Clutch problem.

[GordonE]

Mick, Slave cylinder stroke is dependent on the size (internal Bore) of both the slave & master cyl's.

If you definitely have a 23mm stroke at the Master Cyl Then the following would be the slave stroke
0.75 MC + 0.875 SC = 16.9mm  ***
0.75 MC + 1" SC       = 13.0mm
0.7 MC + 0.875 SC   = 14.7mm
0.7 MC + 1" SC         = 11.3mm
If the Master cylinder stroke differs, so will the figures above.

Any wear (slack) in the system would reduce these figures a little, possibly by up to 10%
These figures are calculated by dividing the MC piston area by the SC piston area and multiplying by the actual master cylinder stroke. They cannot be wrong, it is simple hydraulic physics.

I cannot attest to the manufactures specification of MC travel. The original TR6 series used the top *** setup. A MC stroke of 20-21mm would give close to the 15mm figure bandied about in this and other forums. IGNORE IT.

If the alternative cylinder sizes are used, the slave stroke is REDUCED. Incidentally, the second reason for using hydraulic clutch operation is to gain mechanical advantage (by this i mean operating a heavy clutch with less pedal pressure). The top example give a long stroke but heavy pedal whereas the bottom example gives a shorter stroke but a lighter pedal pressure required. This was the reason why Triumph moved from the 0.75 MC to the 0.7 MC.

I assume that you are using the bottom setup i.e. 0.7MC + 1"SC which would give the shortest stroke.
Dependent on the clutch specification this could be sufficient, but in my opinion would be marginal.
You state you are only getting 8-9mm with a 23mm MC stroke. There is almost certainly air in the system. Try getting a garage to bleed it by forcing a large volume of fluid through with their auto bleed system. ( I assume you have eliminated possible leaks.)

Apart from this you say that the clutch pedal is a bodged affair. If the top of the pedal (the part which exits through the top of the pedal box) is shorter than standard, this could also reduce the MC travel. If the pedal length is too short it may have worked with a smaller slave but not with the 1" bore slave cyl.

As for a broken pin in the clutch housing cross shaft, This is fairly easy to check. Disconnect the drop arm from the Slave rod clevis. Move the arm by hand (Note the amount is moves) in both directions if you get a large rotation the pin is missing or broken.  If not put a piece of pipe over it and apply greater pressure in the direction of the gearbox (do not do the same toward the engine). If the pin is OK it will not move past its normal rotation,  as you will be trying to disengage the clutch which requires more force than you could apply by hand. If you getting sufficient pressure through the hydraulics to move the drop arm by even 8mm I severely doubt that this pin is missing.

I think it would be helpful to Mick if a member with a UK TR6 could measure the actual movement of the top of the clutch pedal (and thereby the MC stroke) under the rubber gaiter where the master cylinder rod is attached to the pedal.

GordonE

 

Edited September 20, 2021 by GordonE

[mhossack]

Thank you GordonE

You understand my questions.

Your quote (simple hydraulic physics) with calculations, prove that this mythical clutch slave cylinder movement figure 15mm is a best guess and not an accurate dimension. 

 I will work through all your answers. 

Mick.

 

Edited September 19, 2021 by mhossack

[Mike C]

Are you sure you have the correct pedal movement ? -"I have just found he has reused the old US clutch pedal, and had to weld a piece of metal at the top, so I have no idea what the correct specifications are for a UK car or where to find them."

[Tim D.]

7 hours ago, mhossack said:

Thank you GordonE

You understand my questions.

Your quote (simple hydraulic physics) with calculations, prove that this mythical clutch slave cylinder movement figure 15mm is a best guess and not an accurate dimension. 

 I will work through all your answers. 

Mick.

 

Mick,  if you have a bodged setup where the pedal hole is not in the correct position you may want to add an adjustable pushrod to the master cylinder. This can be lengthened to push the pedal further up giving more pedal movement and hence more master cylinder stroke. I've done this and can run with a 0.625 master.  Means more pedal movement but also lighter clutch. 

[astontr6]

9 hours ago, GordonE said:

Mick, Slave cylinder stroke is dependent on the size (internal Bore) of both the slave & master cyl's.

