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MG TD TF 1500 - Transmission noise

I'm going to the deep well of TD/TF knowledge to try to get help again. I have a later model '53 TD on which I had done a body off restoration and completed in 2010. I had a first gear problem after I got it running and it turned out that the first gear assembly was bad. Hugh Pite furnished me with a NOS first gear which fit perfectly. I put the gear box together again and it operated well and to my recollection, quietly. I haven't put a lot of miles on it since the rebuild since it was primarily a show car. Now that I'm done showing it and driving it more I have a very loud whinning noise coming from the gear box in the top three gears. This noise increases in volume as the speed of the car increases. When I disengage the clutch, the noise goes away. Also, the noise seems to increase with loads such as when I'm accelerating. When I back off on the gas the noise somewhat disappears but is still there. It is loud enough that bystanders can hear it as I'm passing them. The synchros work great. I have the Barrie Jones DVD which has been a great help, but it hasn't given me any clues as to what might be wrong. I contacted him recently and he suggested a different oil. I sourced an oil from Penrite which cut the volume of noise but I afraid that it is just masking the problem. I've now removed the transmission and have started to disassemble it. Prior to disassembly, I hooked up a drive unit to the input shaft and ran it at about 2500 RPM but could hear no noise even using a stethascope on the various bearings. After removing the tail housing, the bellhousing and the selector rods, I can see nothing wrong. All teeth on all gears look excellent. There has been a very, very small amount of metal flakes in the drain plug but I attribute this to some break-in wear on the first gear. There is no noticable wear on any of teeth. The selector forks, after removal, look perfect. Everything is smooth and all parts turn freely. I have not yet dropped the layshaft and removed the main shafts. I've not yet inspected the ball or needle bearings. Those are next on my list.
My question is this. Based on the current facts that the noise is heard at higher speeds, mostly under load, and that there is no noticeable gear damage or other component damage, what is anyone's best guess as to the source of the problem? What should I be looking for? Perhaps a bad ball bearing? A ball bearing spinning on a shaft? At this point I'm afraid that I might miss something that I should be looking for as I finish the inspection. If a needle bearing was bad, I don't think that it could possibly cause the magnitude of the problem that I am experiencing. Perhaps a bad ball bearing. The problem needs to be a big one in my mind. My other '53 TD is as quiet as can be and shifts nicely. A real study in extremes. I really don't want to just change bearings and put it back into service without a known cause. I won't know if I've solved the problem. My bad back doesn't like wrestling the gearbox in and out on an experimental basis. Driving weather is coming soon here and other projects need to be done on my other cars. I sure would like any suggestions that can be made to help me. I simply cannot figure out what the problem might be.
Thanks,

Mark
Mark Strang

If everything in the gear box is perfect and the noise goes away when you depress the clutch, could the problem be in the clutch release system? Something like a whiney throw out bearing that shuts up when pressure is put on it with the clutch pedal? If you are rolling at 30-40 mph and put it in neutral and let off the clutch pedal, does the noise return? Just a wag from a very non-expert.

Jud
J K Chapin

Hi Mark, are you sure the noise is not comming from the differential? When they are noisy it is most often on acceleration and then pretty quiet on deceleration. Or, quiet on acceleration and noisy on decelertation. In other words - not noisy on both acceleration and deceleration. Did you put 4.3 MGA gears in the diff?
Cheers, Hugh
H.D. Pite

In forth, the 3/4 sliding hub locks the first motion shaft to the mainshaft. I would think that would rule out needle bearings, as there would be no load on any of them. The cluster would be just idling, again with no load. I think. The middle and rear bearings are the ones that spin speed dependently I think, so check those. I think you can remove the rear extension and check that one without disturbing the mainshaft/gears. A sized universal joint can also make really bad noises.
George Butz

Mark did you read Barrie Jones's response to the query by JR McDonald on the recommended clearance between the 1st/2nd sliding hub & the circlip in the thread below? Insufficient clearance here produced a "very noisy box". Barrie recommends a minimum gap of 1mm (40"). I suspect however if this were the problem the box would have been noisy from the get go. The metal flakes don't sound good. If I had to guess I would lean towards one or more of the needle rollers failing. Continue with dismantling the box & inspect as you go as most of the hard work is already done. You don't mention if you had replaced the layshaft, thrust washers, all needle rollers & the 3 bearings back in 2010? I'm sure you would have but if not, as Horst suggests, I would see that as a priority. Be interested to read the results of your investigation. Good luck.
Peter TD 5801
P Hehir

Mark,

My transmission has the same symptoms. But unlike yours the noise fully disappears when I release the throttle.
I hope to minimize the noise by changing to Redline MT90 in a couple of weeks.

And of course I'll follow this thread to learn more...

