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MG MGA - Gearbox noise

Hello! Could I please ask some advice on an annoying problem? I have a '59 MGA that has developed a high pitched whine from the gearbox when shifting. This only happens when in gear and the clutch is depressed. (So am I when I hear this noise) The pitch is proportional to engine speed. At its worst it prevents gear change. Seems to be getting worse. Does this mean removing the engine or gearbox to get to this problem? What am I looking at here? Thank you all for the past help!
Chuck Collins

If it happens with the car stopped with the gearbox in gear and the clutch depressed, it has to be some problem with the clutch. According to Barney, it could possibly be a worn spigot bushing, or worn splines on the clutch disk. http://www.mgaguru.com/mgtech/gearbox/gt203a.htm

It will probably require at least pulling the engine. You should probably do all the driving tests that Barney shows on that page to see if you have other gearbox problems before you pull the engine. Best to fix everything while you have the engine out.

Jeff Schultz

Thank you for the link. It whines when in motion but not when stopped. Gearbox oil is full. I will have to check this closer with the web page in mind. OMG. I just paid 18 large for this car to be restored 18 months ago..........
Chuck Collins

But I'll bet it looks really nice, Chuck.

Does it make the noise when the clutch pedal is pushed down and only when the car is in motion? That's the way I read it.

My first impression is a throwout bearing, but that would squeal even when the car is stationary and the clutch pedal pushed in.

Whoever did the mechanical work on your car would be the first place to stop. Since you paid for a restored car, you probably won't be doing the repairs yourself. If you don't get the right answers to your questions there, I'd look for a better mechanic.

All that said, these cars are kinda quirky. Easy to understand for some, not worth the trouble to others. Another suggestion would be to find a British car club in your area, as members love to help with these kinds of things. And they always know who the specialists are to do the hard stuff.

Good luck with your baby. It's probably not a huge obstacle to overcome.
Tom

It does look nice! Makes this sound only when the car is moving and only when the clutch is depressed. I can also bump the gearchange against 3rd (but not fully engaged) and it is a lower pitched whine than if I do the same with second gear. Holding it against second is a higher pitch. I can almost play a tune with the gearselector by moving it about in neutral, only with the clutch in and the car moving!
Chuck Collins

Here are some thoughts:

When the clutch pedal is depressed the clutch friction plate, which is carried on the first motion shaft splines, is free to rotate relative to the engine. If you begin to engage a gear, the sychro will start to engage the gear. If the car is moving, this will cause the lay gear and first motion shaft to spin up. The rate of spin will depend upon the speed of the car and the gear you select. Of course, third gear will cause a slower rotation than second gear, and therefore if there is a worn part, such as the throw out bearing, first motion bearing, needle bearings in the lay gear, synchro, the sound will in general be lower pitch for third gear than second gear. If the clutch pedal is let out, the friction plate is stabilized by the fly wheel and the throwout bearing is disengaged. As the sound goes away in this circumstance, I'd say the problem is either related to the throwout bearing, first motion shaft, or possibly the lay gear. All require separating the gearbox from the engine to examine.

If the problem is not with the throwout bearing, check for excessive wobble in first motion shaft indicating a worn bearing. Excessive wear in the needle bearings within the laygear can be checked by opening the side cover, leveraging the layer gear, and checking how much transverse motion there is. Note, from that point rebuilding the gearbox is not all that difficult.

Was the gearbox touched during the rebuild? As the throwout bearing is easily checked when the gearbox is separated from the engine, it would be surprising if it were not checked even if the gearbox itself was not gone over.
Steve K

I'm no gearbox expert, but after reading through your description several times, it sounds like a bearing going out. I'd pull the tranny this winter and have it gone through. If it was fully rebuilt in the restoration process, I'd make a scene at the restorer's place. (If he doesn't claim it's his responsibility.)

You haven't told us if there was work done to the tranny in the restoration process. But you should have a detailed list of what was done to the car mechanically, if for no other reason than to know as much about it as possible. If you were charged for a complete transmission overhaul and it's failing so soon, good documentation would probably win in small claims court. But a quality rebuilder would just fix it.

If it's up to you to do the repair, there are specialists that you could send it to. Someone here could recommend one, maybe close to you.
Tom

Thank you all for your thoughts on this. I am not at all familiar with how transmissions work or even what they look like inside. Never got that involved. This gives me some idea of where to direct my attention. The transmission gaskets and seals were replaced during the rebuild.

Yes, that would have been the best time to open the wallet further to make certain this would not happen. I wish I was given the option at that time. I assumed they knew what was best to do considering the car owner wants to spend as little as possible and the shop owner wants to make it worth their time.

This problem seems to come and go. Some days it is smooth and quiet and others it is screaming! Maybe it is a bearing going out as you mentioned Tom. Maybe it could not have easily been seen when it was apart?
Thank you for taking the time to read this and collect your thoughts. I greatly appreciate it. -Chuck
Chuck Collins

Well, Chuck. The repair's on you, so you might as well bite the bullet and put her in the shop this winter. Maybe changing to some Redline gear oil would make the noise a little less irritating until then.

