Clutch snatching

[martynbrett]

In Autumn last year my clutch started to 'snatch', for want of a better word. What I mean is that after depressing the cutch pedal, changing gear and then releasing the clutch pedal, the clutch did not prgressively re-engage butd did so in lurches. I had my local garage replace the pressure plate, the friction plate, the release bearing and the release bearing carrier tube and all seemed well. The work was done in the middle of November and now, less than a hundred miles later and having just begun to use the car again the snatching is starting again.
Any ideas please?

[dasadrew]

If the instruction to your garage was to "cure the snatching clutch" I think I'd be back there pdq. ... unless you instructed them to change the clutch plates, bearing and bearingtube.

Drew

[Lingen]

Martin.
This is such a common problem I'm afraid. It may be that the bearing carrier wasn't sufficiently lubricated when it was replaced. Or more likely, that the two special dowel bolts between the gearbox bell housing and the engine back plate have not been fitted as per the parts book. (Part number 150743). Maybe they weren't there before the clutch was replaced. It is vital that they are in place as all the rest are a fairly loose fit, and these two ensure that the engine and box are fully aligned. Misalignment will cause your problem. I know some people recommend that one of the other bolt holes near the bottom of the bell housing should be carefully enlarged to take a third interference-fitting bolt to further improve the alignment.
Mike Allen

[martynbrett]

Mike, thank you for the information. I do not have a parts book and can't see the dowels you mention in either the ROM or in the Rimmer Bros book. I searched on part number 150743 on the Rimmer web page and it's not recognised.

Regards, Martyn.

[Guest]

I use valve grinding paste to lap the throwout sleeve to the front gearbox nose.
It only takes a little bruise on the nose and bad tolerance on the cross shaft bushes to get these sort of nightmare problems on TR6 also.

"I had my local garage replace the .........release bearing carrier tube"
That is where your problem is likely coming from. (I always much prefer brass throwout sleeves...)

[dasadrew]

Mike, thank you for the information. I do not have a parts book and can't see the dowels you mention in either the ROM or in the Rimmer Bros book. I searched on part number 150743 on the Rimmer web page and it's not recognised.

Regards, Martyn.

http://www.ldparts.co.uk/shop/shop.php?c=viewproduct&pid=230&cat=113&maincat=3&start=0&sid=sidc7522b1bbc28a6b95241baf042605483

Drew

[flying farmer]

I had this problem on my first Stag engine in my TR. It was built with a new clutch so I don't know its previous history but the clutch judder was horrendous. I lived with it for years, but when I fitted the engine to my Estate the much heavier car needed more clutch slip to get it moving and I couldn't live with the problem any more.
Since the clutch looked perfect I had the flywheel skimmed as it had two badly crazed areas on the surface. This cured the problem (and was cheaper than a new clutch)
Neil

[Guest]

I had the flywheel skimmed as it had two badly crazed areas on the surface. This cured the problem (and was cheaper than a new clutch)
Neil

Big difference between Jaguar and Triumph.
Jaguar flywheels nearly always used to be made of high quality STEEL. (The clutch is the same size as Stag).
They are one of the reliable bits of the car, judder unknown, a decent release mechanism.

Here's a little explanation.
Steel flywheels don't craze because there is none of the high carbon crystalline surface structure which favours turning "stress raisers" into genuine cracks as the surface cools unevenly....this means they tend to remain flat.

Iron however is very different.

(brake disks crack because they end up being enveloped in just a fraction of the surface area by a hot brake pad, the moment you pit from a few laps on a circuit..., then park up, so,
they not only cool unevenly but the inner and outer surfaces end up being totally different temperatures too...)

In reality the problem/question with cast iron flywheels is also very much the same as casting camshafts by chilling, except cams are deliberately locally cooled in certain spots by injecting steam into the cam lobe areas to get a good result and a hard area.

Cast iron in native soft state has a high coefficient of friction, which would tend to favour its use for friction materials, however.....

Only on stuff supposed to stay flat and soft,-

but, one area which has little contact compared with another which has high contact and therefore gets hotter with the friction also cause the surface to get suddenly chilled in one spot from very hot to very cold.
You get lots of hard spots build up, which anyone who has ever ground a flywheel will tell you as he machines it.

As we know, sudden chilling from very hot, (eg. clamp a fast spinning clutch plate to the surface) causes the iron internal structure to change to needle shaped crystals which are very hard, all locally of course.

The problem gets worse and worse with judder, progressively making hard and soft spots then crazing as the flywheel or disk cools unevenly.
The surface ends up literally tearing itself apart as the hot bit pulls against the cold & uneven expansion/contraction cycles cause cracks to propagate down the weakest areas where the raw carbon granules stick out.
(On engine blocks it also happens between cylinders when the walls are very thin between adjacent cylinders)

It's an extremely well known phenomenon causing violent brake judder and often accompanied by warping.
Ironically (nice pun eh!), usually with NEW brake disks not good old, well heat cycled ones......

Jaguar?
When the -6 XJS and XJ40 came along, they tried to economise for reasons beyond me, and went to cast iron.
(coincidentally they also used ancient designs of brakes, and later on actually DECREASED the pad area,- suicide by cast iron!)

All the good old aggravations on Triumphs then emerged on the manual 3.6L XJS/XJ40 (I have had loads).
After this XJS saga, they went to a DMF (dual mass flywheel) which was one of the most stupid things I have ever seen in production.
People hated this piece of rubbish so much, it hastened the end of manual transmissions for Jaguar, and none has ever been fitted since 1995-6! As they increased the engine power by supercharging they then DECREASED the efficiency of the brakes too!
Late production crap always end up going backwards!

Triumphs always had cast iron flywheels, and auto versions with their dreadful ancient 3 speed borg warner crap were not so popular.
Maybe being so underpowered had something to do with it?
As they got less and less power from their engines, they increased the weight of the car and the flywheel.
The Spitfire 1500 with it's 70bhp had a flywheel TWICE the weight of the nice little Mk3 spitfire which had the same power, and weighed a good 150kg less!

Same story, later cars went backwards, and as we know they built the cars of Russian steel, which was rusty before they left the factory!

Triumph spitfires are famous for destroying clutches, TR5 & TR6, saloons infamous for judder and general clutch related issues.
It's one of the least reliable bits of the cars.

Funnily enough the TR5 which had a lighter flywheel suffers less than the later TR6 which has a humungous boat anchor flywheel!
You see, the stored energy transferred as the flywheel engages drive, takes longer to dissipate, making life for the clutch plate and face particularly nasty.

Now everyone and their dog believes this myth, that Laycock clutches magically solved the problem.
(TR register old fogeydom again!)

They didn't, they just made the clamp load lower and made the working clearances different, then sold all the stuff to Germany, and rebranded it all under LUK.

(ie. the thickness of a laycock plate compared with AP are totally different, I could say more about the thickness of TR register members but I won't!).

This is one I just had to replace in France.
Not only was the AP clutch cover quite badly worn on the diaphragm spring where it meets the release bearing, but I'm almost sure misalignment and judder killed it.
The plate was clearly OEM(wound Asbestos) as you can see, so must have dated from the date the car came out the factory in 1978.

embrayage_1500.jpg

dud_1500_clutch_2.jpg

cheap is beautiful eh?

[martynbrett]

Drew, many thanks for the pointer to the dowel bolts.