Another clutch mystery for me

Technical advice Q&A

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265bhp
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#1 Another clutch mystery for me

Post by 265bhp » Sun Apr 11, 2021 10:04 am

Hi all

Having replaced the internal seals for my slave cylinder, my earlier problem of a non-returning rod would appear to have been solved which is great, I’ve bled the system profusely and I completely convinced that there is no air in there whatsoever

However, the first push of the clutch pedal still has moderate resistance only, and it is only when pressing the pedal for the second and subsequent times that the pressure is truly what I would expect

So I’m slightly flummoxed

Thinking this through I am wondering if the valve within the master cylinder ....which pushes the small seal at its end, (and which then closes off the supply of fresh clutch fluid) is not being pressed to instantly seal the end of the Master cylinder (by the secondary spring) within the master cylinder

The main spring would appear to be doing its job in returning the piston to its original position but I’m just wondering whether that small seal is not doing its job immediately .....

Has anyone had this situation...and might be blue to shed any light on this

The cylinders were re-bored and had stainless steel inserts done by “Past Parts”..but it was early in the restoration and I don’t believe the springs were replaced...so now that I have replaced all the seals the only thing I can think of is these internal springs......

thoughts would be very welcome

All the best
Jonathan
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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MarekH
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#2 Re: Another clutch mystery for me

Post by MarekH » Sun Apr 11, 2021 11:01 am

The clutch system can simply be gravity bled normally - there is an open path all of the way normally and there is no unsealed part until the pedal is pressed part way down. That means you are suggesting that a seal is deforming under moderate pressure but only takes takes up the final "correct" shape under the second push, i.e. the seal was left flexed/deformed when the pedal is returned. Packing with red grease might help.

If you want degassed brake fluid, just pop round with some fluid and I'll pop it in the vacuum chamber. At zero pressure, it'll soon boil at room temperature and any dissolved air and water will evaporate/boil off, leaving neat brake fluid. (With dissolved gas/water, some of the pedal press is compressing the dissolved gases in the fluid, rather than providing useful brake pressure.)

kind regards
Marek

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christopher storey
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#3 Re: Another clutch mystery for me

Post by christopher storey » Sun Apr 11, 2021 2:17 pm

I just put fluid in the microwave at medium power for say 5 mins, then leave to stand for a day or so . Best done when the other half is not there ! Your problem sounds to me as though it could be that your pushrod is not long enough ( no vulgar jokes please :bigrin: )

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politeperson
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#4 Re: Another clutch mystery for me

Post by politeperson » Sun Apr 11, 2021 2:23 pm

Something quick you could try.

Now the clutch is bled, remove the slave cylinder spring and see what happens.

Worked for me once! Clutch returned to normal.
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#5 Re: Another clutch mystery for me

Post by 265bhp » Sun Apr 11, 2021 4:22 pm

Thanks all

Hi Marek..although I cannot know for certain having bled the system profusely yesterday I am pretty certain air in the system is not the issue

Hi Christopher...do you mean the push rod on the slave please...that’s interesting..I can hopefully adjust

Hi James..do I remove the spring, and use the clutch without it completely please..?

Best
Jonathan
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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christopher storey
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#6 Re: Another clutch mystery for me

Post by christopher storey » Sun Apr 11, 2021 5:03 pm

Jonathan : yes, I am referring to the pushrod between the slave and the clutch operating lever on the bellhousing . Some of them are adjustable in length, and some are not , and which you have seems to be at random. If it is adjustable then it is worth trying lengthening it a little at a time and seeing if it makes any difference. If it is a fixed one then it may be worth making a longer one : if you have welding equipment then welding a stub into the existing one is feasible - an addition of perhaps 6 to 8 mm might be a starting point

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politeperson
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#7 Re: Another clutch mystery for me

Post by politeperson » Sun Apr 11, 2021 8:09 pm

Hello Jonathan,
Yes, remove it completely.
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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abowie
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#8 Re: Another clutch mystery for me

Post by abowie » Sun Apr 11, 2021 9:02 pm

If you are getting fluid refluxing through the filler valve it should be noticeable in the reservoir.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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mgcjag
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#9 Re: Another clutch mystery for me

Post by mgcjag » Mon Apr 12, 2021 9:17 am

What spring are we talking about to remove....the internal or external.......if you remove external then you risk the thrust bearing wearing out .....Steve
Steve
69 S2 2+2 (just sold) & Building a C type replica

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politeperson
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#10 Re: Another clutch mystery for me

Post by politeperson » Mon Apr 12, 2021 12:35 pm

Worth seeing what happens when the external spring is removed.

Just wondering is we are dealing with mix and match parts.

There are a few different slave cylinders floating about that seem to have found new life of various cars with 9.5 and 10 inch clutches.

