HELP! Clutch keeps failing

[overlord]

Hello.  I have a 1980 Spitfire (American).  Last year I took it to a well known sports shop because the car lost power (it would rev high but no torque).  Was told it was the transmission so I bought a used J-type overdrive trans.  A new clutch was installed too.  But the clutch wouldn't engage.  The master and slave cylinder worked fine but had those replaced too.  The shop ordered another clutch but same thing happened.  You press the clutch pedal and the slave worked but it didn't engage the clutch.  The shop welded a small extension onto the part which pushes the throw-out-bearing to engage the clutch.  That seemed to work and the transmission was great!  Less than 15 miles later, a bad vibration started and the clutch wouldn't engage.  Towed the car back and the clutch plate springs were in pieces.  They ordered another clutch and everything was fine again but about 15 miles later the same thing happened and i'm about to take it back to the shop.  At least it's under warranty.  Here's the thing though.  The transmission and bell housing are the same size as the old one, the clutch is correct to the model.  Unfortunately someone goofed and threw away the old clutch so there isn't a reference to what was on there the first time.  Any thoughts?  I'm thinking that maybe looking at the flywheel?  The engine and flywheel are original to the car though.  This shop is supposed to be the best for British sport cars in the Mid-Atlantic region in the U.S. but i'm not too thrilled with their performance so far.  I want it fixed!  HELP!

[neilnaz]

Get them to check whether the engine back plate is warped it sounds like a possibility to me. I had this years ago on my first Spitfire and it was my fault as I caused the warp in the back plate when changing the gearbox. I had a number of clutches fail and this was identified as the cause.

Best of luck, Neil

[JensH]

Make sure trust washers are good (=no vertical play in crank).

[Richard B]

JensH wrote:

Make sure thrust washers are good (=no vertical play in crank).

I think you mean horizontal?   :-/

Put a screwdriver behind the front pulley and try levering it backwards & forwards.

[JensH]

Richard_B wrote:

I think you mean horizontal?   :-/

Put a screwdriver behind the front pulley and try levering it backwards & forwards.

Ah, still need my morning coffee  :-)  

[bodders1]

Hi Overlord

It sounds to me as though you have had two different problems.  The first was a lack of drive (high revving, no torque) which sounds to me like a slipping clutch.  
I'm not conviced that either the gearbox or overdrive would have given these symptoms unless there was a catastrophic mechanical failure which would have resulted in no drive at all (even a slipping overdrive will deliver full torque to the back wheels, albeit at higher engine revs, due to the operation of the uni-directional clutch inside it).

The second problem is the replacement clutches disintergrating.

As neilnaz says, the clutch plate repeatedly disintergrating as you describe is usually caused by the engine backplate being distorted, so that the gearbox is no longer exactly in line with the axis of the crankshaft.  With each revolution of the flywheel, there is a tiny flexing of the clutchplate which leads to metal fatigue and the plate breaking up.

Get the engine backplate checked - it has to be PERFETCLY flat.
The backplate can become distorted during a gearbox change if the weight of the gearbox and overdrive is not properly supported while all the bell-housing bolts are tightened.

In your orignal posting, you say that the first replacement clutch wouldn't engage.  Presumably you meant that, when pressing the clutch pedal, it did not disengage drive from the engine.  Certainly the attempted fix by the workshop of extending the actuating pin would suggest this.  
There have been some slave cylinders available in recent years where the groove for the pinch bolt has been machined too near the tip so that they do not sit far enough into the bell-housing and, consequently, do not push the clutch mechanism in far enough to disengage the clutch properly.  Usually this manifests itself as a biting-point very near the floor and difficulty selected gears when at rest due to a dragging clutch, although in extreme cases it could prevent the clutch from disengaging drive altogether.
Another cause for poor clutch disengagement is if the clutch pivot pin is badly worn, or (as happens sometimes) has been mislaid and replaced by a bolt through the bell-housing.

[Fizzy]

i changed my clutch about 5 times until somebody - probably neil - mentioned the warped backplate. heres what i found when i took it off. no problems since being replaced.

[overlord]

Thanks a lot for the insight!  I've had two other Spits but never this problem before.

[Fizzy]

it only takes one gearbox removal to bend it. when i got my car the clutch was slipping because it was worn. obviously that clutch had been in a long time, long enough to wear down to the rivets. i must have bent the backplate when replacing it, because after that my clutches were lasting 3 months at best, 3 days at worst !!!

[herald948]

Forgive the stray of this thread, but I'm curious: just where and how do the backplates bend?

[Fizzy]

to be honest, i dont know how it bent, seen as its attatched to the engine :-/ but mine was bent along where the big holes are, horizontally across the plate.

[thescrapman]

herald948 wrote:

Forgive the stray of this thread, but I'm curious: just where and how do the backplates bend?

usually by people using the bolts to pull the bellhousing into place rather than realising that something is wrong when it doesn't just slide into place.

Or accident damage.

Cheers

Colin

[willcolumbine]

As said above - The gearbox input shaft and engine will only mate up when all the planets are in alignment, under a full moon and in a leap year. If you try and hurry it along by tightening bolts it will only end in woe!

A way that's worked for me is to put a few studs in the holes on the back of the block and slide the gearbox towards the engine. The weight of the gearbox is supported by the studs which stops damage to the input shaft and you don't put any stress on the backplate either.

[aar0sc]

Well that explains how I bent that back plate on my first spare engine :/

[herald948]

thescrapman wrote:

usually by people using the bolts to pull the bellhousing into place rather than realising that something is wrong when it doesn't just slide into place.

Or accident damage.

Ah, thanks, that makes sense! I've never encountered a bent plate. Of course, when my eyesight was better, I had no trouble "eyeballing" the driven plate to get it centered. In more recent years, I've been lucky enough to have a trashed gearbox in the barn that could yield an input shaft for accurate clutch alignment. (And honest, I didn't trash the gearbox; it was a beat-up and neglected three-synchro three-rail Herald box that someone had thrown into a MkIV Spitfire!)