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MG MGB Technical - Clutch Noise on a New Clutch

I have a 1974 USA spec MGB GT recently rescued from sitting idle in a garage for 12 years with a loud scrapping sound emitting from the clutch. The sound is heard when sitting staionary with the transmission in neutral, foot off the clutch, and occasionally while driving. The sound is only heard after driving the car for 10-15 minutes, so far not heard from a cold start. The noise will completely go away if I depress the clutch pedal as little as 1/2 an inch. I have just replaced the clutch and I used the carbon T/O bearing. The rear main seal was replaced and the pilot bushing inspected/measured and found to be servicable so not replaced. The flywheel was burnished but not turned due to no visible blueing, pitting, or scoring of the flywheel surface. The clutch master cylinder was resealed and converted to DOT 5 (silicon based fluid), the clevis pins and pushrods on the master cylinder and slave cylinder replaced, a Moss supplied stainless steel braided clutch line installed, and a new slave cylinder fitted. The clutch pedal bushing was not replaced but was still round as if replaced not long ago by the former owner. It should be noted that the clutch operates properly without binding or slipping and the transmission shifts smoothly.

I crawled under the car with the engine running and the noise occuring and was able to get the noise to stop by moving the clutch actuator arm either in or out of the slave cylinder less than 1/2 an inch. Here are my theories:
1. The stainless braided hose has an internal restriction not allowing the fluid to return to the clutch master cylinder on release and the sound I am hearing is the sound of a hot carbon T/O bearing making light contact with the pressure plate causing noise.
2. Though the operation appears correct via visual inspection, perhaps the release is not working properly once the fluid/clutch get warm causing the improper release and overheating the T/O bearing. (I.E a problem related to the silicon fluid, though unlikely since I am aware of many MG owners who have converted there clutch hydraulics W/O a problem such as mine.)
3. I am totally wrong on both accounts and someone who reads these links will know exactly what the problem is and how to fix it without removing the transmission.

Jeremy
Jeremy

Did you remember to grease the spigot bushing
and tranny input shaft?

Did you make sure that the T/O bearing and the
contact race on the clutch plate were absolutely
clean and devoid of grease, oil, or (storage) rust
preventative? It should've all been clean & dry.
The carbon in the T/O bearing is it's own lube.

All of the nuts & bolts torqued correctly?

Just thought I'd ask.

Have you tried to remove the rubber boot on the
T/O arm and peek in the bellhousing with a
flashlight?

One of the odd quirks about MGB's is that the
hydraulics are designed so that there is always
a bit of residule pressure in the sytem so that the
T/O bearing is always in contact with the clutch
plate T/O race. This makes the clutch T/O system
self-adjusting.

Some folks home-brew a throwout-arm return spring & return stop limiter gizmo that sandwiches between the bellhousing and clutch slave.
This has it's pluses and minuses.

The "plus" - is that is saves the T/O bearing and
the crankshaft thrust bearing from extra wear &
tear. The "minus" - is that it slightly increases
clutch pedal travel - as well as defeats the
self-adjusting feature of the system. This can
be an issue later when all of the clutch release
components wear and become looser in time,
necessitating periodic manual adjusting.

All that being said, I remember when my B/GT
was still showroom new, that it's clutch, too, would
squeal a bit at idle. The dealer tech said that the
T/O bearing carbon has to take a "set" to the T/O
race on the clutch plate - and to do nothing...and
give it another week or two of running. Just as he
said, the squeal gradually disappeared.
Daniel Wong

This thread was discussed on 26/09/2004

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