Unusual clutch issue (Page 1/8)
stevep914 JUL 24, 05:44 PM
Having used this forum many times for help over the years, and having consulted many clutch related posts on here, I have an issue that stumps me. I am totally familiar with bleeding procedure, including the final step of pushing back the pushrod on the slave at the end of things. I have an 86 v6 Isuzu 5 speed Ferrari F40 clone, that goes out once a week for a 50 minute drive. The pattern is always predictable. It runs and shifts normally for about 45 minutes, and at the end, the pedal starts to soften, and gear selection is impossible. Let it sit for 1/2 hour, and things are normal again. A week later, the same thing happens. I have no visible leaks at the master , slave ( a Dickman unit) or anywhere on the line in between. Due to the close proximity of the slave cyl to the exhaust header, I installed a heat shield over the slave several years ago. I am using dot 3 brake fluid, and have purged the system many times. Might I be boiling the clutch fluid during the run? Would going to dot4 fluid help this? My bleeding procedure is by the book, including the final step of pushing in the pushrod to get the last bit of air out of the slave cyl. Any suggestions would be greatly appreciated! Thanks in advance! Steve
Patrick JUL 24, 06:58 PM
At rest, how high does your clutch pedal sit above the brake pedal?

After running a search Here, I see that you've had quite a history of clutch issues. Has your clutch ever worked properly over an extended period of time?

[This message has been edited by Patrick (edited 07-24-2022).]

cvxjet JUL 24, 10:08 PM
The symptoms make me suspect a heat issue with fluid boiling. Check the routing of your exhaust and hydraulic lines. Replace the fluid and bleed it- take your time and really bleed it thoroughly to make sure you remove ANY air.
stevep914 JUL 25, 04:02 PM
Patrick, thanks for the reply. When I acquired this car years ago, it had sat for several years, so I went through a lot of stuff, and it was a great learning process. My first Fiero. I bought a 2cnd one here several years later, and stripped it completely for parts and the VIN plates needed to make mine legal here in. Mexico ( really LONG story!) After initially experiencing clutch issues, I purchased a Dickman slave cylinder, installed it, and the car performed fine- for the way I use it. It is primarily a toy, not a daily driver. It goes out once a week for an hour or so, and did this well for a couple of years. It has never been driven more than an hour at a time. The Dickman slave seemed to solve the problem; at least for the limited use the car was getting. This replica is low, stiffly sprung, hates speed bumps ( we have lots of them here in Mazatlan) and does not like rough roads ( lots of those here too); The route it gets iits weekly trip is pretty smooth, with some highway driving. I might shift it a couple of hundred times during the drive. This present problem has occurred the last 10 times or so I have driven the car, and always seems to appear at the end of my drive; to the point where I limp it into the driveway sometimes still in 2cnd gear, as it won’t shift into first anymore. I have bled the system twice, as per the suggestions on this forum, and still see no evidence of leaking anywhere. The pedal prior to the problem sits higher than the brake pedal as it is supposed to. Bottom line: everything is perfect until the last 10 minutes of the drive. I,bought some dot 4 brake fluid today, to attempt a fluid change to see if that helps. Has boiling ever been a clutch issue for anyone else? I would assume if I had air in the system somewhere, the problem would be constant, not sporadic as it is now. Steve
stevep914 JUL 25, 04:09 PM
Cvxjet, Thankyou for your comments. Unless someone can offer me an alternative, I am going to assume it may be a heat problem. The slave sits an inch away from one of the exhaust pipes. I did make a heat shield years ago because of this. The engine compartment has two cooling fans directed at the motor, which vent the hot air out the louvres in the F40 rear window. There are also scoops on the sides of the car that vent air into the engine compartment as well. Next step might be to wrap the headers? Steve
Patrick JUL 25, 04:14 PM

quote
Originally posted by stevep914:

Unless someone can offer me an alternative, I am going to assume it may be a heat problem.



Heat is no doubt a contributing factor, but it may not be the actual problem.


quote
Originally posted by stevep914:

The pedal prior to the problem sits higher than the brake pedal as it is supposed to.



Steve, that didn't really answer my question. I asked "how high".

The clutch pedal should be sitting a full inch above the brake pedal. If it's less than that, it's possible you've just barely got enough stroke to fully disengage the clutch under optimum conditions. Perhaps after your car is all warmed up and metal components have expanded etc, the stroke of your clutch pedal is now insufficient to disengage the clutch.

My experience with the Isuzu transmission is that it's very particular with the amount of slave movement required. If your slave is not moving the push rod 1-1/8 to 1-1/4 inches, it will not fully disengage the clutch.

[This message has been edited by Patrick (edited 07-25-2022).]

stevep914 JUL 25, 04:26 PM
Patrick, I will check the pedal height and get back to you. I went back and revisited all my other posts and replies from 2013, Wow! But seems to be the same issue all around. I know back then, I had pushrod travel within the specified amount. I will try to get my wife to help me check that out again.
stevep914 JUL 25, 04:32 PM
Without touching it, the clutch pedal is sitting at least 1 and 1/2 inches above the brake pedal.
Patrick JUL 25, 04:38 PM
I'm surprised it's that high ... but nevertheless, the really important measurement is slave travel.

[EDIT] Is some of that height "slop" in the pedal? In other words, when the pedal is being depressed, how far does it move before it actually starts to push the banjo?

[This message has been edited by Patrick (edited 07-25-2022).]

stevep914 JUL 25, 05:51 PM
About 1/2 inch of slop, which still leaves me 1 inch at banjo engagement. Again, please correct me if I am wrong, but the problem is not consistent; clutch even into reverse with no grinding, works properly for about 45 to 50 minutes, and then my pedal softens. And once the car has sat, and presumably cooled off somewhat, the pedal comes back up and I have clutch function again. Cold verses hot. I would love to think there is some “logical” answer here, and I appreciate we are trying to eliminate causes a step at a time. Your expertise and input is extremely appreciated. The first 50 minutes, this car is a blast to drive! The last 10 minutes sucks. I actually take it out and gear the drive anticipating the problem. So far Ihaven’t been stranded anywhere.