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MG Midget and Sprite Technical - Clutch Dragging
|This might be yet another clutch bleeding thread but I hope not!
Newly re-built engine.
New clutch with an Alan Anstead release bearing.
New slave cylinder push rod (13H3655).
Master and Slave cylinders replaced along with the hose approximately 3500 miles ago.
New clevis pins.
I have a remote bleed point adjacent to the heater tap. I have done numerous bleedings with the Eezibleeder in all the configurations and combinations suggested in the archive, plus a few more: pedal held down, pedal not held down, car on the level, front end raised, off-side jacked up to bring the slave's bleed point to the high-point, parked on a slope at an angle with o/s uppermost. None of these methods have persuaded an elusive bubble to show itself. I haven't tried the glamorous assistant option as the archive suggested that pedal pumping was quite likely to just make any recalcitrant bubbles shuttle backwards and forwards.
The clutch is working and has allowed me to do a good number of test runs BUT while it slips into 1st and reverse with no fuss sometimes when it's fresh out of the garage and cold, after just a couple of miles, it grates if I try to engage 1st or reverse for a standing start. 1st goes in OK if I go via 2nd first but that doesn't work for reverse so I sometimes switch off, engage reverse and start it with the clutch depressed. Before the re-build the old clutch was working fine and going into 1st and reverse with no problems.
There is a small amount of play between the pedal lever and its clevis pin that equates to just over 1/4" at the bottom of the pedal lever. Could that be enough to be causing the problem? One post in the archive suggested that this might be the root of the issue with a new clutch that would not happen with a worn clutch.
Do you think removing the pedal to weld up and re-drill the hole will cure the problem?
|you don't mention if you've tried pushing the slave piston in along the bore and holding it there with a miniature G-clamp or a spacer between the end of the pushrod and the piston, and then bleeding. This method removes the space where the air bubbles get trapped.|
|Thanks David, you saved me having to type exactly that!|
Thank you both, I've not tried that one, I thought I'd read somewhere that pushing the piston in too far can damage the seal but seeing as the method comes with two recommendations I'll give it a go tomorrow.
|No, it won't damage the seal. If you visualise it, the pipe in and the pipe out ( to the bleed nipple) are side by side at one end of the cylinder. So when bleeding, if the piston is down at the other end it leaves a whole cylinder pretty much out of the flow of the fluid. If there is air trapped there it doesn't get carried out to the bleed point. Pushing the piston back up the bore should eliminate this possibility.|
|Just bear in mind that pattern parts can vary regarding construction and machining details. While on a FIAT the parts are very much the same as on a spridget, a guy local to me has an X1/9 and he had to replace a leaking clutch slave cylinder and initially he could not bleed the clutch, he just couldn't push fluid through the system, it was driving him mad. In the end he dismantled the slave cylinder and found the problem, the original cylinder was bored to near the end of the chamber so the piston and seal couldn't cover the fluid and bleed port, the new pattern part was fully bored and the seal covered the fluid port preventing fluid flow, a simple fix once understood as the piston needed backing off a bit so as to not cover the fluid and bleed ports. |
|You don't have to have much wear in the pedal hole to effect the clutch operation
The telltale is pedal height, -if the clutch pedal sits lower than the brake pedal, there is a problem
IF you're going to weld it up, have a good measure up first so that you know where the hole was
They wear away from the master cylinder so don't get caught redrilling in the centre of the worn hole , the original hole will have been towards the master cylinder
I'd be tempted to, (if you're going to weld it up),to weld it and refit the pedal then mark the spot with the pedal sitting level with the brake pedal and even creep up the pedal 1/8" compared to where it was to get a tiddle more leverage/travel
|If that hole in the pedal is worn, then the pivot bush may be too. You might want to add a grease nipple there if you have it apart. But I find it hard to understand how lost movement there would give the symptoms of a clutch that works ok when cold, but not when hot.
If there is still air in the system this will be more dense when cold, taking up less space and being dense, it is less compressible. As it heats it expands, takes up more volume but can increasingly be compressed down, so that might explain the differing operation of the clutch between hot and cold.
Other temperature controlled variables? Gearbox drag maybe? I assume you are using standard 20/50?
An alternative to use of a G clamp is a bungy cord.
Once the car is on twin axle stands at the front so you can do the job from the front, crack open the remote bleed nipple, remove the R clip (if you have one instead of a split pin), remove the clevis pin and keep the pushrod in the slave and then put your bungy cord in the clevis pin hole in the pushrod and then push the pushrod in and attach the other end of the bungy to something suitable at the front of the car, in line with the pushrod. Then bleed the system. Do not forget to top up due to compressed slave piston once pushrod released and reconnected.
|Thanks for all the advice.
I have tried pushing the slave's pushrod all the way in and holding it using a modified Mike Wood method via a long cable tie. The most awkward part of the exercise was removing the split pin that was too well bent back round the clevis pin; thanks for the R clip hint Mike, that makes it much easier.
Sadly no improvement! I'm repeating the exercise over night but don't expect it will be any different as I didn't get any bubbles last time.
