GT6/T2000 Clutch

[Ian Foster]

(not sure if the right section to post in)

I am trying to improve my understanding of the geometry of the clutch release mechanism on the GT6 clutch. Master cylinder stroke and bore vs slave etc.

Reference to the factory WSM shows a spec page where the 'driven plate thickness' and 'maximum travel' have identical measurements.

Is this coincidence, 'engineered' or a misprint, as the travel figure seems to be less than might be anticipated.

I would be interested to see the same page from the T2000 WSM (in theory the same clutch) if someone has one available for comparison.

Thanks in anticipation.

Ian

GT6 Clutch WSM.pdf

[Pete Lewis]

well in true Triumph tradition the 2000/2500 genuine WSM has absolutley diddy squat general information about any sort of   specification  data !!!!

the clutch is used on Vit2ltr.  GT6 2000,2500, Sprint 

if you have some operational losses  apart from pedal pivots and clevis wear.

there can be operational problems on the Vit Gt6  clutch operation with many new throw outs only being 15mm thick the originals are 19mm thick

this make the see saw lever out of mechanical balance and the spherical post needs to be popped out and fit a washer as a spacer to raise the height of the post to equal up the leverage advantage of the throwout lever 

add in worn grooves and pins , in the carrier and lever and a lot of loss is created ...the lever angles get worse

you can renew the pins and reposition the anti spin roll pin to start in a new groove position

a spring cover has a thicker disc than a diaphragm,  you can check thickness  by giving it a light nip in a vice 

to load the crinkle plate ,, the data about clearances and finger positions will be with it set on 3 spacer buttons to simulate the compressed disc thickness

fitting a thicker  coil cover' disc'  in a diaphragm cover will give high clamp but low pedal loads  

where as a diaphragm worn disc gives a low clamp load and higher pedal loads 

do you have some particular problem ?????

 

Pete

 

 

[Ian Foster]

Pete

Thanks for the response. Strange that there no equivalent page in the T2000 WSM. (how about Dolomite Sprint anyone?)

I have undertaken a fairly comprehensive review of the clutch on my GT6 following last years RBRR, when clutch was definitely not happy towards the end of the weekend...poor thing !

Turns out I had the wrong bearing carrier (a steel T2000 item installed as part of clutch kit when I changed to an overdrive back in the late 1970s.....oh the ignorance of youth!), now replaced with my original bronze carrier (which I had fortunately kept) a replacement bellhousing spigot, a correct RHP bearing, an almost new clutch fork and also a new B&B clutch (courtesy of Mr Witor). Pedal and pushrod are also about as good as they are going to get.

Post 2011 rebuild a 7/8" clutch slave had been fitted, but was worn internally by the incorrect geometry resulting from the wrong carrier.

I have had my original Girling 5/8" master cylinder and 1" slave cylinder stainless sleeved by Past Parts and whilst everything is pretty much OK I just felt I need just a bit more clutch travel, some of which I have achieved with the substitution of an adjustable pushrod, which has a slightly bigger head on the bearing end into the cylinder.

The reason for my reference to the WSM in respect of maximum bearing travel is to ensure I am not overstressing the clutch. I can measure master cylinder stoke and hence volume, which can be converted to slave movement and because I know the geometry of the fork, I should be able to determine actual bearing movement (I can also actually measure slave movement).

I am determined to try and  resolve everything before I put the interior back in as it has been in and out more times than I care to count, albeit two of those were down to gear lever 'ball failure'.

Anyway if anyone can assist with information on 'maximum travel' I would be most grateful.

Ian

[Pete Lewis]

on the Vit6 i slotted the pedal box cyl bracket to allow some fore aft shift this can raise the pedal up to an 1" but have to ensure free play on pushrod is maintained in  in foot off or it cant recuperate .

does gain travel , i dont thick there is enough travel  to over stroke the diaphragm with std  cyl diameters etc.

Pete

 

[Nick Jones]

Same clutch again on Dolly 1850 (and even the same release arm) and TR7 4 speed.

The same basic clutch components are used in many Fords and Saabs of the 80s and 90s.

I spent much time researching this when I was mixing and matching Triumph and Toyota parts for my gearbox conversion and had great difficulty getting any solid information.

My conclusion was that if you end up with something that feels like a clutch pedal, with the biting point roughly half way through the pedal stroke and that fully releases without the need to mash the pedal into the carpet, then you are something like right.  This even seems to be true when you use a Toyota clutch plate ~8.5mm thick with a B & B cover intended for a max of a bit under 7.5mm, though you need to over-stroke the cover plate somewhat to gain release and this leaves odd wear patterns on the fingers.

IMO the GT6/Vitesse/1850 arrangement is fussy because the release arm is short and this too easily leads to problems with angles.

I'm dubious of the data shown on the page you attached.  Specifically what the meaning of maximum travel is and whether this relates to the movement of the fingers (possible) or the pressure plate (not possible, it's much less than that).  Unhelpfully it also fails to mention the ratio of the pressure plate (they vary).

