MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - repeated Clutch failures on my 1966 MGB

Hi,

Need some help. I've had my MGB for close to 14 years now, and I drive it daily.

I've recently developed clutch problems that have been persistent even after replacing the pressure plate, the clutch disc and the release bearings.

The original failure was due to wear and tear (after a great many years). As there was also some body rust and some other problems, I decided on a minor overhaul.

The new clutch kit (Borg and Beck) lasted about 3 weeks. My mechanic then replaced it but with similar results. I then got another kit (also Borg and Beck) from a different source (including clutch lever and hose), but the result has been the same (although this time it lasted about 3 months).

The basic problem is that after a while some of the gears become stiff and over a short period, it will be impossible to shift to the gears in question.

My guess is that my mechanic is doing something wrong - possibly with the alignments.

Does anyone have any idea what could be wrong?

Rgds
sudhir menon

Sudhir. Please be so kind as to define what portion of the clutch system is failing. Is it the throwout bearing? Is it the clutch plate (driven plate)? Or, is it the pressure plate that is failing? Or, is the clutch system perfectly OK and the basic problem is with the clutch hydraulic system?

"The basic problem is that after a while some of the gears become stiff and over a short period, it will be impossible to shift to the gears in question."

This information sounds like a hydraulic system failure, not a clutch system failure.

More information is needed to provide an adequate, i.e.better than your professional mechanic can provide, diagnosis.

Les
Les Bengtson

In all three cases, the clutch plate and the bearings were the items getting damaged. I thought that it was a hydraulic problem but the clutch pumps have been replaced, and they still seem to be fine.

At one point I found that double clutching seemed to be help with the changing of the gears - when it got hard to change - but it didn't work for long.

I still have a sneaking suspicion that it may be the hydraulics. But just not sure where to look.

Thanks Les - any help is appreciated.
sudhir menon

What sort of damage are we talking about?
Dave O'Neill 2

"after a while some of the gears become stiff "

Are you sure this is even a clutch problem? If the clutch is failing to release you will get grinding in reverse. If you aren't getting that, and it's just that there is a physical resistance to the lever moving far enough to fully engage a gear, then it's more like a gear selection problem.

Having said that my son's mechanic put four new clutches on his BMW before he realised there was a batch problem with the clutches.

Is your mechanic removing just the engine or the engine and gearbox together?
Paul Hunt

I had a similar problem after replacing the clutch in my '67 B. It turned out to be a dragging transmission input shaft that was due to engine to transmission alignment. The cure was to loosen all of the engine to transmission bolts, by a single turn, and jacking up the transmission just a little bit. I then got into the car, started the engine and shifted the transmission through the gears. It still showed difficulty engaging with ease, so I jacked up the transmission a bit more. I checked the shift action a second time and everything worked perfectly. I proceeded to tighten all of the engine to transmission bolts, removed the jack and have been driving the car for twenty one years with no further trouble. I hope that the solution to your problem is as easy to fix as mine was. Unusual, but not unheard of. RAY
rjm RAY

To Paul's question - every time it has happened, the engine has been removed to replace the clutch.

It would then work well for about 2-3 weeks, before it would start getting a grinding noise when trying to engage the reverse gear, and the 1st, 2nd or 3rd gears (or a combination).

The last time it was replaced, it actually worked well for about 3 months, before the same symptoms started to surface.

My mechanic says he didn't do anything differently the last time.

All of the above could be a result of what rjm RAY describes.

I am trying to get photos of the damaged parts. Will upload them as soon as I get it.

Thanks all.
Sudhir
sudhir menon

Please provide a photo of the clutch plate and thrust bearing after they have deemed to fail. What is their thickness inrelation to the replacement parts. Giving skimpy info makes remote analysis very difficult!
Mike
Mike Ellsmore

If you have grinding then the clutch *is* dragging, either due to mechanical problems inside the bell-housing (bent first motion shaft on first removal or reassembly?) or hydraulic. For the hydraulics measure the travel of the slave push-rod when the pedal is operated and released through its full travel. It's generally about 1/2" to 5/8".

Were any of the clutch hydraulics replaced with the clutches at any time? The disturbance can push a slave over the edge, we had problems keeping the slave bled after replacing the clutch, which needed replacement, even though it hadn't caused a problem before. When you disconnect the slave from the release arm the spring inside the slave pushes the piston and seal out further than it has been used to, i.e. onto surfaces that are probably rusty.
Paul Hunt

I'm sorry for the length of time it's taken to get a pic - I have a video that I can't seem to convert to JPEG.