I am fairly convinced that the problem is a combination of a new clutch with a strong, high spring plus slop due to wear in the pedal's clevis pin and pivot bolt holes. I'm going to order a new pivot bolt but the bushes are NLA. Can anyone tell me the dimensions of the bushes so I can get some from a bearing specialist. Alternatively, I've read that engine/clutch spigot bushes can be used, can anyone confirm this? I will certainly do as you suggest, Guy, and fit grease nipples.
I'll have to wait until I've got the pedals out to decide whether my welding and drilling skills are up to sorting the ovalled clevis pin hole or whether I need to give them to a machine shop to do.
|Use 2x crank spigot bushes (1A1559 iirc) in the pedals, perfet fit, one each end.|
|A 1275 clutch drag fault I have encountered a couple of times:
If the linings are very slighly oversize, or the hydraulic ratio wrong (too great, commonly if an 1100 slave is fitted) the diaphragm centre comes into contact with the plate at full pedal stroke, thus pushing the plate onto the firewall - hence drag.
When drag is encountered our natural reaction is to push harder on the pedal - which makes it worse.
In this scenario there is usually a short bit before full stroke where the plate is free before the diaphragm contacts it, so if dragging with full pedal test be easing off and seeing if the drag reduces or goes.
First time I found this it stumped me till i mounted it all up on the flywheel off the engine and used a press to activate while I watched what happenned.
|Thanks on both counts Paul, I'll add some bushes to the order!
I'm aware of the over-centre possibility as it happens on my Morris with a mechanical clutch linkage. I haven't tested it properly on the Sprite as the bite point on the old clutch was very low. The new clutch is a Borg and Beck and, apart from wear and dirt, is identical to the old one.
I had to replace the engine back plate (My friend did it. Don't ask!) and the replacement turned out to be very slightly thicker (<1mm) than the original. I can't think that would have any effect on the clutch travel, though.
When I stripped the clutch out the last time there was evidence of the clutch 'overthrowing' as Paul explained. I slightly reduced the boss on the clutch plate to give it a bit of extra clearance. All was well after that.
I had wear in the clutch pedal see first photo.
It was elongated so I drilled it and fitted an oilite bearing and a new clevis pin, second photo.
Followed Guy's advice and fitted grease nipples to both the clutch and brake pedals.
|Oilite bearing with new clevis pin and grease nipples on the clutch and brake pedals.
|Thanks Jeremy. That's what I had in mind for grease nipples and the Oilite bushes look just the job. I think I might need to turn to someone with better engineering expertise to fit them for me though.|
|Pivot bolt and bushes ordered.
The manuals suggest that the bolt can just be removed after disconnecting the push rods and return springs. It looks as though the angle strips with captive nuts for the pedal assembly are in the way.
Is 'simple' removal possible or do I need to disconnect the hydraulics and remove the whole pedal assembly?
There's no great rush now as I've just discovered some rust that will need cutting out and repairing before I can go out on the road again. Better I find it now than Mr MoT man or Mr Plod! Rather spoiled an otherwise glorious Easter Sunday.
|You can undo the pivot bolt far enough to disengage from the thread, but not then remove it as it would foul as you have said. One solution is to then file or grind one flat of the hex head down level to the shaft diameter, you can then just withdraw and replace the pivot bolt clear of the support angle irons. Leave the other flats as they are so an open ended will still work when you refit it.|
|Thanks Guy. |
After all the bleeding fuss I really didn't want to disconnect the hydraulics again.
|It's close, and you need to turn the bolt so the new flat aligns pretty accurately to the edge of the reinforcing piece, but it does work. Or at least it did on mine. I don't know how much variation there is between different cars. I also found the bolt quite tight to remove, even when it isn't siezed in position. You cannot easily drift it out as there isn't room to tap with a hammer because of the transmission firewall. I found the way was to get a ring spanner at an angle on the head so that it jammed in such a way that I could both rotate it back and forth and pull/ lever on it as well. Quite a struggle in the confined space of the footwell!
Hopefully, if it ever needs to be out again, my grease nipples on the pedal bushes will mean it will all come apart much more easily!
|It's been well over a month but I finally managed a run out today. I think the Sprite was as eager as me because it fired as soon as I turned the key whereas it usually takes at least three attempts.
The clutch worked perfectly and felt really positive with no slop and a much higher bite point. It can still graunch a little bit if you rush a change but if you're patient and let everything stop spinning it goes into gear smoothly as the clutch isn't dragging any more.
Spigot bushes are shorter than the originals but went in just fine. I doubt they'll wear out in my life time, especially now that I've fitted grease nipples. A note for anyoe considering this: make sure you allow for clearance between the cylinder yoke and the grease gun, I put the nipples centrally on the shaft and just got away with it! My drilling of the clevis hole wasn't as central as I would have liked but the oilite bush effectively regained most of the distance lost through wear.
Best of all, I haven't had to touch the hydraulics.
Thanks for all the advice, pictures and suggestions, you have helped to transform my Sprite's clutch action.
This thread was discussed between 29/03/2021 and 09/05/2021
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.