Detectives Needed - Clutch Mystery !

[Peter Delaney]

Jac Mac, in reply to your post #6, I did some further tests today & found that it does the same "soft pedal" act if I roll down the entire length of the hill in neutral & then come to a fairly firm stop (the road is almost level at the point where I stop).

I then tried the same thing on a flat road - 80kmph, into neutral, then a firmish stop - SAME RESULT (and repeatable) !! So its not the hill or inclination at all - its related to deceleration / braking !

I haven't driven the car "in anger" for a long time - mostly just puddling about the suburbs, maintaining a "safety zone" around the car in traffic, so I guess that explains why I haven't noticed it anywhere else ?

Re the release fork cross shaft lugs/bearings, these were checked out when the box last got re-installed & all was ok then. However, a mate has a "bore-scope" device, so we'll have a look at these areas by poking it up through the inspection hatch when next I visit him.

John O - thanks for the update on the crank thrust bearing - that puts my mind more at ease. If there had been a fundamental problem with push vs pull, I am sure that lots of other people would have had a problem & we would all be aware of it by now.

On the G50, the slave/cyl is tucked away under the g/box & so is well spaced away from the exhaust. However, I will still replace/reco it as a matter of course.

Thanks again guys - I'll keep you posted.

Kind Regards,

Peter D.

 

[John Oxborough]

Hi Peter
Check the crank end float. When you brake , the crank will move forward due to inertia.
The clutch fork may have a ratio of around 4 to 1 ,so 10 thou of end float could end up as 40 thou at the slave cylinder end of the fork, which then is taken up when you press the clutch the first time on a restart.
Sorry these answers are drifting to engine issues (may be wrong thread)
cheers
John.

 

[Peter Delaney]

Hi Guys - for various reasons, I have not been able to do much with the 40 for quite a while, but now I am back into it.

I think that I have found the cause of my clutch problem (I get a very soft pedal when operating the clutch after doing a firm stop with the car in neutral & clutch out - a pump or 2 & all is ok again) :

It looks like it is endplay issue with the crank (already suggested by a few guys on the Forum last year). I can get at the outer edge of the clutch assembly through an inspection hole in the bellhousing & can easily see the movement of the crank assembly. When I pump the clutch a few times, the whole shebang moves back to the point where there is no clearance between the outer rim of the clutch assembly & the edge of the hole in the bellhousing (it is rubbing).

When I lever the crank assembly forward with a screwdriver, I get 36 thou clearance at the same spot !!

The manual says that the "Standard" endplay should be 4 to 8 thou, with a "Service Limit" of 12 thou, so I am way over !

So it looks like I have a major problem with the crank thrust bearing (or worse - my engine builder reckons that there is a good chance the crank is damaged, as well as the bearing) !!

I think I now know how it all came about - when the gearbox was pulled a couple of years ago the gearbox guys mentioned that the g'box input shaft was bearing hard up on the crank, so they machined things out to get some clearance. BUT, I think the damage had already been done by then, and that the root cause was the adaptor plate being too thin.

The whole car is going back to the engine builder for him to assess the situation & then fix it all as a total engine / gearbox package. Perhaps after this, I will have a car that I am game enough to drive "beyond affordable towing distance" !!

I'll let you know how it goes (providing I can still afford my internet connection fees after this hit) !!

Kind Regards,

Peter D.

 

[wanni]

Peter,
You mention it only happens when going down hill & after making the 3 or 4 gearchanges/clutch applications. If you simply use the brakes & only shift from 4th/5th to neutral or first to get underway again does it do the same thing? It might be a combination of the reservoir height, connections on hose fittings to this & the condition of the cups/seals in the master cyl & frequent clutch operation while in the downhill attitude.

I agree with your opinion.
It maight be a problem of eight of the oil tank respect to some high passages of the oil supply piping.
Why do not you try to bleed the clutch system with the rear of the car lifted up???? It may works.
Ciao
Wanni

 

[Peter Delaney]

Wanni, I have a DRB with hanging pedal setup - this means that the m/cyl is about 300mm higher than the slave cyl. The pipe runs down from the m/cyl, along the chassis, then up about 50mm to the slave cyl.

I have replaced both m/cyl & slave cyl, & used well over a litre of fluid in bleeding the setup repeatedly - there are absolutely no leaks, & there can't be any air trapped in the pipe.

So it looks like it is the crank endplay (way over tolerance) - the fact that I can replicate the problem in the garage pretty much locks it in. If I lever the crank forward with a screwdriver, I get the "soft pedal" problem every time.

Thanks & Kind Regards,

Peter D.

