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Clutch drag
https://www.ausmini.com/forums/viewtopic.php?f=2&t=28760		 Page 1 of 1
Author:  TimB [ Sat Mar 03, 2007 7:09 am ]
Post subject:  Clutch drag
I've just installed a new primary gear and while I had it apart a new throwout bearing carrier and bearing. Put all back together to find the clutch is binding and won't allow me to select any gears while the motor is running. I can select any gear with the engine off then start the car without it taking off.

Armed with my 'Mini Expert' magazine I keep reading over the section on clutch drive strap alignment and from what I can gather a gap between the straps and the pressure plate horn will cause disengagement problems. When I checked mine the straps appeared to be just touching the horns, athough the straps appear to have been bent up slightly, not perfectly flat as pictured in KC's mag.

If mine were flat I'd say the pressure plate horns would be pushing on the straps which would be more likely to cause clutch slip.

Any suggestions?

PS. The good news is, I was able to take it for a small drive and the whining seems much better with the new primary gear :)
Author:  drmini in aust [ Sat Mar 03, 2007 7:22 am ]
Post subject: 
How tight was that new primary gear on the crank? They are supposed to have around .003" radial clearance, with end float of between .0035" and .0065".
If it's tighter, it won't slip easily on the crank with the clutch depressed.

I recently fitted a new MSC floating front bush to a 1275 primary gear, and had to machine the end of the bush away to prevent jamming- it was too long.
Author:  TimB [ Sat Mar 03, 2007 8:02 am ]
Post subject: 
End float was .003 - .004 as for the running clearance I didn't have any way of measuring it but it certainly wasn't tight. What's the best way to measure it.
Author:  drmini in aust [ Sat Mar 03, 2007 8:25 am ]
Post subject: 
It's hard to measure radial clearance accurately with it in the car, but as long as it turned freely by hand it should be OK.
If so, it's a clutch adjustment thing.
Author:  superSeven [ Sat Mar 03, 2007 9:14 am ]
Post subject: 
we had the exact same problem after an engine rebuild we did. first test drive was ok, then the primary gear binded against the crank, couldn't select any gears with engine running. then it freed itself up. then it binded up again, and never free'd itself. Engine out, oxy torch to heat it up was the only way to get it off! We installed it with clearances as stated in the workshop manual but it was still too tight. i can't remember the clearances we ended up machining it to but it was fine ever after.
Author:  TimB [ Sat Mar 03, 2007 6:36 pm ]
Post subject: 
Hmmm, I will be pulling it down again maybe tomorrow otherwise it will be next weekend. I was having similar trouble initially after the rebuild but that was with the old primary gear with too much clearance. I actually thought the cause was the bearing carrier so I replace that with a new one. Plus a new Timken throwout bearing. The new primary gear felt perfect spinning freely. What is different is I had to use an old pressure plate (which appeared to be in good nick) because I snapped a bolt off in the other one, so maybe that's not helping.
I might take it for a spin later and see if it settles in.
Author:  TimB [ Sun Mar 04, 2007 2:37 pm ]
Post subject: 
Took it for a spin and it seems to be acting normal again.
First & reverse gear still seem harder to select than everything else, if I pump the clutch a few times it helps. Would this indicate that further bleeding of the clutch system is required?
Author:  drmini in aust [ Sun Mar 04, 2007 4:42 pm ]
Post subject: 
TimB wrote:
Took it for a spin and it seems to be acting normal again.
First & reverse gear still seem harder to select than everything else, if I pump the clutch a few times it helps. Would this indicate that further bleeding of the clutch system is required?

6 or so pumps will get the air out. No need for more.
It could be MC seals worn, that adds to free play at pedal, as they then don't seal until the pressure forces them out against the cylinder.
Could also be too much gap at the stop screw on clutch cover, set to .o20" with spring removed, then refit spring.
Could also be slave cylinder piston hitting the circlip, check if pedal goes to floor (should) or stops hard before floor. If the latter, remove circlip from slave cylinder to get more slave piston travel.
Could also be (long shot) wrong bore clutch MC, it should be 0.750" diameter. I've seen lots of Minis with Clubby alloy/plastic brake MCs used for clutch, they barely move enough fluid to work. Diameter is marked (sometimes) on outside of MC.

<edit> if you keep getting air out with the fluid at first bleed, suspect the slave cylinder seals are worn- they can let air in when you let pedal up.
Author:  TimB [ Sun Mar 04, 2007 4:54 pm ]
Post subject: 
Kev, you diagnosed the wrong MC a few months ago when I was having disengagement touble. It was 100% better after puting the .75" MC on but as it is now still difficult to select 1st sometimes so maybe it is the slave cylinder. Although should one gear need more clutch than the others?
Author:  drmini in aust [ Sun Mar 04, 2007 6:01 pm ]
Post subject: 
1st in a Mini all synchro box is always hardest to engage at standstill, that's why Issigonis never fitted a synchro 1st gear back at the start.
If the slave is not recent, clean it out, spend $8 and put a new seal kit in it.
:wink:
Author:  bnicho [ Sun Mar 04, 2007 7:28 pm ]
Post subject: 
Check for a severely worn ball on the end of the clutch arm. I had a similar problem, and that was the cause.

Cheers,
Author:  willy [ Sun Mar 04, 2007 7:35 pm ]
Post subject: 
bnicho wrote:
Check for a severely worn ball on the end of the clutch arm. I had a similar problem, and that was the cause.

Cheers,


Me too, on my rover (stubby arm) the ball had snapped completely off, and a jagged edge was all that was actuating the thrust bit.

The ball was being ground deeper and deeper into the thrust bit (whatever its called)

I'll see if i can find it and chuck some pics up!

Very bad Japanese maintenance :P
Author:  TimB [ Sun Mar 04, 2007 8:46 pm ]
Post subject: 
Everything in the clutch system has now been replaced; all clevis pins, hoses, arms, bearing, bearing carrier etc the only thing left is the slave cylinder so I'll start wih a kit.
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