MG-Cars.info

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

Recommendations

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 - Woe is my clutch

So, after considering myself lucky that the broken clutch on my '64B occurred right in front of my house, I proceeded with the full replacement, including the flywheel ring gear while I was at it. The need for the replacement became clear once I had the engine and gearbox separated and found a large chunk of the center of the pressure plate had broken loose. So, no problem, I thought, as I have done this before. Of course, this time I was doing the replacement over several weeks due to work and other commitments, but I failed to grasp the significance of this factor. So, long story short, I finally got everything back together on the last sunny day here in Oregon, and looked forward to one last blast before the winter monsoons. The first thing that went wrong was apparently when I put the center of the oil filter conversion back on I failed to tighten it properly and I quickly pumped three quarts of oil out onto the garage floor. After cleaning this up and correcting the problem, I went through the usual convoluted clutch system bleeding, eventually getting the slave piston to move the clutch arm about 0.6". Unfortunately, despite all my best efforts, the clutch still will not disengage, and I am thus unable to shift into gear with the engine running. Obviously, this is a great disadvantage! So, is there maybe something obscure I may have missed in my haste to get things back together or am I faced with pulling the engine/gearbox again and having a look inside??
don scott

Don,
Does the clutch dissengage when the engine isn't running ?
I had a perminently engaged clutch after an engine swap...tried countless operations to free it ..eventually had to take it apart again and to my embarressment I had fitted the friction plate the wrong way round !
0.6 inch is about right.
Good luck

Dave G
Dave G

"broken clutch on my '64B occurred right in front of my house"

Mine waited until it got into the garage. I'd been feeling a vibration through the clutch pedal for a while when pushed fully down, so simply didn't push it that far down! Then when on a run about 60 miles from home it started to get worse, so I vowed not to use the clutch unless I really had to. I got the 60 miles home through junctions, traffic lights and roundabouts without having to use the clutch once, just 4th and OD 4th. I even reversed it into the garage without using the clutch. Then two tentative pushes on the pedal and the release bearing broke.

0.6" is about right (I usually 1/2" to 5/8"). By far the easiest way to bleed the clutch is to cross-connect the right front caliper and clutch slave bleed nipples (they should be the same size), open both, and use the brake pedal gently to bleed, or even fill, the clutch. If bleeding make sure you siphon some fluid out of the clutch master first, and make sure you keep an eye on the brake master and don't let it get too low. I've done this on two cars and it only takes a few minutes.
Paul Hunt 2

So, here is the update. I pulled the engine/gearbox again,(new personal record 2.5 hrs working alone) and found the friction disk was not perfectly centered, causing it to be bound by the pressure plate. Apparently I failed to appreciate the difference in the design of the new clutch assembly relative to the old, and didn't pay close enough attention. Okay, so it was back in with everything and everything seems to be working okay now in that I can again shift with the engine running. However (there always seems to be one of those!) when starting from a stop and beginning to engage the clutch there is a groaning sound coming from the clutch - it goes away when completely engaged and does not seem to affect the operation of the clutch. Is this normal or have I left one gremlin undiscovered??
don scott

What you found when taking it back apart sounds very odd. It is very hard to install the gearbox to the engine unless the disk is centered. After the clutch has been used onece the disk would center its self. Is the pilot bearing (bushing) in the rear of the crankshaft worn out or missing?
J Heisenfeldt

I agree with the above.
It is usually a pain to get the box to mate with the engine even when using a clutch centring tool.
It won’t go together unless they are perfectly aligned. At least that's what I have found.
Dave

D M Tetlow

Don. I have measured the travel of the push rod on four working cars. Average was .368" or just less than 3/8".

As the others have said, the engine and transmission should not have mated if the disc was not properly centered. The first motion shaft (input shaft) has to fit through the center hole of the clutch and into the pilot bushing. The pilot bushing's inner diameter is about .002"-.004" larger than the outer diameter of the input shaft. If the clutch plate is off, the input shaft will not mate into the pilot bushing. At least, now without damage.

Did you replace the oil seal on the first motion shaft, replace the gasket on the front plate and reset the shim pack? I normally do this with a clutch change. Surprising how often I find broken shims inside.

Did you replace the pilot bushing. Did the inner surface show signs of damage? I had a car that made similar sounds shortly after I had bought it. When I removed the transmission, the pilot bushing had been spinning in the crankshaft and the bushing could be removed with the fingers. Also found broken shims on the shim pack of the tranny.

