaks; nothing on the lines, calipers, or from the master cylinder. The fluid in the reservoir doesn’t drop and I have bled the living daylights out of both fronts.

Any procedures you can recommend trying? Anything I should be looking for?


Cheers,
Spencer

 

[Downey]

Assuming you blead properly and are loosing no fluid, the only other thing that comes to mind is that you may have damaged/destroyed the rubber hose when pinched with the vise grips. Now when you push the brake pedal, the hose merely swells up into a big bubble of fluid. Have a helper push the pedal while you look at the hose?????

 

[MANUCHAO]

how long did you left the reservoir empty?
I had issues with my brake system after it sat for a long time on empty... so I went ahead and upgraded to a 4runner MC and Calipers....... they are nice and firm now

 

[jvazquez53]

Sounds like a lot of air bubbles in the system!

 

[orangefj45]

i'd foloow jim's advice and get a good look at the brake hose where it was pinched with the vise grips. if you have to use them on soft brake hoses, then wrap a rag around the hose a few times first so the teeth of the vise grip can't hurt the rubber hose. also, you don't need to pinch the heck out of the hose; there's no pressure in the hose when the brake is not applied. personally, i don't like using the vise grips unless absolutely necessary like when you're going a field repair. it's just as easy to undo the brake line and put a vacuum plug over the end.

after inspecting the line, iwould attempt to bleed it if the line looks ok. if any air got in the master, then you might have to bench bleed it. otherwise it can be tough to get all the air out of them.
if no air got in the master, then fill up the reservoir and gravity bleed the lines until the fluid comes out cleam. make sure to keep the reservoir full so no air gets in there.
once you get clean fluid, shut the bleeders and then pressure bleed the brakes. tap the calipers with the plastic handle of a screw driver to knock any air bubbles loose from the casting; they like to stick to the cast walls inside the calipers. do so while bleeding them.
hopefully this will take care of your issues. i go thru the same procedure when bleeding a clutch hydraulic system.

hth

georg @ valley hybrids

 

[cando john]

x2 on the bench bleed

 

[Crash_AB]

Excellent, I will try those this evening: Inspect the hose, knock the calipers as best I can, bleed the master cylinder, gravity bleed the system, final pressure bleed. In that order...

If that doesn't solve it, I really don't know where to do next.

Thanks for the advice guys.

 

[orangefj45]

any news?

 

[Wile E Coyote]

Air would be #1, so if above doesn't pan out:
Did you jack up a brake piston bore inside the caliper? If you had to spread the pads a bit to get them to fit over the rotor, and cocked the piston in it's bore or otherwise damaged it then that caliper would be toast. Don't overlook the idea that the fronts are okay and air got into the back portion of the system.