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MG Midget and Sprite Technical - Bleedin' Clutch
Christian and I have spent several days and many litres of Dot4 trying to restore good functionality to his clutch hydraulic system, with no real luck.
We have tried everything we can think of, but the pedal is still spongy, and the clutch isn't fully disengaging.
It worked until recently (can't remember when it started being a problem) and the linkages seem unworn.
We have done the following, in no particular order:
- Rebuilding the master
- Replacing the slave
- Slave nipple confirmed to be in the top hole
- Pressure bleeding with gunson, both low and high pressures
- Bleeding with vacuum bleeder
- Pressure bleeding with master off and raised up
- Bleeding with slave off and hanging
- Pumping the slave cylinder piston in
- Reverse bleeding with syringe
- Bleeding the old fashioned way
- Bleeding and tapping various bits
Any thoughts, we have run out of ideas!
Not a fun job. One method I have used that worked is a take-off of the old fashioned way with one variation. Not my idea originally, and cannot recall who should get credit, or blame!
With all components in place with the master filled I have an assistant pump the pedal a dozen (or more) times to work fluid through the system. Access the slave bleed screw through the access plug with a hose attached to the bleeder routed into a reservoir with a bit of fluid. Open bleeder screw with the pedal down to allow air to purge, and repeat at least two times, basically the old fashion way.
Re-fill the master, and pump again with the bleeder screw closed. This time remove the bleed hose to the reservoir, and place a finger over the bleeder screw. With the pedal down, open the screw with light pressure from your finger on the bleed screw opening. When you feel the pressure from the fluid stop press your finger down tight, and close the screw. Repeat as required until you see movement in the slave push rod. Clean everything with de-natured alcohol.
Hope this helps,
|Larry C '69 Midget|
|I reckon it's air trapped in the slave, at the front of the piston.|
Prior to swapping to a concentric with my type9, I can remember this happening to me. I know yours is a 1500, and mine was a 1275 , but it sounds like the same thing to me.
To fix, I pushed the 'slave' piston all the way in, and then opened the bleed valve on the slave cylinder, to expel any air, until fluid came out. Then keeping the piston clamped in, I closed the bleed valve.
Don't let the slave piston back out.
Keeping the slave piston clamped in as far as it will travel, I then bled the clutch master, via the slave bleed valve, until I had a nice clear column of fluid in my tube.
Then release the slave piston, and problem solved.
Have you tried that? Not just pumping the piston in, but keeping it in, whilst you bleed the master all the way through.
|Well this one worked well for me - OK its for A series but in principle should be the same.|
Good point, I forgot to add that part to the method I suggested for Josh. I believe I fashioned a small wooden stick the correct length, and wedged it against the gearbox to keep the slave piston pushed in. Then used my final method in my previous post.
I seem to be forgetting a lot these days. I had better add this to my maintenance notes so when number one son inherits PON307G he'll know what to do when he has to deal with this ;)
|Larry C '69 Midget|
I always used to use that method before I too "went concentric", with the piston pushed up inside the slave, as a matter of course. And it always worked.
But I thought that was what Josh meant he had already tried when his list included:
- Pumping the slave cylinder piston in.
|That's why I put, that he shouldn't pump it, but keep it in all the way whilst bleeding the master.|
But you may be right, he may have tried it already, in which case, he's got problems. ;-)
|I read it as "Pumping (with) the slave cylinder in"|
Josh, if its a 1500, are you sure that the problem is air in the hydraulics. If it isn't fully disengaging it could be the old 1500 problem of the clutch lever fulcrum pin dropping out. Have you checked for that?
|We have tried variations of that Lawrence, but I will follow those exact instructions and see what happens.|
Its not the clutch lever pin Guy - thats in and fine.
The problem began after an engine rebuild - with a new gearbox, and new clutch pressure plate and friction plate and new clutch release bearing and different clutch release arm and new master seals and new slave cylinder... so in theory the problem could be elsewhere. However... the pedal is really not firm enough - which makes us still believe is hydraulics... when i drive joshs car and then get in mine - it feels like there is no pedal at all!
|C L Carter|
|And you did of course put the friction plate in the right way round?|
|Yes I did.|
|C L Carter|
|OK, just thought I would ask. |
Wrong way round would mean that it wouldn't release properly, and also that the clutch diaphragm "fingers" would be bent, would creak and feel sort of springy/ (spongy?) So it was a possible and worth checking.
|my two pen'th |
check new master seals
did you replace flexihose?