If there's not a specialist for Brit gearboxes in your area, I remember some talk about a place called Quantum Mechanics or something similar.
Tom

Chuck, you may want to take it to MG Limited on Forest Home and have Dick take a listen to it.
John H

I frequently get a loud squealing or howling sound from my transmission when the clutch is slipping coming up to engagement in first or reverse. Sometimes also when shifting from first to second, or third to second. I've been told that it's chatter from the throwout bearing caused by the fact that the "ears" on the bearing are not 180 degrees apart - and they aren't on the currently-available poorly-cast ones. According to a mechanic I trust, it's a fairly common problem with the current crop of replacement parts.
David Breneman




David's problem first (being the more common one). -- A loud howling noise when letting the clutch up on a dead start (1st, reverse, or even 2nd if you try it) comes from the driven disc chattering between the flywheel and pressure plate. This is s resonance driven noise where the frequency is dependent on the mass of the vibrating part, in this case the clutch disc. As such, the frequency is always the same and builds in amplitude with continued excitation. That is, it starts small and gets louder very rapidly, but at a fixed frequency. This chatter motion is "allowed" by looseness in the mounting parts, such as a worn spigot bushing in the crankshaft (fairly common) or loose splines (common with a rebuilt clutch disc).

The chatter might be initiated by a glazed clutch disk or by a drop of oil on the disc. This is why it might sometimes seem to be fixed by slipping the clutch for a little while. You can alleviate this problem considerably by giving a little more throttle and letting the clutch up a little bit quicker. You do not have to over rev the engine or pop the clutch or spin the wheels. This is just a slightly more aggressive start, even with the same initial engine speed. When I encounter this problem I tend to banish it by training my feet to dance in the right sequence to avoid the noise, and re-consider the problem next time the engine is out for some other reason.

Chuck's problem is more rare, almost unique. -- It has a whine with clutch depressed and frequency proportional to engine speed (not the typical clutch disc chatter). When shifting, a nudge against 2nd gear synchro gives a higher pitch than a nudge against 3rd gear synchro. That means the frequency is proportional to speed of gearbox input shaft, or speed of the clutch disc. Ergo, the frequency is proportional to the relative speed between the flywheel and the clutch disc, and therefore likely nothing to do with the release bearing. Noise described as a "whine" implies a higher pitch similar to a bearing noise. My first guess is a spring has popped out of the clutch disk and is rubbing against the flywheel to crankshaft bolt heads. However, making noise in motion but not when stopped goes against my first guess. Noise requiring rotation of the input shaft may imply a failing input bearing. The common symptom of a bad input bearing is hissing noise with clutch up in neutral (input shaft turning) that goes away with clutch pedal depressed (input shaft stopped). This begs checking. In any case, the engine will have to come out to fix this one.
Barney Gaylord

David's problem, as I understand it, is from the throwout not being centered, and therefore vibrating. I had a similar elusive problem with a TR3 in which the transmission rebuilder removed and didn't replace the clutch shaft bushings. Most times, eveything was fine. But occasionally, I'd get a whiny/squealy sound. Not while using the clutch, just driving along. Put the clutch in and it would align well enough to stop for a while, maybe. I only remember it happening 3 or 4 times, but I finally found that the bushings were gone.

I'm still puzzled by Chuck's problem, would like to hear the solution. But it sounds like his synchros are good, or he'd be grinding as well as playing a tune. Maybe too much clearance somewhere, affecting the gear mesh.
Tom

Hi, Barney - Yes, you describe the noise perfectly. Always the same frequency, and engaging the clutch "briskly" prevents it (usually not an option in reverse). However, all the bearings were replaced when the engine was rebuilt 4 years ago, the the problem started a few months after the car was back on the road. The only other option I was given was that the transmission input shaft bearing might be spinning in the transmission case, and that sounded pretty expensive. Someone else who had this problem told me she could alieviate it to some extent by occasionally spraying brake cleaner on the clutch assembly (through the hole the fork passes through).
David Breneman

Thanks fore the info! Nice to have some insight on this unusual problem. It seems this may have not been easy to spot during a 2 month restoration that had so much ground to cover and NOT an unlimited wallet. Since I just ironed out all of the last little bumps with it and it cost me so much, I am not inclined to have it ripped apart too soon. If I find out I will let you know. Thanks again!
Chuck Collins

Winters are long, the car's probably gonna be laid up anyway. If you're bold, you can set the box up on a workbench and go through it yourself. There might even be a step by step rebuild page on the 'net somewhere. The parts probably won't be too expensive. Or live with it for a while. I've had a weak 2nd gear synchro for years now, only grind it occasionally. It's not getting any worse.
Tom

This thread was discussed between 14/08/2007 and 26/08/2007

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