If you definitely have a 23mm stroke at the Master Cyl Then the following would be the slave stroke
0.75 MC + 0.875 SC = 16.9mm  ***
0.75 MC + 1" SC       = 13.0mm
0.7 MC + 0.875 SC   = 14.7mm
0.7 MC + 1" SC         = 11.3mm
If the Master cylinder stroke differs, so will the figures above.

Any wear (slack) in the system would reduce these figures a little, possibly by up to 10%
These figures are calculated by dividing the MC piston area by the SC piston area and multiplying by the actual master cylinder stroke. They cannot be wrong, it is simple hydraulic physics.

I cannot attest to the manufactures specification of MC travel. The original TR6 series used the top *** setup. A MC stroke of 20-21mm would give close to the 15mm figure bandied about in this and other forums. IGNORE IT.

If the alternative cylinder sizes are used, the slave stroke is REDUCED. Incidentally, the second reason for using hydraulic clutch operation is to gain mechanical advantage (by this i mean operating a heavy clutch with less pedal pressure). The top example give a long stroke but heavy pedal whereas the bottom example gives a shorter stroke but a lighter pedal pressure required. This was the reason why Triumph moved from the 0.75 MC to the 0.7 MC.

I assume that you are using the bottom setup i.e. 0.7MC + 1"SC which would give the shortest stroke.
Dependent on the clutch specification this could be sufficient, but in my opinion would be marginal.
You state you are only getting 8-9mm with a 23mm MC stroke. There is almost certainly air in the system. Try getting a garage to bleed it by forcing a large volume of fluid through with their auto bleed system. ( I assume you have eliminated possible leaks.)

Apart from this you say that the clutch pedal is a bodged affair. If the top of the pedal (the part which exits through the top of the pedal box) is shorter than standard, this could also reduce the MC travel. If the pedal length is too short it may have worked with a smaller slave but not with the 1" bore slave cyl.

As for a broken pin in the clutch housing cross shaft, This is fairly easy to check. Disconnect the drop arm from the Slave rod clevis. Move the arm by hand (Note the amount is moves) in both directions if you get a large rotation the pin is missing or broken.  If not put a piece of pipe over it and apply greater pressure in the direction of the gearbox (do not do the same toward the engine). If the pin is OK it will not move past its normal rotation,  as you will be trying to disengage the clutch which requires more force than you could apply by hand. If you getting sufficient pressure through the hydraulics to move the drop arm by even 8mm I severely doubt that this pin is missing.

I think it would be helpful to Mick if a member with a UK TR6 could measure the actual movement of the top of the clutch pedal (and thereby the MC stroke) under the rubber gaiter where the master cylinder rod is attached to the pedal.

GordonE

 

My 1973 RHD car came with the .70 bore master cyl. the operation of the clutch was only marginal from new. After 2years of use I had to rebuild the hydraulics and the mechanical side. 

Clutch pedal clevis hole was very oval along with the master cyl. push rod. This had a major effect on the amount of travel applied to the clutch operating arm. The nylon bushes in the clutch pedal were shot. I sorted all this out including putting a marine bronze bush in the clutch pedal clevis hole and cut out all the backlash. Went back to the .75" bore master cylinder and have never had any more trouble.

Bruce.

[mhossack]

 

Thank you Mike C.

I appreciate all the answers given.

(Are you sure you have the correct pedal movement) no I do not know that is why I asked the question after Saturday, unfortunately a lot of the helpful people here seem to obsess about the clutch slave cylinder travel.

GordonE understood my question, and knew I was asking about the clutch master cylinder travel, and explained better than I could how to measure clutch master cylinder travel, I hope I get an answer.

I also appreciate that as I have explored my problem I have unintendedly not given the information needed to get the correct answer.

I am very lucky my friend Paul understands hydraulics, I am going to attach Paul’s clutch operation calculator.

I went with Paul Saturday to measure the clutch master cylinder travel, Paul measured 23mm, when measuring Paul spotted the bodged pedal, that is why I then asked if someone could measure an original TR6 UK car clutch master cylinder travel.

Thank you Tim D.

As you said I have been researching an adjustable master cylinder pushrod they are available, because I have an almost new pushrod I am going to create an adjustable pushrod myself.

The first reason I am going to do this is because my bodged clutch pedal has a little free play at the top, and not because of wear at the bottom, I also appreciate a too long pushrod will raise the clutch pedal up, but at the moment it is slightly lower than the brake pedal.

