Wj master and booster issue

So I just upgraded to mc and brake booster from a wj.
Trouble is that the brakes still won't work until the pedal is pressed almost to the bottom. I bleed the mc and the brakes like instructed. I'm not sure if my drums are adjusted right but that shouldn't affect the front brakes and the pedal right? Since they are two different circuits. Anyone know what this is?

I was expecting some really firm brakes with the wj upgrade

Update: there seems to be a spot right before the brakes take, about 1/2 way down where it feels like the car is actually picking up speed. Like locking brakes in ice.

Is it safe to assume that the linkage between the pedal arm and the MC is the correct length? Were it to be a bit short, you would get a no response result as the space needs must be taken up prior to the piston actually starting to move.

Given that the WJ MC has a larger bore, installing one should improve the braking force. If it were me, after verifying the mechanicals involved (linkage length and drum adjustments) another round of bleeding would be in order.

Replacing an MC always results in a longer bleed cycle than replacing any other component other than the proportioning valve. For obvious reasons.

I trust you are using the XJ prop valve? The WJ is setup for rear disks not drums. Makes a bit of difference.

It is actually pretty amazing how much pedal travel is involved to take up even a small amount of linkage error. All you have to do is measure the distance between two points to get an idea of the travel requirements involved.

The first dimension is from the arm pivot to the MC push rod pivot and the second is from the arm pivot to the pedal itself. Divide the larger by the smaller and that gives a percentage of increased travel required to get the MC piston to move. If I had the dimensions at hand, I could give a more meaningful response here.

But, all it really matters is if the rod seats into the replacement MC in the same fashion as it did in the original. Basically, any play in the linkage is an issue.

You could just run the pedal by hand to see if you can feel when the piston starts to move.

The new booster lines up just like the old one on the pedal and I assumed that since I bought the mc that "belongs" with the booster they would line up.
Now that I think about it I might not have bled the rear correctly. I replaced the line from the prop valve to the rear and when I bled I might only have bled the axle lines. The air just pushing the fluid until I thought it was ok.

O-Gauge Steamer said:

Given that the WJ MC has a larger bore, installing one should improve the braking force.

Click to expand...

It doesn't have a larger bore. Same 1" bore as the XJ MC.

I would make sure all the linkages line up. Booster valve rod to pedal, booster hydraulic push rod to master cylinder. I would then bleed the MC alone than do a full brake bleed. What prop valve are you running?

How can they not line up? The mc goes on a rod inside the booster and the booster bolts on to the pedal.
I did bench bleed the mc. I think my problem lies with the front to rear line. I'll do another bleed on that tomorrow. I also noticed that the brake warning light is on, so I guess there is more air than fluid in the rear lines.
I am using the stock prop valve.

The brake pedal moves about 3-5mm before I can feel it pushing the mc. Is this alright?

The light can indicate a problem in the rear or front. You either have a leak or air in the system.

You've got air in the system. When I did my wj swap I had to bleed the he'll out of them. I used clear tube and connected them to the bleeders on each wheel and stuck the other ends into extra fluid containers and pumped the he'll out of them while my wife kept filling the master. Finally I got the air out and then just bled them regularly. I tried like 5 times before and then gravity bled them before I went the clear tube route. It was a real pain for me but it worked.

Ok, so I adjusted my rear brakes. That made a huge difference. The pedal is a it firmer l, but still there is a couple if inches before it seems to activate the master. There is also a kind of suction sound on the way down to where the brakes take.

Talyn said:

It doesn't have a larger bore. Same 1" bore as the XJ MC.

I would make sure all the linkages line up. Booster valve rod to pedal, booster hydraulic push rod to master cylinder. I would then bleed the MC alone than do a full brake bleed. What prop valve are you running?

Click to expand...

My bad. I was under the impression the WJ had a 1 1/16" bore.

How much pedal travel is normal? Is there a way to adjust anything?

Wj seems to travel a little further on mine.
make sure you have properly bench bled the MC. then bleed prop valve. then bleed rears. then fronts. be thorough.

I didn't think to bleed the prop valve, figured it would bleed out with the rest.
How much does yours travel?

Check the dimension of the booster's pushrod into the master cylinder. Should be minimal clearance.

http://www.autoshop101.com/forms/brake05.pdf Page 56.

What year of XJ did you do this on?

1992

How do I adjust the pushrod?

A 92
How can I adjust the pushrod?

you have to seperate the master from the booster. the rod is adjusted by turning it like a bolt. where did u get the setup at. if it is an aftermarket it could just be a bad unit or poor quality. i went to the boneyard and pulled mine.

Alright thanks.
They are both new/reman from rockauto.