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I've found denatured alcohol to work well, household isopropyl
has a pretty high water content.

Hey guys,

Bought myself some denatured alcohol and have begun flushing out my master cylinder. At the very beginning of the bore there is some rust/pitting, but from there it appears to be fine and blemish free. so far it seems the master cylinder is okay, with minimal sediment.

Question: Is the rust at the beginning of the bore a problem as far as the performance of my brake system goes?


Thank you,

-Garrett

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I would hone it smooth if it's significantly rough. As long as the rough spot is far enough back that it does not approach the sealing area where the piston cup rests or prevent the piston from returning to it's full relaxed position against the stop ring, then it should not be an issue.

I'm amazed at how rusty the cylinder is for something fairly young. Is there any kind of gasket between the booster and cylinder or was the unit submerged to get water inside like that?

Quote:

Hey Howard,
I don't have a gasket between the booster and cylinder. MPB didn't include anything like that in my kit. The unit was never submerged, and I've never even driven in the rain. It is very odd to me as well that water was able to find its way in there. Luckily the piston comes all the way back to a relaxed position (albeit over the rough spot), but this whole issue with my brakes is very confusing. It is the newest system on my car and, the one that has deteriorated the fastest. I'm concerned that this problem may happen again because it didn't take long for it to happen this time.

-Garrett

My MPB didn't have a gasket either. Perhaps they figure those units are going to be mounted high on the firewall & well out of moisture. Down low like ours are it could be catching some road splatter. I didn't like it that way so added a gasket being careful to keep the adjustment between the booster plunger and the cylinder piston at the recommended clearance.

Adding a thin gasket is not too much an issue. It increases the clearance between booster plunger and piston but not by more than a few thousandths--probably stays well within spec range. I lengthened the plunger adjustment the thickness of a gasket just because. If a gasket were removed then the adjustment becomes more critical to make sure there is adequate clearance so the piston returns all the way.

Hey guys,

The system has been completely cleaned out with alcohol and compressed air. Luckily the front wheel cylinders were in much better shape than the rear so I was able to reuse them after a good cleaning. To help prevent the re-occurrence of this moisture/sediment contamination, I made a little shield out of sheet metal to protect my reservoir. It pivots up so the only tools needed to add fluid are your hands. I had thought about moving the reservoir to a different location, but where it sat seemed to be the prime spot.

Also, the brass covers for the master cylinder are only held in by the friction of the rubber cups. So, to make sure they don't go loose inside their seat I made some copper wire retainers.

Tomorrow I will bleed the entire system and adjust the brakes accordingly. If the prior problems I was having remain, I am pretty certain the problem is the master cylinder. But... I'm crossing my fingers and hoping for the best.

Cheers!

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I like your reservoir cover. We have different types and in different places but same issue of being close to water. The reservoir I bought has a rubber membrane inside so at least one less worry there.

We think alike on that friction fit O ring for the caps. IMO, a failure waiting to happen. The way my unit is mounted was even more vulnerable so caps were secured early on. As usual, most go simple and easy -- I can only think in terms of overkill.

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Hey Howard,

Thank you, there is always tree debris building up on the fender drip rails that finds its way onto my reservoir, so some form of cover was in order. I like your setup with those U-bolts. I would have liked to have used those, but I don't think there is enough clearance with the steering column. I'm hoping these modifications are enough to keep my brake system clean and in good working order.

Well...

A whole lot of work and the brakes still seem the same; the pedal is too soft. The pedal used to be extremely firm when I would press on it (engine off), to the point that it would hardly move. Now... The darn thing travels its full motion with engine off. I assume this means my master cylinder is to blame? The wheel cylinders are good, and the brake hoses are still really nice.

I feel so defeated right now. I really don't understand how or why this happened in the first place. They were working fine until I let a little fluid out a few weeks ago

It really sounds as if there is still air in the system. How are you doing the bleeding -- pressure or the conventional moving of the pedal.

I have had no luck with vacuum units at the wheels and also had issues with that particular master cylinder with getting it to completely eliminate the air out of one side. I wound up having to bench bleed the master so I could turn and position it to let the air escape and then carefully reinstall it so as not to get any air back in the thing.