Welcome to our resource for MG Car Information.
MG Midget and Sprite Technical - Clutch Bleed help
|For the sake of my sanity and what is left of my knuckles, all help appreciated.|
My '76 midget has been sat for several years.
I reached the point where the only problem with it was the empty clutch master. I refurbished the master and filled with fluid. Whilst the master was out I decided to bleed the system with the master elevated. Got lots of air out, far more than I would have thought possible, by working the piston by hand. Eventually I was unable to get the piston to move and took this to mean all the air was expelled. Put everything back together........ No clutch pedal movement. Didn't STAND on it but used a fair amount of pressure, no movement.
Took the slave off to see if I could see any problem there. All looks sound. No leeks.
When I put a small screwdriver in, i can push the piston and it returns slowly??? Is this right?
The screwdriver is taking the job of the Pushrod.
The actual Pushrod has free movement.
A dab hand at removing and replacing both cylinders now 😄
I don't fully understand how this works, and that isn't helping me to sort it.
Summary, bled the clutch, now have rock solid pedal.
Many thanks in anticipation.......
my thoughts would be if the master cyl has sat empty of fluid for a few yrs it sounds like it has rusted and the seal is binding on the rusted bore i would strip and check the bore very easy to remove the piston spring etc check the bore any signs of rust pitting on the bore discard and get a new master cylinder otherwise buy a seal kit
if in doubt buy new..
when it comes to bleeding us a power bleeder works of the car tyre mine was about
|J D Craddock|
Is there a circlip in the slave to prevent the piston from popping out, and has the piston reached the end of its travel so that it is resting up against the circlip?
|C R Huff|
missed that bit about the pedal being solid
is the slave cylinder seized? not allowing you to press the pedal ??
loosen off the blead nipple on g/box then see if you can depress the pedal and force fluid through...if you can i would look at the slave cylinder
the only other question .... are you pressing the correct pedal... hehe
|J D Craddock|
|Thanks for the quick replies.|
JD, yes, correct pedal. 😄
Charley, there is a circlip but the piston in the slave moves smoothly in and out when I used a small screwdriver to push it.
So it would appear that the slave is not seized.
BUT, with fluid in the system, the master and slave not in situ, I push the slave piston in, it goes in smoothly and then returns just as smoothly. Should it do this?
If I connect the master to the pedal and press the pedal, the screwdriver is pushed out. When the pedal is released the slave piston just sits there until I push it back in.
I am using a screwdriver is just as a mimic of the Pushrod.
|surely the pressure plate pushes the slave cylinder back in?|
|J D Craddock|
|I might have misunderstood, but here's my take on it:|
You've got the slave cylinder disconnected from the bellhousing, so the clutch pushrod isn't there to push the slave piston back into place when you take your foot off the pedal.
You put your foot on the clutch pedal, which pushes fluid into the slave cylinder, pushing the piston all the way out.
You take your foot off the pedal and the slave piston stays where it is, so the master cylinder piston sucks extra fluid from the reservoir to make up the difference in volume.
Then you put your foot on the pedal again, and find it won't move. Could it be that all that extra fluid now has nowhere to go, since the slave piston is at full travel already?
At this stage I'm hoping I've misunderstood the issue.
If you're bleeding with the slave elevated, the pedal should only move if the bleed screw is open. Once the air is out of the lines, open the bleed screw one last time and push the slave piston back in. Close bleed screw. Reinstall.
|Update: I think I have misunderstood. Good. |
Yes, the slave piston, in the absence of a pushrod, will gently move to the extent of its travel. Some even have a light spring inside to help this. This takes up any slack in the system, the idea being that the clutch spring is much heavier than the little return spring.
If, when installed and at rest, your slave piston is at or nearly at the extent of its travel, then you've got a broken clutch or it could be that your pushrod is too short. (Never had any complaints myself- bu-dum, tish!)
|Or a bent clutch lever arm. It would also mean that the clutch cover didn't push the slave piston back up its bore, so it isn't "primed" for the next use.|
|Thanks for understanding my ignorance of clutch systems. I've never had to deal with one before. A picture is beginning to form. |
From all the above posts it would seem to me that the master, slave and hyds inbetween all appear ok.
So, the Pushrod. Should I be seeing any resistance on this whatsoever? There is total free movement in and out of about an inch, no resistance, no spring......
