Clutch Master Cylinders

Pete C. wrote:


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

How are you bleeding the system? The preferred method is to pull a vacuum on the top of the reservoir and drawing out any air.
When you pump the pedal is the effort different than when the clutch does work?
It almost has to be on the top if your not using any fluid. Perhaps pull the master and see what the bore looks like, it almost sounds like the piston seals are bypassing fluid.
--
Steve W.

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snip
I don't know this application - on the cars I am familiar with with hydraulic clutch, there is no "pump" in the master cylinder, so any air in the system is critical - the only and I mean ONLY way to bleed these (on this particular car) is via a pressure bleeder. Air in the system will cause the kind of effect described.
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Bill Noble wrote:

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

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.
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wrote:

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
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Gunner Asch wrote:

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

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.

--
Steve W.

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"Steve W." wrote:

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.

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You might also try alt.trucks.chevy, since a truck part is involved.
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Tim Wescott wrote:

Tim, that's about as simple a hydraulic project as there is. The pressures are laughable. The only real consideration is whether the volume of the MC is sufficient to move your slave piston the required distance. There are dozens of of clutch master cylinders available in the aftermarket hot-rod catalogs. I'd bet money you aren't the first one to do this exact project. Persoanlly, I'd call Craig Taylor at Taylor Engineering in Dallas. Nice guy, very helpful, and I bet he can tell you exactly what you need off the top of his head.
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wrote:

You need the same overall mechanical advantage - main thing is the bore of the master cyl - assuming the leverage on the pedal is the same.
Measure the bore of the clutch slave and the master of the original install - calculate ratio. Then calculate the mechanical advantage of the clutch pedal as a lever. Multiply them for the total MA.
If your replacement setup is close, you are OK. Low MA makes a heavy pedal.
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On Tue, 21 Jul 2009 12:03:46 -0500, Tim Wescott wrote:

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).
--
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