Master cylinder service

[Luke_Healey]

I removed and tore down the master cylinder tonight so I thought I'd post some photos. I got the car in over the summer of 2007. Someone had rebuilt it completely in 1992. I imagine this was the last time the master cylinder had attention.

The master cylinder was wet with fluid and crusty.

The pushrods were crusty

I polished the pushrods with 1000 grit sandpaper, but they are both pitted. They are relatively smooth now.

Popping the piston cap revealed nastiness

Popping the top revealed that I'd been clutching and braking with pressurized baby poo

Cleaning ensued. The cylinders aren't horrible. The rust that was present was down at the bottom. I imagine water was in the brake fluid. Possibly the previous owner was using DOT 5 fluid.

I cleaned out the reservoir and cleaned the passage holes

The springs both have broken plastic tips, and one side had this white plastic part in the rear. The other side had this copper hunk back there

A closer shot of the damaged tips on the springs

Most of the stuff cleaned up well. I didn't find any damaged seals, and all of the seals were made in England. My kit looks identical to the parts

So here are my questions:

How important is it to have absolutely no pitting in the cylinder bores? How important is it to have no pitting on the pushrods? Does anyone sell the replacement plastic tips at the end of the springs? I don't see them on VB or Moss website. Finally, that plastic cone that sits behind one of the springs, do I need two of them, or is it for one side only?

Thanks for any info.

 

[Trevor Jessie]

I personally like to have a clean bore (esp on the brake side). Small pits are OK, but may shorten the seal life or could case leaking (depending on where they occur).

 

[jvandyke]

So here are my questions:

How important is it to have absolutely no pitting in the cylinder bores? How important is it to have no pitting on the pushrods? Does anyone sell the replacement plastic tips at the end of the springs? I don't see them on VB or Moss website. Finally, that plastic cone that sits behind one of the springs, do I need two of them, or is it for one side only?

Thanks for any info.

Remember, from a newbie (whose spent a lot of time on his MC though):
I could feel slight pitting near the end (front) of the bore, this is the secondary seal area I believe and not quite as critical as deeper in the bore where the main seal squeezes the juice back toward the outlet lines. I don't know about the plastic tips on the springs, I don't think they're all that important to be honest with you. That other plastic thing is little check valve for the brake side, only supposed to be on that side. I got a little hone off the shelf at Napa I think for $20 or so, two stone spring loaded deal, very lightly honed just enough to clean it up and leave a tad of cross hatching in the bore which is how it's supposed to be I was told. I used a common drill with the hone but ran it through a rheostat just so I could slow it way down. Push rod pitting doesn't effect anything but aesthetics. One of mine has a slight bend to it which I found weird. As seen here , same pictures as the other thread.

 

[Roger]

Dead right, ivandyke. Hone the pitting out of the bores.

 

[nomad]

I am afraid the broken plastic pieces on the springs may be somewhat critical. I've rebuilt several and as I remember these are the ends that fit inside the cups that pressurise the system. Maybe you could get someone to turn them on a lathe out of nylon. Check with a bearing supplier or machine shop if you can't find them anywhere. Maybe a member has a spare set. When you put it back together be sure to use Dot 4 (LMA) fluid

 

[jvandyke]

I have a vague memory that my springs had metal ends to fit into the cups. Maybe your right, naked spring ends may wear on the cups I guess. Someone here will surely have something laying around to send him? To be honest, what I do in this situation is go to the hardware store and start looking, in this case, a "finish washer" might just do it.
Like this

 

[Luke_Healey]

I'll have to buy the other hone. I think I have the receipt for the 3 prong one I bought, so I'll exchange it.

I'm not planning on putting things together until I have those spring tips mitigated. I was thinking cable tophats made of brass or aluminum might work. Even if I have to fabricate something, I think it's important to have a flat surface pushing on that rubber plunger.

Something this shape, but without the cut in it:

I use DOT4 fluid in all of my old vehicles because it absorbs the water and doesn't allow things to rust and pit like this. I'm surprised how many old guys I talk to that put DOT5 in their restored vehicles that they rarely drive.