Told you I didn't have a clue about clutches 😄
If you mean the pushrod at the gearbox end, then the answer is no, it should not have free, no resistance movement of 1". The clutch cover springs push against the clutch release bearing and this pressure is transmitted all the way back up the clutch lever, push rod, piston, hydaulic fluid etc to the master cylinder and thence to the clutch pedal.
Its a push you, pull me system with your foot at one end and the clutch springs at the other. Both ends can only push on the system. There is no mechanism to pull on the end of the "train", only push from either end. (other than light springs in some versions to take up slack)
If that push rod is slack like that then either the clutch itself, or the release bearing or the clutch lever is faulty in some way. The release bearing may have broken up, or the clutch lever arm may have become bent. Check that it isn't fouling against the cut out hole where it comes through the bell housing, before it pushes the pushrod back up against the slave cylinder piston.
|Thanks Guy. Yes, I meant the Pushrod at the gearbox end. There is movement in all directions and it will push in and out without any resistance by about an inch. |
I will crawl back under just to double check the clutch lever arm when I get a chance.
I appreciate everyone's help, many thanks
|Hi, the lever arm is not fouling on anything. Moves freely in and out with the push rod.|
Looking likely I will have to open it up and get my crash course on clutches, unless there are anymore words of wisdom?
Have you at any stage replaced the pushrod? I believe that there are two lengths available. Maybe if you replaced it you got the wrong one?
Just eliminating that possibility, although I doubt that is the problem as there isn't as much as an inch difference in them. It seems more likely to be a problem with the release bearing.
|No, I haven't replaced it Guy.|
Do you have everything back together (rather than operating the slave while it is not bolted on)? If is is all together, is the slave moving the lever arm?
If it is moving it, how far is it moving it?
Also, with the slack taken out of the lever arm, pull the rubber dust cover off of the slave and see how much free room the piston has before it hits the retaining circlip.
Given your self confessed lack of knowledge of clutches, I suggest you not be too hasty to pull the engine out. You could end up doing that for nothing if you don't properly diagnose the hydraulics first.
Speaking of self confessed lack of knowledge, I'm not really familiar with the 1500s, but I suspect they are similar to the earlier models in this respect.
|C R Huff|
|Hi Charley, with everything back together thee is no movement whatsoever on the lever arm, the clutch pedal is rock solid (apart from taking up the mechanical slack).|
When the slave is out, there is around two inches of movement on the slave piston when operated with the pedal.
earlier you said "There is movement in all directions and it will push in and out without any resistance by about an inch"
Now you say: "thee is no movement whatsoever on the lever arm"
So a bit confusing! I also admit I was also confused,thinking that this was an A series car, but I see its a 1500. So some of my earlier advice is not relevant.
On the 1500 the pushrod is enclosed when the slave cylinder is installed. One fairly common fault that happens with a 1500 clutch is that the pivot pin drops out of the clutch lever arm. The pressed steel arm then stays more or less in position but the leverage is lost and the clutch either doesn't disengage fully, or the slave travel is all taken up and the pedal goes solid. Sound familiar?
Undo the slave cylinder clamp and pull the slave sufficiently clear that you can grasp the end of the pushrod or better, the end of the clutch lever arm. Jiggle it around and see if you can determine if the other end of it - the drivers side of the gearbox - feels if it is moving around a fixed pivot pin, or if it is very sloppy. The pivot is a vertical pin which is an interference fit but can, and does, drop out.
Feel for the hole beneath the pivot end of the lever and try pushing a pointy screwdriver (cross-head type) up the hole to see if there is a pin in there or not.
If it is missing, it is possible to drop something like an 8mm coach bolt in from the top as a replacement. Although not exactly original, this will work and last for year (well, mine did!) To do the job "as original" is an engine out job.
|Hi Guy, sorry to confuse you.|
With the slave cylinder out, I can grip the push rod and move this, which is connected securely to the clutch release arm, quite freely in and out by about an inch. Also, the pedal works fine and with a cross head screwdriver in the slave, the slave piston moves in and out just fine.
But, put it all back together again and the pedal is rock solid.
I am beginning to think you hit on something in your earlier post when you mentioned the release bearing.
If this was holding the plates together then the slave piston would be allowed to relax into its extended position. Would this not make the pedal solid?
