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odd clutch slip problem
https://ausmini.com/forums/viewtopic.php?f=5&t=20490		 Page 1 of 1
Author:  simon k [ Sat Jun 24, 2006 9:32 pm ]
Post subject:  odd clutch slip problem
I'm after some guidance on this one.... it's got me stuffed, let me do a bit of a brain dump - I'll be taking the clutch cover off for an inspection soon - probably next weekend

I had a fiddle with stainless' mini today (rumble bee - yellow/black with a gigantic ICE setup) and he has a very odd clutch problem.... it's as if the clutch is worn out, but it has maybe 300km on it since being replaced as a kit by Tim at the Mini Garage in Wagga (I've never dealt with him personally but I'm led to believe he's a good operator), it was replaced because the rear main seal had failed and spat oil all over the clutch plate.... so, hows this:

the symptom is a really bad clutch slip in all gears, as if the clutch wasn't allowed to fully engage, or the clutch plate is worn out or the pressure plate is weak

stock-ish 1330 with 45mm weber
car is driven around once per month
Taking the car for a drive, it's really easy to make the clutch slip
rear main seal does not appear to be leaking, no oil coming from flywheel housing
new clutch 300km old - good brand and 'competition' pressure plate
tested and satisfactory master cylinder, slave cylinder and hose
good condition clutch arm ball-end (replaced by me this afternoon - the old one was excessively bent leaving the return spring slack)
properly adjusted throw-out stop
excessive adjuster bolt to arm clearance (adjusted to around .060", but even up to 1/4" made no difference - still able to select gears)

even with the adjuster bolt screwed in giving about 1/4" clearance to the clutch cover, the clutch is fully disengaged with only 1/2 of the pedal travel actually pushing the clutch in - IE pushing it half way stretches the return spring, then to the floor pushes the pressure plate spring - and we're still able to select 1st & reverse gears.

if there wasn't enough 'pre-load' on the pressure plate spring, the clutch plate would slip, wouldn't it?

I recall Kev (Dr Mini) said the spring should be set so that's horizontal across the flywheel face when engaged, so there is plenty of spring pulling the backing plate in, but allowing enough movement to disengage the clutch. I'm thinking that if the flywheel/backing plate is worn, the posts on the backing plate are too long and the pressure plate spring doesn't have enough tension on it, therefore letting the clutch plate slip

thoughts?
Author:  Morris 1100 [ Sat Jun 24, 2006 9:49 pm ]
Post subject: 
The clue here may be the fact that it is a new clutch.
New parts are not good because thay have not been tested!

Has it always slipped? (like from the moment he picked it up?)
Did it start doing it slowly or did it come on suddenly?

My guess is either the diaphram spring has snapped or ........ something else!
Author:  stainless [ Sat Jun 24, 2006 9:56 pm ]
Post subject: 
Morris 1100 wrote:
Has it always slipped? (like from the moment he picked it up?)
Did it start doing it slowly or did it come on suddenly?

My guess is either the diaphram spring has snapped or ........ something else!


nope it hasnt slipped before (except when there was oil all over it) i picked it up and have driven it about once a month since then with no problems, then when i took it out for its monthly wash and strap around the hume weir it was slipping as i left town so i put it back in the garage and got in contact with simon. and now we are at the point as per simons post.

thanx
Author:  simon k [ Sat Jun 24, 2006 9:57 pm ]
Post subject: 
Morris 1100 wrote:
The clue here may be the fact that it is a new clutch.
New parts are not good because thay have not been tested!

Has it always slipped? (like from the moment he picked it up?)
Did it start doing it slowly or did it come on suddenly?

My guess is either the diaphram spring has snapped or ........ something else!


apparently didn't slip until the last time he went to take it for a drive - had been sitting a month or so.... so came on suddenly.... could it be that it's taken 300k's for the 'newness' of the clutch plate to wear off and is now just thin enough to make it slip between the backing plate & flywheel?

what sot of symptoms would you get from a snapped spring? would you get any clutch at all?

that "something else" sounds like it might be the problem :D
Author:  feralsprint [ Sat Jun 24, 2006 9:57 pm ]
Post subject: 
have they machned the flywheel and backing plate without machining the 3 posts the same amount and the clamping pressure is not enough :D

Jon
Author:  9YaTaH [ Sat Jun 24, 2006 10:06 pm ]
Post subject:  Glazed??
skssgn wrote:
Morris 1100 wrote:
The clue here may be the fact that it is a new clutch.
New parts are not good because thay have not been tested!

Has it always slipped? (like from the moment he picked it up?)
Did it start doing it slowly or did it come on suddenly?

My guess is either the diaphram spring has snapped or ........ something else!


apparently didn't slip until the last time he went to take it for a drive - had been sitting a month or so.... so came on suddenly.... could it be that it's taken 300k's for the 'newness' of the clutch plate to wear off and is now just thin enough to make it slip between the backing plate & flywheel?

what sot of symptoms would you get from a snapped spring? would you get any clutch at all?

that "something else" sounds like it might be the problem :D


The other remote possibility is that it is glazed...what sort of driving has it had....has it had a chance to bed in?? has it had lots of slipping trying to be gentle???

Just whack some Ajax in the inspection hole like they did at Bathurst :idea: :lol:
Author:  Morris 1100 [ Sat Jun 24, 2006 10:06 pm ]
Post subject: 
A broken diaphram will not lose all the tension, just a fair bit! So it will slip fairly easily.
Author:  drmini in aust [ Sat Jun 24, 2006 10:14 pm ]
Post subject: 
Simon,
I had a similar prob with my boss's (mate's) 1275LS he bought a year ago.
It had clutch slip under slightest provocation, even though motor was very tired- but when I took it apart the plate (Borg & Beck) was almost new- wear was about 0.5mm only.

I did a trial build on it with a new plate, the diaphragm was nowhere near flat when assembled.
I had to machine 1.5mm off the 3 lugs to get it right. Works well now.
Whoever had worked on it in the past had machined both the flywheel face and the backplate numerous times, but left the 3 lugs... :?

See Chichm's analysis of clutch building, here-
http://www.minimania.com/web/DisplayID/ ... ticleV.cfm

Works for me- I'm running an orange plate now, it grips well and pedal effort is lighter than my old blue plate was.
Author:  simon k [ Sat Jun 24, 2006 11:40 pm ]
Post subject: 
thanks guys, I appreciate it.... that about confirms what I was thinking - we'll pull it apart and look at how flat or not it is...

I don't think I'll try the Ajax Mick, but I'll keep that in my bag of tricks.... I use ajax for honing dashpots already ;)
Author:  9YaTaH [ Mon Jun 26, 2006 12:39 pm ]
Post subject:  Yez
skssgn wrote:
I don't think I'll try the Ajax Mick, but I'll keep that in my bag of tricks.... I use ajax for honing dashpots already ;)


Good idea Sime....I think they had a slightly weeping seal wetting the clutch.....so in with the Ajax....the things people do to keep racing :?
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