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MG MGA - Clutch problems

I wanted to drive last night, and got in the car in the garage to find out that the clutch was not working... it was absolutely fine last week

So a quick fiddle and a MAJOR adjustment of the rod at the MC got it working.

Tonight I thought I'd look a bit closer.

The slack at the pedal was too much, but the adjustment at the rod was pretty much used up on the clutch side. This is a Caparo MC that is about six years old and to date has shown no problems at all. Clutch (MGB type with all the correct bits to go with five speed in an MGA) is new (about 2000km). When I switched the engine about 100km ago, everything in the clutch looked just fine. Slave is about five years old, and is the original type aluminium body with a steel piston. I haven't looked under the car yet as I was still in nice clothes.

So I tried a bodge, and threw a bearing ball into the MC piston to space out each of the rod a bit more on the adjustment. I have adjusted the rod to allow a little free play on the clevis pin/fork at rest.

I can't engage a gear, and after starting the car in gear, even with the clutch pedal full to the floor, the car is moving slowly.

No signs of leaks, pedal pressure is firm, pumping the pedal has no effect, MC is full.

So the question:

What am I missing?
dominic clancy

Cracked/bent release bearing fork?
Neil MG

Neil might be on the right track. The release bearing fork on my Type 9 wore its bush very quickly because of too big a gap between it and its pivot bracket. The release bearing ran badly off centre, causing bad vibrations on gear changes. If I had not caught it when I did I think greater damage would have quickly followed.

Steve.
Steve Gyles

stumped. I tried again this morning and everything is working as it should....

dominic clancy

Weird. Unusual for you to be stumped Dominic. Sounds possibly like air might have got into the system and it bled itself after standing over night. But this would seem unlikely if the car had been standing for a few days, having been running ok prior to that.

Steve
Steve Gyles

Dominic
I used to have this exact same problem with my Elan
The piston in the master cylinder wouldn't fully return sometimes and would leave me with a floppy pedal with heaps of clearance and a clutch that wouldn't clear
It would only happen randomly and if I sat in there and gave it about 20-30 quick full pumps it would come right and stay right till the next time a week or three later
Reco'd the m/cyl and haven't had an issue since

I'm thinking, now that yours is working you need to get rid of that ball, make sure your m/cyl is returning right back and readjust the pushrod --and probably a kit in the m/cyl soon ????

My theory is--no proof mind you, is that--
Sometimes changing brands of brakefluid causes the cups to slowly swell and cause problems like this

cheers
willy
William Revit

I have not changed the fluid type or manufacturer since I restored the car in 1988. This morning I have driven 20km through the city with no problems at all, so I'm going to leave it as it is for now.

But thanks for the various comments
dominic clancy

Steve,
I have just had my clutch release bearing fail on my car with a type 9 box ,it has completley worn down in about 1200 miles,can you explain in more detail,perhaps with a photo or a drawing of what the problem is.I have had no problem on the conversion that I did on my 1959 1500 several years ago it has now coverd 12,000 miles

Regards

David Speak
D M SPEAK

David

Picture attached. You can make out the off centre marks on the thrust bearing.

Excessively fast wear could also be caused by other factors including riding the clutch (foot resting on the pedal during normal driving); or no slack in the clutch operating rod in the MC.

Steve

Steve Gyles

Steve,
Thanks for the photos mine has also worn enevenly and als has a crack in the casting from the rim to the round fixing pin ,it is not due to foot resting on the pedal or lack of slack in the operating rod .Was wondering if it could be the master cylinder piston not returning fully as I have had problems with the brakes sticking on as well and was wondering if the seals have swolen as I am using silicon fluid.On my 1500 I had to have 30th machined off the piston so the the bleed hole in the piston could operate

David
D M SPEAK

David

If you have been reading the threads on this BBS over the last few months you will have seen that I had disc brake slow release issues for a number of years. I always thought it was the MC, perhaps even fluid or seal issues, but it turned out to be poorly manufactured calipers (lip seals damaged during assembly).

I have an (unproven) suspicion that the constantly binding brakes on my car caused the fluid to overheat, degrading the seals over a period of time. The heat would also evaporate any water in the system resulting in the soft brake/clutch pedal operation I experienced from time to time. Left overnight the system would bleed itself and return to normal feel at the pedal.

What I am trying to say is that the item that fails is not always the cause of the problem, just one of the symptoms.

Steve
Steve Gyles

Steve,

I am interested in your release bearing problem as I have had something similar on my ZB Magnette with T9 box and MGB 3-main engine and clutch. It started with a pulsation in the clutch pedal, and to cut a long story, when I removed the engine to investigate I found a misaligned bearing fork and odd wear marks on the clutch pressure plate (see images).

At the time, I spoke to Peter Gamble and he told me he had problems with some pivot brackets that were inaccurately cross-drilled. He replaced the bracket and the bearing fork and this largely corrected the pulsation.



Andrew Dear

Second image shows the odd marks on the clutch pressure ring but the carbon thrust has symmetrical markings. Suggests the pressure ring is not flat.

I now have quite a bad clutch squeal but am not sure if it is the clutch withdrawal bearing or the spigot bush. Now I wish I had replaced the clutch when I had the engine out, but it was almost new.

Andrew Dear

Andrew

I had one of the early pivot brackets (2000). In my photo above I noted that the locknut had apparently loosened a bit. In fact I think the real problem was the bracket gap was slightly too wide for the fork, allowing some lateral fork movement which accelerated the bush wear. I spun a new bush in the lathe, then, if my memory serves me right, put a couple of very thin shims either side of the fork, then torqued up the bolt enough to make the fork a light interference fit. It's been fine for the last 10 years.

I guess that distorted fork accounted for the edges being taking off the bearing.

Steve
Steve Gyles

Steve,

Actually the edges of the carbon bearing are fine, it looks a bit odd in the picture but that is just finger prints etc from handling. The carbon face was totally perfect.

The pressure ring on the other hand is clearly not flat as the wear marks do not form a complete circle. I suppose this may be the cause of the chirruping noise I get when engaging the clutch although it has been suggested that this is a problem with the flywheel spigot bush. I have been trying to think of a way to determine which it might be before removing the engine again.

Andrew Dear

This thread was discussed between 12/06/2015 and 15/06/2015

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