Brake Booster & Master Replacement;'78 FJ40 (4 Viewers)

[tls3601]

So I just pulled off the master and no gasket between it and the booster, but some gooky looking fluid on inside of booster(see pic). I did order a gasket for that area and now wonder if I should put it in as there apparently was not one there?? Also do I need to remove the carb to get out the old booster and put in the new/rebuilt one from SOR?? I have like a half inch clearance from what appears to be the bell area of the carb. Has anyone done this recently? Help........

 

[Racer65]

So I just pulled off the master and no gasket between it and the booster, but some gooky looking fluid on inside of booster(see pic). I did order a gasket for that area and now wonder if I should put it in as there apparently was not one there?? Also do I need to remove the carb to get out the old booster and put in the new/rebuilt one from SOR?? I have like a half inch clearance from what appears to be the bell area of the carb. Has anyone done this recently? Help........View attachment 1080740 View attachment 1080741

What you need to do is to remove the bolts on the clutch Master Cylinder, remove the spring on the inside, and move it to the side without disconnecting the fluid line. Then, you'll have enough space in the lateral direction to take the booster out.

 

[Racer65]

I don't have a gasket in mine, and I wouldn't put it in for two reasons:

1. It changes the clearance between the booster rod and the master cylinder piston, which is just a hair
2. When the MC has a leak, which is apparently the case here, the gasket prevents fluid from dripping out. Usually sealing a fluid leak is a good thing, but not in this case, because the fluid ends up entering the booster, and eats up the seals inside.

 

[tls3601]

And that is how my booster probably failed................. Thank you Racer65!

 

[tls3601]

Won't be putting in that gasket

 

[Racer65]

You're buying a rebuilt booster for $$$$OR? Before you shell out 500 big ones, I'd check out Parts Geek.

 

[tls3601]

Heard too much questionable stuff about Centric, so ponied up................

 

[tls3601]

Yep, $$$$OR, but not 500 clams

 

[tls3601]

So installed booster and master(pics below) AND connected the red wires which were never connected before! So now my brake light goes ON but does not go off even when I release the parking brake. I suspect the light is going ON because I have no pressure in the system yet as the pedal goes to the floor. I believe I have lots of bleeding to do...............correct? BTW no leaks but I am replacing BOTH wheel cylinders in the driver side rear wheel with new OEM.......then of course bleed. Any ideas on the brake light??? It does flicker very briefly when I release the parking brake but does stay on. Thanks!

 

[tls3601]

What does everyone think?

 

[Racer65]

What does everyone think?

Did you check the booster rod to MC piston clearance? The spec is only .1 to .5mm! You may very well get a low pedal if it's not in spec. When you get a rebuilt booster, there is no telling what the rod length is set to (I'm talking about the MC side rod).

I suggest you click on my Sig and download the "City Racer Brake Booster Install Guide" on the right hand side of the page. Even though it's not for your booster, the same tips apply. Take a look at page 6 (Troubleshooting Tips), as well as Appendix 2 and 3 covering this topic.

The assumption is that you did try to bleed the brakes already. Otherwise, it's too early for a diagnosis...

 

[62Cruiser]

What does everyone think?

Racer pretty much said it. I just did this recently as well but with the centric booster. Make sure you don't have air in the lines or master cylinder, and that the rod from the booster to the master cylinder isn't engaged (but very close) before you press your brake pedal. One last thing, it is a pressure loss causing some pedal irregularity/feeling not just indication? That "attached a red wire that was never attached before" statement made me think it might have been that way for a reason (right or wrong). Pressure sensors on the master?

 

[tls3601]

Thanks guys and yes I have not bled the system yet, so way too early to diagnose. The hose the dealership sent me for the booster to intake manifold is too short, so will have to get another. However I noticed something peculiar. The attachment point for that hose on the intake manifold has a little vent pipe-next to connector pipe with blue tape on it(looks like a vent pipe to me-see pic) that has been uncovered for who knows how long?????? Could this be creating a vacuum leak???? I put a vac plug on it for now. Does anyone know what this should connect to? My rig is desmogged with no EGR or air pump. Incidentally I have low speed stumble issues at idle and that was one of the reasons for replacing the booster AND master.

Thanks

 

[Racer65]

Thanks guys and yes I have not bled the system yet, so way too early to diagnose. The hose the dealership sent me for the booster to intake manifold is too short, so will have to get another. However I noticed something peculiar. The attachment point for that hose on the intake manifold has a little vent pipe-next to connector pipe with blue tape on it(looks like a vent pipe to me-see pic) that has been uncovered for who knows how long?????? Could this be creating a vacuum leak???? I put a vac plug on it for now. Does anyone know what this should connect to? My rig is desmogged with no EGR or air pump. Incidentally I have low speed stumble issues at idle and that was one of the reasons for replacing the booster AND master. View attachment 1081440 Thanks

That tube on the intake manifold is called the "Union". On my car it's just a tube going straight up. The part # is 90404-51007. It's supposed to be the same from '75 to '80, so I'm not sure why yours has a second tube coming off of it. I think you will have a vacuum leak if that tube is left open.

By the way, the union tube can be a little soft. When you pull the hose off, it might even bend (guess how I know). You might consider replacing it. It costs less than $10 bucks.

I see that you're in Arizona. You might consider switching to a Silicone hose for the brake booster vacuum line, so that it won't get hard again from being cooked in the heat.

 

[tls3601]

Thanks Racer65, BTW any ideas on why the brake light stays on????

 

[bj40green]

That circuit is a bit complicated. There are 2 circuits but one indicator light. Both circuits are connected to the brake/stop switch.
1. The parking brake is hooked up to the B B' section
2. The pressure sensors are hooked up to the A A' section.
With the key in the "on" position the light should be on when the brake is pulled and goes off when the brake is released or when you step on the brake pedal indicating that there is pressure build up in the MC. If the light doesn't go off it means you have a problem with the MC. Low fluid or a leak in one of the circuits.

The adjustment of the brake switch (Warning + Stop light Switch) is essential for good working for both circuits.
Get your brakes in good working order before you start chasing problems.

Rudi

 

[tls3601]

Rudi.....yes I would have the job finished but messed up one of my wheel cylinders so now have to wait for another........bonehead move on my part....... But I am learning from these mistakes! Thanks guys for all the usefull input, much appreciated!

 

[DSRTRDR]

the brake light will also stay on if the brake switch at the pedal is not adjusted correctly relative to pedal travel or if the little bumper in the brake switch is missing

 

[tls3601]

Thanks CityRacer, just checked out your link and DSRTRDR I called Tools R Us guys in Mesa.

 

[jgeoffr]

Thanks guys and yes I have not bled the system yet, so way too early to diagnose. The hose the dealership sent me for the booster to intake manifold is too short, so will have to get another. However I noticed something peculiar. The attachment point for that hose on the intake manifold has a little vent pipe-next to connector pipe with blue tape on it(looks like a vent pipe to me-see pic) that has been uncovered for who knows how long?????? Could this be creating a vacuum leak???? I put a vac plug on it for now. Does anyone know what this should connect to? My rig is desmogged with no EGR or air pump. Incidentally I have low speed stumble issues at idle and that was one of the reasons for replacing the booster AND master. View attachment 1081440 Thanks

That union "nipple" goes to the A/C idle up actuator on my carb. Do you have factory A/C?

-Geoff