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Re: Very odd clutch problem

PostPosted: Mon Mar 23, 2015 1:49 pm
by Asolepius
Onlinemetals does have the right tube, but $90 shipping is a bit steep! I can only get stupidly long pieces here in UK.

Re: Very odd clutch problem

PostPosted: Tue Mar 24, 2015 6:16 am
by Asolepius
Hooray, just found 1 foot of the correct brass tube at a model engineering outlet in UK. Now I can sleeve my spare master cylinder.

Re: Very odd clutch problem

PostPosted: Tue Mar 24, 2015 10:27 pm
by Charlie Tolman
That is good news on the brass tubing front.

I was about to offer an arrangement, where I could purchase a foot of tubing, have it mailed to my house, and then I could mail it to you via the US Post Office. The total cost for everything would have been about $35 (USD). Still expensive.
I suspect that the tubing you found in the UK has a lesser cost.

Charlie T.

Re: Very odd clutch problem

PostPosted: Tue Mar 31, 2015 9:13 am
by Asolepius
Thanks but no need of course. Mind you the tube hasn't arrived yet, out of stock at supplier. Carriage only GBP4.

Fortunately I won't need to bore the cylinder as the tube is 7/8" OD and 3/4" ID so I can just press it in with some silicone sealant. Most difficult job is deburring the ports after drilling, or they ruin the seals.

Re: Very odd clutch problem

PostPosted: Thu Nov 05, 2015 10:16 am
by Asolepius
The saga is not yet over. I did sleeve the master (both bores), and made new pistons on the lathe. It all went together well, and has performed faultlessly for nearly six months. But the other day I drove off and noticed a slight rattling from the transmission area. This was followed by some odd clonking which I could feel strongly through the pedal. The pedal travel has increased a lot, but the clutch just about disengages. I then saw a lot of fluid on the floor, and looking in the engine bay could see that this was coming from the slave. The master isn't leaking at all, and the level is fine. Fluid has sprayed out of the slave, and found its way past the rubber bung into the car interior. The car is just about driveable but this looks bad. I haven't investigated further yet as the weather is foul and I was in the middle of sorting out my ridiculous stock of spares so can't get the car into the garage right now. I'm hoping that the problem is confined to the slave (which was a new one about 5 years ago), but I have a very bad feeling about it. I'll keep you guys posted of course.

Re: Very odd clutch problem

PostPosted: Fri Nov 06, 2015 11:35 am
by Asolepius
Right, the rain has stopped, I have cleared the garage, and had a look inside the clutch housing. The release bearing has no visible carbon, just the steel. It seems to have broken up. I despair of obtaining good quality, reliable parts. This bearing lasted no more than 800 miles. Oh well, I can get the engine and tranny out in 2 hours.

Re: Very odd clutch problem

PostPosted: Sat Nov 07, 2015 1:14 am
by Charlie Tolman
It appears that the clutch linkage or hydraulic components was/were not "releasing" enough, so that the throw-out bearing was slightly dragging on the clutch release surface.

How is this related to the fluid and slave cylinder issue that you mentioned ?

Does anyone have any experience with a ball bearing release mechanism, or a hydraulic system that fits inside the transmission bell-housing ?

Charlie T.

Re: Very odd clutch problem

PostPosted: Sat Nov 07, 2015 6:48 am
by Asolepius
Hi Charlie - you can always be relied upon!

When assembled I ensured that there was correct clearance for the release bearing. I checked the travel of the slave and ensured it wasn't pushing the clutch too far. The failure of the bearing was sudden which suggests breakup not wear.

I am now less confident about my set-up, which to reiterate is:

948 engine and flywheel
3/4" master
7/8" slave
1098 gearbox
1098 release fork
1098 release bearing
1275 clutch
Thin backplate

To get this to work I have a slave pushrod which is just over 2" from hole to end. I have just been reading the Gerard's Garage site (http://gerardsgarage.com/Garage/Tech/TO ... arings.htm) and he says that a 1098 box should not be used with a thin backplate as the input shaft is longer and it can bottom out in the spigot bearing. I am now wondering whether I should use the 2" slave and the thick backplate (I have one in stock). What do you think?

Re: Very odd clutch problem

PostPosted: Sun Nov 08, 2015 12:46 am
by Charlie Tolman
A contributor to Sprite Spot was having transmission problems, and his shop suggested that damage done was due to the wrong combination of engine back-plate and transmission.

