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Upside down slave cylinder and 9.5mm throw


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Hi Les

I made this pushrod before I diagnosed my clutch hydraulic problem, before I corrected my problem I had some mechanical movement at my clutch master cylinder, this was designed only to take out that movement, when I corrected my clutch hydraulic problem I did not have any mechanical movement at my clutch master cylinder, so next to useless and not fitted.

I appreciate you were talking about a clutch slave cylinder pushrod. 

Mick.  

 

1309389954_Clutchmastercylinderpushrod.thumb.JPG.e71ca89f1edace9956ea38460b7ff4d3.JPG

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Mick,

You adjusted it too much, and did not allow the pushrod to pull the cylinder back, to allow new fluid into the cylinder from the reservoir, have a look at the drawing of the master cylinder and I think you will see where you went wrong.  I have an adjustable rod on my setup and works fine, just takes the clearance out of the pedal pin hole.

John

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Hi John

I wrote in my reply to Les I never fitted that pushrod as it was not needed. It is in fact set but not tightened to the correct length although hard to see as some of the pushrod is hidden by the rubber boot.

Thank you anyway all ideas help.

I know you followed my topic clutch problem and it was my bodged US to UK clutch problem that was at fault.

Mick.

 

2015745777_Clutchmastercylinderpushrod.thumb.JPG.cafd2c19b7ad4a36aafa2b122f18f3f2.JPG

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Hi Mick,

You read my thoughts exactly. Whatever the length of the pushrod it can only move by the displacement of the piston.  Not sure now why they market an adjustable one.

I am happy to be going back to standard. My Lockheed 993640 has just arrived in the post from Rich so I will hopefully fit it on Thursday and report back. Really excited at the prospect of having a pleasant car to drive again.

I know clutches have been covered many times before on the forum so I am very grateful for everyone's patience with me.

Regards

Les

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They make the adjustable slave rod to stop the thrust bearing rubbing on the fingers like the previous versions, it needs a spring to pull the piston back to its end, and then adjust the rod so there is a little free movement before the release bearing touches the fingers.  The downside of this is if you don't recheck the adjustment periodically, as the clutch plate wears the fingers come further out and puts a lot of pressure on the release bearing and if not adjusted it allows the clutch plate to not have enough pressure on the plate and so it slips, plate wears out.

The current ones there is a spring in the slave that holds the release bearing in contact with the fingers all the time.

John

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1 hour ago, John L said:

The current ones there is a spring in the slave that holds the release bearing in contact with the fingers all the time.

Hi John

Just for clarification does the OEM Lockheed require an external spring to pull the rod back?

Andy

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Andy,

That detail I'm afraid I don't know, just pop the piston out and see if there is a spring inside, if you want to make it into a manual adjustment with the adjustable slave rod, leave the internal spring out.  You may have to juggle the position of the slave cylinder on the mounting bracket to get the adjustment into a good position for the rod.

John

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Hi All,

New slave cylinder is in, the correct way up, bled thoroughly and the push rod is in the middle hole but I still only get 10mm movement. I'm glad I changed the slave cylinder as, on inspection, the old one was full of muck (see below). Maybe I could have cleaned it, but happy to have  a  new one with the correct length push rod.

I now think the problem may lie in the master cylinder which is a new TRW one fitted during a restoration. I can push the master cylinder push rod back 3mm before it connects to the piston in the master cylinder. Anyone come across this before? Is there a cure? Surely they should be in permanent contact. Another new master cylinder? Maybe a 0.75" for more volume?

I see from an earlier post that Mick made a very smart adjustable push rod. I've never seen one before, does anyone sell them?

So grateful for your help as I am starting to lose hope.

Regards

Les

Gunge in slave cylinder.JPG

Gunge on slave piston.JPG

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Les,

Keep the faith! You’ve certainly made an improvement by changing that slave cylinder, so clearly a step forward. My next step would be to remove the master cylinder, strip it down, check everything is ok/correct size and renew if not. Then rebuild, refit, bleed etc. and then see where you are. I did this recently. I’m no expert but just took my time, checked and double checked and it was not difficult. Chasing issues like this can be demoralising but you will get there and especially with the support of the good folk on this Forum.

