T5 Concentric Slave & Throwout Bearing

[ackbullchang]

Does anyone know if the tremec t5 throwout bearing needs any preload on the clutch fingers?

Has anyone changed the standard throwout bearing for a different type?

After having a new clutch fitted by a well rated tvr expert, the car has been back 4 times with slave issues over a period of 1300 miles. Today I can't properly disengage the clutch, I.e put the car in neutral from when in gear. The tvr expert has worked on hundreds if not thousands of these yet cannot find anything inherently wrong with my car. I've decided to drop the box and have a look myself, but cannot find anything information about how much preload, if any, is required. I am suspecting that there might not be enough throw in the throwout bearing as the clutch wears to release the clutch. I suspect that the expert may have set it like this to preserve the life of the clutch fingers when the clutch was new, and that the tolerance was so tight that any small wear in the clutch has meant that the throwout required is slightly more than initially set.

Car is a 2003 tuscan.

Many thanks in advance.

[Steve_D]

I'll start by saying I don't know this specific installation but will throw in some thoughts for you.

Most concentric cylinders do not include any sort of spring to provide a preload so all that happens is the cylinder gets pushed back as the clutch fingers move out as the clutch engages. The cylinder/release bearing will then sit just clear of the fingers until next required.

What could be happening in your case is a distorted or cracked pressure plate spring disc. In this case one or more of the clutch fingers will sit higher than the others when the clutch is engaged. The result is that this finger will push the release further back. When you next apply the clutch the release has to travel much further to first deal with the high finger then complete the depression of the pressure plate. By this time the master cylinder runs out of travel.
Try doing a rapid double pump on the clutch and see if that helps. Might give some clues as to what is going on.

A similar thing can happen to race car disc brakes where heavy side loads can push back the brake pistons resulting in a long pedal when they next go to brake. Bikes can do the same thing after a 'tank slapper'.

Steve

[ackbullchang]

Thanks Steve, that makes sense. I'm going to drop the gearbox next weekend and see if I can see what is what (as much a learning experience as fault finding). I am confused about a distorted pressure plate though because the whole clutch pack was replaced 1300 miles ago. I don't drive the car like a nutter, so I would think that all component should be in good condition.

Another thought from a friend is that the master cylinder is ever so slightly loosing pressure. Would there be any definitive way of testing this?

Thanks

[Steve_D]

ackbullchang said:

Thanks Steve, that makes sense. I'm going to drop the gearbox next weekend and see if I can see what is what (as much a learning experience as fault finding). I am confused about a distorted pressure plate though because the whole clutch pack was replaced 1300 miles ago. I don't drive the car like a nutter, so I would think that all component should be in good condition.

Another thought from a friend is that the master cylinder is ever so slightly loosing pressure. Would there be any definitive way of testing this?

Thanks

The clutch could be distorted due to poor manufacture or by overheating. The normal arrangement is a disc with fingers to the middle where the release bearing sits. This disc is spring steel which in manufacture is hardened and tempered. If the temper is not uniform the disc can distort.

Test the master for internal leaks by starting the car, depress the clutch and select a gear but keep the clutch down. If the cylinder is leaking the clutch will gradually engage and the car start to move off.

You have of course gotten down in the footwell and confirmed the master is not leaking externally?

Steve

[jamieduff1981]

I know that a few bellhousings need to be machined down slightly to disengage the clutch properly. In most cases they just fit but there are odd-balls out there. Do you have the Raceproved slave or standard TVR one?

[ackbullchang]

Steve - thanks. At nearly £900 a pop, i would hope that AP could harden their clutch components properly, but maybe I've just had a duffer. Re master there is no fluid in the footwell as far as I can see, but I'm not sure if you are familiar with the tvr tuscan pedal set up, but it's a bit of a beach to see, even when you've got the pedal cover plate out of the way. The car was inching slightly with the clutch pedal down, but I put this down to not disengaging. I'll try holding the pedal down to see.

Jamie - thanks for the additional thoughts. I am on a standard slave. The tvr expert had indicated that the next step would be to try a new bell housing, but I'm not fully convinced. Since I bought the car 2 years ago I've covered 7,000 miles, without any sign of clutch issues until 1300 miles ago. I would have thought that something like bell housing machining would have shown up prior to my recent issues?

I'm going to try an iterative approach to try and determine the problem. Is it unrealistic to ask the tvr expert to have it back for a 5th time at his cost when ultimately it might be something intrinsically slightly off with my car?

[Geoff Ashcroft]

Could it be something so simple as insufficient pedal movement? Have you wound the pedal stop bolt in, perhaps a turn or two to get a bit more pedal movement to push the bearing a bit further and free-up the dragging clutch... I've heard of them pushing too far and over-stroking, which can lead to premature finger failure. Just a thought.

[ackbullchang]

Thanks Geoff, another thing that I will check. I will do this first.

Thanks guys.

[jamieduff1981]

ackbullchang said:

Jamie - thanks for the additional thoughts. I am on a standard slave. The tvr expert had indicated that the next step would be to try a new bell housing, but I'm not fully convinced. Since I bought the car 2 years ago I've covered 7,000 miles, without any sign of clutch issues until 1300 miles ago. I would have thought that something like bell housing machining would have shown up prior to my recent issues?

You'd think so but I think I've spotted a few people talking about different length or stroke slaves. They may have been fine as they left the factory but if renewed with a "standard" size slave that's when the issues start. I know Barry at TVR Ecosse was having similar head-scratchers about this very recently. He had 3 bell housings laid out on the floor and several slave cylinders. They all looked the same but on customer's car just didn't fit properly. IIRC is was just the thickness of the flange the slave bolts to that was slightly different - but it was just enough to prevent a normal Raceproved slave from fully declutching.