The current issue is that the clutch cover is loose. There does not seem to be any other damage.



sudhir menon

I take it the friction plate has been installed correctly each time, it does only go on one way round. This has been mentioned occasionally in the past. Having said that the last time I replaced one I had a look at what would happen if you tried to install it the wrong way, and it was blindingly obvious in that the friction plate wasn't even touching the flywheel, as in the attached.

There is also the question of incorrect parts, as well as batch faults if they are obtained from the same source each time.

Paul Hunt

I would suspect the pilot bushing. If it's worn the the clutch disc will wobble to find itself.
I had a 1954 TF and was 400 miles from home when I had a terrible vibration each time I shifted. I found the I would just pop the clutch rapidly eventually it would centralize itself until I had to change gears.
Upon getting home I found the disc had started to seperate from it's center and the pilot bushing was toast.
I don't know which came first.
Sandy
3:0:5^110:0:5^127:0:2

Another possibility is oil getting onto the friction surface. Not much, but this makes the driven plate stick to either the flywheel or the pressure plate, causing difficulty in shifting.

Herb
Herb Adler

Thanks all.

To Sandy's question: I did have a vibration on the clutch pedal every time I depressed the clutch - it was noticeable. Is pilot bushing the same as the release bearing?

To Paul's question:
To date, I've been getting the Borg and Beck Clutch Kit (albeit from different sources). I do want to try a different make just to eliminate the possibility of a faulty batch.

The Quniton-Hazel used to be available before, but does not seem to be available now from Moss (or anywhere on the internet).

There is also a heavy duty/competition version from Borg & Beck which I haven't tried.

Can anyone recommend any? preferably with a website to buy from.

sudhir menon

The pilot bushing is embedded in the end of the crankshaft.It stabilizes the front end of the primary input shaft of the transmission. The release bearing is the two eared unit that pivots and presses on the pressure plate to release the clutch disc while shifting.
Sandy
3:0:5^110:0:5^127:0:2

Ordinarily I'd say Borg & Beck rather than QH.

We still don't know exactly what damage is being sustained over such a short time. I can understand a worn pilot bearing causing vibration, but the friction disc should be a snug fit on the first motion shaft irrespective of that. I can imagine separation causing drag as the clearance when the pedal is operated is pretty small.
Paul Hunt

Has anyone had any experience with the Powertune Clutch Kits? Its aftermarket I think, and available from Moss.

Thanks
sudhir menon

I understand that QH have gone out of business, and that any QH stock arround is residual.
Whilst no clutch brands are ever without fault, I have found that the Borg & Beck failure rate is well lower than anything else.

Some photos would definitely help. There is always the possibility of the release bearing being the type where the carbon is retained by a pin rather than a proper shrink fit. These invariably result in premature failure and at one stage notwithstanding my comments above the Borg & Beck kits had this type of bearing. I could be that some of these are still in circulation.
Paul Walbran

I am attaching a couple of pics for you from the 1st Borg and Beck clutch kit that I bought. The video I wanted to send is from the 3rd clutch kit that I bought (also B&B).

photo1.jpg is the clutch disc. The part in the middle (where my fingers are on) is loose . This is also the case with the 3rd clutch kit (and is what the video shows). I understand from the mechanic that it is not supposed to be loose.

Photo2 shows the same clutch disc with a flat indentation on the part that is loose (the blue arrow marks it). There are 3 of these on that loose component. Is this meant to be the case? Thanks


sudhir menon

Cant upload 2 at the same time. Here's the other one

sudhir menon

Paul (and others),
Q&H have been back in business for a while now but I'm not sure if they still cover the full range they used to - http://www.qh.com/
Nigel Atkins

The three flats are standard, see attached.

Paul Hunt

I can't remember (and I broke the habit of a life-time and didn't keep the old one) how that piece attaches to the diaphragm springs, but I would expect some movement to be possible because as it is pushed in and out by the release bearing the position of the spring fingers will change slightly with respect to the central part as well as each other. I can imagine that the ends of the fingers just sit in a groove going all the way round the edge of the central part. Difficult I know but given the repeated failures I'd by trying to set up a dummy bell-housing so I could operate the clutch and see just what was happening.

Something has been running on the some of the fingers just outside the central part, what might that be? Any witness marks on the release arm? What is the pivot bolt and bearings like for the arm?

Paul Hunt

In my opinion, you have a misalignment issue between the engine and the transmission. Until this problem is rectified, the car will continue to eat up clutches. I have a heavy duty Borg and Beck clutch in my supercharged '67 B. I use the roller bearing that came with the kit. It's been in constant service since '93 and never given me any trouble at all. RAY
rjm RAY

This thread was discussed between 06/11/2014 and 15/11/2014

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now