I bought my refurb kit from James Paddock and it did contain components “surplus to requirements” as it obviously has more that one application.

Good luck!

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Hi Paul,

I was so disappointed last night, I left the clutch pedal jammed down overnight in case it made  a difference - it didn't. I must say the clutch now feels lighter and smoother than it did before I changed the slave cylinder just not quite as much throw as I would like. I am really puzzled why the master cylinder push rod is not in constant contact with the master cylinder piston. If I could eliminate that 3mm of free play I think it would help at the slave cylinder end. All the clevis pins are a really nice tight fit so this is the only play I can detect in the whole setup. Has anyone come across this before?

I think you are right, a strip of the master cylinder sounds like the way forward but it has only done 400 or so miles since new, so hardly used. (Assuming a new one was put on my car during restoration, but it is certainly not the original I had on the car since 1978)

Regards

Les

 

Clutch master.JPG

Clutch pedal jammed down.JPG

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Its more than likely the wrong pushrod, this is quite common with the cheap repro cylinders, Adjustable pushrods are available if no one has an original they can let you have.https://www.revingtontr.com/product/rtr4357k/name/push-rod-kit-adjustable

Stuart.

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22 minutes ago, Les Pettitt said:

Hi Paul,

I was so disappointed last night, I left the clutch pedal jammed down overnight in case it made  a difference - it didn't. I must say the clutch now feels lighter and smoother than it did before I changed the slave cylinder just not quite as much throw as I would like. I am really puzzled why the master cylinder push rod is not in constant contact with the master cylinder piston. If I could eliminate that 3mm of free play I think it would help at the slave cylinder end. All the clevis pins are a really nice tight fit so this is the only play I can detect in the whole setup. Has anyone come across this before?

I think you are right, a strip of the master cylinder sounds like the way forward but it has only done 400 or so miles since new, so hardly used. (Assuming a new one was put on my car during restoration, but it is certainly not the original I had on the car since 1978)

Regards

Les

 

Clutch master.JPG

Clutch pedal jammed down.JPG

Does your clutch pedal wobble from side to side?

If so the pivot bushes need renewing.  There were ghastly plastic bushes used at one time on factory fitted pedal assemblies which were replaced with proper metal backed bushes.   Item 52

A trick/bodge to allow more pedal movement on RHD cars is to bend the metal pedal stop tag  outward so the pedal travels further.  BUT it comes at a price as you fully compress the spring inside the master cyl.  Visible in the pic below.

The use of an adjustable master cyl push rod is a good solution if repro m/c has the wrong one installed.

image.thumb.png.00131dff8368c1d706305b0316fd28d5.png

Edited by BlueTR3A-5EKT
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Les,

I’m no expert by any measure but thru my own experience the operation of clutch is trickiest part of my TR6 experience. The biggest improvements I’ve had with it was the replacement of the bushes on the pedals - mine were non existent when I got the car (item 52 in Blue’s note above) and made a big difference. The other big impact was to bleed ALL the air from the system. I’ve no easy ways or good suggestions to achieve but just keep going at it. Amazing how a little bubble can make a big difference. I think the pipe layout and design hinders bleeding a lot unfortunately. Anyway hope you get it sorted. 

Regards Martin

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Hi All,

No side to side play at all in the pedal but I can push the pedal down by hand around 50mm before I meet any meaningful resistance. As I had the wrong length push rod in my slave cylinder, I wouldn't be surprised if I had an incorrect one in the master cylinder.

I will remove and strip the master cylinder tomorrow afternoon and report back. In the meantime, could someone please tell the correct length for the master cylinder push rod. What odds for a broken spring? or a master cylinder full of gunge like the slave cylinder?

Thank you again for your continued help. I have got over my disappointment and am determined to push on and find the cause. Forty years without clutch problems and now all this hassle.

Thanks Stuart for the tip about Revington selling adjustable master cylinder push rods. If everything else seems ok in my master cylinder I will go that route.

Regards

Les

 

Edited by Les Pettitt
missed abit out
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I have had a similar problem to yours recently when I slowly started to experience clutch drag, especially when the car got warmer such as when stuck in slow moving traffic.

Measuring the movement of the clutch arm I was only getting 11mm, whereas it should be 5/8"" or 16mm.

