Overdrive(?) slipping

[heraldcoupe]

First a bit of backgorund:

Car is a 1500 Spitfire, laid up since 1993 according to the last tax disc.
I've done a few jobs since acquiring it three years ago, it officially went back on the road in April, though it's actually done nothing more than a few test drives since.

Driving the car to it's MOT, and subsequent retest, a few faults became apparent.
Firstly, when engaging overdrive (J-type) under power, there was massive slippage, presumably from the overdrive clutch. Backing off the throttle briefly made everything fine, full throttle was fine once the overdrive had been engaged.
Second fault was a very woolly feeling clutch pedal. Having commented on this to the MOT tester, the clutch disintegrated on the way home from the (passed) MOT.

I now have a new clutch fitted, so the second fault has been sorted. But fitting a new throttle cable (old one was fraying) has manifested some changes. The new throttle cable is awful, and sticks badly over the first inch of travel. This means something of an on/off throttle action. As the revs rise rapidly, what I presumed to be slippage of the overdrive clutch  is happening in first and second gears, ie those where the overdrive is switched out. Again, backing off the throttle makes everything fine. I'll make up a new cable this afternoon, but no I know there's slippage, I want to deal with it.

I've yet to change the gearbox/overdrive oil or clean the filters due to access issues, but that should be done in the next couple of days. But are issues here likely to cause slippage in the non-overdrive gears? I would expect slippage of the internal clutch to be with overdrive either in or out, but slippage in both states suggests something else to me.
I've little experience with the J-type overdrive (lots with A and D though), so these faults are quite new to me.

Cheers,
Bill.

[Davemate]

I found this chap very friendly and helpful
He took the time to talk to me in a way I could understand
     
overdrive spares in Coventry
tel: 01788 540666
There is a web site

[Jason]

Bill, a knowledgeable sources says "late Spitfire 1500s had a sintered UDC cage and can display the issues you have found as a result. Rectification is substitution by the earlier non sintered cage - most would now fit a complete new UDC"

[heraldcoupe]

Thanks Jason. I'll see if I can rustle up another J-type to rebuild then swap it out,

Cheers,
Bill.

[Richard B]

Would you be better off replacing the clutch with a recon unit?

I know, they're about £110.

[heraldcoupe]

Richard_B wrote:

Would you be better off replacing the clutch with a recon unit?

I know, they're about £110.

As the box has to come out (again!) I'd like to get something built up ready to swap.
It will stay for now, once I've got rid of this godawful throttle cable, I can live with it for a while.

Cheers,
Bill.

[Doug Paterson]

Had exactly this on my Spitfire - slipping when OD was out.  

Appeared to be down to the cone clutch - but I chose to take the chance to swap OD and gearbox for reconditioned ones.

D

[Doug Paterson]

As for the throttle cable the new ones are awful.  

Throw it in the bin (having reclaimed the end bit which anchors it to the bulkhead above the pedal.

Then go down to your local bike shop and buy a suitable (lined) cable there and modify it to fit.  Plenty of bike cables fit the carb end just fine.  For the pedal end I use a choke cable clamp with a washer to clamp the cable so that it sits nicely in the slot on the pedal.

[heraldcoupe]

Doug_P wrote:

Then go down to your local bike shop and buy a suitable (lined) cable there and modify it to fit.  

Funnily enough that's what I went down to the local bike shop for this morning. Unfortunately, the owner was out for the day and the lady minding the shop, though helpful, knew even less about bike brakes than I do!  I'm calling back tomorrow for the relevant bits though, so should be done over the weekend,

Cheers,
Bill.

[Nick Moore]

Even betterer, use motorcycle throttle cable. The one on my Herald is teflon lined and a very fine-threaded stainless steel. The motorcycle mechanic made it up for me in his workshop for a tenner.

[Van]

Have only just seen this thread but FWIW when working on the OD only I found it easier to take the OD off the box and leave the box in the car. If you do this you need to jack the engine/box up quite an angle so exhaust and rad hoses might want removing.

I don't know if this is a peculiarity of J-type ODs but the OD will be very hard to remove if you don't do a magic sequence of events before removing OD from car.
Disconnect prop from OD
Start car, drive up to about 60 mph up through the gears and into OD (car is stationary!)
Put foot on clutch and disengage OD while OD flange still spinning
Switch off engine
Then you should be able to get the OD off easily.

Don't try to diagnose faults without oil level being correct.
If it slips in 1st and 2nd, it is the roller clutch.
If it slips in 1st and 2nd when you put your foot on the throttle after the car has been coasting, but it is OK when pulling away from stationary, then it is probably the angle of the ramps in the roller clutch (there are good and bad types)
If it slips while overdrive is engaged, it is the cone clutch.
If it slips so much when overdrive is engaged that it actually goes slower than the equivalent non-OD speed, then you have both faults. Persistent use of an OD with knackered roller clutch can knacker the cone clutch, so this does happen.


Cheers
Van