New Clutch Slave Cylinder - problems bleeding or maybe another problem?

[Trever the rever]

After lavishing money, time and effort on my 1972 TR6 this year in a number of areas. Famously eliminating my age old fuel smell problem and more significantly cash spent on my 132k miles engine to breathe new life into it. As well the gear box being extracted for primarily a noisy first gear, the lay shaft bearing had landed up in the overdrive with no additional damage thank goodness. All back together with a new clutch to suit. Whilst fettling with the cars induction over the past week or so to get things just right, I noticed the clutch master cylinder had dropped to almost empty, however on filling it up I noted I hadn't lost prime and clutch activation. (The garage hadn't needed to disturb the clutch hydraulics.)

 

The symptoms were loss of fluid from the slave cylinder under the car, the colour of the fluid on the floor was a dirty black colour. Also the bottom of the master cylinder was full of black 'mush'. which I removed as best I could.

 

I fitted a new slave cylinder yesterday and relocated the linkage to the top hole on the activation lever. With the help of my son I have bled the system numerous times (Dot 4) through a rubber tube into a flooded jar, with no evidence of air bubbling through, and although the pedal feels fine I cannot engage gear. On starting the car in gear with the clutch disengaged there is slight clutch drag, but the car cant be driven. I haven't measured the throw of the slave assembly pin, but it looks like about 15 mm.

 

There is no evidence of leakage from the master cylinder, however removing the rubber gaiter, the piston is fouled with black residue. I'm beginning to think the master cylinder given the evidence above is now problematic. I'd love to hear the readers views on this experience.

 

Best Regards Trevor Hughes

[DaveN]

First thing to check. What is the condition of the clevis pins and the holes they fit through? They have a habit of elongating the holes and crankshafting the pins. Looking at the moss catalogue items 21/22/37/43 and of course the pedal itself.

 

Next I would strip the m/c check the condition and fit new seals.

Edited June 23, 2018 by DaveN

[Trever the rever]

Thanks for this, the 21/22 on the slave assembly look good; I'll check the master assembly tomorrow.

[Trever the rever]

Hi again, Given the visual evidence with the master cylinder, I bit the bullet and bought a new one from Moss on Sunday. It came thankfully this morning (Tuesday) and I have duly fitted the unit. I was on my own, so I was reliant on the rubber tube submerged in brake fluid method for a successful bleed. However as soon as I removed the clevis pin, there was an obvious problem, as highlighted by your good self above. I would say there was 3mm excessive movement in the elongated hole in the pedal unit. Well, it has been in situ for 46 years!

 

I was able to bleed the system only properly with my neighbours help, and can now engage a gear thankfully. Its a little notchy into first and reverse. I played around with a fine cut down allen key (hard steel hopefully) and used this to take up the play. This improved matters again, but as this was temporary investigative bodge, I removed it. So the next question, do I order a new pedal (Moss £78) and try to fit before I'm off to Le Mans next Wednesday, or is there a more semi permanent fix to take up the slack. I don't really want to strip the pedal assembly down and find more problems in the short term. I need a few good ideas from the mechanical men people out there. Starter for ten I was thinking about shimming the hole with something hard and fit for purpose, unsure what, aluminium can may be too soft? Help please!

 

Regards Trevor

[marki]

Hi Trevor.

Take the pedal to a local garage and get them to weld up the hole, then redrill with the correct drill size.

It'll be cheaper than a new one and quicker.

Cheers Mark.

[RogerH]

Hi TRevor,

you need to put the slave rod into the middle hole on the drop arm. This will not help but is correct !!!

 

As Mark suggests you need to get the hole in the pedal as round as possible.

 

If you haven't got time to weld the pedal is it possible to drill the hole round and insert a steel bush.

If you can;t drill the hole is it possible to weld a pair (one either side) of steel washer for the pin to work on. It will wear quite quickly but should get you to LeMans and back.

 

Roger

[Trever the rever]

Thanks guys, great ideas. Im off a club meeting tonight, so be nice to give it a run. I already feel a little re energised on this, so Ill see tomorrow about taking the pedal out. Cheers Trevor.

[RogerH]

Hi TRevor,

another thought.

