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MG MGA - Clutch problem

After re-installing my clutch into my new 1600 engine I still sense an issue that seems to be getting slightly worse. When I first start out while cold every thing is fine. As it warms up, and I try to start out, I have to pump the clutch a few times to acquire pressure. Once I have pressure I can sit forever with the clutch pushed in with no problem. The master was rebuilt 4K mile ago by apple and operated fine prior to my unexpected engine change. I re-used the clutch that was bought new from Moss. I installed the lighter MGB 3 main flywheel that I had cleaned and cut. I do hear a slight squeal from the clutch at times. In reverse it is starting to chatter while engaging to start moving. Forward is fine. I have no problem with oil leaks at all!
Can not decide if it is a hydraulic issue or the clutch!
WMR Bill

Hi Bill. Having to pump the clutch pedal indicates that there is air in the clutch hydraulic system. Check the clutch hydraulic system carefully to insure there are no leaks. Sometimes it is tricky bleeding the clutch, so persistence is sometimes necessary.. The judder you feel might be due to loose driveshaft flange nuts. Make sure that your driveshaft flange nuts are tight. Good luck, Glenn
Glenn Hedrich

Hi Bill. Another possibility just came to mind. There were 2 different master cylinders that would fit the MGA, one being from an Austin Healey sprite, the other the proper MGA master cylinder. The sprite master cylinder has smaller diameter bores. Althught the sprite Master cylinder will bolt in and work, one sometimes has to pump the pedals to get full travel of the hydraulics, due to the smaller bore diameters. You might want to check and see if your master cylinder has the correct larger bore diameters. Cheers, Glenn
Glenn Hedrich

I'd be interested in learning more about the squeal you're hearing. Mine squeals like a harpooned penguin when pulling away from a stop with a little "too much" throttle, also when riding the clutch in reverse, and sometimes shifting up between 1st and 2nd (or down from 3rd to 2nd). I'm told it's either the throwout bearing (because the two "ears" aren't symmetrically placed in the casting) or (ouch!) the transmission input shaft bearing is spinning in the transmission housing casting. It's been getting slowly worse the past few years, and now sometimes when I first start the car it will start squealing as soon as I put it in gear. Pumping the clutch pedal helps a bit.
David Breneman

MGA master cylinder has 7/8" bore. The 3/4" bore unit comes from the 1098cc Spridget cars. The bore size is cast into the side of the reservoir in raised numbers, but you may have to dismount the unit to see it. The small bore master cylinder requires full pedal stroke, right into the carpet sometimes, to release the clutch.

The 7/8" bore will produce 5/8" of travel of the slave with full stroke. The 3/4" bore will make only 7/16" travel for the slave. It needs about 3/8" travel to release the (standard) clutch, so it should release at about 60% of full pedal stroke (on the first stroke, no pumping required).

If you don't get enough travel of the slave push rod, most likely it has air in the system. The MG clutch is notoriously difficult to bleed properly, See here:

Another common problem with a newly rebuilt master cylinder is sticking piston that may not return completely to the proper rest position, resulting in short stroke of the master cylinder piston. The give away symptom here is long pretravel of the pedal and master pushrod before you feel feedback force from the master cylinder.

A loud low pitch squeal (chatter) from the clutch as you lift the pedal slowly comes from the clutch disk vibrating violently. Contributing factors may be worn splines (reconditioned disc with older core), contamination on the friction surface (glazing or oil), worn spigot bushing (quite common), or worn input bearing in the gearbox (far less likely). See here:

Barney Gaylord

I'm inclined to think that worn bearings are not the issue because the problem first surfaced several months after the engine and transmission were completely rebuilt by a very well regarded MG shop in my area. What about the possibility of the asymmetrical throwout bearing casting? Have you encountered that one, Barney? I've seen some that have the two tabs almost a "half hour" out of parallel (if viewed as a clock face). I'd hate to have to pull the engine out to replace a relatively inexpensive part, but it's better than replacing an expensive one.
David Breneman

I have a newly rebuilt master and haven't been able to bleed it. Have tried both conventional method and the reverse method without success. The line feels blocked, but I have blown it out with ease. Perhaps I put the master together wrong. There was a check valve on one of the lines, brake I think, and the MG book indicated it should have been on the other side. Which side should the valve be on? What else could be blocking the flow?
Thomas Lennon

David, -- I have never seen a release bearing with the ears "out of clock". The two ears are machined in a single setup, so they should at lease be perfectly coaxial, even if they were off center. Ears being out of alignment would place the release bearing off center, but that's not a big issue with the carbon bearing as it does not have a specific rotational center.

If it was far enough off center the ID of the release bearing might rub on the gearbox input shaft. It can otherwise do this if the release arm pivot bolt and bushing are excessively worn. In that case you can wiggle the release arm sideways at the pushrod end.

Thomas, -- The check valve belongs in the brake master bore. For the MGA that is the right side if you're in the driver's seat, or left side looking at the pushrod end of the casting.

If the clutch master piston is stuck part way down the bore and not returning all the way to rest position, then it will not flow fluid to bleed properly in either direction. Check to be sure the master pushrod is not too long. It should have a time bit of wiggle clearance when at rest, giving up to 1/4-inch pretravel at the pedal before the master piston starts to move.
Barney Gaylord

This thread was discussed between 08/10/2008 and 19/10/2008

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This thread is from the archive. The Live MG MGA BBS is active now.