|Nigel, I don't think the 1500 uses a rubber flexihose like the A series arrangement. But there is a permanently fixed section of semi-rigid plastic pipe IIRC where he clutch pipe runs across over the transmission tunnel by the heater.|
I don't think it has been mentioned, but with the larger bore hydraulic pipe used on the 1500 a rather different pumping technique is needed when bleeding. Normal thing is to press down on the pedal (brake or clutch) with slow even strokes so as not to churn up the fluid and introduce air bubbles. This works well with the narrower bore pipe, but with the wider bore I think it allows the fluid to pass through, bypassing any air bubbles in the pipe. These are prone to collect in the pipe where it loops through 180 degrees just after leaving the master cylinder,- this being the highest point in the system. The slow moving fluid doesn't carry the air bubbles with it to purge them from the pipe.
The better technique on these is to pump the pedal rapidly up and down 6 or 8 times with the bleed nipple cracked open,to get a decent current of fluid through that upper part of the pipe and flush any air bubbles out. Once this is cleared then the normal steady pump method should be employed to clear any small bubbles from the slave cylinder.
I would still also use the method Lawrence describes of pushing and clamping the slave piston well up the cylinder bore for this final stage as well. The idea of this is to avoid air lurking within the cylinder whilst the current of fluid being pushed through comes in the inlet pipe and craftily nips straight out of the adjacent bleed nipple, leaving stagnant fluid (and air) in the main body of the cylinder.
|Thanks for the thoughts everyone.|
I think we need to try clamping the slave piston in all the way somehow and bleeding.
If that fails we will dismantle the master and check it is OK.
Noboby seems to read/comment on the link I posted to Spriteparts.com Colin notes exactly the point you are making - i.e gentle movement of fluid is not sufficient - hence his technique of removing the bleed nipple to start with etc.
Works for me.
|>>Nigel, I don't think the 1500 uses a rubber flexihose like the A series arrangement<< cheers Guy I'll try and remember that (emphasis on try)|
they were quick dashed off comments only but thinking about it now I'm sure there was discussion before on bleeding the clutch on a 1500 (or was it brakes) so it'll be in the Archive (if I'm right)
|Ah Richard. My apologies, I hadn't followed your link to Colin's web site. Hadn't read that before, I was just speaking from my own experience of ownership of a 1500 some years ago so interesting to get that confirmation of the method.|
These days I have a 1275. And a concentric clutch slave. The bleeder on that is to a remote valve by the rear corner of the block and, once filled when first installed, it now bleeds almost automatically. All I have to do is slacken the bleed nipple for a moment and the fluid syphons through - I don't even need to pump the clutch pedal!
|Clutch bleeding seems to give most nightmares to most folk on here by the number and frequency of the threads attributed to the matter yet I, over many years of Spridget ownership have not experienced the problem.|
I have a 948 Frogeye and a 1275 Sebring rep neither of which have experienced the problems others have. Is this because I keep my halo polished or is it perhaps that both are fitted with remote bleed valves sited high up on the clutch housing and the "head" of fluid solves the problem. The only other variance is that I for many years have used silicone fluid in both systems.
Sometimes I bleed with Eezibleed at low pressure or others if a helper is to hand by pumping the pedal.
|When I did my 1500 clutch slave and hose replacement this past summer, I elevated the master well above its mounting point to remove the "loop" in the new hose. Then I used a MityVac to bleed from the slave. After mounting the master and testing the system, there were a few tiny bubbles in the hose loop (fortunately it's transparent and you can see them), so I elevated the master again and tapped the hose with a spanner to shock the bubbles loose, at which time they rose to the reservoir. Then I replaced the master and tested again, and when no bubbles reappeared in the hose, I decided I was done.|
There was certainly a difference in operation, in that the chronic "graunch" I was getting going into first was gone. Sadly, it's gradually come back. I don't see any bubbles in the hose, so maybe I need to do another bleed from below.
Anyway, that's how I bled my 1500, and it worked. At first, anyway.
|Definately check the MC, when i did mine last year I failed miserably as the old MC was just not good enough to rebuild and the new seals leaked. I gave up and bought a new MC and used ezibleed at higher than recomended pressure to basically blast any air frrm the sytem. At low pressure I still had bubbles in the flexi pipe as the fluid just flowed round them. At about 25psi they did not stand a chance! You do have to be quick though as at that pressure the ezibleed reservoir bottle empties really quickly. I seem too remember I also had the slave piston clamped closed to minimise any chance of trapping any air in there.|
Seems to have been ok since :-)
This thread was discussed between 16/11/2012 and 21/11/2012
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.