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MG MGB Technical - Transmission Noise? What's normal?

I have a 73 MGB. When I got the car it was not running, so I have nothing to compare against,thus I am asking for help here. I had the engine rebuilt and a new (rebuilt) overdrive transmission installed. The car runs great and the transmission shifts smooth and strong. However, what is the normal or acceptable amount of noise that should be coming from the transmission? The shop that installed the overdrive is very well known here in Atlanta, and they
have been doing British cars for many years and have a reputation for being honest. They tell me that the nosie is normal, and the companies that sell the rebuilt transmissions use the original gears, so there is usually some noise. The noise is mainly in third and fourth gear. The best description I can give you for the noise is, when you are in third or fourth gear in your own cars,and you rest your hand on the shifter, putting a load it, you will hear a roaring nosie. Well, I get this all the time in third and fourth gear. Is this normal or should I be concerned? Again, the shop keeps acting like it is nothing and I am worrying about something I should not worrying about. Should I be concerned or worried? Should I be concerned that there is something wrong with the transmission, but the shop does not want to have to pull the engine and put in a new transmission? The transmission only has about 800 miles on it since it was installed. Also, I have never really noticed the nosie before last week, when I had a new top put on the car. I had never
driven the car with a top on it before, so I admit that may be worrying for no reason. Comments please.
Robert Browning

the shifter is not connected to the "go" gears in the tranny. when you hold down the shifter what you are doing is defeating the anti rattle stuff that is on the end of the shifter. you are probably just hearing amplified normal vibrations.

just drive, enjoy and turn up the radio or install K&N filters....

my tranny sounds like this:

first gear zoom mmmmmmmm

second gear mmmmmmmm, zoom...mmmmm

third gear zoom, zoom, mmmm
third od mmmmm

fourth gear zoom

fourth gear od mmmmmmmmmmmmmmmmmmmmmmmmmmmm.

any questions?
rn
RN Lipow

Robert!

The source of noises is easily mistaken or confused. Here are some things you can do to try to identify the source. Sit in the driveway, start the engine, leave the gearbox in neutral and the clutch released. Slowly bring the rpm from idle up to about 5,000 rpm. If you detect the noise you've been hearing, then the culprit is most likely the exhaust. Remove the gear shift knob and drive it through the rpm/mph range that usually gives you that noise. If it's gone then the knob is the problem (wooden knobs exacerbate gearbox noises incredibly!).

There is nothing in the gearbox that would make noise in just 3rd and 4th. If it were there in 2nd, 3rd, and 4th I'd suggest a problem with the layshaft/lay gear. If it was just in overdrive, I'd suggest the overdrive as the problem. If it was just on acceleration, on deceleration, or "free float" then I would suggest the differential.

There is ALWAYS some "swishing" from the gearlever -- which rises or falls if you have your hand on the lever or not.

Try these tests and let us know what you find.

John Twist
University Motors Ltd
John H Twist

oh, you can also install Redline MTL...

rn
RN Lipow

I bow and defer to John's superior and comprehensive knowledge

rm
RN Lipow

OK, What is Redline MTL?

Maybe I need to clarify the nosie. What I am saying is, when you put pressure on your shifter, you hear a roaring noise. My transmission makes this nosie all the time in third and fourth gear - but, I am not touching the shifter. My transmission just makes the same "type" roaring nosie in third and fourth.
Also, when the car is in neutral, and clutch out, you hear the transmisson - not roaring noises, but gear movement nosies. I first thought it was a bad throw out bearing, but found out that MG's do not use a "bearing" type throw out bearing. Again, the shop told me that transmission "gear" noise is normal. Does this sound normal? Also, the roaring nosie does not happen when I rev the engine, it only happens when I drive the car, so I do not think it is the exhaust. Also, I have already tried removing the shifter knob and it makes no difference, as John suggested.

I just want to know if I should be concerned?
Thanks
Robert Browning

Also, above, RN Lipow said to install K&N filters. What are K&N filters?
Robert Browning

Yes, even the soft top when raised amplifies any noise from the transmission, at least. I had a noisy axle for a while which was really only noticeable with the hood up, I think this is a combination of the folds of the hood when down by the rear shelf acting as an acoustic insulator as much as trapping noise inside the cabin when erected. I believe GTs had the tube-type axle from new as the banjo type was noisier and more intrusive in the closed cabin. The overdrive in my V8 (4th only) makes an additional noise when engaged, more noticeable at slower speeds, that is a sort of gear wheels spinning (funnily enough) noise. I don't think I have noticed additional noise from the roadster overdrive, even when the hood is up, although this year it hasn't been up at all! If you are only aware of it with the hood up, and the oil level is correct, I would say leave it alone. Obviously if it starts getting significantly or suddenly worse then you may have to consider an OD and possibly gearbox rebuild sooner or later.

Additional noise when resting your hand on the gear lever is normal, and I can imagine it being described as a roaring noise. There should be a nylon bush between the ball on the end of the gear lever and the remote control shaft on the gearbox, if this is missing or split it will add to noise and gear lever slop. With a good bush there should be virtually no free play in the gear lever when in gear. I had to replace the one on my V8, and although it fits into the remote shaft I found putting it in here first then fitting the gear lever just pushed it out of the bottom of the shaft. I fitted it to the lever first, then the lever to the gearbox.

I must say I would be a little concerned seeing as how it is a newly rebuilt and installed unit. Funnily (well, not really) enough I was watching a talk show last night and Michal Palin (of Monty Python fame) was describing a car he once had that kept going wrong. The garage he bought it from always said "Oh, they all do that" or "Well, these things can happen, bring it back in and we'll have a look at it" without ever taking responsibility for the problem. Hopefully not the case for you. I think your best bet is to get together with some other OD roadster owners and compare noises.

There *are* roller bearing type release bearings for MGBs, I was stupid enough to fit one when I changed the clutch, and soon after it started making 'twittering' noises, but only as the pedal just begins to take up or finally releases the pressure. I say stupid because unless you ride the clutch the release bearing should last the life of the friction plate, and I very much doubt I am going to leave that old roller bearing release bearing in there when I next replace the clutch, which on past experience and mileage will be in about 2020.

I use K&N air filters on the V8 because the original cast manifolds and lobster-claw air filter boxes are gone, but I would be very chary about using then in the OD, don't see how they would reduce noise in any case, and from their listings they only appear to do *engine* oil filters.
Paul Hunt

Redline MTL is a superior lubricant for an overdrive. I used to use non-detergent 30wt - i now use MTL in the od tranny. Shifting is smoother and quieter. talk to your tranny repair person before you do this.

K&N filters are low restriction air filters - an they do not "filter" out the loud sucking noise of SU carbs.
If you put them on, you won't hear the tranny.

rn



RN Lipow

Why not let somone who is familiary with the cars but not involved drive or ride in it. Seems logical to me. Makes more sense then worring yourself!! Bob Thompson/International Auto
Bob Thompson

This thread was discussed on 02/11/2003

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