Clutch Master Cylinders

Normal pedal bleeding, depress, open bleeder, close bleeder, release pedal, repeat... over and over and over.

Not noticeably, I think it's applying pressure to the clutch, but that the reservoir valve in the MC isn't sealing properly at the start of the stroke, so it doesn't have the displacement to fully release the clutch.

The bores are fine and no fluid is leaking from the MC, so not bypassing those seals. The design of the MC is pretty crappy IMNSHO, with a coaxial seal at the front of the piston that is supposed to seal off the hole to the reservoir at the start of the stroke and then the spring behind it just compresses as the stroke continues. Worse yet is this is just a round pseudo-o-ring seal on a flat surface, not a real hard seat soft seat seal setup. I think I could fab a much better design as well as increasing total displacement a bit to provide more headroom.

Air in the system will cause a spongy pedal feel (which I don't get) and will not be intermittent (which this problem is).

I see that there is a Valvoline brand DOT3/DOT4 fluid rated at 480 deg F and seems to be compatible with regular DOT3, so I should be able to upgrade by just flushing that stuff through. I'll also put some heat wrap around the exhaust pipe in the problem area to try to keep the heat in there, and fab a radiant shield (probably AL since I have material) to put between the pipe and clutch line.

Unless its a 94 or later Ford Ranger clutch...(Mazda included)

Then you have to mount the master...and pull the circlip that holds in the clutch piston..and very gently pull it out until fluid starts to drain on your floorboards. Only way.

Gunner

'In the first place, we should insist that if the immigrant who comes here in good faith becomes an American and assimilates himself to us, he shall be treated on an exact equality with everyone else, for it is an outrage to discriminate against any such man because of creed, or birthplace, or origin. But this is predicated upon the person's becoming in every facet an American, and nothing but an American... There can be no divided allegiance here. Any man who says he is an American, but something else also, isn't an American at all. We have room for but one flag, the American flag... We have room for but one language here, and that is the English language.. and we have room for but one sole loyalty and that is a loyalty to the American people.' Theodore Ro osevelt 1907

'97 Chev. clutch. It bleeds and will work properly, the problem is intermittent.

Try vacuum bleeding it. MUCH easier and you only need a hand pump to do it.

TSB - 01-07-31-002B Improved Bleeding Procedure for Hydraulic Clutch Release System

Covers 2007 and prior GM cars and light trucks.

The basics are that you use a hand pump and a cover adapter and pull a

15-20 inch vacuum on the reservoir. Fill reservoir. Repeat as needed until the bubbles stop or the fluid level doesn't drop.

Could be that the piston has a small tear or defect that prevents a seal.

Unfortunately I need to get a rebuild kit for my Mighty-Vac.

On four or five different MCs? Design flaw is my take on it.

Comments here, plus perusal of some ads in Street Rodder (_why_ didn't I think of that before?) lead me to think that I can make a suitable linkage to place the clutch MS in decent place, then I'll use whatever seems to have the right bore (hopefully cheap, from a junkyard).

DOT4 is a direct compatible replacement. Dot5 requires a flush - generally alchohol or BrakeKlean.

I'd go with Dot4 for simplicity. Heat wrap causes premature pipe failure.

there is now a DOT 5.1 that is another breed altogether. Apparently it's non-silicone and has some compatibility with other types.

DOT 5.1 fluids!

Historically, DOT 5-level performance (specifically boiling points and viscosity) could only be achieved with silicone-based fluids. However, modern compounding has created glycol ether-based fluids which now meet DOT 5 bogeys in these key areas. Consequently, the DOT 5.1 moniker was created to differentiate between these two very different chemistries which both meet DOT 5 performance requirements.

In so many words, DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements. Because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they are even referred to as ?DOT 4 Plus? or ?Super DOT 4? fluids because they are more similar to a conventional DOT 4 fluid by chemistry than they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially comprised of Borate Esters.

While it may not be obvious, the big advantage of the DOT 5.1 fluids is that they contain all of the nifty water-absorbing characteristics of the DOT 3 and DOT 4 fluids while simultaneously providing for very high boiling points and relatively stable viscosity over a wide range of temperatures. The best of all worlds, you could say. The table below sums it up quite nicely. PROPERTY DOT 4 DOT 5 DOT 5.1 Dry BP (F)@ 0.0% H2O 446 509 509 Wet BP (F)@ 3.7% H2O 311 356 356 Chemical Composition Glycol Ether / Borate Ester Silicone Based Glycol Ether / Borate Ester

(As stated earlier, the table data above contains the minimum properties for a fluid to be called a certain type. For example there are many racing brake fluids with Dry BP performance at or above 590o F and Wet BP at or above 390o F.)

So, what is the downside of the DOT 5.1 fluids? Like most things in life, the good stuff isn?t cheap. DOT 5.1 fluids typically cost three to four times as much to manufacture as a conventional DOT 4 fluids. There?s always a catch?

Given the small quantities used, I would expect the cost difference is pretty negligible.

Agreed. I have used Dot 5 in the past for my project vehicles. I'll probably use DOT 5.1 in some now.