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MG MGB Technical - Weird clutch woes with new clutch

Steve and I renewed the whole clutch assembly in my MGB due to a faulty pressure plate. Now I can't barely get it into 1st and reverse grinds like crazy even if I set the gears first. This is a 4 synchro box with OD. I have never experienced anything like this in the 35 years I've owned the car. We also renewed the spigot bushing. So here's the story. We're both mystified.

New Clutch assembly - pressure plate, throw out, disk, spigot bushing

Checked disk on input shaft first by sliding it on splines no issues although I don't recall sliding it the entire length of the splines maybe just the front half. Spines looked fine. Disk was installed in proper direction.

Checked fork bushing and pin which I renewed 18K miles ago - still fine just greased it up. Put in new nylock nut and checked to make sure the fork moved freely.

New spigot bushing which had oil pushed through it - checked pilot bushing on shaft prior to install and used the proper tool to install it. Went in straight.
Greased input shaft lightly

On reassembly we had some alignment problems which we tapped the grearbox with a rubber mallet from behind. We had to reset the clutch disk and try again. Slid in further but the last inch or two required more tapping. This happened last time so I didn't think much of it.

After it was back in the car and the engine running first is very hard to get in. Reverse is just about impossible. It grind even If I set the gear. It grinds like I don't have the clutch in.

I checked the slave and its moving the pin full travel. I bled it just to see and while the peddle is slightly firmer there's no difference.

Through a week of driving with not much change I tried feathering or burnishing the clutch - no change. Holding the clutch in and reving it to maybe loosen a tight spigot bushing - no change.

More background --

Here are some interesting observations:

1. It was cold here (well for Cali) and it was much better going over to Steve's. Didn't grind as much and went into gear easier. Halfway through the canyon when it got hot it went back to its old bad ways. This gave me hope thinking metal expansion maybe alignment (loosening the bell housing bolts and shifting the tranny) would do it.

2. We had the car on jack on all points. After nothing helped alignment wise I later started the car again while it was on jacks and kept the clutch in and asked Steve if there was drag on the wheels. He could stop the rear wheels with one finger. I rev'd the engine while the clutch was in and he said there was a barely perceptible increase in drag but one finger kept the wheel from spinning.

I am really giving up. Is it the pilot bushing? Is it not too bad cold but when it heats up it binds? Or is it something else?

We noticed that the old one we removed which was only in the car for 18K miles looks like it spun in the crank once of twice. It was such a tight tolerance that it polished the input shaft. However, aside from the funky pressure plate I have no trouble getting it into gear.

IF its the pilot bushing will it wear into tolerance? Or will it eventually spin like the old one?

Further testing:

Here's what I believe can be discounted and why:

1. Hydraulics. The throw of the pushrod in the slave is fine. Its identical to 2 MGBs I've measured. I also rebuilt the slave.
2. Flywheel is fine even though it was surfaced several times. I bought a midget push rod for the slave which is .20" longer (although comparing it to the standard MGB one it looked longer than that). I put it in today thinking the xtra throw would hopefully solve it. NO change what-so-ever
3. Pilot bushing. As mentioned Steve could stop the wheel with one finger when the clutch was in and even when I raised the RPMs with the clutch in. When I'm on just the slightest grade and I have the clutch in the car will roll forward or backwards depending on the grade.
4. TO bearing. I did measure the new one against the old one and they were identical.

So that means its something in the clutch/pressure plate assembly. Without simply buying a new set and replacing this one I have no idea what we will see. We would have to take it to a clutch shop and see if they can find something. Its a Borg and Beck by the way.

Steve said he doesn't know how much drag can still affect the synchro in first and reverse. Meaning maybe a little.
GMA Alpern

Can you start the car in gear or does it try to drive the car? If its that bad it drives the car the clutch plate may be in backwards. On the other hand if it is just hard to get into gear you may have a slight warp in the plate due to miss alignment at assembly. There is a procedure that can help here, it sounds drastic but it usually works. Start the car in "top gear" then with the brakes on rev the engine hard and drop the clutch. Do this a number of times and then test your result. Dont do it so much as to "cook" the clutch, Maybe half a dozen times then test.
Denis
Denis4

Are you saying that there is no clutch drag (observation 2)? Then the clutch must be releasing properly - which would suggest that your gear selection problems are not clutch related...?

Does it go into gear with the engine stopped? If so then that would suggest that the problem IS clutch related?

Can you explain 'alignment problems' in a bit more detail?

N
Neil22

Clutch disc is in the proper way.

Car goes into gear easily and normally with the engine stopped.