Nick

[trigolf]

Ian, when I refitted my recon uprated j type box from Kippings c/w new borg beck clutch I had slight clutch drag. The master & slave had been rebuilt and the system bled several times. I also checked I had the correct thickness  release bearing , as Pete mentions. I also fitted a new release bearing carrier. So everything was in order but still getting crunching. I ended up putting a couple of thick plain washers under the slave cylinder mounting lugs. This moved the slave cylinder very slightly nearer. Result - no crunching at all. Has been fine ever since. 

Gav

[Ian Foster]

Thanks all (Nick and I have been corresponding on this for a while).

Nick, I agree the travel figure looks dubious and is as you say undefined, which is why I queried it.

Pete, interesting to hear that you believe the clutch can't be overstroked with standard components.

Gav, It does sound as though the set up is a bit marginal, although I would have thought that just moving the slave nearer to the fork with spacer washers would have just taken up some of the hydraulic self adjustment. Mind you if it worked !

Mr Witors website offers a 7/8" slave (longer travel than 1") as being 'better with all aftermarket clutches 2000 & 2.5.

Will continue the quest for a perfect clutch.

Ian

[Pete Lewis]

as all these have a static slave moving the cyl has no effect other than moving the start position of the piston within  it.

it can only assist if you have bottomed out its range of travel .

i always feel collapsing the piston as far as possible aids removing trapped  air , even 'end upping'  the cyl to get trapped air out.

its a good idea on Vit GT6 to add a length of tube/hose with the bleed in the engine bay for ease of use without trying to fight back to front spanners and wonky fingers when the tunnel is in place

Pete 

 

 

[NonMember]

1 hour ago, Ian Foster said:

Mr Witors website offers a 7/8" slave (longer travel than 1") as being 'better with all aftermarket clutches 2000 & 2.5.

I put a 7/8" slave on my Vitesse and it's definitely improved the clutch release / reduced the tendency to drag. The GT6 has no such problem but then it's still running on the clutch I decided was "good enough for now" when I rebuilt the engine in 1993...

[Nick Jones]

5 hours ago, Pete Lewis said:

as all these have a static slave moving the cyl has no effect other than moving the start position of the piston within  it.

This is true, and the same should be true of longer pushrods.  The only effect of these measures that I can think of is to compress the spring inside the slave a bit more, perhaps with the effect of adding a bit of pre-load and holding the mechanical elements together, reducing lost motion a little.

Found this on the AP Racing site

https://www.apracing.com/product_details/performance_upgrades/special_tuning_clutches/high_performance_cover_assemblies/ø215mm_cover_assemblies/cp2246_family-ds_type-straight_finger.aspx

This was the most comparable example I could find.  Still lacking detail.

Full race metallic clutch data is a bit more comprehensive

https://www.apracing.com/product_details/race_car/metallic_race_clutches/ø215mm_types/single_plate_cp5241_family.aspx

And the drawing gives a bit more again including maximum travel.  It's not on this drawing but I found a different one earlier that had a note stating that max travel is measured at the contact ring of the fingers and is the maximum compression allowed from the point then the release bearing makes contact.  It also stipulates the use of a pedal stop to prevent over-stroking.

https://www.apracing.com/drawings/cp5241-1cd.pdf

[Ian Foster]

From the AP racing spec, maximum release travel:-

link 1 = 9.00mm

link 2 = couldn't find it

link 3 = 6.0-6.5mm (has a diagram showing the figure relates to the bearing/fingers)

Travel is in the same general ball park as plate thickness.

That makes the 7.36mm (0.29") Maximum travel figure from page 2.107 of the WSM look sensible.

For the GT6/Vitesse arrangement, measurements of the fork (approx.) pins to pivot = 51mm. pivot to pushrod =81mm.

Movement required at pushrod = 7.36x81/51=11.7mm

Master cylinder 5/8" dia (15.88m),  area = 198mm2

Stroke (say 30mm) volume = 5.94cc

Slave cylinder 1" dia (25.4mm), area = 507mm2

So assuming no losses, resulting pushrod travel = 5.94x1000/507=11.7mm

So seems to check out.  

Fitting a 7/8" (22.2mm) slave, area = 388mm2

Pushrod travel = 5.94x1000/388=15.3mm (ie additional 3.6mm or 31%)

Ian

Pete I have a remote bleed system and very useful it is too!

Update I have contacted the technical department of Frontline (Borg and Beck) to see what they have on the spec. Could be interesting

[Pete Lewis]

we used to check truck clutches with a load cell to plot the clamp and input  load against travel

(Not AP) recons were a complete nightmare of reground faces to be well beyond any serviceable use, tin pot diaphragms and coils springs all odd lengths , all in a nice box.

the hysterisis of the diaphragm is an interesting curve on compression and release all very different 

doesnt help much just some waffle 

AP were good at tech support but all dispersed and no contacts now ( as i retired in 2002)

Pete

 

[Ian Foster]

Update following response from the Senior Engineer at Frontline (Borg and Beck).