 

Is your slave cylinder bleed nipple at the 12-o-clock position. This gets ALL the air out.

It is possible to fit it with the nipple at 6-o-clock.

 

Roger

[Trever the rever]

Yes it is Roger, happy with that. In summary the leaking slave cylinder was the start of the story. The master was probably on its last legs given the heavy contamination observed in the fluid reservoir. Creeping up behind was the wear in the clutch pedal waiting to take the glory when everything else was on a knife edge!

 

I had replaced the master cylinder about ten years ago, but had n't noticed or considered the pedal element. Live and learn as they say!

 

Thanks Trevor

[RogerH]

Hi TRevor,

not sure how it happens but the fluid in my clutch Master cylinder always goes black within hours or new stuff being put in.

 

Roger

[colin3511]

Drill it bigger and put use a nut and bolt. There's plenty of meat there. The only negative is getting The rubber boot back on.

[Waldi]

Hi Trevor,

An adjustable push rod in the slave cylinder to compensate for the wear is another quick fix.

The middle hole in the clutch cross shaft is the correct one.

Waldi

[Trever the rever]

Thanks Waldi, yes I've seen the adjustable push rod option, something to consider. I've reviewed the pedal box removal and I'm now reluctant to do this. The bolts in the engine bay have previously been painted over in another of my exercises over the years and I guess I'm been too 'car proud' to do this in the short term. I've spoken to a local 'restorer' who has done excellent paintwork for me over the last year or two, and am taking the car to him on Friday morning to review the larger hole or welding on the washers option, in situ too.

 

I set out to the Essex Group meeting last night, but abandoned the drive after a few miles, as the clutch operation just got unmanageable. I've bodged the gap in the elongated hole this morning and will do one more bleed exercise today. You can see how bad the hole is in the attached photo.

 

I'll let you know how things progress on Friday.

 

Best Regards Trevor

[Rogcastle]

Hi Trevor

 

I went through a similar problem last year. Have you checked the push rod length on the new M/C against the old one. I found the one on the new one was shorter than on the old one. A quick swap cured the problem.

Also had problems getting the air out of the system. A good trick is to use a piece of wood to hold the clutch pedal down to the floor overnight. For some reason this gets rid any air in the system. Good Luck

 

Roger

[JochemsTR]

 

Hi TRevor,

not sure how it happens but the fluid in my clutch Master cylinder always goes black within hours or new stuff being put in.

 

Roger

 

mine too. Drives my crazy.

Brakes no problem....clutch black as my heart.

 

jochem

[RogerH]

Hi Trevor

 

I went through a similar problem last year. Have you checked the push rod length on the new M/C against the old one. I found the one on the new one was shorter than on the old one. A quick swap cured the problem.

Also had problems getting the air out of the system. A good trick is to use a piece of wood to hold the clutch pedal down to the floor overnight. For some reason this gets rid any air in the system. Good Luck

 

Roger

Hi Roger,

this is a trick told by Stuart and appears to work very well. There may now be an answer.

 

Recent brake calipers have not bled very well and the above trick sorts them out.

It would appear that the seals on the piston are too stiff and draw the piston back too far thus requiring more pedal travel to operate.

Keeping them depressed overnight causes the seal to distort in the right direction.

 

There could also be another answer !!!

 

Roger

[Waldi]

There could also be another answer !!!

 

Roger

Possible explanation:

Every gasket and seal has a leak rate.

For industrial applications tests are done at pressure+temperature to confirm they are acceptable for their intended use.

The seal in the cylinders will leak too, also a new seal, although not visible for us.

And it is only pressurized for less than an hour per ride.

Since air molecules (N2,O2 mainly) are much smaller than the brake fluid molecules, the trapped air may be pushed out, while (most) of the brake fluid will stay in.

Waldi

[RogerH]

Possible explanation:

Every gasket and seal has a leak rate.

For industrial applications tests are done at pressure+temperature to confirm they are acceptable for their intended use.

The seal in the cylinders will leak too, also a new seal, although not visible for us.

And it is only pressurized for less than an hour per ride.

