Inadequate clutch throw

[JohnC]

On 11/20/2025 at 7:25 PM, Z320 said:

great to hear you are pleased with the smaller 0.7" master.

It has a smaller surface, this produces more pressure BUT pumps less fluid.

Ummm. I think you mean that the same hydraulic pressure (which is generated by the distance at the slave end) on the m/c piston, which has a smaller surface area, generates less pedal force. Then, as you say, the downside is that the smaller area x the same master cylinder travel results in less fluid being pumped and therefore less travel at the slave.

We have a choice: for the same m/c travel we can have a lighter pedal but less travel (reducing the tolerance for any play in the system); or heavier pedal but tolerance for play in the system. FWIW I have fitted the even smaller diameter 0.625" m/c and I'm very happy with it. Also doubled up on cross-shaft bearings, roll pin in the cross shaft, nice round holes everywhere and an adjustable m/c push rod. The last is probably the most important.

YMMV,
JC

[Magz]

56 minutes ago, BlueTR3A-5EKT said:

?   Have you also renewed the clutch pedal shaft bearings, welded up and re drilled the clevis pin holes in the pedal, fitted new clevis pins, welded up and re drilled the master cylinder fork ends.  All to match the new clevis pins.   .?

 

Next test.   Under the car, disconnect the slave cylinder push rod from the lever.   Push by hand the lever as far rearwards as you can.   Now move the lever towards the engine gently and slowly.   When resistance is felt take note. Now push the lever a bit further and more firmly towards the engine.   Did you get a bit more movement of the lever?   Your clutch cross shaft pin has sheered.   
Fitting  longer throws and bore size changes will makes the slave push rod go further to enable clutch disengagement, but it comes at a price.   Heavier pedal pressure.is required and the cross shaft pin inside the bell housing remains broken.

The car has 50K original miles, and the visible wear on those parts is minimal. I checked all the clevis pins and holes and shaft bearings and they are tight and perfectly round, and were well-greased by the previous owner of 20 years. The master cylinder fork is brand new as it is a new master cylinder.

As for the pedal effort, it is a bit heavy but I like it that way. My previous fun car was a 2019 Dodge Challenger Hellcat Widebody 6-speed with a dual plate clutch, so I'm used to heavy clutch pedals.

As far as pulling the trans, I'm working my way forward with a staged performance rebuild. This winter I'll be welding up the differential mounts, installing a Quaife ATB in the carrier, HD springs, swapping in Goodparts CV axles and hubs with upgraded studs, and rear disk brake conversion. Then I plan to drive the car in the nice weather, followed by pulling the engine and trans and doing a performance rebuild on the head and block and installing a Rotrex C30-84 supercharger and intercooler running 12psi boost. Induction will be a Ramtech EFI system.

Considering the major torque and HP boost I'll probably also swap out the trans for the Vitesse 5-speed, as for sure the J-type overdrive won't handle the power.

So, as long as it runs well until I pull the engine and trans, I'll be very happy. BTW, it runs great, exactly as a 50K Mile engine should.

[BlueTR3A-5EKT]

2 hours ago, Magz said:

The car has 50K original miles, and the visible wear on those parts is minimal. I checked all the clevis pins and holes and shaft bearings and they are tight and perfectly round, and were well-greased by the previous owner of 20 years. The master cylinder fork is brand new as it is a new master cylinder.

As for the pedal effort, it is a bit heavy but I like it that way. My previous fun car was a 2019 Dodge Challenger Hellcat Widebody 6-speed with a dual plate clutch, so I'm used to heavy clutch pedals.

As far as pulling the trans, I'm working my way forward with a staged performance rebuild. This winter I'll be welding up the differential mounts, installing a Quaife ATB in the carrier, HD springs, swapping in Goodparts CV axles and hubs with upgraded studs, and rear disk brake conversion. Then I plan to drive the car in the nice weather, followed by pulling the engine and trans and doing a performance rebuild on the head and block and installing a Rotrex C30-84 supercharger and intercooler running 12psi boost. Induction will be a Ramtech EFI system.

Considering the major torque and HP boost I'll probably also swap out the trans for the Vitesse 5-speed, as for sure the J-type overdrive won't handle the power.

So, as long as it runs well until I pull the engine and trans, I'll be very happy. BTW, it runs great, exactly as a 50K Mile engine should.

Sounds like you have a cunning plan to get the whole thing how you want it.   Well done

[Z320]

4 hours ago, JohnC said:

Ummm. I think you mean that the same hydraulic pressure (which is generated by the distance at the slave end) on the m/c piston, which has a smaller surface area, generates less pedal force. Then, as you say, the downside is that the smaller area x the same master cylinder travel results in less fluid being pumped and therefore less travel at the slave.

We have a choice: for the same m/c travel we can have a lighter pedal but less travel (reducing the tolerance for any play in the system); or heavier pedal but tolerance for play in the system. FWIW I have fitted the even smaller diameter 0.625" m/c and I'm very happy with it. Also doubled up on cross-shaft bearings, roll pin in the cross shaft, nice round holes everywhere and an adjustable m/c push rod. The last is probably the most important.