One of those cases where "If it's more expensive, it must be better..." I guess.

 

[Bayless]

When compromising, remember that your life depends on those brakes. One trip to the ER costs much more than a new cylinder. That's true even if you do survive.

 

[jvandyke]

Not sure replacing obviously fail-prone plastic bits with metal ones is a compromise or not......

 

[Luke_Healey]

Ahh, the e-brake is mechanical :wink: I've already had to use it a couple of times.

Hunting for the appropriate piece to use gives me something to do in the meantime.

None of the places I've hunted for online list the part by name even if it's unavailable.

(the piece circled in black)

 

[jvandyke]

Yep, I remember those little metal bits. I may have a couple, if so I'll send them to you although I still think you could take the spring and seal into a hardware store and walk out with something that would work in 5 minutes. Or maybe walk into a brake shop and get something? There's a brake supply house by me that I'm sure would have something like that.
I wonder what happened to the bits of plastic that came off those rings? Hate to think of them blocking a line or tearing on seals somewhere. Yikes.

 

[sparkydave]

I use DOT4 fluid in all of my old vehicles because it absorbs the water and doesn't allow things to rust and pit like this. I'm surprised how many old guys I talk to that put DOT5 in their restored vehicles that they rarely drive.

One of those cases where "If it's more expensive, it must be better..." I guess.

DOT 5 does not get water in it the way DOT 3 or 4 does. Those attract moisture from the air, even through the rubber hoses, whereas DOT 5 repels water. True, if you introduce water into a DOT 5 system it won't mix, but about the only way that's going to happen is if you pour water into the master cylinder, or you get some severe condensation under the master cylinder cap. I've had DOT 5 in the clutch and brakes for years now. No rust anywhere. Even General Electric did testing where they immersed brake hoses in water while filled with brake fluid. DOT 3 got very wet. DOT 5 didn't get any water in it.

Incidentally, it was originally developed for the military so their brake systems wouldn't attract moisture and get rusty while they were in storage.

 

[Luke_Healey]

OK. I just went out and educated myself. I'm guessing what happened is that DOT3 or DOT4 fluid was used, but the car sat, undriven for so long that moisture got into the fluid and depleted the moisture handling materials.

Somehow, rust formed along the bottom of the cylinder bores, but mostly towards the outter seals.

In my own garage in March every year, there are beads of water sitting on any metal surface. That's just how humid it gets in there each spring as the snow melts and the outside temperature rises.

In my case, I drive my cars regularly in the summer time, so keeping up with DOT4 brake fluid changes is not really an issue. The fluid seems to not live its life past 5 years in any vehicle I own before I completely bleed it out.

In any case, once I fix the master cylinder, I'm hoping that it'll never get crusty like that under my watch while I own the vehicle.

 

[PAUL161]

Moisture, I cover our car where the cover comes down to the floor and then place a 100 watt bulb under the car and leave it turned on all winter. No moisture what so ever. But of course, our winters are mild compared to yours.

 

[Luke_Healey]

This is what my motorcycle looked like last March, just sitting there:

I can't explain it other than things just seem to get wet to a ridiculous level in my garage. The garage has cement floors and insulated walls.

I figure the car is British, so it should be immune.

 

[mightymidget]

I like the light bulb idea, My garage picks up moisture when it rains for two days in a row

 

[nomad]

Light bulb idea is excellent!! I bet it'll work anywhere. By the way, I've had DOT 5 in my MGB for over 30 years and have'nt even bled it. Brakes are perfect.

 

[walshja]

my garage does the same thing with condensation on the cars and motorcycles. What's happening is as warmer weather approaches, humidity increases in the air, and when the air gets warmer it takes longer for the metal items in our garage to warm up. the moisture in the air will condensate on the cooler items in your garage. once the items warm up to room temperature, the moisture will go away.

the best thing to do is seal the garage up and put a dehumidifier in it, or air out the garage well, so the metal items can warm up more quickly.