GCC228 Borg and Beck Clutch:- The design travel to release the clutch is minimum of 8mm to maximum of 9.5mm.

So with the GT6/Vitesse fork geometry, minimum movement required at slave pushrod is 8x81/51=12.7mm, maximum is 9.5x81/51=15.1mm

30mm of master cylinder stroke with a 1" slave gives 11.7mm and with a 7/8" slave gives 15.3mm. Absolute maximum stroke in the master is about 32-33mm.

This does seem to show that with the current GCC228 B&B  cover with the GT6/Vitesse fork geometry, the available travel with the 1" slave is not quite enough and with the 7/8" is at maximum. This supports my recent experience/observations.

Now if I can just get the flexible stainless pipe and the remote bleed to seal properly in the slave, I'll be sorted (hopefully substituting nitrile Dowty washers for copper will do it)

Ian

[Nick Jones]

Thanks for the figures and calcs!

Use EPDM or FPM Dowty washers if you can...... nitrile really doesn’t like brake fluid

[Ian Foster]

B****r!! Will have to order the right type!

Ian

[Pete Lewis]

there is nothing like the pressures in the clutch hydraulics , and copper works well on brakes ... much higher psi. 

this shouldnt be hard to seal    ?????

Pete

[Ian Foster]

Pete

Slave is new, so nice flat surfaces. Pipes are good and new copper washers, so agreed it 'should' seal.

Have tightened as much as I dare considering a thread into aluminium, but still weeping! (me and the slave).

(Have now sourced some Viton Dowty seals)

Ian

[Pete Lewis]

Ha , i as usual you investigate all the known to find the unkown and it never cures the problem....classics   who would have one 

when i did mine i used a flared pipe and sleeve nut , even and old brake hose with flare seated end should seal , same as the nipple does 

or in your street  ...not  

have you got a bottle of loctite hydraulic seal   we used that on production ... makes undoing a pig  but works well 

Pete

[Ian Foster]

37 minutes ago, Pete Lewis said:

....classics   who would have one 

Pete

It does feel a bit like that at times, but must soldier on !

I was trying to avoid squirty sealant stuff, but had considered it.

Hoping the Dowty seals will do the job.

Ian

[Nick Jones]

On 02/04/2019 at 13:04, Ian Foster said:

Update following response from the Senior Engineer at Frontline (Borg and Beck).

GCC228 Borg and Beck Clutch:- The design travel to release the clutch is minimum of 8mm to maximum of 9.5mm.

So with the GT6/Vitesse fork geometry, minimum movement required at slave pushrod is 8x81/51=12.7mm, maximum is 9.5x81/51=15.1mm

30mm of master cylinder stroke with a 1" slave gives 11.7mm and with a 7/8" slave gives 15.3mm. Absolute maximum stroke in the master is about 32-33mm.

This does seem to show that with the current GCC228 B&B  cover with the GT6/Vitesse fork geometry, the available travel with the 1" slave is not quite enough and with the 7/8" is at maximum. This supports my recent experience/observations.

Now if I can just get the flexible stainless pipe and the remote bleed to seal properly in the slave, I'll be sorted (hopefully substituting nitrile Dowty washers for copper will do it)

Ian

Just for the record, can you confirm whether your calcs are based on the standard 5/8" clutch master?  My usual cheat is to fit bigger ones for more displacement......

[Ian Foster]

Nick

Yes that's the standard 5/8" jobbie.

Didn't know cheating was allowed !

Ian

[Nick Jones]

‘S not cheating...... alternate technical solution!

[Ian Foster]

Using a 0.7" master increases bore area by 25% compared to the 5/8".

This would give a theoretical stroke of 14.6mm on a 1" slave and 9.2mm at the bearing.

So pretty much on the money for hitting the 8.0-9.5mm range for the B&B clutch.

With my GT6 I am restricted to using the small reservoir master cylinder due the proximity of my Girling Powerstop servo and don't know if this size is available with a 0.7" bore.

PS Doing a quick rough and ready CAD exercise shows the down angled geometry of the slave looses a bit of movement.

Ian

[Pete Lewis]

Is  the 0.7 the std landrover   cheapo  version that s marketed as an upgrade got the small reservoir ?? 

Pete

[trigolf]

Ian,

Re: the  'weep' probably stupid question , but has your slave pipe got a double or single flare at the slave cylinder end and do the two match ?  Something else maybe to check, I bought a replacement rear brake cylinder not long ago and could'nt get it to seal properly. When I took it off the car and peered down the bore the coned seat had been machined off centre, so was never going to seal properly. Needless to say it was replaced. Sadly another pattern part ( from Italy )!

 

Gav