25 minutes ago, Yarb said:

If you’re keen on replacing the master cylinder that’s up to you. Take your phone and take a pic of the bottom side of the m/c mounting points.

I’m rather keen not to if I don’t have to.

Looks like it’s leaked in the past for sure.

Update: I got the wheel cylinder repair kit from zcardepot (and new shoes, springs) so took the wheel cylinder off the driver side. I noticed immmediately that there was more of the greenish crystalline goop under the circular dust protector. Quite a bit really. I see some pitting on the piston. The walls of the cylinder aren’t pitted except a bit down by the bottom. The spring was a little rusty looking. Is this level of pitting ok with new seal? Or do I need to just replace the whole unit?

The pitting in the cylinder is what needs to be cleaned up and honed so the seal can work properly. Still looks useable. The cylinder is the later type so readily available new if you want to replace.

Bought a honing tool. The pads can’t touch the bottom of the bore so just used some steel wool on that. Sides look ok to me except for right at the bottom where some pitting remains. Salvageable? What would failure look like if I use this? Leaking brake fluid all the time and eventually mushy rear brakes?

You can give it a try, That’s a lot of work to risk brake fluid on the new shoes. Personally If it’s feasible, replace both cylinders.

1 hour ago, Yarb said:

You can give it a try, That’s a lot of work to risk brake fluid on the new shoes. Personally If it’s feasible, replace both cylinders.

Thanks for evaluation. I ordered new ones for both sides.

20 hours ago, Warty said:

Bought a honing tool. The pads can’t touch the bottom of the bore so just used some steel wool on that. Sides look ok to me except for right at the bottom where some pitting remains. Salvageable? What would failure look like if I use this? Leaking brake fluid all the time and eventually mushy rear brakes?

Too much pitting in that to be useable. Just buy new cylinders rather than wasting time chasing leaks.

On 8/22/2026 at 12:30 PM, SpeedRoo said:

@Warty most times they just need a good flush with brake cleaner. The rear proportioning valve is difficult to disassemble so just blow it out with air pressure then flush it with brake cleaner. Then put brake fluid in and seal with some caps until you reinstall it. The check valve comes apart pretty easily, again clean, flush and refill with brake fluid.

cool, thanks.

So new wheel cylinders finally came and I installed them and tried to bleed the system. I had blown out all the hard lines and removed the proportioning device and kind of spiffed it up but yeah not much to be done with that.

what I’m seeing is this:

Fluid gradually transfers from front tank to rear tank as brake is pushed and let up. If I push brake down the front driver wheel won’t spin (1 person team so can only reach driver side wheels). Except then it will spin after a bit.

I took the master cylinder off again and checked the seals. Looks like I initially had one of the seals in the piston closest to the firewall reversed. Can’t see that in FSM but found a couple photos online. But when I put it all back together and rebled the cylinder and wheels I get the same thing. Feels like the transfer rate is a bit less this time.

time to give up on this master cylinder? One thing that is odd and probably wrong with it is that one of the valves has a gray kind of cup at the bottom that is not attached to the MSA whereas the other one that cup is solidly attached (or seized depending on what’s correct). The front valve is the one with it fixed in place rear valve it can move.

I’m not seeing any available early style master cylinders. Anybody know of a source? Failing that I buy a tube bender and cross the front and back hard lines to work with the newer style large tank in bank cylinders?

No need for a tube bender if you’re not set on authenticity. Install a couple of flex lines.