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Why is there play in the clutch master cylinder push rod?


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14 minutes ago, ntc said:

Les

If you are getting fluid around the threads you will never get the air out as you draw it back in when pumping even more so with silicone 

I was thinking the same thing. If you use the foot pedal method then press down with the bleed screw open, close bleed screw and then let pedal up again. If the bleed screw is open when the pedal is allowed up then air is likely to be drawn in around the threads of the bleed screw. This is why I use the Eezibleed kit because that supplies pressure all the time to the system. Stuart has just pipped me to the same conclusion.

Only problem with the Eezibleed is if you don't get a proper seal on the master cylinder then brake fluid ends up everywhere.

I have tried using a plastic syringe with some silicone hose on a bleed screw to suck the fluid out. Less likely to get air in the system but you will see bubbles because it will suck air in around the screw threads.

To be honest bleeding brakes and clutch are jobs I hate doing. No matter how careful I am I always end up with brake fluid where it shouldn't be. 

Keith

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I fear I will get shot down for suggesting this, but I have used PTFE tape wrapped around the bleed nipple threads to stop it bypassing. I was careful not to block the bleed hole and didn’t take the tape to very end (wet end). This has worked for me. I will in future try the brass nipples based on recommendation. This was using a vacuum gun to suck the fluid rather than pressurise from m/c. But fully agree its the worst job and really struggle to bleed. Just need lot of time and patience (which I don’t have!).

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Hi All,

In my simple minded way I was thinking that the nipple was only open while my wife was depressing the clutch pedal, so air shouldn't get in while fluid was being forced out.

I'm sure Neil, Stuart and Keith are right and it was a false assumption.

It was leaking quite a bit (I thought at first the slave cylinder seal had failed) so I will change the nipple for the 1973 original. If that doesn't work I'll go to the supplier Stuart kindly suggested. Then with Tim's pipe into a modified master cylinder cap it should be all systems go.

Thank you forum for being so patient but the car was so awful to drive with a dragging clutch that I want to get as much throw as possible and can't afford any air in the system at all.

Thank you for all your suggestions, there is nothing worse than being stuck on your own and not knowing what to try next. It is comforting to know others find this a pain.

I am very grateful for all your help.

Regards

Les

Edited by Les Pettitt
better wording
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11 minutes ago, Martin50 said:

I fear I will get shot down for suggesting this, but I have used PTFE tape wrapped around the bleed nipple threads to stop it bypassing. I was careful not to block the bleed hole and didn’t take the tape to very end (wet end). This has worked for me. I will in future try the brass nipples based on recommendation. This was using a vacuum gun to suck the fluid rather than pressurise from m/c. But fully agree its the worst job and really struggle to bleed. Just need lot of time and patience (which I don’t have!).

Not shot it could get Les out of prison and hopefully not go back to the issue but why was the replacement part sent like that?

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Hi All,

I have three clutch slave cylinders, the Lockheed original fitted to my car in 1973, a repro one and a refurbished Lockheed which is currently fitted to the car.

The bleed nipples on all three display side to side play if they are undone by a quarter turn. Martins idea of PTFE tape is very interesting, I wonder why I haven't come across it before. It would certainly take out the play and stop fluid running down the bleed nipple thread which was my problem on Wednesday. Before going this route, I compared all three nipples that I have (see below). The left hand one is the original on the car in 1973. The centre one was on the reburbished slave cylinder and the right hand one was on the repro cylinder. What fascinated me was the original had a flat top and the repro one came to a point - exactly the opposite to my findings when sorting a brake fluid leak from a slave cylinder (see earlier topic) when the Girling original was pointed but the TWR was flat topped and a different profile.

Going back to clutch nipples there is a subtle difference between the 1973 original and the one from the refurbished Lockheed. (left and centre below). I fitted the 1973 original, used Tim's pipe idea and found I was no longer getting any fluid passing along the thread although I only undid it maybe one hex. I was soon getting a decent clutch movement but thought I would try one more time and more air came out, so you have to persevere with this. I am now getting 14mm throw on the slave push rod which is the maximum I can get from 28mm at the master cylinder. To get any more I would need a longer master cylinder push rod but that would bring the clutch pedal higher and it is currently exactly in line with the brake pedal.

Stuart was absolutely right about the importance of good nipples.

Thanks to everyone who helped me on this, it has been a long haul but I now have a completely new clutch system which is working properly.