 

[dave harris]

Hey Peter,

If you have too much end play be sure to check your pilot bearing in the rear of the crank. If it is not ALL THE WAY IN, you preload the thrust bearing on the crank when you tighten down the trans axle - - - and this situation is exactly what happens - - Don't ask how I know!!!!! if this is the case you are in for a really good clean-up / rebuild of the engine as bearing material will have gone everywhere.

When you re-assemble it, make sure the pilot bearing is all of the way in and pre-test assembly without the clutch to make sure you have a gap from the pilot bearing to front flare / spline area of the trans axle input shaft.

and, yes, i need another pilot bearing too!!! crap ....

dave

 

[flatchat(Chris)]

Dave, pm me your address I'll send you another:- [email protected]

 

[Peter Delaney]

Dave,

Flatchat (Chris) has kindly offered to provide me with a new pilot bearing, & before that goes in, we'll thoroughly check the old bearing to see if we can find where the problem was (eg. depth of the hole for clearance on the end of the input shaft, signs of wear at the back of the bearing & on the flare / spline area of the shaft as you mentioned below, was the bearing all the way in, etc).

Chris confirmed that the adaptor plate should be 0.5" thick at the mating surface with the bellhousing - mine is just about spot-on 0.5", so that rules this out as a cause. So it looks a bit like incorrect fitting - we'll see.

I'll make sure that we do a pre-test assembly (without clutch) as you suggest & check clearances in the hole & at the flare. Not sure how we'll do this yet - maybe a bit of plasticine in the bottom of the hole & a bore-scope for the flare.

Any ideas ?

The thought of bearing material wandering throughout the engine makes my hair stand on end !! Its like deja-vu - last time (only 8000kms ago), it was a lifter's needle roller bearing that collapsed & seeded the bits everywhere. Crank & cam were stuffed, & one way or another, we ended up with $8,000 worth of 331 ci upgrade / rebuild !! It would have been cheaper to have just bought a short crate motor !

BTW, Chris mentioned that he strongly recommends installing the Brace Rods between the engine mounts & the adaptor plate - apparently without these, there is the potential for flexing between the engine & the transaxle which can lead to pilot bearing problems (or worse).

I see that Chris has offered to provide you with a new bearing - you'll find him very helpful & very knowledgeable.

Thanks & Kind Regards,

Peter D.

 

[dave harris]

Hi Peter,

I would not worry about checking clearance at the hole bottom in the rear of the crank unless the bearing does not go in for some reason - plus, you can see thru one of the side openings in the G50's bell housing area (without the clutch in) to the input shaft / pilot bearing fairly easily (and even better if you have a small mirror on the end of an extenable handle (most auto parts stores have them cheap). But plastic gage around the input shaft would work well too.

As to the bearing material - sorry, but it will have traveled if it is the center thrust bearing that's degraded very much. The good news was that it was not large chunks in mine - it just stuffed up oil passages etc. Send a PM to Jac Mac and he can tell you EXACTLY what to look for - I did not take his advise the FIRST time but sure followed it to the letter this time!!! (I will never doubt you again Jac!!!).

As to the brace rods - Yep - have them - made my own - always thought that was a weakness in the G50 / SBF combination.

Good luck!!

dave

 

[Peter Delaney]

Thanks Dave,

I got the bearing from Chris, along with a detailed drawing which shows all the key measurements.

As you suggest, I'll check everything without the clutch in. Then, I think its worth checking the clearance of the front/centre of the driven plate (female splined hub) to make sure that it doesn't foul the back of the pilot bearing.

"In search of the lost bearing " - I'll PM Jac Mac & get "the good oil" !!

Thanks & Kind Regards,

Peter D.

 

[Peter Delaney]

Problem found & fixed !

The main thrust bearing on the crank was chewed out - apparently caused by the clutch "over-throwing" - going past the release point & available spring movement, then hauling the crank backwards against the thrust bearing.

All my fault !! I never knew about the need for a pedal-stop - in my ignorance, I just thought that when the pedal stopped hard, it was just the m/c bottoming out & all would be good - but no, it was me fighting the thrust bearing !

Fortunately, there was no damage from bearing material through the motor, & the crank itself was ok.

So new main & thrust bearings, a wacking big adjustable bolt as a clutch stop, a wacking big bill, & we are on the road again !

I wonder what the beast will be throwing at me next ??

Thanks for all your help guys.

Kind Regards,

Peter D.

 

[Randy V]

Thanks for the follow-up Peter... Hopefully you were able to just replace the main bearings and didn't have to go any deeper... I will be mindful of this on my own car...

 

[zollis]

Clutch problem can be a main bearing problem . Learning by other peoples experience has just paid my half hour visiting this site .


Z.C.

 

[Peter Delaney]

Thanks Guys !

It is always way better to learn from other people's mistakes, rather than from your own !!

Kind Regards,

Peter D.