thickness of a new TR4A-TR6 clutch disc

[Z320]

Hi there,

this is a general gearbox and clutch issue.

Can anyone tell me or measure the thickness of a new TR4A-TR6 clutch disc, diameter 216 mm.

The one on my TR4A (Borg+Beck) was 7 mm about 8 yaers / 25,000 miles ago

It is now (the left one) 6.65 mm, down to the rivets it's 1.0 mm on both sides, to me this seems to be good for another 10 years?

 

On the right side you see the Borg+Beck which came with my spare part engine, the gear box side up.

It looks like short time used, thickness is 7.25 mm, down to the rivets is is 1.35 mm on one side and 1.10 mm on the other.

Also this looks good for a another 10 yeras? Any ideas.

Ciao, Marco

Edited April 19, 2020 by Z320
This is a general gearbox andd clutch issue

[BRINDUS44]

Hi Marco,

I have a new B&B plate measures approx. 8.0mm. 
Regards

Ian 

[Waldi]

I tend to  with you Marco, and am not aware of a rejection-thickness. FWIW: some web info says 7.93 - 8.00 mm for new, and 7.0 mm is “fully worn”.

off course, the pressure to the plate is not linear with wear, and once the slits disappear it is over.

Waldi

[Z320]

Hi Ian, thank for your answer and effort!

Hi Waldi,

I remember I made a test in 2012:

how close do I have to bolt the clutch compression palte to the flywheel to get the friction plate fixed; result was 3.15 mm

I did this again today: with 2.60 mm gap the friction plate still slides, reduced to 2.5 mm it is tight between flywheel and compression plate.

 

As the spring is pre loaded I think this is OK and I will use both again.

Also checked this with the friction plate from my spare engine: with the gap 3.0 mm the friction plate was fixed, this would be better but I don't know how the plate worked before.

The compression plate on both engines is a Borg+Beck, but they look different - and the gap with the spare engine's plate it 5.0 mm (!) without the friction plate in between (fast fitted for a different issue).

I think I have to sleep a night over it and make a photo tomorrow, perhaps anyone knows something about.

Ciao, Marco

Edited April 18, 2020 by Z320

[Waldi]

Hi Marco,

I did too:)

With the thinner friction plate, the axial travel which is required to “free” the part worn item you have will reduce, and with this I think also the travel of your pedal.

And the pre-load is lower, so less torque can be transmitted before slip occurs.

So if a new plate is 8.0 mm and yours is 6.65 is may start slipping soon? Was yours indeed new when you measured it at  7.0 mm? Than it may be different and you could re-use  it. But a friction plate is cheap...

Waldi

[Z320]

Hi Waldi,

sorry me to cause a question abour the 7.0 mm of my friction plate in 2012.

This was how I found it on my TR when I had the gearbox out for a repair,

it was already used.

Ciao, Marco

[Waldi]

Hi Marco,

then your friction plate is probably almost worn, and may start slipping soon, or do you see it differently?

Waldi

[Ralph Whitaker]

Ask yourself this; Do I really want to have to take it all to bits again if it starts slipping?. Also if it gets down to the rivets it could take out both the pressure plate and the flywheel. I would put a new one in.

By the way, the B+B name is now used by a spurious supplier and the quality is not what it was, so I would not be tempted by any B+B offering on such as ebay. I made that mistake when restoring my Austin A35, the clutch was really heavy and juddered badly. Within 12 months I had taken it out and replaced it with an AE item from one of the specialists. Twice the price but a million miles away in terms of quality.

[Z320]

I don't know.

Perhaps there's someone out there who can tell us.

On the german VW Bully forum I found the statement everything is OK as long as the gap I measured is more than 2 mm.

[Waldi]

Someone should have a worn (slipping) plate laying around under the work bench, can you measure how thick it is? Marco needs data and we can all learn from this.

Cheers,

Waldi

[Z320]

4 minutes ago, Waldi said:

Someone should have a worn (slipping) plate laying around under the work bench, can you measure how thick it is? Marco needs data and we can all learn from this.

Cheers,

Waldi

THAT WOULD BE GREAT!

I think to know the range from new to worn could be a interesting information for all of us.

Edited April 19, 2020 by Z320

[Ralph Whitaker]

34 minutes ago, Ralph Whitaker said:

Ask yourself this; Do I really want to have to take it all to bits again if it starts slipping?. Also if it gets down to the rivets it could take out both the pressure plate and the flywheel. I would put a new one in.