Regards

Les

Clutch slave cylinder nipples.JPG

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On 12/2/2021 at 11:33 AM, stuart said:

Make sure there is no lots motion in the pedal clevis and the slave clevis too. When bleeding make sure you have quality bleed screws as the cheap ones are such a poor fit that when you slacken them to bleed your drawing air back in around the thread. I always use Brass Automec ones .https://automec.co.uk/collections/fittings/products/brass-bleed-screws-unf

Stuart.

Hi Stuart 

The link takes you to 1/4 x 28 UNF is this the correct size for the CM and the front and rear brake callipers as I might as well replace them all now.

Les pleased you eventually got the system working and kept folk updated.

Andy 

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2 hours ago, Les Pettitt said:

the right hand one was on the repro cylinder.

the angle seems different compared to centre and left.  Narrower.

 

PTFE is an option. Alternative: Stahlbus bleeder valves. Screw and glue in the valve. done.

Edited by JochemsTR
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16 hours ago, PodOne said:

Hi Stuart 

The link takes you to 1/4 x 28 UNF is this the correct size for the CM and the front and rear brake callipers as I might as well replace them all now.

Les pleased you eventually got the system working and kept folk updated.

Andy 

Sorry forgot to do the drop down option, it should be this one https://automec.co.uk/collections/fittings/products/brass-bleed-screws-unf?variant=13048922079255 3/8 x 24

I will edit the other one now.

Stuart.

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21 minutes ago, PodOne said:

Thanks Stuart so that's for front and rear brakes as well?

Andy

Yes theyre all the same.

Stuart.

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9 minutes ago, PodOne said:

Thanks Stuart will order some.

Andy

FWIW I use all of their brake pipe ends too.

Stuart.

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I've a brake pipe/fuel and clutch set from them but if I ever need any I'll bear it in mind

Thanks for the advice.

Andy

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On 12/3/2021 at 7:36 PM, JochemsTR said:

the angle seems different compared to centre and left.  Narrower.

 

PTFE is an option. Alternative: Stahlbus bleeder valves. Screw and glue in the valve. done.

Hi@JochemsTR- what length of Stahlbus valve do you have? They have 16mm & 22mm in the 3/8-24UNFX22mm version. They are expensive, but probably worth the money if they get rid of the bleeding issues.

Cheers, Robert

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  • 3 months later...
On 12/5/2021 at 9:09 PM, rwest said:

Hi@JochemsTR- what length of Stahlbus valve do you have? They have 16mm & 22mm in the 3/8-24UNFX22mm version. They are expensive, but probably worth the money if they get rid of the bleeding issues.

Cheers, Robert

Robert -

A bit of a delay, but the thread should be 16mm long.  These are available on FleaBay, sometimes with the cap included and sometimes you need to purchase the Stahlbus cap separately.  Am hoping that this will assist with bleeding my newly fitted NOS Girling 0.75" bore Clutch Master Cylinder...

Mark

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Just now, mrehke said:

Robert -

A bit of a delay, but the thread should be 16mm long.  These are available on FleaBay, sometimes with the cap included and sometimes you need to purchase the Stahlbus cap separately.  Am hoping that this will assist with bleeding my newly fitted NOS Girling 0.75" bore Clutch Master Cylinder...

Mark

See https://www.stahlbus.de/lng/en/stahlbus-bleeder-valve-38-inch-24unfx16mm-m-steel.html - Product Code is SB-110511.

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On 12/2/2021 at 9:18 AM, Les Pettitt said:

Thanks everyone.

Good to know there should be bit of free play. Thanks Stuart, it makes perfect sense not having any pressure held in the line. I have now fitted my new Girling master cylinder which only had a single seal. In retrospect, maybe I should have asked the question about free play on the TRW before assuming it was faulty and buying the Girling. I do like the idea of the double seal on the TRW. I have now replaced the master cylinder with new Girling, the slave cylinder with new Lockheed (mounted the correct way up), new flexible pipe and new 82mm master cylinder push rod but I still only get around 12mm throw at the slave cylinder. I guess I need to look again at the bleeding.

I have left the clutch pedal jammed against the floor overnight and will check later if it has made any difference.

Does anyone have any foolproof tips on bleeding the clutch system? I started with a 'Vizibleed' and then moved onto two person.

Thanks

Les

Hi Les! some years ago when I stripped out my clutch hydraulics because of gear crunching. I found the following:

The clutch pedal clevis hole had worn oval, it was bad. I had a choice to weld up the hole and re-drill to size. But I chose to turn up a marine bronze bush and fit as an interference fit. This has lasted over 35 years with very little play still in the clevis pin. I also went back to the .75" master cylinder which my car did not have as it was a 73 CR car. This made a tremendious difference to the movement on the clutch operating arm, gear crunching gone!

Bruce.

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