Since air molecules (N2,O2 mainly) are much smaller than the brake fluid molecules, the trapped air may be pushed out, while (most) of the brake fluid will stay in.

Waldi

Nice.

[Waldi]

Thanks Roger,

One of my rare brainwaives.

They are setting fewer nowadays:)

Cheers,

Waldi

[Rogcastle]

Thanks for that one Waldi I will try ro remember that One!

 

Roger

[Trever the rever]

See photo (soon) for comparison of the old and New push rods. They are virtually identical, albeit photo shows the new one slightly longer! Today refitting re bleeding and using centre hole, though is slightly oval on close inspection, I wasnt able to engage gear. Relocating to the top Hole has enabled gear selection just. Hopefully tomorrow Ill be able to drive to the garage. Im going to put my son in the car overnight to keep the pedal depressed!! .

Edited June 28, 2018 by Trever the rever

[Trever the rever]

I set out this morning with hydraulics understood to be okay. The slave pin in the top hole ???? and my own bodge taking up the slack in the elongated hole in the clutch pedal. It was a 12 mile 40 min drive in slow urban traffic. On arrival the clutch operation had deteriorated to a crunchy reverse and first gear. My man Terry did as advised and welded quite a thick washer to one side in the original position. He advised there wasnt simply enough room at this stage for another one the other side without modifying the master pin. Also the clevis pin was now too short. A nut and bolt was used. However on the way home I was able to resource a longer clevis pin from a nuts and bolts outlet in Benfleet. The clutch works okay and I am able to drive the car reasonably confidently once more. The mid term solution no doubt is to get the pedal out of the car and do a proper job. Thanks for all your helpful comments. Regards

Edited June 30, 2018 by Trever the rever

[astontr6]

Hi TRevor,

you need to put the slave rod into the middle hole on the drop arm. This will not help but is correct !!!

 

As Mark suggests you need to get the hole in the pedal as round as possible.

 

If you haven't got time to weld the pedal is it possible to drill the hole round and insert a steel bush.

If you can;t drill the hole is it possible to weld a pair (one either side) of steel washer for the pin to work on. It will wear quite quickly but should get you to LeMans and back.

 

Roger

Roger's idea of using a bush, in my view is the best solution. I made mine out of marine bronze and made the o/d an interference fit into the hole that I had drilled into the pedal arm. This has last over 25 years and is good at wearing out clevis pins but they are simple to replace. There has been very little wear on the bronze.

 

Bruce.

[Trever the rever]

Post Le Mans update - Well the TR6 made it to Le Mans and back. Driving to our overnight stay in Neufchatel en Bray, the clutch operation deteriorated to the point where first or reverse was not available at a standstill and clutch drag clearly evident. I managed to improvise and negotiate with engine starts in first and quickly move on. At our campsite we took time to bleed the clutch as best we could, and could demonstrate the slave cylinder rod was moving as soon as the pedal was depressed. No improvement and we all agreed (as my friends Healy 100 was in trouble too with an engine problem!) we would take the motorways to Calais. We all made it home. The problem is clearly an internal clutch problem as far as I was concerned.

 

Tuesday quick call to our classic car concern in Benfleet and an initial look at the problem. They could demonstrate considerable free movement in the cross shaft before resistance is felt. In summary effective clutch operation was only on the last inch or so of pedal movement. They were sure there was no problem with the tapered pin when the new clutch and gear box was refitted recently. My records show (I've had the car since 1995) a new hardened tapered pin was fitted in 1999! about 50k miles ago. The car is booked in for next Tuesday 17th July for gearbox removal and investigation. It looks like the tapered pin?

 

Now given the clutch is new (still less than 1000 miles) and may look okay, and if it is the tapered pin/cross shaft, should I still put another clutch in? Its taken a bit of a battering, as has the gearbox with numerous close calls. I'll get them to change the oil to look for contamination too. I've agreed to take out the centre console radio, radio, carpets etc to reduce turnaround time.

 

Welcome your thoughts.

[Waldi]

If it is indeed the tapered pin, and the clutch and plate look ok, I would re-use them.

Make sure to add an additional (roll) pin in the cross shaft, even if the tapered pin is fine.

Best regards,

Waldi