new clutch issues after conversion

DamianZ28

Active Member
Hi Guys, Having trouble engaging the gears after completing the conversion from auto to LT77 sd1 manual on my V8 P6

Have just fitted a new braided flexi pipe between the clutch master & slave cylinder, bled using a self bleeding kit.
Clutch plate & pressure plate is an AP Performance version, release bearing, release arm are new, when I first drove the car it was fine but know after say about 15 miles I have to pump the pedal & push right down the floor to engage any gears. I've checked for leaks but all dry on both new cylinders, master is a 3500s and the slave is a SD1 for the g/box.
It could be a tiny a bit of air in the pipe still hence having to pump the pedal, maybe I need to do the traditional way of having some work the pedal while I open & close the bleed valve.
Could it be the AP clutch kit is a tad too strong perhaps? cant see it personalyl, other thought is that the new clutch plate has worn in slightly and perhaps the push rod from the slave cylinder to the release arm is a bit to short? clutching at straws a bit any ideas will be great, thanks Damian
 
Hi harvey, yeah I think that's the first thing to do, cant think it to be any thing else really, other thought is possible faulty master or slave cylinder but again no fluid loss that I can see.
 
Not sure what sort of piston is used in your master and slave cylinders but recently had a problem with a plastic piston which when under pressure opened an unseen crack in the plastic allowing fluid to go to the low pressure side, very hard to diagnose.

Graeme
 
Bled it the again with my other half working the pedal and myself opening the bleed valve, this did make a difference but still not briliant but a vast..ish improvement.
I think I'll swap the coverplate as the AP performance version is a tad too strong, fine for a track day car I guess, I think I'll get another standard SD1 clover plate, keep the new AP clutch plate though.
So tonite after 9 days putting the car back on its wheels it'll be back on ramps & axel stands to remove the gearbox again :roll: at least I can renew the spigot bush this time, the old SD1 one was ok but a new one will do no harm & keep the input shaft true.
Graham, I unbolted the slave cylinder, removed the rubber cover & looking at the slave cylinder piston, Its metal not plastic, but I didnt know that some are plastic! so thanks for the heads up on that.
 
Could it be heat soak boiling the fluid in the master cylinder after a few miles of driving given how close it is to the exhaust manifold?
 
Hi Paul, that was a worry but it's a good inch clearance gap between the cylinder & exhaust pipe, I've bought some proper heat wrap to go around the cross over pipe for extra insulation.

kman1600 (Tim) runs the rally 3500 with same conversion but with the master cylinder located in correct place as the 3500s, his slave cylinder is closer then mine to the exhaust, scroll down a tad: viewtopic.php?f=21&t=8425&start=570,
one thing did occur is that the heat from the manifold is getting under my master cylinder, I have the old heat sheild bolted inbetween them but there is also gap underneath for the heat to get in, I may buy another one & trim it slightly and bolt to the inner wing on its side underneath to box in the master cylinder from below. Also I'll wrap some of the insulation around the back of the n/s manifold for added heat protection.
I'll still swap out the AP clucth coverplate as it'll be a leg liller on long journeys, espcially in slow moving traffic.
Cheers Damian
 
DOH, Paul sorry I miss read and thought you said slave cylinder, sorry about that, but I think I've explained both heat soak issue and & hope fully resolve them! cheers Damian
 
Hi,

Even with a standard clutch cover the pedal is heavy on our car by modern standards and I’m guessing heavy by classic standards as well. I really can’t see that the strength of the cover being your issue and it’s a lot of work to change it out as a test!!! As bleeding the system resolves the issue, even if temporally, then it has to be either air ingress or aggressive break down of the fluid most likely due to heat.

We used to suffer from a very rapid fall off in brake feel and pedal travel before we did the rear Jag conversion, long periods running very near brake fade territory!!! Bleeding would always return the system to good feel etc…. fluid coming out was discoloured and thinned, when bleeding you knew when you’d got the bad stuff out!!!! once overheated the effect was very quick, almost instant.

What grade of fluid are you using, would a race fluid have a greater tolerance to heat?

Good luck, Tim
 
Hi Tim,

Thanks for your input, makes sense, as you say its a big job to remove the box again! I'll think I'll go with fresh fluid (non halfords) as I did use left over halfords fluid which had been through the system via the brakes previously :oops: not sure of the grade, I guess race fluid has a much higher temp breakdown?

I'm thinking as you & Paul both advise its possible heat soak, I'd say more from the o/s exhaust manifold rather than the slave cylinder, I'll make another heat sheild & wrap it in the insulation material to fit under the Master cylinder so in effect box it in without a lid if that makes visual sense!, I have a huge roll of this heat wrap so mite as well use it! I'll wrap the o/s exhaust manifold rear end and the cross over pipe under the slave cylinder, also partly wrap both cylinders to give a bit more protection, bit of an over kill but cant hurt I guess.

I've fitted a new braided flexi pipe ordered from Merlin motorsport with correct covnvex unions, so fresh new fluid, a session of wrapping and see what results occur, I bet this fixes it then the bloody box will go bang LOL,

Thanks Damian
 
I think that I am suffering from a similar problem. It has an LT77 conversion with quite a heavy clutch pedal. 3500s master, not sure about the slave. Should it have a heat shield as standard (I think that it needs one)? I'm going to go down the heat wrap route as it is the easiest option...
 
[quote="DamianZ28"

I'll think I'll go with fresh fluid (non halfords) as I did use left over halfords fluid which had been through the system via the brakes previously :oops: not sure of the grade,[/quote]

If you're reusing old fluid the grade is Gnats P***!
It's really not worth it, brake fluid absorbs moisture in use - for the cost in time alone it is best to use fresh.
Recommended use for the old stuff - bung it on a Bonfire (carefully!) on the 5th.
 
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