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MG MGB Technical - Clutch pedal

First off, thanks for all the help & advise I received from you guys with the previous problem on my 74 BGT. After doing some checks on the distributor, I bought Points, Condensor & Low tention lead. Changed the Condensor & Low tention lead, BGT now starts in One with the help of the choke.I believe the problem was the low tention lead. Also changed the color to Black Tulip, superb. Thanks again for all the Help.
The problem I have with my 69 Roadster, the clutch pedal is very soft and it vibrates when I disengauge the clutch. Gear change is not as smooth either & the bite is very low. Some months ago I had to change the clutch release bearing as the lining went to pieces. I also bought a new Clutch master cylinder & Slave cylinder at the time of changing the release bearing. Fitted both, bled the system and could not get any gears at all. Put the old slave cylinder back on and was able to get gears, but the bite point is very low. Bled the system until no bubbles is seen in the fluid, but the problems still remain. I cannot see any leaks & I don't have to top up the fluid. Any help or suggestion would be greatly appreciated.

Many Thanks

G Thompson

It sounds to me that you have two seperate problems. One, did you replace the clutch assembly when you replaced the throwout bearing? If not, you are experiencing what is called a fierce clutch. This results from oil building up on the disc coming from the rear main seal of the engine or the front seal of the transmission input shaft. The remedy is to replace the clutch and repair the leaks. Secondly, the spongy clutch pedal would indicate some remaining air in clutch hydrolics. Remove the slave cylinder from the transmission, hold the slave piston firmily in the base of the cylinder with a "C" clamp, and bleed the system making sure that the bleed screw is in the highest position relative to the slave cylinder. This should remove the remaining air in the system. Ray

Thanks Ray, I knew it would involve removing the engine again. I did not change the clutch as it was still in good condition. I had not done alot of mileage since it was changed about 2 years ago. If there was any play on the first motion shaft, what effect would that have?


G Thompson


If it were my car, I would certainly sort out the hydraulics and see what happens before pulling the engine again. What Ray suggest sounds pretty effective, and there are several other techniques that may work too.

I would have to get out a book to check shaft numbers because I don't rebuild transmissions very often. I think in terms of input shaft, main shaft, and counter shaft (or lay shaft), but that may be because I'm in the U.S.

However, if you didn't take the transmission apart, I am guessing that you mean the shaft that the clutch plate rides on (what I would call an input shaft). If that is the one that had the play, do you mean up-down and side-to-side play rather than end play?

It would be normal to have some up-down play because, when the transmission is out of the car, there is only a bearing on one end of the shaft. The other end is supported by the pilot (spigot) bearing in the end of the engine crankshaft. Of course you could have too much play, and that would not be normal.

C R Huff

The clutch is a pig to bleed because of the long vertiacl section of pipe with the U-bend at the top. Conventional bleeding requires that any air in the pipe must be pushed all the way down the relatively large-bore pipe before it can exit the slave nipple - difficult enough with a continuous pressure bleeder conencted to the master, nigh-on impossible with the pedal. Having heard of others problems, when I replaced the master, slave and flex pipe I opted to fill the system using reverse-bleeding, by connecting an EeziBleed on very low pressure to the slave nipple, watching the empty master until I could see the fluid level rising, then topping-off as normal. Since then, and on a bleed rather than a fill, I used a tip I came across subsequently which was to interconnect the right brake caliper and clutch slave nipples (they are the same size), open both, and press the brake pedal gently to reverse-bleed the clutch, removing some fluid from the clutch master beforehand to prevent over flows. This was even easier than using the EeziBleed, and in both cases I got the full travel of 1/2" to 5/8" of the clutch slave push-rod without further ado.

Spongy brakes is one thing, but isn't applicable to the clutch as the pedal is supposed to go to the floor anyway and with little change in pressure for most of the travel. Another cause of low biting point is wear in the master linkages of push-rod, pedal and clevis pin. I reckoned I was losing 1" of travel at the pedal, and sorting that made a noticeable difference. Note that wear in the mechanical linkages at the slave end is *not* an issue as the design of the hydraulics compensates for this. If the biting point is very low this will also make gears difficult to engage as the clutch isn't fully disengaged. In this case you will get grinding when selecting reverse. No grinding when selecting reverse usually means problems with the gearbox or selector mechanicals.

A fierce clutch means it is snatching with very little slip. This is different to a low biting point, and can be caused by oil contamination of the friction plate, i.e. a leaking rear crankshaft seal. This is usually revealed as oil dripping out of the hole at the bottom of the bell-housing, which should contain a split-pin to keep it open. Note that a leaking gearbox front seal will also leak out of here, but is less likely to contaminate the friction plate.

If you feel vibration when the pedal is *fully* depressed this can mean the release bearing is rubbing on the cover plate, and will eventually wear through and break (BT, DT). Vibration *as* you operate the pedal could be rough surfcaces on the linkages at the master or slave. Vibration when the pedal is partially pressed and held in a fixed location could be problems with the flywheel, cover-plate and friction plate surfaces, or the pilot bearing (in the end of the crankshaft) or the input shaft to the gearbox that fits in the pilot bearing. Judder as it takes up the drive is something else again, but can also be caused by these components.
Paul Hunt 2

I recently went through exactly what you describe about your clutch pedal on my 73 roadster, Glenroy. I had a leak in my slave (which was only 2 yrs old) which I replaced. I could not get the system to bleed no matter which of the above methods I tried. In desperation, I pulled the guts out of my master cylinder, and found the internal spring to be broken right at the halfway point. The front half of the spring had wound itself into the rear half, creating a spring with twice the compression rate, but half the travel. I replaced that, bled the system in 30 seconds with my Eezibleed pressurizing the master cylinder, and have had a perfect clutch ever since. Now that its working properly, I can tell that it hadn't been fully right for a long time, and that the two half springs worked their way into themselves over a period of time to make the change in the clutch gradual.
I offer this in case yours turns out to be the same problem. I was able to rebuild the master without removing it from the car (attaching the lines is a major PITA).

Hopefully the vibration when engaging the clutch is not serious, but it would seem to me unrelated to hydraulic issues.


Erick Vesterback

Thanks guys, I haven't been able to do any work on the car this weekend and won't be able top next weekend. But I will let you know how I get on, thanks for the advise. Paul that technique using the brakes to bleed the clutch is very impressive. I am going to have to try it for myself. Thanks
G Thompson

I unfortunately had a premature failure of a fairly new throwout bearing that behaved much like what you describe. Clutch hydraulics don't cause vibrations like that. Check also that your clutch fork isn't wobbling excessively on its pivot bolt.
Sam Good

Thanks Sam, I will have to make a thorough investigation of the hydraulics and mechanics of the clutch system. I won't get any time over the weekend and maybe next weekend as well, but I have to get this sorted. My other everyday car has given up on me and I would be throwing money away getting it fixed. Plus a new addition to the family(the dog) is going to be taking up my time at weekends.
Will be back with my results of the what ever I do, I will try and keep the forum going so I can do this. Any other suggestion or hints will be appreciated.

G Thompson

Hi guys, just to update you. My mg was stolen from outside my Flat between Thursday 6th march 2008 & Sunday 9th March 2008. Its a 1969 mgb roadster in Old English White Reg: CWA902H. If anyone should come across it, please get in contact with the police.
That would be much appreciated.

G Thompson

This thread was discussed between 28/02/2008 and 09/03/2008

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