Brake upgrade

[Joshooha]

Hey guys and gals. I have an 89MJ 4.0 5spd peugot STOCK 2wd

Recently I swapped out my stock master cyl/booster from a 2000 XJ, and made some new steel braided front whip lines for it. Well I did it at my house and then once I was all done and bled the brakes I realized the damn pedal is about a mile and a half too high!

So I took it over to my shop and it had the best brakes I have ever had on a stock vehicle in my life haha. Well I decided in order to lower the pedal I would take it all back apart and cut the Eyelet that the brake pedal bolt goes through from the booster and crop it. I measured my install length (to the center of the bolt) on both the stock booster and the 2000 booster. It showed that the 2000 booster moved the pedal 1.5" further towards the driver, so obviously that was the problem. The other problem I had was the the eyelets were different sizes and I couldn't re-assemble the brake pedal and brake light switch correctly as they had 2 different styles switches. I believe the first design was 1984-1990 and from there it changed to the design you see on most late models.

I cut the eyelet off the old booster and welded it to the new booster. Re assembled everything and now the height is exactly what it was stock. After dealing with minor brake fluid leaks from several areas I have an issue with the brake pedal being really spongy from when I originally put it all together. I have bled the brakes, but its still spongy. Also my "brake" light is illuminated on the dash. The only thing I can think of doing is driving for a few more days, hopefully it will let a little more air surface so I can re-bleed the system.

After all of that, is their any possible way I could have damaged that booster or cylinder when I pulled it apart? I did separate the cylinder from the booster when I welded everything and the booster was sitting inverted on a table so I could weld on it.

Any other ideas other than bleeding the system would be appreciated! thanks!

 

[yossarian19]

The "brake" light is usually illuminated when the proportioning shuttle valve has uneven pressure on it's two sides, shoving it one way or the other to complete the circuit. I had to guess, I'd say you had air left in one chamber of the MC or in the prop valve.

 

[Joshooha]

That's the only thought I had as well. When I separated the master cyl from the booster I did not open up any lines to cause it, but I did have a slight leak at the prop valve to the rear of the truck and the banjos were leaking at the calipers.

 

[shortxjdoug]

Do you still have the load valve in the rear?

 

[Joshooha]

Ya, it's all still there, but the rod from the block to the rear end housing isn't. So it doesn't function.

 

[shortxjdoug]

It has a funky bleeding procedure iirc. Mine are all deleted completely.

 

[Joshooha]

Ya, I did consider doing that actually. After all that shit I had to do, I should have in retrospect. I'm gonna run it as is for now, if it becomes an issue I will for sure get rid of it. Eventually I would like to do a limited slip D-44 and disc brakes on the back.

 

[cruiser54]

Best booster upgrade is the WJ option.

The rod is the correct length but needs to have a flat ground on it. The metal tubes have flexible braided parts to them making that easier also.

 

[87manche]

It has a funky bleeding procedure iirc. Mine are all deleted completely.

this.

the third brake line is a fail over line. It must be bled first.

the FSM tells you to pop a front brake bleeder and then step on the pedal until the brake fail light comes on. That indicates that the prop valve has shuttled to block the front brake circuit.
That will open the bypass line to the rear brakes. Bleed rear brakes with the front bleeder open.
After it's bled, close the front bleeder. Now bleed the system normally.

this is also a very good time to make sure that the fail over line still works. Remember, it's 25 years old and hasn't moved in a while.

If you don't want to deal with it, take off the rear prop valve, send it to me if it still functions, and replace your front valve with an XJ or XJ valve, depending if you've done rear discs or not.

 

[tbburg]

take off the rear prop valve, and replace your front valve with an XJ or ZJ valve, depending if you've done rear discs or not.

What he said.
If you're not using the load valve, it's just an extra failure point in the system. There's a few horror stories about people loosing brakes under panic-stop conditions because the seals in the load valve failed under high pressure afer years of non-use.

 

[Joshooha]

alright. I'll take all this into consideration here. I'll probably dive into it a little this week. thanks!