Brake bleeding issue??

[Thardy]

Ever since I swapped the axles on my 96 runner I have not been able to get a good brake peddle. I can bleed the crap out of them and get a solid peddle then as soon as I turn the key on I lose it. I took it over the the local shop and had them try and they got the same results. They want to change the master cyl and the booster. My dad called his mechanic buddy and he thought it sounded ABS related. Any thoughts on this???? I really don't think its the booster or mc because I had no problems until I swapped the front axle. Then it got worse when I swapped the rear.

Any thoughts would really help. That is all I have left before its ready to hit the trail..

 

[Kevin B.]

How do you still have ABS, Ty? Your sensors are on the axle in my driveway.

I remember you had brake problems the last time you played with your axles. If memory serves, a hard pedal that gets soft when you turn the truck on is a bad master... ?

 

[Thardy]

I still have all the bits minus the sensors. The mechanic buddy thought it might have something to do with removing the sensors and not disabling the system. I am going to pull the fuse and see what happens. I just thought I would get some expert opinions.

When I bleed it I get a good solid peddle and it holds until I turn the key on. If if were the MC wouldn't it bleed off as I hold it even with the key off???

 

[Jinx]

Vacuum booster or hydro booster?

i am guessing vacuum. Some where you are introducing air into the lines. What does it looks like when you bleed them? Lots of bubbles?

Also do you see any leaks? Air in usually means fluid out.

Be patient we can figure this out.

Last question: how are you bleeding them? Pumping the pedal, gravity, or vacuum or other?

 

[Thardy]

I couldn't find any leaks and there didn't seem to be much air. We have been bleeding via pumping the brakes. I could try gravity.

 

[zmotorsports]

It could be the ABS pump/module. On the early Kelsey/Hayes systems I have seen debris get caught in the dump valve and it act just like that. It won't send an ABS light either because the earlier systems didn't monitor actual dump valve positioning.

Mike.

 

[boogie_4wheel]

Do you have to cycle the abs motor like you do on a GM truck?
My late 90's GM had a high spot in the ABS unit and 'required' the scan tool to force run the ABS motor to pump the air/fluid from this high spot as part of the proper braking procedure.

 

[LJENS]

Soft/squishy flex lines maybe?

 

[bobdog]

If the calipers on your new axles are bigger than the old ones you probably need to swap in a master cylinder with a bigger bore.

 

[Thardy]

So new master cylinder, new booster, bypassed and removed ABS system, had it to a garage and put another new master in and power bled it, still very soft pedal. It will stop, but I worry about getting on a rock and it not being enough. Any thoughts?????

 

[Jinx]

Did you bench bleed the MC before installation?

When I first replaced a MC I was blown away with how much air I got out of the new master cylinder following the bench bleed protocol in the instructions.

I am running a stock cj MC on one ton brakes and calipers with no issues.

 

[Thardy]

I don't know. My dad did the first one and the garage did the second one. I will ask in the morning.

 

[zmotorsports]

You mentioned after swapping axles. I am wondering like someone mentioned above about the calipers having larger volume and now with the stock master cylinder you are not able to fill the calipers and have enough volume for a firm pedal all in one push. If you pump the pedal more than one time does the pedal get hard. If so it definitely sounds like a volume issue.

Mike.

 

[Thardy]

I looked into that and a stock Master should supply plenty. I believe it has a 1" bore and a 3/4 ton Chevy has a 5/8 bore. Not positive, but that way the impression I got.

 

[bobdog]

No. 1/2 ton chevy was 1 1/8 and 3/4 ton was 1 1/4

 

[Thardy]

You're right. I don't know where I got that inf . Even the jeep that I got the axles from has a 1 1/8 bore.

I haven had it out on the trail yet, but just on the road it doesn't feel that bad. It soft at first but stops fast and holds well.

 

[blznnp]

this might be stupid, but maybe a suggestion, are the lines on the right spot on the master? The only reason I say that is I am having a similar issue, not as soft of brakes from the sound of it. It stops, have bled the brakes multiple times, but when going down hill (offroad only) i have all my weight on the pedal and it just crawls down, usually at a good speed for the spot but I can't stop it if I have to. When I was in Moab this last summer with other s10 guys, all with V8's and upgraded brake systems, seemed that a couple of them had their lines reversed at the master from mine. Everything I have read and look at shows mine are set up right, but from what they told me, its different from theirs and they could stop on the same down hill spots that I couldn't. Made it hairy sometimes if we didn't have enough room for the rigs at the bottom. again, might be stupid and not make much sense, just something i am gonna try.

 

[Thardy]

Makes sense. I'm going to see what it does offroad and check it that as well.

 

[Chase39]

yeah go chevy master cylinder and never look back. Took me 30 minutes to build a 3/8 plate for my 91. you can get the master for like 40 bucks and it will work wonders.

I plumbed my brakes with the old 1 inch bore stock before I swapped and it could never push the volume. once I got the Chev master on its like having brand new brakes again.

 

[Thardy]

yeah go chevy master cylinder and never look back. Took me 30 minutes to build a 3/8 plate for my 91. you can get the master for like 40 bucks and it will work wonders.

I plumbed my brakes with the old 1 inch bore stock before I swapped and it could never push the volume. once I got the Chev master on its like having brand new brakes again.

How hard is it to make a Chevy Master fit in a Toyota??