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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #1 of (permalink) Old 05-09-2009, 02:26 PM Thread Starter
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back to the clutch!

Ok so i have worked on the clutch a bit to narrow my problem down. What i can tell you now is that when its morning and everything is cold it works perfect, heats up and it no longer has the pressure it needs to function. no air leaks in like previously thought.

1990 YJ 258 l6 3.5 BDS lift

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post #2 of (permalink) Old 05-10-2009, 06:18 AM
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You mean that when it gets warm the clutch doesn't fully release?

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post #3 of (permalink) Old 05-10-2009, 09:01 AM Thread Starter
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That is exactly what i mean

1990 YJ 258 l6 3.5 BDS lift

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post #4 of (permalink) Old 05-10-2009, 10:40 AM
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Well, that has me stumped. This is an internal slave cylinder, like a donut around the transmission input shaft, right?

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post #5 of (permalink) Old 05-10-2009, 11:33 AM Thread Starter
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You are correct! The only thing i can think of is vapor lock since it is hydraulic and uses glycal brake fluid. Oh and my pedal has wear on it so maybe not enough throw. It has a good inch of play in it.

1990 YJ 258 l6 3.5 BDS lift

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post #6 of (permalink) Old 05-10-2009, 11:45 AM
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If it were wear to mechanical parts I wouldn't expect it to change noticeably cold to hot.

If it's hot enough inside the bellhousing to boil moisture dissolved in the fluid, that's could cause your problem. If that's what's happening, it would behave the same as if there's a little air in the brake system, so you should be able to get full release by pumping the pedal quickly several times and then holding it down. But don't I recall from your previous post that you've been fighting this for quite a while and have bled the system numerous times? If so, the fluid should be fresh and moisture-free.

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post #7 of (permalink) Old 05-10-2009, 11:58 AM Thread Starter
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And once again you are correct! But i had a discovery last night! When i re did my exhaust to make room for my front drive shaft we put the exhaust extremely close to my clutch's brake line. So would it be possible that its heating it up enough to lose even a little pressure and then combined with the play/loss of throw in my pedal it doesn't have the pressure to work properly?

1990 YJ 258 l6 3.5 BDS lift

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post #8 of (permalink) Old 05-10-2009, 12:11 PM
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DOT 4 glycol brake fluid has a very high boiling point, suitable for disk brake systems that can glow red hot. Of course the calipers aren't that hot, but they wrap around the rotors, and can boil fluid that's been contaminated with water. That would make me skeptical about the exhaust system getting the line hot enough to boil fresh fluid. But it's an easy enough theory to test. Wrap the tube or the exhaust pipe, or both, in some fiberglass insulation, or just push a wad of it between the pipe and the tube. If it cures your problem you've confirmed your theory.

On the subject of mechanical wear, when the system is cold, how far off the floor does the pedal get before the clutch starts to grab? If you have an inch or more, I doubt that there's serious wear in the linkage.

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post #9 of (permalink) Old 05-10-2009, 12:51 PM Thread Starter
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In terms of hydraulics, i am using dot 3 that boils at 250 and mechanical, the pedal moves forward an inch before it even starts pushing in the rod to the master.

1990 YJ 258 l6 3.5 BDS lift

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post #10 of (permalink) Old 05-10-2009, 01:00 PM
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Check that the bellhousing is bolted tight to the engine (check at the bottom and both sides too) and the transmission is bolted tight to the bellhousing.

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