 | Home > Puma (Tdci) > clutch fail... how to diagnose slave cylinder? |
 
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3208   
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What do you mean by
I would think that the pedal would have very little movement to take up the slack between the master cylinder push rod and the MC piston. Then pedal should become rock solid. If there are no leaks from bell housing, then maybe the non return valve in the MC has failed, and leaking hydraulic fluid back into the reservoir. Check if the reservoir level gets higher when an assistant presses the clutch pedal to confirm the theory. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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18th Nov 2022 12:13pm |
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| Samblers Member Since: 29 Jan 2014 Location: Perth, innit Posts: 63  
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Ummm... yes, maybe not the clearest, sorry
I clamped the hydraulic line just about the slave cylinder, and then pressed the clutch pedal. It went quite far down and then firmed up but yes, now thinking about it, it shouldn't do this at all... presumably should firm up immediately ? Is the reservoir level supposed to get a little higher when pedal pressed, or not? I will check for this next If it's master cylinder, not slave, then this would be better for sure |
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18th Nov 2022 3:09pm |
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| Samblers Member Since: 29 Jan 2014 Location: Perth, innit Posts: 63
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I guess also that I cant be 100% sure that my clamping of the hydraulic line was a total seal...
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18th Nov 2022 3:51pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 16879  
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I didn't think that there was a non-return valve in the clutch m/c, is it not similar to an old-school single-circuit brake m/c when the piston seal simply passes the reservoir orifice to seal the fluid path? If so, the failure of the piston seal would cause the behaviour the OP is describing, since the fluid would simply pass the seal when the pedal is pressed. It certainly sounds to me more like a master cylinder failure than a slave, especially since there is no evidence of fluid leaking out. |
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18th Nov 2022 4:14pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 16879
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No, in a fully-functioning system the level will drop slightly as the pedal is pressed and return when the pedal is released. If the m/c piston seal is leaking the level may fluctuate a little but will essentially be the same irrespective of the pedal position. The reason the fluid level normally drops slightly is, of course, because you are pushing fluid from the m/c to extend the piston in the slave, and fluid from the reservoir will enter the m/c to take up the space behind the (now extended) piston seal. As you release the pedal the piston and seal return to the rest position displacing this fluid back to the reservoir, and the slave piston retracting pushes the fluid displaced through the pipe back to the m/c. If the slave cylinder seal had failed, if a lineor hose had failed, or if the flow restrictor was leaking, there would be evidence of fluid loss. The m/c is really the only component which can suffer an hydraulic failure in a manner which prevents the clutch from working without a puddle of fluid appearing somewhere. |
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18th Nov 2022 4:21pm |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3208
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There is a non return valve, which I am pointing to in below pic. On the casting, at the end of the bore, there is a little orifice that connects the bore to the reservoir. This is the orifice that can see when viewing down the bore. The orifice that goes to the circuit is on the side, but is of course also all the way down on the bore. The non return valve should be open when the pedal is not pressed, so fluid from the reservoir can get into the circuit if there is fluid loss. But once the the pedal starts moving, it should close the non return valve right away. The fluid in the reservoir should not rise if functioning correctly.  Click image to enlarge 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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18th Nov 2022 5:58pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 16879
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Ah, ok thanks.
I've not (yet) taken a TDCi clutch m/c apart and I have to say that's not quite what I was expecting to see inside. Overcomplicated compared to the (entirely satisfactory) designs of old, but no doubt there's a reason for it. |
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18th Nov 2022 6:30pm |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3208
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I had once a failure of that non return valve on a brake master cylinder. Same operating principle.
The effect was that if you wanted to slow down gently, by applying slight pressure to the brake pedal, the pedal simply goes slowly to the floor as the fluid is pushed into the reservoir rather than into the calipers. But used to work fine when the brake pedal is pressed abruptly to push the non return valve against the reservoir... so was getting used to see many cars too close to the rear cross member in the rear view mirror  1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black |
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18th Nov 2022 6:50pm |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 19574
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My MC lasted 15 years, I finally changed it to a new one Genuine one this year.
To avoid faffing about and you are swapping identical parts I took a measurement from the end of the threaded MC adjustment section to the back of the lock nut. (Micrometer is idea). Providing its identical parts especially nuts then when you swap over it will mean you wonβt need to mess about with pedal height. Saves messing about, as the pedal height was perfect on mine before replacing once the new one is fitted then it was perfect after too. Just a little tip that I did, however this was swapping a genuine MC to genuine MC so if you change MC manufacturer it may be different but can be a damn good guide. Also when my clutch went early this year, as there was fluid loss I presumed it was MC. It wasnβt, but was needed to be changed as the seals were going and fluid black. Then I thought it maybe the Slave, which I knew meant a new clutch anyway. When it came to it was a spring failure where a spring had come out of the friction plate, and all the rest of the springs were loose too. This was the Genuine LR clutch, first one all the slings were loose. The second all springs were loose and one came out and that blocked getting her into gear. Other than replace MC, check pipework or hoses and ensuring the bleed valve is closed there is little you can do or check outside of the transmission. Diesel$ Live$ Matter. β½οΈπ’οΈπ¨βπ§π§°βοΈ RED, WHITE & BOOST! π¬π§ |
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18th Nov 2022 7:29pm |
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| Samblers Member Since: 29 Jan 2014 Location: Perth, innit Posts: 63
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Thanks to all for the replies and info... it's sounding more like a master cylinder problem, which is a surprise given that I fitted a genuine Lucas/TRW replacement less than two years ago.
The only reason I replaced was to solve the creaky/ notchy operation (see my other posts) caused by the pitting of the (domed, and un-greased) end of the push rod on the piston. Off to the garage to diagnose... |
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19th Nov 2022 1:04am |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3208
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I had a Lucas MC fail after 8 months. I opened it up to investigate why, found the piston was not properly deburred and gouged the bore, rendering the complete unit as scrap. Unfortunately it was a time where local warranties were only until you hand your hard earned cash in. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing
2012 90 CSW, 2.2TDCI, Santorini Black |
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19th Nov 2022 6:50am |
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| Samblers Member Since: 29 Jan 2014 Location: Perth, innit Posts: 63
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New master cylinder has solved
(fingers crossed)
I took apart the old one but could find no mechanical problem or damage - but (and i take back what I said in the orig. post, I hadn't looked properly) the fluid was filthy... probably due to have been blown past the seal(s) and mixing with whatever grease was inside. So this might have just compromised the seal. Given the struggle to get the m/c out, I wasn't willing to risk cleaning the old unit up and putting it back in, but it might've been ok after a clean. Another point to note, for future reference - my clutch switch failed a few months ago. This failure was picked up when i noticed the engine holding onto revs after a gear change. Bypassing the switch improved the drivability so much that i never bothered replacing this switch - but i'm raising this switch failure as a possible symptom of impending m/c problems, since it's likely it could've been down to the filthy fluid getting in all the small bores. Thanks for all your help Sam |
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19th Nov 2022 10:33am |
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| custom90 Member Since: 21 Jan 2010 Location: South West, England. Posts: 19574
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Which MC did you fit? Diesel$ Live$ Matter. β½οΈπ’οΈπ¨βπ§π§°βοΈ RED, WHITE & BOOST! π¬π§
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19th Nov 2022 11:21pm |
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| Samblers Member Since: 29 Jan 2014 Location: Perth, innit Posts: 63
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I put another TRW/ Lucas in
... my third I think |
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20th Nov 2022 6:56am |
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