If there is drag it is ever so slight. One finger can stop the rear wheel on jack stands with clutch in and reving the engine with clutch in creates an ever so slight more drag. In talking to an old BMC mechanic he said there should be zero drag with the clutch in and in gear.

Denis4 - he also recommended trying this and while its severe I might as well give it a try. If nothing works I'm pulling the clutch again anyway. I have been slipping the clutch in at times trying to burnish it with no luck.
GMA Alpern

Give it a try as it sounds like a small clutch center warp. Drop the clutch fast, its no harder on the clutch than a hard power takeoff and it does work. Let it stall or almost stall the engine. Remember Top Gear, brakes on. Check after the first few and if necessary try a few more. It works more often than not.
Denis
Denis4

"Now I can't barely get it into 1st and reverse grinds like crazy "

Surely clutch drag. If there is enough drag to turn a rear wheel even slightly, with clutch fully down and engine revving, given the friction of the gearbox and rear axle, then there is going to be more than enough drag to cause baulking and grinding. The drive to the gearbox should be *completely* disconnected and the gearbox first motion shaft and clutch friction plate stationary when the clutch pedal is fully down.

Are you sure you got the friction plate the right way round? Did you lubricate the splines (shaft and friction plate) as well as spigot bearing and release bearing pivots with the grease that should be part of the clutch kit?

You say you have full pin travel but don't say what this is, in my experience it should be about 1/2".
Causes of insufficient travel are air in the hydraulics and wear at the pedal to master pivot. You may say that you didn't open the hydraulics to let air in, but when you remove the engine you allow the spring in the slave to push the piston fully out. In theory this simply sucks more fluid down from the reservoir to fill the space, but it could just as easily have sucked in air from the slave boot especially if the slave seal is resting on a rough, rusty previously unused surface when fully extended. Been there, done that.
Paul Hunt

Friction plate in correctly - 100%

1/2" throw. Same as 2 other perfectly working MGBs I compared it to.

The only thing I haven't tried is dumping the clutch fast which I will do.

I have tried slipping the clutch half dozen times and holding the clutch peddle in and revving it a dozen times.
GMA Alpern

hi,you said you have renewed the spigot bush,i had the same problem as you,bit of a job to get 1st and reverse, i removed the bush and fitted a new one again ,all was fine hope this helps.
da wright

A new clutch takes more travel than a good used one, because the friction facings have nubbles and the disc cushion springs are at max spring. Engagement is normally close to the floor for a hew clutch. Assuming there is no air in the system, one common cause of this problem is carpet padding or carpet wadded up under the pedal. Another is the aforementioned wear in the MC pushrod/pedal clevis. There should be just perceptible free play at the pedal - more than 1/4" indicates significant clevis wear, 1/8" or less is more like new. The slave cylinder and pushrod are self adjusting, and should not be messed with, assuming there is no obvious major wear, to the point where the piston comes up against the circlip. Longer pushrod will just give trouble later in the clutch life, when it will cause premature failure from slipping. As others have said, if you can stop the rear wheels by hand with the engine running in gear, the drag is not much, but it is the cause of the problem.
After you check and sort the preceding, drive it; start it in gear if you have to, but taking it apart again won't fix it unless you managed to bend the disc with your "some alignment problems".

FRM
FR Millmore

New clutch master 18K again. No leaking.

Clevis pins all renewed - aircraft quality

No bunching of carpet.

I posted somewhere else too and it seems half the people are divided between spigot bushing too tight and friction plate issues.
GMA Alpern

"Clevis pins all renewed - aircraft quality"
Doesn't matter, what's the free pedal movement, and the movement after it contacts the MC piston and before it hits real pressure against the pressure plate? Check with your hand on the pedal.

FRM
FR Millmore

Proper clearance and I also had the hole in the peddle that accepts the clevis pin which had elongated welded and re-drilled.

Its not the hydraulics.
GMA Alpern

Hi - just a thought (everyone else seems to have covered all my other musings!) - did you check the actual' throw' of the new release bearing against the old part? (i.e place both on a flat surface and use a steel edge - that caught me out once, only a couple of mm but enough to cause problems).
Best of luck with it!
Regards
Andy
A S Duff

Throw of the release bearing? These are designed to wear down getting on for an inch before failure, the design of the hydraulic system takes up all this variation and more to give a relatively constant biting point at the pedal.