As many people have said I need to chase out any wear, as all they does is compound my problem.

I may need a new clutch pedal, but first I will get the specifications of a new pedal and compare, could be a good time to ask does anyone have an old UK clutch pedal they want to sell.

Thank you Bruce.

Looking at the clutch operation calculator I now realise at best even with a brand new car my set up is marginal. I am coming to the conclusion one of my new cylinders will need to be changed.

I think I would like to keep my new Girling clutch master cylinder .70 and change the clutch slave cylinder to a .875 giving a clutch slave cylinder travel of 14.72 which should work.

This is not about money so if I need to replace my clutch master cylinder I will.

This has gone on for a long time because I had a minor operation that stopped any work, but with all the help given I will now have to work through and correct any problems.

Mick.

[tim hunt]

On 8/19/2021 at 10:05 AM, astontr6 said:

Re-Pro Borg and Beck which are not OEM as First Line have bought the Trading name, made these Re-pro ones in China and have only 8 rivets and s/b 16 as original OEM. They have now amended that to 16 rivets. If it turns out to be that problem and you know who supplied the clutch you have a case against the supplier. Not fit for purpose? You might be able to get a free replacement?

Bruce.

I was a bit concerned reading this. I purchased a 'Borg & Beck' clutch kit from an autojumbler some time ago. Friction plate as below has 16 fastenings, eight from each side so presumably is OK. Is the idea that eight from each side gives more security perhaps?

Tim

[astontr6]

25 minutes ago, tim hunt said:

I was a bit concerned reading this. I purchased a 'Borg & Beck' clutch kit from an autojumbler some time ago. Friction plate as below has 16 fastenings, eight from each side so presumably is OK. Is the idea that eight from each side gives more security perhaps?

Tim

That packaging looks to me to be the old genuine Borg & Beck. As long as it has 16 rivets  which yours has you are OK!  Firstline use different color packaging but show Borg & Beck.

Bruce

 

[Z320]

Hi,

in my opinion the brown friction material contains asbestos.

I tested a set of original old asbestos brake pads 1 or 2 years ago, they have been aged and very hard,

caused an ugly sqeuking after about 500 km (?) and I kicked them off the car again.

I do lots of experiments on my TR, but I would not to the experiment to fit this friction plate.

Cheers, Marco

[tim hunt]

11 hours ago, astontr6 said:

That packaging looks to me to be the old genuine Borg & Beck. As long as it has 16 rivets  which yours has you are OK!  Firstline use different color packaging but show Borg & Beck.

Bruce

 

Thanks Bruce that's reassuring.

Tim

[stuart]

11 hours ago, Z320 said:

Hi,

in my opinion the brown friction material contains asbestos.

I tested a set of original old asbestos brake pads 1 or 2 years ago, they have been aged and very hard,

caused an ugly sqeuking after about 500 km (?) and I kicked them off the car again.

I do lots of experiments on my TR, but I would not to the experiment to fit this friction plate.

Cheers, Marco

Au contraire I would say that will work fine, I still have original asbestos pads in my 4a and they work fine, squeaking is often from lack of squeal shims and copperslip on the cylinder faces.

Stuart.

[Z320]

They are hard like glas and sadly one of them had a gap through the friction material,

I post a photo later this evening

[mhossack]

Just an update.

I decided to remove the pedal box as the geometry of my clutch pedal could not be correct, due to the welded bodge.

As soon as I removed the pedal box, I could see straight away I would need to replace the clutch pedal to get the geometry correct. I also found out he had drilled holes 5/8" back from the correct fixing positions to make the clutch master cylinder work.  

I vaguely recall reading about poor quality reproduction pedals, I tried to buy a second-hand clutch pedal without success.

Before I decided I needed to remove the pedal box I emailed Moss for dimensions of their new clutch pedals, pedal box shaft and clevis pitch. I got a very quick reply from Adan in technical who was very helpful, and even sent me a photo of the clutch pedal next to a metal ruler.

I purchased my new clutch pedal from Moss, I was very happy with the quality. I have spoken with Adam before and Adam was in when I went to collect my clutch pedal. I had a good chat, Adam advised me I may need to ream out the bronze bushes to fit my pedal box shaft, I did not have to, they were a very good fit, a little tapping with my rubber hammer and the clutch pedal was on the shaft.