Many thanks for your continued support and suggestions.
|1500 uses a roller release bearing, so it is far less likely to break up than the carbon type used on an A series car. So, I may be wrong but I doubt that is the problem.|
"With the slave cylinder out, I can grip the push rod and move this, which is connected securely to the clutch release arm, quite freely in and out by about an inch" I suspect that this is also about right. But when doing this could you get an idea of whether the fulcrum pin at the other end is still intact? Was there excessive slack and side to side movement of the clutch release arm?
The release arm is made of pressed steel with a pivot (fulcrum) pin at one end, and the attachment to the pushrod at the opposite end. In the middle the pressing widens out and has a hole in the middle that the gearbox input shaft goes through. At that point it carries the clutch release bearing. If the pivot pin does drop out, the release arm is still held loosely in the normal place because the release bearing is still around the input shaft. But the pivot pin end flaps about, stops it operating properly and you loose all the clutch take up so the pedal may feel solid.
|Hi Guy, The clutch release arm appears to be connected at one side and pivoting about this point. There is no lateral movement of the release arm. It would appear that the push rod and release arm are working correctly.|
|It sounds to me like your hydraulics are working fine, it's the clutch end of the push-me pull-you system that's letting things down. |
When the slave cylinder is installed on the car and the system at rest, the pushrod should hold the slave piston in by a good inch. If, when installed, the slave piston is near or at the extent of its travel then you've got a broken clutch or release linkage, and it's engine out time.
|Thanks Growler, looking that way to me too now :-(|
Unfortunately I am away for a little while now but I will report back to close this thread down when it's up and running.
All, many thanks for the education and help and advice. It's appreciated.
|Yes, it does look that way. |
Just one other thought that would be worth checking. You are attaching the slave cylinder correctly? The slave is cylindrical and fits into a cast collar that then bolts to the bell housing. There is a clamp bolt to grip the cylinder. There is a groove machined in the outside of the cylinder, and the clamp bolt needs to align with this groove. I cannot now remember but maybe it is possible to fit the cylinder too far back so the clamping bolt doesn't align with the groove. This would mean that the piston met the end stop circlip (and went solid) before activating the clutch.
Seems unlikely, but it would be an easier fix than removing the engine!
|Ah, good one, Guy. I didn't know that's how it went together but just checked and it is all aligned correctly. The bolt does indeed sit in the groove. I was hoping this might be it. Alas not!|
|Pity, that really would have been a nice solution!|
I think I have run out of ideas. It does seem like the problem is hidden within the bellhousing then. I think all other possibilities have been exhausted.
If I understood, you were trying to figure out how floppy the clutch arm is while it was still attached to the plunger rod. You might try to assess it when it is disconnected. Also, with a lever you might be able to pry on the clutch lever arm to see if you can feel it work the clutch springs.
|C R Huff|
The clutch arm moves about its pivot and allows the push rod to move about an inch in and out. There is absolutely no resistance at all and I now believe there should be resistance provided by clutch springs.
So it is looking more like I will have to open it up.......
|Well Chris, it is sounding more like an engine out job, but be aware that the resistance provided by the clutch springs will probably be more than you can overcome by hand, which was why I suggested trying to pry it with a lever.|
|C R Huff|
|Chris, The slackness that you can feel at the pushrod is the movement of the lever arm and release bearing whilst it is clear of the clutch cover. Its the movement that you would expect before the release bearing ever begins to compress the clutch springs. That is why Charley is saying you would need some sort of lever to actually compress the clutch.|
There should be some free movement of the pushrod, as this allows the release bearing to back away from the clutch in normal use, and also allows clearance to take up wear in the clutch plate. But from what you describe, it seems that there is too much free movement, suggesting damage to the clutch itself. This would mean that the slave cylinder piston was not sufficiently far up the bore of the cylinder to give the travel needed to operate the clutch
|Hello CJ - before you strip out anything I did take some pictures of my 1500 when I rebuilt the gearbox and clutch -some are on this partly completed share site|
Take a look it shows some of the internal bits - lever arm , pivot point and release bearing assy - did you have any of this apart and did it work before you laid it up?
I am not sure - but can the clutch springs be seized in position - I know they work on an overcentred action to clamp the friction plate to the flywheel - but if its been sitting long while can the assy get seized and prevent the springs from flexing?
This thread was discussed between 03/06/2013 and 06/06/2013
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.