Try starting it in gear with the clutch pedal fully down, handbrake off. If the starter is trying to crank the car forwards then for whatever reason the clutch doesn't sound to be disengaging at all. If the car is only easing forwards very slightly if at all, try easing the clutch pedal up vey slowly. If the car immediately starts moving forwards more strongly, then the clutch isn't *fully* disengaging, i.e. could be warped friction plate or faulty cover plate. If you can ease the pedal up an inch or so before it starts moving forwards more strongly, i.e. around the usual biting point, then it sounds like pilot bearing dragging on the first motion shaft.
Paul Hunt

Paul - I was trying to be helpful and share my experiences - this I stand by - how on earth it could wear down by an inch is beyond me - there's only a 1/4 inch of material in the first place
Regards
A
A S Duff

I plan to pull the lump this weekend. I'll let everyone know what I find.
GMA Alpern

You are certainly a glutton for punishment!
What were the results of Paul's suggested tests? Or mine?
Paul, Denis, and I are suggesting this is probably a minor break-in problem, based on your description.
What do you expect to find and how are you going to test it?

"We noticed that the old one we removed ...looks like it spun in the crank once of twice."
>>Happens all the time; I've taken many out that were free in the crank and on the shaft - no problems.

"It was such a tight tolerance that it polished the input shaft"
>>The shaft should always be polished.

"Halfway through the canyon when it got hot it went back to its old bad ways."
>>This pretty well tells you that the drag from the cold gearbox oil is sufficient to overcome the clutch drag.

The bush is not so tight that it won't bed in, and/or the nubbles on the disc will wear in. A few days of driving will almost certainly fix it, assuming you drive where you need to shift. Don't know where you are, but a good ride through San Francisco city streets ought to do.

FRM
FR Millmore

A S, we are all trying to be helpful. I didn't and still don't understand the reference to 'throw of the bearing' nor 1mm. OK, my guess of the thickness of the carbon ring on an MGB release bearing was a little OTT but it is still 5/8" which is closer to an inch than 1mm and a lot more than 1/4". All of that is available for wear as long as the carrier remains co-axial with the cover plate as it should.
Paul Hunt

Pull it out if you must but you may not find anything visible and end up with the same problem after a couple of days of work later. The clutch dump method just helps align the integrity of the plate a few thou. and usually works. This problem does not happen with people that do this for a living but now and again with home mechanics, who may have a bit more trouble getting the G/box in.
Denis
Denis4

I really do NOT want to pull it. I put about 200 miles of city driving on it and it remains the same.

I have tried everything mentioned here. Believe me I wish it had worked.

I will be pulling the engine at a British Mechanic's home. Hopefully his trained eyes will be able to spot anything not right.
GMA Alpern

The clue is in your statement that you had to tap the box to get it to mate - it should just slide together without force.

So either you have burrs on the clutch spline - unlikely - or the spigot bearing was damaged on insertion, made of sintered bronze, these will distort if hit with a hammer to fit.

There is obviously drag with the clutch depressed, that it is enough to turn the wheels indicates it is pretty severe drag.
Chris at Octarine Services

GMA,

You said:
We had the car on jack on all points. After nothing helped alignment wise I later started the car again while it was on jacks and kept the clutch in and asked Steve if there was drag on the wheels. He could stop the rear wheels with one finger.

When you did that, were both rear wheels up in the air? If so, didn't you just check that your differential was working rather than test the clutch drag? You would have to lock the opposite side wheel for this to tell you anything about the clutch.

Charley
C R Huff

"There is obviously drag with the clutch depressed, that it is enough to turn the wheels indicates it is pretty severe drag. "

Without a doubt. With the clutch fully and properly released the gear shafts should stop turning when it is out of gear, let along when you have the additional drag of being in gear, an OD, diff and everything else on the axle.
Paul Hunt

Just got back from a very long day.

The good news is trans slides perfectly and easily into gear and reverse has so grind even without setting the gears.

The bad news is it was a warped clutch disk. A British Mechanic who let me do the work at his place (he's been working on Brit cars since the 60's). When we took apart the clutch assembly he showed me the clutch disk was was wearing on the outside edge on one side and on the inside edge on the other. His conclusion is the clutch disk was warped. He's well aware of how we put it together and said there is no way we could've warped the disk because its locked in place. The disk was always on the splines of the input shaft. There was nothing wrong with the pilot bushing. Plenty of clearance there.
GMA Alpern

Gary-

"On reassembly we had some alignment problems which we tapped the grearbox with a rubber mallet from behind. We had to reset the clutch disk and try again. Slid in further but the last inch or two required more tapping."

"unless you managed to bend the disc with your "some alignment problems"."

"The disk was always on the splines of the input shaft."