Check the pedal travel etc first, but all I'm saying is don't presume you have a 'normal' bellhousing just because it used to be fine because this is not unheard of even if it is rare

Best of luck with it

[ackbullchang]

Jamie, thanks once again. Thinking about this logically, if the bellhousing to slave connection flange is not machined 100% as to not give enough throw, then this should be solved relatively easily by using a spacer? I.e this would hold the slave further off the bell housing therefore giving greater throw on the bearing, depressing the clutch pressure plate fingers further and allowing greater disconnection of the clutch away from the flywheel?

Thanks all. I love these forums as I've gone from not knowing much about clutch operation, to having loads of swell ideas.

I will check, in order:

1 Clutch pedal stop to see if there is further stroke allowance
2 Master cylinder by holding clutch down when in gear and seeing if the car eventually starts edging forwards
3 Drop gearbox and examine clutch and clutch pressure plate for distortion or maligned fingers
4 Visual of bellhousing to slave flange
5 Visual of slave cylinder and throw out bearings for scoring etc and replace seals

[jamieduff1981]

It's the other way around. The slave cylinder mounts to the bellhousing from the gearbox side, not the flywheel side. It positions the slave cylinder too far away from the clutch fingers. A spacer would make it worse. The solution in those (fairly rare) cases is to machine the bellhousing flange thinner (i.e. move the mating surface closer to the clutch).

[ackbullchang]

Ah, I see. Every day is a learning day! I had it visualised in my head how I thought the slave attached/worked, but it looks like I had it totally wrong. I'm hoping it will make more sense when the gearbox is off!

Out of interest is it possible to see the hydraulic operation of the throw out bearing with the gearbox in place I.e is there a viewing hole on the bell housing? If not can you drop the gearbox without first removing the slave hydraulics and visually see what moves when the clutch pedal is pressed? I am suspecting not!

Edited by ackbullchang on Monday 25th August 10:26

[ackbullchang]

Jamie, quick question. Whilst the pic below isnt a t5, the principles are the same. The slave is bolted on to the transmission at the opposite end of the bellhousing to the clutch and flywheel. Surely the way to get the slave closer to the clutch (to enable greater push on the clutch fingers) is to put a spacer/shim behind the black bolts in the pic. I.e space the slave slightly away from the transmission? Please let me know if I've got this totally wrong!

Copyright http://home.earthlink.net/~dvgreimann/largeimages/...

[m4tti]

From what I remember when I took my engine (although I didn't remove the slave) out you'd either need to machine where the recess where the slave locates deeper or machine the bell housing mating face as mentioned. Possibly easier to find a new bell housing if you can take yours along and compare depths.

[Marto]

ackbullchang said:

Jamie, quick question. Whilst the pic below isnt a t5, the principles are the same. The slave is bolted on to the transmission at the opposite end of the bellhousing to the clutch and flywheel. Surely the way to get the slave closer to the clutch (to enable greater push on the clutch fingers) is to put a spacer/shim behind the black bolts in the pic. I.e space the slave slightly away from the transmission? Please let me know if I've got this totally wrong!

Copyright http://home.earthlink.net/~dvgreimann/largeimages/...

Your thinking is right but the set up of the slave is different. the slave is mounted into a recess on the bellhousing from the gearbox side. When you drop the box, the bellhousing is left behind (Pretty much as Jamie D says). The slave cylinder is fixed by 4 allan key screws on the gearbox side. The slave unit and bearing then sits 'through' the bellhousing and mates with the clutch finger followers.

If you drop the box, then drop the bellhousing, you will see the set up. The flywheel and the clutch are bolted to the crank and remain connected to the engine when you remove the bellhousing.

If you put a spacer between the slave and the bellhousing, then it would in effect take the slave further away form the clutch fingers. Jamie is totally correct in what he said. If the 'throw' of the slave is not fully disengaging the clutch, then yes, one option would be to machine away a small amount of material in the slave recess on the bellhousing.
Google 'Varleyhyd speed 6 manual', which has pics of it in situ.

HTH

[Marto]

m4tti said:

From what I remember when I took my engine (although I didn't remove the slave) out you'd either need to machine where the recess where the slave locates deeper or machine the bell housing mating face as mentioned. Possibly easier to find a new bell housing if you can take yours along and compare depths.

Spot on m4tti. That exactly the sort of pic I was thinking of.

[ackbullchang]

Thanks for all the informative posts. The picture helps to paint a thousand words!

I can see now the error in my thinking, as I was assuming that the slave bolted directly on to the gearbox face, not the bell housing face. My worry is now tolerances. I obviously need to change the throw sufficiently to better disengage the clutch, but don't want too much to overstretch the clutch pressure plate.

Can you see inside the bell housing in situ? I would like a visual of the throw out working before I drop the box and bellhousing.

[m4tti]

You can only really determine the throw with the box off. Is the master cylinder plunger definitely at its maximum travel.
Temporarily for fault diagnosis it shouldn't hurt the spring fingers.

Stupid question. Have you removed the pedal plate and the pedal travel stop. Basically if it worked before it'll work again it's fairly simple.

Edited by m4tti on Monday 25th August 16:56

Edited by m4tti on Monday 25th August 17:00

[ackbullchang]

Cheers Matti, it's the first thing on my list to do, above. Unfortunately the car is some distance away, so I can't go fault finding until the weekend. Thought it was better to get some pre-ideas on here first, so thanks to all.

[jamieduff1981]

Sorry about that! I presumptiously assumed you had seen it all apart previously and were familiar with the arrangement. Without the context of having seen it my posts would have been rather unclear!

That photo above is perfect.