I refitted the new clutch pedal and old clutch master cylinder in the pedal box, it all worked correct. I also did this to get the correct accelerator pedal height, I did not like the way it was also bodged.

I had to retain the accelerator pedal shaft position to reattach the accelerator cable, I kept the accelerator pedal and shaft. I tried to do a more professional job with the parts I had. The accelerator pedal had no provision for a return spring, in my opinion quite dangerous. Not required but I added an accelerator pedal return stop, this made it easier to get the correct position for the accelerator pedal return spring.

Not required but because I had the old clutch pedal, I cut off 13/16" of the clutch pedal barrel with bush, to use as a bush between the thin metal tabs between the brake and clutch pedal.

I will add photos to make the above clear, and show the difference between the 2 clutch pedals.

I have started to refit the pedal box, and will need to bleed the system as I must still have air in the system, hopefully that will be the end of the clutch hydraulics.

I have purchased Gunson Eezibleed, so hopefully that will help bleeding the clutch.

Mick.

[RogerH]

Well investigated Mick and  a very good result.

 

Roger

[mhossack]

Thanks Roger.

I will keep you posted, not out of the woods yet.

Mick

[Casar66]

Just my "experience" with an "original" B6B clutch-Plate.

 

 

 

[Z320]

I see the friction plate only connected with 3 straps and rivets with the center part, all 3 broken.

Two original B&B friction plates in my workshop have 8 straps with 16 rivets.

Edited October 21, 2021 by Z320

[mhossack]

Hi can anyone help me, I may have a new problem.

I refitted the pedal box and when I put in the brake pedal servo push rod clevis pin, the brake pedal did not return enough to engage the brake light switch.

The brake pedal is lower than the clutch pedal, but because the clutch pedal is new I do not know if they should be the same height.

Although my car is not driveable yet, I could turn on the engine to see if getting a vacuum in the servo would help return the brake pedal, to what to me should be the correct position, it did not.

My pedal box was only out of the car 2 weeks and I did not touch the brake servo.

Thank you,

Mick.

[Casar66]

Quote

 see the friction plate only connected with 3 straps 

that was the problem with the B&B plates for some years. I guess that was one of their Chinese phase.

 

Quote

to see if getting a vacuum in the servo would help return the brake pedal

I do not think that the servo will and most of all should help return the brake pedal. 

[Z320]

Lovely photo, keep it and the parts to show others 

[GordonE]

8 hours ago, mhossack said:

Hi can anyone help me, I may have a new problem.

I refitted the pedal box and when I put in the brake pedal servo push rod clevis pin, the brake pedal did not return enough to engage the brake light switch.

The brake pedal is lower than the clutch pedal, but because the clutch pedal is new I do not know if they should be the same height.

Although my car is not driveable yet, I could turn on the engine to see if getting a vacuum in the servo would help return the brake pedal, to what to me should be the correct position, it did not.

My pedal box was only out of the car 2 weeks and I did not touch the brake servo.

Thank you,

Mick.

Mick, From the photos of your pedal box, I notice that there are an unusual number of washers etc on the brake light switch. Normally, the switch would abut the bracket and be secured with one shakeproof washer and nut. This would move the switch slightly closer to the pedal. If you have fitted new bushes to the pedal shaft it is possible that the resting position of the pedals have changed.

[mhossack]

Thanks GordonE

Nothing has changed with the brake pedal.

I have not changed any bushes or washers, and at the moment the brake pedal is 6mm from the switch, and the push switch button has an extra 5/6mm movement required, so the brake pedal needs to come back about 12mm.

Mick.

 

[Casar66]

And you are sure that you have bleed the clutch correctly? 

 

Another, maybe stupid, idea poped up: did you change the switch?

Edited October 24, 2021 by Casar66

[Z320]

What I always notice: clutch problems with the hydraulic / way of travel/ bleeding seems to be always and only a TR6 problem.

I do not remember a 4cylinder owner ever reported.

Edited October 24, 2021 by Z320

[mhossack]

Hi Casar66

I was just about to post a final update, and I now know I did bleed my clutch correctly.

I did not change the switch, if I can't sort out the brake problem I am going to start a new thread, but I have a few ideas.

Thank you,

Mick.