A nice gentleman called Steve posted a nice list once-

Adjustable C21470 (superceeds part C16989) with external return spring 80mm length used up to engine No 7E4606
Hydrostatic Self adjusting C24145 without external spring 95mm length used from engine 7E4607
Adjustable Modified non Hydrostatic C29801 with external spring 95mm length used from7E18356 (ots&fhc) & from 7E5558(2+2)
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#11 Re: Another clutch mystery for me

Post by 265bhp » Tue Apr 13, 2021 11:19 am

Hi all

The removal of the external spring to the slave cylinder seems to have worked...but now reading Steve’s post I am not so sure it is a good solution..?

Next I can certainly try extending the pushrod.....and presumably put the spring back on....?

My slave is a Girling one from memory..it is the 80mm body type and I am using what I assume is the original adjustable pushrod from the car

I changed the 3.8 style clutch to a later 10” 4.2 litre type when I rebuilt the engine....would that have anything to do with it..?

All the best
Jonathan
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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mgcjag
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#12 Re: Another clutch mystery for me

Post by mgcjag » Tue Apr 13, 2021 1:20 pm

Yes it could......did you fit the correct trust bearing......there are a few different models and as far as im aware they are deaper in length.......it shouldnt be that difficult to sort out with the external spring removed move the clutch fork fully rearwards so the thrust is in contact with the clutch cover......now unlock the pushrod and unscrew it from the fork...it should be able to unscrew untill it bottoms out in the slave cylinder......if it dosent then its too short.......you can just use a piece of threaded stud rod to make a new one...available from diy shops...unf thread...make sure you adjust when completed as per service manual so that with the pushrod fully in there is a 1/16 in play.........then reconnect external spring.....it should hold pushrod fully in and hold the thrust bearing off the clutch.....Steve
Steve
69 S2 2+2 (just sold) & Building a C type replica

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#13 Re: Another clutch mystery for me

Post by 265bhp » Tue Apr 13, 2021 5:38 pm

Hi Steve
Did all that...unscrewed at least a cm and tried it again....makes no difference..once the return spring is re-fitted I still have a soft pedal on the first push, then hard pedal with the second push....
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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#14 Re: Another clutch mystery for me

Post by mgcjag » Tue Apr 13, 2021 5:45 pm

If you have a soft pedal then a hard pedal on second push then you still have air or a seal problem. .the hydraulics push the pushrod out...it should be able to do this with the external spring.......if all your doing is removeing the spring to make it work then the hydraulics are strugling to overcomes the spring.....thats just my thoughts..........i would bleed the slave again.....open nipple..press pedal down and hold it down..close nipple...release pedal..then repeat....on your last push down..hold pedal...then befor closeing nipple press the pushrod fully in......this can often expell any traped air in bottom of slave.....close nipple......Steve
Steve
69 S2 2+2 (just sold) & Building a C type replica

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#15 Re: Another clutch mystery for me

Post by 265bhp » Tue Apr 13, 2021 8:17 pm

Okidoki.....always worth trying again.. :bigrin:
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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madjack4
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#16 Re: Another clutch mystery for me

Post by madjack4 » Wed Apr 14, 2021 8:29 pm

Hi if its a good pedal with no spring u have got to have adjustment wrong must be too much free play first push is taking up play
Regards

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politeperson
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#17 Re: Another clutch mystery for me

Post by politeperson » Thu Apr 15, 2021 9:09 am

Jonathan,

Do you have free play in the clutch arm with the spring removed, once the clutch pedal has been depressed a few times?

If so, I would think your clutch throw out bearing should last a fair while and all should be well!

If you have no free play when your foot is off the clutch, your throw-out bearing wont last long at all, so its back to the drawing board.

So what is the current state of play?
James

L.J.K. Setright was right.
"You just cant beat a good E-type"

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#18 Re: Another clutch mystery for me

Post by 265bhp » Thu Apr 15, 2021 8:29 pm

Hi James

To be honest it’s too cold in the evenings to be in the garage and I don’t have any free time during the day until the weekend, so I haven’t done anything since your last suggestion

I have literally just braved the cold :bigrin: and done a quick check, and ....when the return spring is removed (and the clutch pedal depressed half a dozen times) I would say I actually don’t have any real free play at all at the fork end so I’m not sure that I can dispense with the return spring entirely

One thing I could try is to use the old spring...(it was a little less stiff than the new one from SNG....) and see if that pulls the rod in a smaller amount and somehow works....?

I’ll have one more go at bleeding the system over the weekend and also extending the return rod as much as possible...I still have a little more thread left to use up

Best
Jonathan
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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#19 Re: Another clutch mystery for me

Post by 265bhp » Sat Apr 24, 2021 9:38 pm

Evening all

Just to bring this thread up-to-date .....and thank you to Steve for the telephone advice..... I have persevered with bleeding of the system Periodically over the course as the last week ....and have managed to extract a few small additional bubbles of air

The clutch is still slightly soft on the first push but is better than it was when I wrote this original post and as I have also taken the car out for a number of very short drives it does work ....so I’m going to continue with bleeding once in awhile and keep up the short drives...( no numberplate or windscreen... :bigrin: ) in the hope that it eventually returns a firm pedal on first push

Thanks to everyone for your help

J
1963 3.8 FHC in slow restoration mode
1974 2.7 Carrera now as an RS Touring

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