Master cylinder to booster gasket question

[Coelacanth]

I got a paint gasket kit for a 1970 Charger that included these 3 gaskets for the master cylinder to brake booster. Unfortunately there's no mention of how they should be installed. My master cylinder is leaking where it bolts to the booster. The 3 gaskets include a grey paper gasket and 2 foam gaskets. I'm confused how these should be reinstalled after I bench bleed the master cylinder.

 

[R413]

No gasket goes there.

 

[Coelacanth]

I wonder why they'd make a gasket that perfectly matches the shape of the master cylinder mount point? Plus, I'm already leaking there so simply removing and reinstalling the master cylinder with no gasket would probably not solve the leaking.

 

[Rishi]

I believe on power brake systems, there are two gaskets. One at the firewall (the same for both power and manual) and an o-ring, between the booster and the master cylinder.

IMO, the master cylinder gasket at the firewall doesn't really do any sealing, nor stop or prevent any leakage, it just insulates. You want this gasket installed, yes, but if you're seeing leakage, I suspect you have a leaky M/C in need of a rebuild.

The white foam gasket, with the trapezoidal hole, and four bolt holes, is the common gasket that goes on the four bolts coming through the firewall holding the booster (on power) or master cylinder (directly on manual) to the firewall.

The paper gasket, just like the foam one, is an alternate you may choose to use. The other white foam gasket with the round hole is also an alternate to the first white foam gasket, if you choose to use it. Often we match the new gasket to the old one on install.

While googling to confirm information on the o-ring, I see reminders not to overlook this o-ring during a rebuild.

 

[turbine68rt]

You may want to consider rebuilding or replacing your MC.

 

[RemCharger]

They go on the front and back of the booster support plate?
If the mastercylinder is leaking. .. you need to deal with that.

 

[Coelacanth]

It's leaking from the bottom right where it bolts and seals to the brake booster. Logically this mating surface would require a gasket. I doubt it would be metal-on-metal. I haven't removed it yet as I'm doing a steam-clean of the engine bay, but it'll have to come out and be bench-bled. It's not leaking where the booster bolts to the firewall.

 

[R413]

The gasket is for manual brakes to seal the inside of the car from the engine compartment. The booster has a gasket where it mounts to the car also.

Yes the factory bolts a disc brake master cylinder to the booster metal on metal

Yes if you have a leaking master cylinder a gasket won't fix it, it is an internal problem that needs addressed. Pitted bore or failing seals.

There is no o-ring between the master cylinder and booster. There is a round ring that is a pushrod retainer on manual brakes.

Mopar Manual Brake Push-Rod Retainer, Bushing, Clip Rubber Grommet

 

[R/T Boy 67]

If you have a leaking master cyl. you want to be able to see it quickly, so you can fix it. The last thing you need is a gasket in that location.

 

[Coelacanth]

The car hasn't been started or run in 12 years. It started leaking of it's own accord right beneath the lower 2 bolts about 6 months ago. Well, it's gotta come off the car anyway, I'll rebuild it if necessary.

 

[Rishi]

I've seen more than one master cylinder "go bad" on a vehicle while the vehicle was stored for many years.

For clarity, and to emphasize what others are saying, and I think we are all in agreement:

The gasket you refer to DOES NOT SEAL. Regardless of where it is placed, the master cylinder is a sealed plunger assembly, and should not be leaking at all. You may need to remove the MC, and possibly rebuild/replace it to resolve the leak.

 

[gtx6970]

I got a paint gasket kit for a 1970 Charger that included these 3 gaskets for the master cylinder to brake booster. Unfortunately there's no mention of how they should be installed. My master cylinder is leaking where it bolts to the booster. The 3 gaskets include a grey paper gasket and 2 foam gaskets. I'm confused how these should be reinstalled after I bench bleed the master cylinder.

View attachment 1699919

one on the right I dont remember ever seeing.
middle is between master cyl and booster ( or between master cylinder and firewall plate for manual brake cars ) , paper gasket on left is alternate for the middle one, but most commonly power disc brake cars


ps, the gaskets are to keep dust and water out , If the master cyl is leaking thats a problem

There is also a foam gasket between the booster to firewall plate and the firewall itself
like so

 

[Coelacanth]

I haven't had time yet to remove the master cylinder, I want to check the bottom and see if it's a Bendix or not. My car is a power drum/disk brakes car. I can't remember if the m.c. was every replaced, but I removed and refinished it myself about 15 years ago, painting it with Rust Bullet, which gives it a nice silvery-gray color that's super tough. I think Rust Bullet even holds up to brake fluid. When I either rebuild or replace the m.c., I'll probably switch to DOT 5.

When I pulled the cap, I noticed that only the rear pot (front brakes) was leaking, the front pot fluid level wasn't changed.

 

[Coelacanth]

I pulled the master cylinder today and looked on the bottom, it appears to be a Bendix 22268 but not sure about the last two numbers...2226824 perhaps...anyone? This is a good one then, not a repro, from what I've learned. The piston diameter is over 1"...I'm thinking 1-1/8". I looked for rebuild kits and only saw a Dorman one on RockAuto but that's for a 1" bore. Looking at replacement MC's, I'm mostly only seeing those with the line fittings on the driver side, not the engine side like mine.