Clutch slip when hot

Hi to all
I have finally got round to sorting my clutch slip when hot
I am using the un1 gearbox mated to a BMW 3.2 evo e36 with a bmw clutch
Having stripped it down last week i cam across the following problems
The pressure plate badly burnt
The flywheel badly burnt with a hairline crack in it
The release bearing was stuck at the end of the guide tube there is a groove in the release bearing at an angle
The release bearing has a welded piece of steel on it the bearings are gone
The clutch release fork was nearly touching the gearbox casing when the clutch is disengaged
The release fork is slightly bent at the top
I now need a new release fork and a bearing set up ( I think )
The total length of the bearing is 50mm from where it is in contact with the release fork to the end
I have 10mm clearance between the end of the bearing to the pressure plate when the release fork is right back do I need this
Not that good at putting pen to paper hope you can understand this
Any help i would be very grateful
Enclose a couple of photos
Thanks Jon

tidxv.jpg at Free Image Hosting

Howard Jones

If you can convert your clutch to the Renault system then there are several upgrades that are being used. Being in the UK will be helpful. Otherwise you will be replacing what you have now.

Since the flywheel is cracked I would start there. Get some advice for a replacement clutch based on your engine power. The stock Renault pieces seem to be good up to about 250HP. Then have your new flywheel drilled so that you can bolt on the clutch. You may need to work out a pilot shaft bearing adapter. Now you can use the renault parts. Lots of them available in the UK. Ask the GTD guys. They have been helpful to me in the past.
If all else fails try calling in at Wealden Engineering. They seem to have a lot of knowledge about our dream machines.

Mike Pass

From looking at the pic it looks like you have the Renault bellhousing and release arm. From your symptoms it looks like the set up is not correct with the BMW clutch. The severe overheating and clutch slip would point to the clutch not fully releasing due to insufficient clearance for the clutch in the bellhousing. As the clutch you have is for the engine you have I would guess that the clutch is up to job of handling the torque from the engine. If the clutch does not full release then it will slip causing severe frictional heating of the type you describe.
I would suggest you fit new parts and then take these measurements using a digital caliper to measure the clearances in the bellhousing.
Place a straight edge across the face of the bellhousing and then measure the distance from the face to the clutch release bearing in both the retracted and extended positions.
using blocks and a straight edge measure the distance from the bellhousing mounting face on the engine block to the place on the clutch where the release bearing meets it. Do this measurement twice - once with a new clutch plate installed and once with a worn plate installed. This will tell you the changes as the clutch wears.
From these measurements you can work out if the spacing and movements are giving you the clearances for the clutch to work and release properly.
When doing the clutch on my GTD I found that the spacings were all wrong and had to machine and make up spacers to get everything correct. Then I found that to get a good operation on the clutch I had tomake up a new rod connecting the slave cylinder to the clutch arm. If you need to do this cut off the pin which goes through the release arm, make up a new rod from a bolt and replace the pin with a suitable HT bolt. You need to adjust the length of the new rod so you have a small amount of play in the mechanism to ensure that the clutch fully releases. watch this clearance in use as it will close up as the clutch wears. Make up a few rods of different length which are easily swapped or engineer an adjustable length rod.
I use a sleeved down slave cylinder to get the correct amount of movement and minimum clutch pedal pressure on my setup. You will have to experiment with your setup as I have no experience of BMW stuff.
I originally had a Renault clutch but it was not up to the torque of my SBF and I had to upgrade it and hence had to re-engineer the clutch operation. Takes time but a bit of careful measuring and adjusting and thinking it through will do the trick.

Hi Thanks for all your replies
I have now measured using the old flywheel and clutch my (new one arrives on thursday or friday) from the contact point where the thrust bearing hits the clutch lever fork fully back has far as it will go to the start of the clutch pressure plate i have a total of 61mm i will redo this with my new flywheel
What would be the best bearing length

Mike Pass

I am a bit puzzled as to why the release bearing was stuck at the end of the guide tube. Is the guide tube damaged? I have an original Renault UN release bearing and carrier if you want them as I have fitted one of Chris Cole's upgraded items (just pay the carriage.)
If the release bearing was stuck at the end of the guide tube this would prevent the clutch releasing and may be the problem in this case. Question is - why was the release bearing sticking on the guide tube? Do you have pics of the bearing and guide tube?