While searching the Internet, I found Gerards Garage, and it stated that the input shaft of smooth case and rib case transmissions are different in their length, and I posted the web link in the Mk I Bugeye section of this forum, about two or three days ago. The length difference was new to me.

A rib case transmission, and its longer input shaft, should not be used with a engine that has a thin back plate. The input shaft might bottom-out in the pilot bearing region of the crankshaft.
Likewise, a smooth case transmission should not be used with a engine that has a thick back plate. It appears that the front end of the transmission input shaft might not be supported by the pilot bushing.

This was a little surprising to me, since I used a rib case transmission with a 948 engine, and it worked well with a thin back plate and also with a thick back plate. The clutch was a 1275 unit, including the throw-out bearing. The clutch slave cylinder was a 1098 unit, and I needed to use a slightly longer slave cylinder push rod.

In your case, I would try the thick back plate with the rib case transmission.

Charlie T.

Re: Very odd clutch problem

PostPosted: Mon Nov 09, 2015 6:25 am
by Asolepius
Yesterday I pulled out the engine and gearbox and found that yes, the carbon release bearing has broken up. Some of the bits had fallen into the release fork gaiter and jammed the fork, so when I hit the pedal it didn't move and fluid was forced out of the slave. There is no evidence that the input shaft has bottomed out in the spigot bearing, or that the clutch has been overthrown. This seems to be simply a failure. I have thought about a roller release bearing but remain a bit doubtful, as it won't run concentrically. The carbon can accommodate that. Peter May Engineering sells a concentric roller bearing system but it only fits a Formula Junior engine. The 1275 clutch doesn't move as far as the coil spring one so the eccentricity should not be as severe.

To be on the safe side I have fitted the thick backplate and have ordered a 1275 slave. I will weld up the pushrod to suit. So I will have a 100% 1275 system and if the bearing fails again it will definitely be a quality issue. The new one I am putting in is not the scroll pin type.

Re: Very odd clutch problem

PostPosted: Tue Nov 10, 2015 1:29 am
by Charlie Tolman
Les,

Sounds like a good approach.

In addition to a standard clutch slave cylinder rod, I had welded-up three additional longer rods, of three slightly different lengths.

To help the concentricity of the release bearing, I would often replace the bushing in the main clutch fork, in addition to replacing the bolt. I also might have used a very thin shim/washer between the clutch fork and its mount on the transmission's front cover mounting ears.

Charlie T.

Re: Very odd clutch problem

PostPosted: Wed Nov 11, 2015 4:02 pm
by Asolepius
It's all back in the car now. I ordered an adapter for the slave cylinder because the hydraulic connection is bigger, but would you believe they sent me an adapter for the master not the slave! When I phoned they said I didn't need a slave adapter. I definitely do! So I have had a merry time making one on the lathe. After 3 attempts I think I have one that will work. I'll find out when I bleed the clutch. All this of course meant that I had to remove the slave from under the car, having fitted it to the gearbox when it was out of the car. I had forgotten what a deeply unpleasant task that was!

I also made a new bush for the lever - from a brass manifold nut.

If the release bearing fails again I will definitely think about a roller bearing. I hear a Ford Sierra one can be made to fit.

Re: Very odd clutch problem

PostPosted: Thu Nov 12, 2015 12:56 am
by Charlie Tolman
As I remember, the 1275 clutch slave cylinder uses a flexible hose, several inches long.
The threaded input on the cylinder body probably is larger than the end on a solid tube line.

CT

Re: Very odd clutch problem

PostPosted: Thu Nov 12, 2015 8:01 pm
by Sprite33
I have used a ball bearing TO bearing on my race car for well over 20 years. It has never given me any problems and I hope that continues because that particular unit is not available anymore. I think they were designed specifically for the 1275 clutch. I was not to impressed with it when I got it because it made out of plastic. It must be a very good plastic because the contact surface of the fork has worn more than the TO bearing.

When I was using the carbon type TO bearing, I had to replace them often.

I suspect your fluid leak was due to the broken carbon material be gone, allowing the slave to move out too far and the seal could not seal properly anymore.

Re: Very odd clutch problem

PostPosted: Sun Feb 07, 2016 1:54 pm
by Asolepius
Yes folks, I'm back! The carbon release bearing has failed yet again. After less than 500 miles. I tried to get a good quality one but that seems to be a lottery. Time for a roller or ball bearing I think. But does anyone have any thoughts about the concentricity issue? And why do these carbon units keep failing? I never used to have this problem. I have of course checked that everything installed has correct dimensions and clearances.