Of course it was, that's how you bent it. The pilot was not in the bush, >>"last inch or two"<< and the several feet/hundred pounds of gearbox was acting as a lever on the driven plate hub. And I'd like to see this "tapping with a rubber mallet."
I'd also like to know exactly what you were doing to elicit this: "After nothing helped alignment wise ", since once engine and gearbox are bolted together there is nothing you can do. I have pictures of all the bolts being out in the car, again with the box hanging on the clutch hub.

People do get away with this stuff most of the time; your bad luck is that you had bad luck as well as bad practice. And a crappy alignment tool, and a bad eye.
BTW,a common error is to bolt the clutch down with the tool in place, thinking that that will align things correctly. The disc will move laterally when being bolted down, especially if care is not taken to get the cover aligned correctly first, and then tightened evenly and progressively. If the tool does not come out (and back in) freely, with the least possible grip from oiled little fingers, then it's not aligned correctly. Slop in the tool that is more than the actual shaft will finish you off. I've not used one of the plastic wonders they sell you today, but the few I've tried for fit did not impress greatly.

I have put clutches in with no tool but my eye, which is too nervous-making, wooden dowels wrapped with tape, old bolts, assembled gauges of assorted shaft collars and the like, purpose made mandrels, and used first motion shafts. Can't recall ever having to reset a disc, once I realized that it can and does move as you are tightening it down, and the final check, whether by eye or feel, must be done with the cover tight.

Anyway, glad you are mobile again! At least you actually found the problem.

FRM
FR Millmore

Thanks FRM for your clear assessment - I love your posts!

I had a problem assembling the gearbox to the engine on my TR6 - it just wouldn't slide in the last inch or so. Having bolted the clutch to the flywheel with the tool in place, I refused to accept for the longest time that the clutch plate could be out of alignment. A more experienced friend assured me that this could be the only problem preventing final insertion and, sure enough, loosening the clutch and resetting the tool so that it slid in-and-out with minimal drag solved the problem.

If you wonder why I am on this board, I previously owned a 73 MGB and just love the activilty and knowledge available here. Much of the advice is transferable to all British cars of similar vintage.

Best regards and commiserations to all those other owners who have put their car away already. After a glorious weekend, the forecast is for sun and 18C today!

Barry
BJ Quartermaine

I used the plastic tool and found it fitted the splines extremely closely, so needed to be gripped more than lightly oiled fingers (or should that be oiled little fingers?) would allow. Slightly concerned initially that it wasn't going to come out, but a good pull on the finger ring at the end did so. At least I had confidence that alignment was good, and the two pushed together without any difficulty at all. Before the final push I checked that the gap between back-plate and bell-housing was the same all the way round i.e. the two were square to each other, as well as the bolt-holes being aligned i.e. correct height and sideways alignment.

Subsequently a pal had terrible problems getting his two together, even with the gearbox jacked right up the front of the engine wouldn't go down far enough to get it square as well as at the right height because the pulley was resting on the steering rack. Eventually it went together with a good shove, but now he has got it on the road he is having similar problems to this, but intermittent. Sometimes the gears baulk/grind, sometimes they are as smooth as silk. At the moment I'm hoping it is an iffy master seal from being dry for some time.
Paul Hunt

I need to address some things. When we did it the first time we never, ever let the tranny hang. If it didn't go in we pulled it out.

We did check the alignment and did it as you mentioned. We tightened each bolt a little at a time while holding onto the plastic alignment tool checking alignment all along the way. It easily slide in and out with the lightest pressure.

If it didn't go in we'd pull it back out. The whole tapping issue was simply because there was a packing blanket that got wedged in the bottom. Once discovered and pulled over it slide in.

The 'last inch or two' was in error. After doing this again the bolts aren't even long enough for an extra half inch. So we're talking about 1/4". We just didn't have the lateral pressure like we did yesterday.

Each time we pulled the tanny back out and did our best to support it do it was alway level and there was no undue torque vertical pressure.
GMA Alpern

Hear, hear FRM !

The alignment of the driven plate has to be spot on to ensure that satisfying clunk as engine slides into place.

There is only a few thou (never actually measured it) clearance between a new spigot and the shaft so the driven plate has to be within a few thou too.

The plastic tools are pathetic, eyeing up the concentric circles of throwout ring, splines and spigot is at least as accurate! Yes - both do work but more by luck than judgement.

I use old input shafts and hang the driven plate on them while half tightening the cover bolts - then tapping the end of the shaft sideways until the shaft slides in & out freely before final tightening and rechecking.
Chris at Octarine Services

This thread was discussed between 31/10/2009 and 11/11/2009

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