By the way, the B+B name is now used by a spurious supplier and the quality is not what it was, so I would not be tempted by any B+B offering on such as ebay. I made that mistake when restoring my Austin A35, the clutch was really heavy and juddered badly. Within 12 months I had taken it out and replaced it with an AE item from one of the specialists. Twice the price but a million miles away in terms of quality.

Sorry Marco, didn`t realise until I read your thread about hydraulic clutch bearings that you were obviously an accomplished engineer and probably know all of the above anyway. I didn`t mean to teach grandma how to suck eggs !!!.

[Z320]

Ralph,

your post was welcome!

[Z320]

Here are both of them,

left the one that came with my TR4A, 3 fingers painted green, looks more like from a modern industrial production

right the one that came with a TR4A spare engine, two fingers painted yellow, locks a little bit like "hand made".

Sorry, both compress the friction plate the same, the 5 mm gap was from the 3 dowels.

The one from my TR is not that solid and I guess its weight is 2 kg less than the one from the spare engine.

So I further use my compression plate, if not anyone has reasons to convince me different.

Ciao, Marco

 

[Waldi]

Hi Marco,

I lack thorough experience on the “replace or re-use” - question for these components. I inspected my old clutch like you do, found little/no wear and it worked before disassembly. Added to this I did read about issues with new components, and my limited expected use.
So I thoroughly cleaned the components, lubricated the pivot points to reduce friction (I was not sure if needed but felt it could not hurt, off course just a little bit), and re-used all existing components, with the exception of the throw out bearing, which I replaced by a RHP per Rogers recommendation a couple of years ago.

Waldi

[Z320]

Hi,

I'm very sorry no one has a worn and slipping friction disc to measure. Well, never mind, anyway I can give you this idea:

I made two dummy friction plates from wood fibre board, one 5 mm thick (totaly worn friction plate) and one 8 mm thick (new friction plate).

With the 5 mm one the gap is 0.7 mm when its fixed by the compression plate - and bolted tight on the flywheel the fingers of the diaphram spring are maximum out.

It looks like this, the bar touches the fingers about 45 mm in distance of the flywheel.

Next with the 8 mm one the gap it 3.7 mm when it's fixed by the compression plate, tighted on the flywheel the fingers are maximum in.

Bar is still the same, distance is also 45 mm, looks like this:

 

Distance is about (max.) 10 mm now, that's what I need for my hydraulic release bearing project.

I further will calculate with 7 mm free play for a new friction plate.

So this is about 3.33 mm movement of the fingers out for every 1 mm wear out of the friction plate.

The fork moving the release bearing is 67 mm long, the leaver outside the gearbox is 87 mm.

So every 1 mm wear out of the friction plate is 3.33 mm x 87/67 = about 4.5 mm less play of the leaver (middle drill)

When you fit a new friction plate (or check yours) you only have to measure and notice the play on the the leaver,  for every 4.5 mm less the friction plate is 1 mm worn. This is "the same" but some [mm] different with another badge of clutch.

I know, you perhaps never asked yourself this - but maybe it helps

Ciao, Marco

Edited April 21, 2020 by Z320

[Waldi]

Hi Marco,
you did a nice job again. The ratio of 1 mm plate wear giving 3,33 mm fingers moving out (to the back) and then with the lever this magnifies that to 4.5 mm for the lever going forward per 1 mm wear! I bet very little people know that (I did not).
You are right, there may be slight differences between individual items, but “the lever vertical if all is in good order” is something more generally known. Now we better understand why.

Thanks again for your nice analysis.

Waldi

[Z320]

Hi Waldi,

this is why you have to adjust a classic (not self adjustion) clutch from time to time.

I knew this and the fact about two mulitplicators but not how much.

This was a special point of discussion when my friends and I made the calculation for our hydraulic release bearing.

Ciao, Marco

 

[Waldi]

Hi Marco,

The TR6 clutch is self adjusting, as the friction plate wears, the soft spring inside the slave cylinder will move the piston out to compensate for wear.

Yes, a TR6 is a highly modern masterpiece of engineering

Cheers,
Waldi

[signalredshaker]

On part worn friction plate thickness- mine, which has only done around 8K miles Is 7.34mm. Its a Borg & Beck TR4a diaphragm variety, even though my car is a TR4. 

I did replace it  a couple of weeks ago, and yes, I may have wasted a few quid, but removing and replacing an OD gearbox must be one of the most physically taxing  aspects of TR ownership.

Unless you pay someone else do it for you of course. Why don't TR owners do that? Its in the blood, that's why, from years of running a TR as a first car on a shoestring budget, with no spare cash at all. Remember those days? Well, now I can afford a new clutch plate but still regret spending the money!