MG Car Repair/noisy rumble/knocking from rear.
QUESTION: I have just put a 1973 MGB GT back on the road after lot of welding and body work. The car had not been driven for at least 6 years prior to my purchasing it, and now on test driving, I find a rumbling/knocking noise when you get to about 30mph and above in all gears. Also it starts first time in the mornings, but after approx half hour of driving, when stopped, it will not start until you leave it for about 10 mins.It does not overheat at all and has excellent oil pressure when hot. Any help or advice would be gratefully received.
ANSWER: Hi John. You have two separate problems.
1) The rumbling sounds like a worn bearing or possibly a worn universal joint. You need to locate it more accurately. It could be a wheel bearing, the main differential bearing, the gearbox rear bearing. I would pop into a garage and get a mechanic to go for a short drive. They will tell you where it is and how much it would cost to fix. They should not charge you for the advice. Then get back to me before you have the work done.
2) The restart problem is probably due to modern fuel with added ethanol causing localised overheating of the carburetter float chambers. It is a complex problem which we are currently researching. On a 73 MGBGT it will be made worse if you have a broken or incomplete heat shield. I like the stainless steel heat shields that are being advertised on eBay. Also, if you are using 95 octane supermarket petrol, then I would recommend a change to either BP or Shell 99 octane (Such as Optimax). It is a bit dearer but it will fix the hot restart problem.
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QUESTION: Thanks for the swift reply. I have now changed to the petrol you have suggested, but I cannot give you any feedback, as I have not driven it for too long due to the noise from the axle. A mechanic has had a look at it for me, but cannot tell me for definite what it is, but strongly suspects the planet gears, as I have taken off the inspection cover of the axle, and they appear very sloppy, and the crown wheel is pitted on a few teeth. I am currently trying to source another axle, as a straight change over, due to the work involved with cogs and whatnots. I will keep you informed as I go.
Best Regards, and thanks for your advice.
ANSWER: Hi John
You can get a good second hand axle from Andy Jennings.
He charges £60 plus carriage and VAT.
Go to: http://www.mgcars.org.uk/andyjennings/mgb-axle-transmission.htm
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QUESTION: Hello again and sorry for the delay in getting back, but I have just finished fitting the new rear axle, and just road tested the car.You were correct,it was the rear axle bearings, so I replaced the axle with one I purchased.I had already bought one before your recommendation Re Andy Jennings, but I will keep his number for anything else.
I still have the hot starting problem, and the heat shield is fine, so I will have to keep trying other things until I get it right.
Thanks again for you help, and hope to let you know if and when the problem is sorted.
Thanks for the feedback.
Your hot restart problem sounds like fuel evaporation due to high under-bonnet temperatures.
As an experiment, please try filling up with BP Ultimate or Shell Optimax petrol next time you are getting low. No need to fill the tank to the top. Then drive home, stop the engine, leave it for 2 minutes and see if it refuses to restart. My guess is it will be OK.