Jasper
JL Nederhoed

Mark, I agree with George - when in 4th gear the input shaft and the mainshaft are spinning as one unit so any noise is most likely coming from the ball races. However, again in 4th, there would be no lateral force on the ball races so it doesn't make much sense that they are bad since the noise mostly goes away when there is no load on the drive train. As George said it could be an universal but my money is on the diff.
Cheers, Hugh
H.D. Pite

Hi Guys,
Well, I've got it all apart. Hugh, when I overhauled the car, I just changed bearings and seals in the rear end and on the axles. I had parts of the diff apart but kept all of the spacers in place. I kept the 5.125 ratio. The noise that I am hearing is a high-pitched sound. Not the lower sound that I would expect to hear from the diff area. Perhaps I'm wrong on my thoughts of the frequency and pitch of a bad differential. Peter, I read the post and other info that Barrie had talked about. The play in my gear box is 0.081" in the location that was discussed. Since it is within what Barrie says is okay and was probably there from the start I'm not going to do anything about it. The first gear that I got from Hugh measures 1.495"in width and is within 0.002 of what was in the car originally. The gear also has a modification that has the leading edge of the teeth beveled to allow a smooth entry of the mating teeth. The hub that it sits on is the original hub that had no problems in the past. I have examined, under a magnifier, all of the needles and their fits on the various shafts. I had replaced all of the needles, radial bearings and the layshaft when I originally rebuilt the gearbox. This included the spacers and brass washers on the layshaft assembly. The three radial bearings are as good as I can determine without being under load. Their fits are good but I have not mic'd them and probably won't since I needed force to remove them. There is no noticable wear on any of the teeth now that I can get a better look. Since the laygear assembly is "locked out" when in fourth, I've given up on that theory and can assume that it is not the problem. As a matter of fact, my thoughts all along have been along the lines of some common components that are always in play such as the radial bearings or some preloading of some part. I don't think that I have preloaded any bearings since the needle rollers allow for some axial play and the two main radial bearings are fixed in their original positions with the snap rings. I've checked the thckness of the original bearings against the new bearings that I installed in the past and they are the same thickness as I would suspect.
I'm sort of out of ideas. The gearbox looks as good as one could expect. The only area of concern is that one of the ball bearings has gone bad. The little particles of metal in the oil are, I'm sure, just from the new first gear and i'm not worried about them. Unless someone has another thought, I guess that I'm going to have to put it back together with new ball bearings and hope for the best. I hate to do that. The engineer in me just doesn't like that idea. Hugh, perhaps you are correct. It really sounds like gear whine or a ball bearing with a bad fit and that was what caused me to investigate the gearbox. Anyone else have anything to add to this rambling note? I have to add though, that after talking with Penrite down under, and adding their lube that was designed in the 50's for TD'S, that the noise was reduced quite a bit. That's why I still think that the problem is in the gearbox. The u-joints were new within the last 1500 miles. I also had the drive shaft dynamically balanced at the time of the rebuild.

Mark
Mark Strang

Mark, Just one more wild card to consider while apart-- Check to make sure there is a good pilot bearing in place on the crankshaft since it stabilizes and aligns the front of the trans input shaft.
Richard Cameron

Richard,
Thanks for adding that bit of info. I did in fact check that out as soon as I got the transmission out of the car. It is in great shape.
I should correct my earlier post about a radial bearing going bad. I don't know this for a fact. I'm only guessing that one bearing may have failed and shows up under high speed. I'm going to cut them apart to see what the inner races look like. It's the last thing I can think of. Some sort of motion(axial?) is taking place either in the diff or the gearbox under acceleration putting presssure on a part that is causing the noise. I now believe that since it is in all speeds that most of the internal parts in the gearbox can be eliminated.
Mark
Mark Strang

Mark,

Two points which have not yet been suggested: Do the front and centre bearing have circlips fitted? some time ago a supplier was selling bearings without these circlips. Was the flange nut tight?

John

J Scragg

Mark, is the gearbox noisier in some gears than others. The reason I ask this is that the loading on the main shaft rear bearing varies dependant on the overhang of the gear selected. Using this theory the greatest noise would be produced in third gear which is farthest from the bearing and therefore causing the greatest offset loading and also mismatch of gears as the bearing goes out of alignment
Iain MacKintosh

John,
The circlips are installed properly, in good condition, and tight to the housing. I made sure of this when I replaced the first gear a while back.
Iain, it seems as if the noise is the same in all gears although as I increase the speed of the car in any gear, the noise gets louder as one would expect. I understand what you are saying and that may in fact be the case, but wouldn't I see some signs of early bearing failure? I've disected the radial bearings and examined them under a glass have not found any signs of wear. The needle bearings are perfect as are the seats that they ride in. I mentioned earlier that I installed some real heavy gear oil into the gearbox and it made the unit more quiet. Based on that and the fact that the noise was in the cockpit area, I believe the problem to be gear related.
I've just received the bearings and related parts to complete the assembly. I'll try to get it done in the next couple of days and then back into the car for a test drive. I'm not too optimistic at this point though, that the problem is solved since I haven't found anything to "fix". However, I never give up. If the noise is still there when I test it I guess I'll have to have my wife crawl into the back with floor panels off and try to figure out if in fact, it is the diff. I've wanted a good cruising ratio in the diff so maybe this will be a good excuse to find someone that wants to do a ratio change. I hate to lay it up for a long time though with driving season coming on. The good news is that after going through the gear box three times I know that I have a good unit that in my lifetime shouldn't have to come apart again. The real odd thing about all of this is that I enjoy it! The thrill of the hunt!
Mark
Mark Strang

This thread was discussed between 02/03/2014 and 06/03/2014

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