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MG Midget and Sprite Technical - Clutch problems.
|The clutch on my 1972 midget has always bit very near the bottom of its travel since i have had the car.Its been stood for 2 years with a few trips up & down the drive while I have been overhauling the brake system.I then took the car for its mot, which it passed, but on the return journey, it became more difficult to get the car out off gear when changing gear.I decided to try & bleed the clutch, found the slave cylinder was leaking, changed it but was then not able to bleed the system, inspected the master cylinder & found the seals were worn. As i now bleed the system again I notice that slave pushrod is always in the pushed out position, should the clutch release arm push the pushrod back into the cylinder ? With the slave disonnected from the clutch release arm,the arm has about 1.5" of movement, with no resistance of any sort, is that correct ?|
|Sorry I'm a bit lost, as well as the s/c have you changed the m/c or just its seals?|
I was told that changing seals itsn't always sucessfull and to change the m/c is the best way to go and of course flush thro' the exisiting seal contaminated fluid
there's been a thread on this just recently too you might want to look at that thread
First the clutch arm will move about as described and when normal the clutch slave cylinder will hold it up against the resistance point in position. To achieve this the rod in the slave cylinder will be a bit out and if you tried you would be able to push this back into the cylinder and then have a far bit of free play in the arm.
I hope that answers your question mate.
Regarding bleeding the clutch before opening the bleed nipple push the rod as far into the cylinder as possible. Then open the nipple and push down on the pedal. Now close the niple and release the pedal. Hopefully doing this a couple of times should bleed up the system.
When finished the first push of the pedal will push the rod out of the cylinder and put the arm into hard contact with the clutch cover. Then on subsequent pushes the clutch should engage and disengage correctly
|Robert (Bob) Midget Turbo|
|When I got my Midget (it's a 1500 so a bit different), my engagement was on the floor. After a few days it wasn't working at all. I was lucky and a clean of the bore got the slave working properly (I didn't even change the seals!) but bleeding it was a nightmare.|
Eventually I had the S/C hanging from its flexi-pipe, detatched from the bellhousing. With the internals of the S/C held in their rearmost position (a combination of a bolt and some cable ties, with the outerboot removed) I was able to angle it so the nipple was uppermost and of course there was no freeplay in the internals. A few open, pump pedal, close, up pedal and all was fine, and has been since.
Once it's all back together it will self-right according to how the mechanical parts work (freeplace in the pedal linkage, release arm, etc) and you should be fine.
Thanks for the advice, I investigate further tomorrow.
On 2 occassions over the years I have helped with difficult clutch hydraulics on 1500 Midgets. On both occassions I have done exactly the same as you have decribed. The key ingrediant being pushing back the piston fully into the Slave Cylinder. If this is not done whether a 1500 or a 1275 then air can get stuck inside the cylinder itself.
Sometimes it is not necessary but often it is.
|Robert (Bob) Midget Turbo|
|Alan, It may help to consider the position of the components in the system starting from the clutch pressure plate, rather than from the clutch operating pedal.|
When in the "at rest" position (i.e.clutch engaged)the pressure plate will move rearwards and push the clutch release bearing back. There is nothing that will move it any further back other than the slight jostling of the rotating parts. In this position it requires minimum movement to begin compressing the pressure plate springs when you do disengage the clutch.
The release bearing in turn moves the clutch fork and this, via the pushrod, will move the slave cylinder piston part-way back up the bore. The piston won't move any further up than the clutch pressure plate pushes it. In this position it is "primed" and ready to disengage the clutch pretty well as soon as the slave cylinder begins to move.
If you have now replaced parts and successfully bled the system you should have a "bite point" fairly well up from the floor. However it may be that the slave piston isn't moving far enough forward in the cylinder to give you the required movement to disengage the clutch before it reaches the end of its travel in the cylinder. This can happen if either the slave pushrod is worn too short, or the clutch fork can become bent, or the release bearing has collapsed. The first and second of these can be temporarily fixed by inserting a 7/16" nut inside the conical end of the slave piston so that it sits on the end of the pushrod - effectively lengthening it slightly. If this improves things you just need to buy a new longer pushrod.
|The two most common causes of not disengaging till near the floor if there is no air in the hydraulics are wear in the clevis pin/yoke etc between pedal and m'cyl, and a disappearing release bearing.|
From your observation of the positon of the slave cyl pushrod, I suspect the release bearing could be an issue. With the range of wear (or even break-up)possible with a carbon bearing, the slave cyl piston would have to move a fair distance out to take up. This in turn draws further fluid into the system from the reservoir, and may well suck in air and push marginal hydraulics over the edge. Even with the hydraulics fixed, if the bearing is on its way out the underlying problem is still there.
Unless your clutch was renewed recently, I certainly would check the bearing first. With a bit of luck and a mirror you may be able to do so via the clutch arm slot with the gaiter removed.
As the low pedal has been with you for a while, I would also check for slack at the pedal/m'cyl pivot.
I've just been through all of this, your chain of events sounds very similar to mine! - check out my "Bleedin' Clutch" thread.
This thread was discussed between 07/08/2010 and 09/08/2010
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.