4 replies to this topic

[herringson]

Hi Everyone,

This is my first post here even though I've been reading up for a while, hopefully I'm not asking dumb questions =) I've got a 1975 clubman that's been having problems changing gear, I had it fixed a few months back but the problem has returned and I'm hoping I can fix it myself to save some $.

When the clutch is fully depressed but the car is in gear you can hear the motor working a bit harder than if it's in neutral which I assume means the clutch isn't disengaging fully. I'm also getting crunching when changing down from say 4th-3rd when slowing down and when going into reverse, if the car is still rolling to a stop it's really hard to get into 1st or second too.

The clutch pedal is a bit spongy and if I pump it I can usually change ok.

My first guess was the slave cylinder so I've tried bleeding it a couple of times (a bit new at it). The second time I'm pretty sure I got it right and the pedal felt nice and tight afterwards and the first few changes went well. Once I'd driven for a bit and changed gear a few times though the problem is back, the pedal is spongy again and I have to pump it to change gear.

Am I right in thinking that it's probably the master cylinder letting air into the system now? The slave was replaced not that long ago so I'm hoping that's ok still. Are there any other likely culprits for air getting into the system? A master cylinder isn't super expensive so I guess I could try replacing it myself, is it a particularly hard job?

I guess what I want to avoid is going to all the effort of changing it myself to find out that the problem was something else.

Let me know if anyone has any input.
Thanks!
dylan.

[govig]

From your description it is a clutch release problem. Was it a new slave or a repair kit that you used? Do air bubbles come out when bleeding?

[tiger99]

I suggest that you set up the clearance on the stop bolt (non Verto) and the overtravel stop correctly before condemning the master cylinder, because the cost of adjusting it is zero. And, check that the clutch cover bolts are tight, although I think you would know all about it if they were seriously loose.

The master cylinder is quite likely, but first check that the flexible hose is not bulging under pressure.

The worst possible cause is crankshaft endfloat, meaning the thrust washers have failed and possibly reduced the crankshaft to scrap. but it is prudent to check all the easy and cheap things first. The end float can be checked. Push the clutch pedal to push the crankshaft towards the radiator. Using a lever on the bottom pulley, push it back again, the movement should be scarcely visible.

Other nasty possibility is that the clutch is not dragging, but the primary gear is not running freely on the crankshaft. May need new crankshaft and/or gear, and you should not run a well-used gear against a new one, so it means changing all the drop gears to do a job that will last.

I would give it a 90% chance of being the master cylinder.

[bourney]

Sounds like either a leak or master cylinder. Have you checked the seal on the slave? Pull the dust boot back and have a good look at it

[Cooperman]

Here is my clutch drag diagnosis document:

CLUTCH DRAG

Clutch drag or failure to disengage is not an uncommon problem with the Mini.
There are several possible causes as follows:
A. HYDRAULIC SYSTEM
1. Wear in the pedal spindle or failure of the pedal to master cylinder clevis pin.
2. Failure of seals in the clutch master cylinder.
3. ‘Ballooning’ of flexible hose due to internal hose degradation or damage
4. Air in system due to inadequate bleeding
5. Failure of slave cylinder seals

B. MECHANICAL SYSTEM – WITHDRAWAL MECHANISM
1. Wear in top clevis pin
2. Wear in lower clevis pin
3. Bent arm
4. Worn or broken ball at lower end of arm where it engages into plunger.
5. Wear in plunger ball seat.
6. Incorrect setting of overthrow stop nuts
7. Incorrect setting of adjusting screw
8. Corrosion between plunger and clutch cover due to lack of lubrication.
9. Thrust bearing failure – accompanied by a lot of noise.

C. THE CLUTCH ASSEMBLY
1. Failure of clutch diaphragm spring due to fatigue or distortion
2. Centre plate hub not sliding on primary gear splines.
3. Clutch plate surface de-laminating or breaking up
4. Distorted clutch plate.
5. I fitted, clutch plate shock springs broken and causing a ‘jam’.
6. Primary gear not rotating freely on crankshaft due to either: i) Insufficient primary gear end float, ii) Primary gear bushes seizing on crankshaft, or iii) Primary gear bushes breaking up