Brake problem....YJ with Chev axles

[Brett]

Well, here's the deal. My friends YJ has been totally converted to a Chevy drivetrain....axles, engine, tranny and so on. Unfortunately, we can't get the brakes to work properly. We tried using the stock YJ brake booster in it for a while, but it wouldn't provide the needed pressure to squeeze the brakes. So, we swap in a Chevy booster, figuring that would work. Well, same problem. He says that it feels like it's got air in the lines, though we have bled it multiple times and even bled out the master cylinder.

So, we are kinda stuck right now on figuring it out. Everything is hooked up the same way that it was in the Chevy. It's got new calipers on it. New lines and all.

The only thing that we can come up with is that the stroke is to short on the pedal to completely engage the brakes, though we aren't sure how it could be too short.

If anyone's got ideas or things that we could try out, let me know so I can relay and get this beasty stoppin under it's own power.

 

[Shawn]

Did you tap on the calipers with a hammer? Some times air gets hung up in there.

All so, how did you fab the chevy booster to the stock peddles? I had a stroke problem but mine was to much stroke.

Portioning valve?

 

[Herzog]

You need to work on bleeding the system better. You should have plenty of power assist to stop it.

Gravity bleed them first (un-hook the lines at the axles and poor fluid in the resivor and let them run through, hook them back up then pressure bleed.

When pressure bleeding start on the line that is furthest away from the resivor (ie: passenger rear side) and work your way to the shortest distant line. ( pass rear, driver rear, pass front, driver front ) That should help get all the air out. If the pedal feels at all 'spongy', repeat the process.

 

[Brett]

Originally posted by Shawn
Did you tap on the calipers with a hammer? Some times air gets hung up in there.

All so, how did you fab the chevy booster to the stock peddles? I had a stroke problem but mine was to much stroke.

Portioning valve?

Haven't tried tapping the calipers with a hammer, so I will relay that to him.

As for the fabbing.....we did cut a little off the stock chevy rod from the booster to the pedal so that we could match it up to the Jeeps brake pedal. It should have plenty of stroke still, because it is still maxed at the top of the pedal's stroke.

Yep, got the proportioning valve on there, though, that could possibly be a problem. Have to take it out and check it.

Would running smaller than stock(Chevy) lines make any difference???

 

[Brett]

Originally posted by Herzog
You need to work on bleeding the system better. You should have plenty of power assist to stop it.

Gravity bleed them first (un-hook the lines at the axles and poor fluid in the resivor and let them run through, hook them back up then pressure bleed.

When pressure bleeding start on the line that is furthest away from the resivor (ie: passenger rear side) and work your way to the shortest distant line. ( pass rear, driver rear, pass front, driver front ) That should help get all the air out. If the pedal feels at all 'spongy', repeat the process.

Yep, we have done all that multiple times now and the pedal still feels extremely spongy.

If we can't figure it out, we're gonna drop it a brake shop and tell them to figure it out, cause this is getting frustrating!!

 

[Shawn]

Originally posted by RedRockXJ


Haven't tried tapping the calipers with a hammer, so I will relay that to him.

As for the fabbing.....we did cut a little off the stock chevy rod from the booster to the pedal so that we could match it up to the Jeeps brake pedal. It should have plenty of stroke still, because it is still maxed at the top of the pedal's stroke.

Yep, got the proportioning valve on there, though, that could possibly be a problem. Have to take it out and check it.

Would running smaller than stock(Chevy) lines make any difference???

Git rid of the proportioning valve (stock one) if you need one get an after market one.
The front chevy lines are quite small, so this shouldn't be a problem.
Like Herzog said, you have an air problem.
Tap the calipers and bleed the Sheet out of it.

Oh, and make sure that the bleeder is Vertical.

 

[Brett]

Originally posted by Shawn



Git rid of the proportioning valve (stock one) if you need one get an after market one.
The front chevy lines are quite small, so this shouldn't be a problem.
Like Herzog said, you have an air problem.
Tap the calipers and bleed the Sheet out of it.

Oh, and make sure that the bleeder is Vertical.

Okay, can it go without a valve period or is that gonna screw things up too much?

We'll try to bleed them again this week....it's up on a trailer right now...so...gotta get it back on the ground first.

 

[Caleb]

when I swapped my other axles I had this same problems...gravity bleeding works and is the best way to do it...pressure bleeding can break up the air and cause it to spread out...I kept pressure bleeding my brakes and it never got any better...I then gravity bled them and went through 2 big bottles(32oz each or something like that) and it fixed my problem I used the stock YJ brake setup with it too...you can run without the vavle but if you are running drums and discs it could cause a problem because drums take a lot less pressure than disc do...check wilwood and such they have these little things that go in the lines that hold pressure at each wheel...like 2 psi for the drums and 10 for the discs...that way it takes less to get the brakes to work...just an idea...I say go gravity bleed them some more

 

[Brett]

Originally posted by supergper
...check wilwood and such they have these little things that go in the lines that hold pressure at each wheel...like 2 psi for the drums and 10 for the discs...that way it takes less to get the brakes to work...just an idea...I say go gravity bleed them some more

What the heck is Wilwood?

We will try gravity bleeding them tommorow.....might have a hard time checking them though until we get a fuel tank or cell installed.

Thanks for the info. If you guys have anymore ideas, let me know.

Brett

 

[Caleb]

Wilwood is a brake company(specializing in aftermarket, specifically racing)...I will try and find the vavles I am talking about for you...

 

[Caleb]

here I found them...they are called residual pressure valves...here is a link on for them on their site...

http://www.wilwood.com/products/master_cylinders/rpv/rpv.asp

 

[Caleb]

another thing they mention on their site is that if the master cylinder is too large then it could cause you to have to press harder on the pedal...

 

[Brett]

thanks for the info.....we're still workin on it.....weather is kinda screwin with us right now though

If we need more help, I'll let ya know

PS....I might be working at MEPCO now