Les
Les Bengtson

The groaning sound, I believe, is from the realization that the engine will have to come out again.

Wayne
Wayne Pearson

I agree with the comments provided, I thought it was odd that the box and the engine would go together if the disk was not centered. My supposition was based on the fact that I couldn't figure anything else out. I did notice when I separated the box and engine that the part of the pressure plate that the release bearing pushes against seemed to be not parallel to the engine back plate and flywheel, which seemed very odd to me. However, once I took things apart and very carefully reassembled them, everything looked fine. I didn't check or replace anything in the gearbox as it was a newly rebuilt overdrive unit. I did replace the flywheel ring gear, the clutch disk, pressure plate and release bearing. The other observation I didn't mention was that I was surprised I could hear the groaning over my quite loud exclamations of disappointment! I guess I will be going for a new engine removal record.
don scott

I just replaced the clutch in customers MGB and I could not get the gearbox to engage with the engine running. I have installed a lot of clutches so the chance of a misplaced part was remote. The clutch master was rebuilt and the slave a aftermarket replacement from Moss. I bled the clutch and everything looked fine but the clutch still would not work. I removed the slave cylinder from the transmission and removed the rubber boot from the end. using a C clamp to stop the piston from popping out I bled the system with the bleeder at the top with the slave hanging down. I found a pocket of air that I could not bleed out. The clutch is perfect now. If you look at the angle of the bleed screw when the slave is mounted you will see that it is at a 45 degree downward angle with a portion of the cylinder above the bleed screw. Make sure the clevis pin at the pedal and slave push rod are not worn.
Jim Pelletterie

Don,

If your going for that new record, while you're at it, I would replace that pilot bushing - regardless of apparent condition. Make sure you have the correct pilot bushing for the '64B. The later ones have a larger inside diameter, and there was a conversion pilot bushing made to put a four-synch box on a three-main engine. You might have gotten one of these by mistake.

I guess you got the disk with the right side forward at least the second time or it wouldn't have worked at all. What really makes me curious is the off-center position of the disk when you took it apart! As others have said, if you installed it off-center, and had you somehow gotten the engine and transmission mated that way, it would have righted itself either in mating or running. But how would it end up that way when you took it apart again?

FWIW,
Allen
Allen Bachelder

It isn't odd if the clutch plate is back to front!!
Chris at Octarine Services

I once encountered a clutch that would not disengage after everything had been replaced. After chasing down the usual suspects, I loosened all the bell housing to engine bolts and jacked the transmission up a fraction of an inch. Then I tried the clutch and it worked perfectly. After tightening all the bolts back up and removing the jack all was well. I assume that the the input shaft was dragging on the pilot bearing and raising the trans centered it.Ray
RAY

Based on everyone's comments it appears the latest problem is probably the pilot bushing,since that is the only part involved which I have not changed. I do know for sure that the clutch plate is in correctly, is centered, and the system is bled properly as the arm moves just over 0.5". None of my service manuals say anything about changing the pilot bushing, so what is involved, other than removing the engine/gearbox again?
don scott

You pull the old bushing with an internal puller on a slide hammer. You can also thread it with a tap and run a bolt in to push it out. Soak the new one in oil for a day before installling it.
John H

Another neat way that has worked for me all but one time: fill the cavity with grease, find an object of the same diameter as the opening (OK, slightly less) and pound it in with a BFH. I used a socket wrench on an extension. a suitably sized wood dowel will work. The hydraulic pressure forces the old pilot bushing out.
Allen Bachelder

Don. Tech article and photos of the process on my website at www.custompistols.com/. Article also appeared in MGB Driver if you save your old copies.

Les
Les Bengtson

Well, out of desperation and an unwillingness to pull the engine/gearbox yet again, I tried Ray's technique and as luck would have it, it appears to have worked! Today was a beautiful sunny day, rare for Oregon in November, and I took the B for an extended drive, following the winding country roads and enjoying the fall colors. It couldn't have been a better day. And the clutch stopped groaning as well - life is good again. So, I also tempted the jealousy thing again by painting some rear suspension parts for the TD! Thanks for all the advice and comments.

Don
don scott

Don, While you were enjoying a lovely ride in the country I had to leave my MG in the garage and split firewood for the winter months. Glad that the bizzare adjustment that I stumbled accross worked and saved you the hassle of pulling the engine/trans. Ray

RAY

This thread was discussed between 22/10/2007 and 06/11/2007

MG MGB Technical index

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