YMMV,
JC

Two yeses

[Z320]

Hi,

this is my calculation with a "long throw" clutch slave cylinder, for the case its diameter is 7/8":

The original slave's piston is 1", the surface of a 7/8" piston is ony 0.875² / 1² = 0.765625 = 76,6525% of the original.

This causes (1 - 1 / 0,7656) x 100 = 30,6% more stroke / throw (as promissed)

BUT with still the same pressure from the master (1 - 0,7656) x 100 = 23,4375% less force against the clutch cover!

The force needed for the clutch cover is fixed / an issue of the clutch cover.

To get this force again on the clutch cover with the smaller 7/8" slave the pressure in the system

and force on the clutch pedal must be ingreased by ...... 23,4375 / 76,6525 X 100 = 30,6%

Easy rule:

30% more stroke you don't get as a present, you have to "pay for it" and step 30% stronger on the pedal.

The hydraulik pressure in the can be ingreased in the system with a swap from a 0.75" master to a 0.70" for about 15% and with a 0,625" for about 31%.

BUT both with less fluid pumped by the smaller master cylinder - and less stroke of the slave again.

What you win is zero.

This is why Robert's explanation does not match for me.

Longer stroke on the slave with less force on the clutch pedal is not possible.

This would solve the wourld energy problems.

Sorry me, Marco

Edited November 21, 2025 by Z320

[BlueTR3A-5EKT]

12 minutes ago, Z320 said:

Hi,

this is my calculation with a "long throw" clutch slave cylinder, for the case its diameter is 7/8":

The original slave's piston is 1", the surface of a 7/8" piston is ony 0.875² / 1² = 0.765625 = 76,6525% of the original.

This causes (1 - 1 / 0,7656) x 100 = 30,6% more stroke / throw (as promissed)

BUT with still the same pressure from the master (1 - 0,7656) x 100 = 23,4375% less force against the clutch cover!

The force needed for the clutch cover is fixed / an issue of the clutch cover.

To get this force again on the clutch cover with the smaller 7/8" slave the pressure in the system

and force on the clutch pedal must be ingreased by ...... 23,4375 / 76,6525 X 100 = 30,6%

Easy rule:

30% more stroke you don't get as a present, you have to "pay for it" and step 30% stronger on the pedal.

The hydraulik pressure in the can be ingreased in the system with a swap from a 0.75" master to a 0.70" for about 15% and with a 0,625" for about 31%.

BUT both with less fluid pumped by the smaller master cylinder - and less stroke of the slave again.

What you win is zero.

This is why Robert's explanation does not match for me.

Longer stroke on the slave with less force on the clutch pedal is not possible.

This would solve the wourld energy problems.

Sorry me, Marco

Add a vacuum operated servo to the clutch hydraulic circuit.   Was done many times on TR6 for owners as they aged and were unable to work the left pedal sufficiently 

Edited November 21, 2025 by BlueTR3A-5EKT

[RobH]

23 minutes ago, Z320 said:

Longer stroke on the slave with less force on the clutch pedal is not possible.

This would solve the wourld energy problems.

You are absolutely correct Marco.   You can't get something for nothing in mechanics.  I think Robert has acknowledged that the resulting pedal effort is higher. 

[Z320]

a small 0.625" master converts any TR clutch with its 1" slave to an easy clutch,

if all air is bleeded out (problem at TR6s, specially all LHD) and the play in the mechanic is mostly out

Edited June 30 by Z320

[Magz]

2 hours ago, Z320 said:

Longer stroke on the slave with less force on the clutch pedal is not possible.

This would solve the wourld energy problems.

Sorry me, Marco

When did I say there was less force on the clutch pedal with the long throw slave? Answer: I didn't.

I said the clutch felt a bit heavy, but I like it that way. 

So the world's energy problems can carry on as previously...

[Z320]

On 11/20/2025 at 3:50 AM, Magz said:

I have now tried various combinations of 0.75" and 0.70" masters and standard and "long throw" slaves, and the winning combination for me was the 0.70" master with the long throw slave. Engages and disengages smoothly each time, no issues getting first from a cold start, runs through the gears are smooth. 

Long Throw Slave:

https://www.sportscarpartsltd.com/Clutch-Slave-Cyl-Long-Throw-TR6_p_655.html

This it started, sorry me to understand „engages and disengages smoothly“ wrong.

edit: anyway, I myself (and maybe others) learned a lot about the miracle of the "long throw slave"

Edited November 22, 2025 by Z320

[Tom Fremont]

I gained some throw after years of annoyance by grudgingly bleeding the !@#$ master cylinder, all other measures taken short of pulling the gearbox to find...who knows? I suspect the SACHS pressure plate isn't releasing like it did when new ( has ~ 70K miles on it, wasn't available new when the LUK driven plate failed at 59,000 miles so was re-fitted ). I poured [silicone] fluid in while pushing the clutch pedal with one foot while standing on the garage floor with the other, watching the proceedings. I'd say it halved the issue. 

Forgive me if this has already been mentioned; I haven't read the preceding 100+ posts  There is a beefier M/C clevis rod with longer pin ( if that hasn't been mentioned either ), RIMMER supplied mine.