In the end, speaking to Simon at TR Enterprises, he suggested I check the length of the master cylinder pushrod, as LHD ones have a shorter pushrod, and there have been a number of LHD ones supplied with repro master cylinders.

A RHD pushrod is 82mm and a LHD is75mm. When I checked I had a LHD one fitted.

Replacing the arm with a RHD version fixed the problem, giving me 16mm movement of the clutch arm, and a noticeable higher clutch bit point.

Therefore I suggest before you go any further you measure the length of your clutch master cylinder pushrod.

Regards, Martin

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Hi MJF

You wrote (A RHD pushrod is 82mm and a LHD is75mm. When I checked I had a LHD one fitted.)

I don't think your dimensions are quite correct, if you look at my drawing previous reply you can see the length is 90mm,  I got this dimension from both the M/C below, one was an aftermarket M/C and one was an NOS M/C and both were the same length.

I fitted the NOS M/C and my clutch is now working correctly. 

I agree with you this should be checked before the M/C is removed, and very easy to do. I am still waiting for Les to give me the M/C pushrod travel and the bore of both cylinders, I will then calculate what the S/C pushrod travel should be, again before removing the M/C.

I would like other people to reply about the 50mm clutch pedal free play that sounds like air to me, but as I don't know I am not able to comment.

Mick.

860290374_Oldandnew.thumb.JPG.f7a0c7bebef18527bfe464ffbac6a237.JPG

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I will just add I used silicone clutch/brake fluid.

I renewed all my clutch hydraulics and bleed it the old fashion way and it worked first time.

If you read my clutch problem topic that is not factually quite correct because I first was only getting 11mm travel and my clutch was still not working, I then went on to find my clutch pedal and M/C position were wrong, when corrected my clutch worked without rebleeding.

My next problem straight away was my brakes, my car is 4 miles from home not easy just to go out and check dimensions, but because Les has a similar problem yesterday I asked a friend to meet me at my garage because my car is up on axle stands and easy to measure my S/C travel, I only measured crudely with a plastic ruler but got about 14.5mm travel, what I would expect from new hydraulics and my clutch calculator result.

Fact not theory 

Mick.

Edited by mhossack
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Hi All,

Following on from Mick's request I quickly measured the throw of my master cylinder push rod which is about 25mm.

As the bore of the master cylinder is 0.7inch and that of the slave cylinder 1 inch and given that area is a squared relationship, the cross section area of the master cylinder is .49 that of the slave cylinder. Therefore the master cylinder push rod must move roughly twice as far as the slave cylinder push rod if there are no other losses.

To get a movement of 16mm at the slave cylinder the master cylinder push rod would have to move 32mm which is not possible. From rest to where it hits the carpet is only 25mm. I will only ever get 12.5mm at the slave cylinder. The clutch pedal appears to be in the correct position when at rest ie in line with the brake pedal. I will measure more carefully this afternoon when I remove the boot. I will also check the length of my master cylinder push rod before dismantling.

Could someone else please measure their master cylinder push rod throw so we can compare?

Many thanks to you all.

Les

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Hello again Les

Reading the Moss catalogue pages 44/45 it would appear that you can either fit the 0.70 or 0.75 inch bore MC's. The 0.70 according to Moss was introduced to give a 'lighter' clutch pedal but the downside was that the travel was less on the slave cylinder. To get more travel on the slave cylinder it looks as if the 0.75 bore MC might solve your problem but the clutch pedal would be heavier.

Keith

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Mick,

Sorry for any confusion, I think the lengths I quoted are for the effective length of the pushrod, this is the distance between the centre line of the clevis pin holes and the end of the operating arm, as this is the length which determines clutch operation.

Referring to your drawing, you show the overall length as 90mm, and the centre line of the clevis pin holes inset by 8mm. This therefore gives an effective length for the pushrod of 82mm.

Les,

With the LHD (75mm) pushrod I measured a linear movement at the master cylinder of approx. 24mm.

Replacing with a RHD (82mm [or 90mm depending of definition – see above]) pushrod I measured a linear movement at the master cylinder greater than 30mm.

Replacing the clutch master cylinder pushrod fixed the clutch problem, but it did move the clutch pedal higher off the floor, which took a while to get used to.

Martin

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