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MG MGA - gearbox mounting bush
Does anyone out there know the correct outside diameter of a new gearbox mounting bush? I've recently bought one from Moss and I'm sure it's too big! I appreciate it's meant to be an interference fit but 20 thou over the 1.875" hole diameter seems a lot to me. I have visions of the aluminium surround cracking when pressing or tapping it in. |
m.j. moore |
I may be mistaken, but isn't the bush tapered? you might try it the other way around. j |
John B |
Hi MJ. You are correct about the mount being quite oversized, and NO the bushing is not tapered. I replaced my transmission mount a few years ago. The one I received from Moss Motors was about .025" too large in diameter. This was excessively large enough that I worried about breaking the aluminum mounting ear on the transmission case. After measuring the mounting hole in the tranny, I chucked the defective oversized mount in a metal lathe using a long bolt and nut as a mandrel, (and tail stock dead center) and skimmed off the excess material from the circumference of the transmission mount. I machined the mount to .001" larger than the mounting hole. I put the mount in the freezer over night to shrink it a bit. I greased the mounting hole and proceeded with installation. The freshly machined mount installed quite easily with some forceful taps from a 16 oz hammer. I used a suitably sized piece of pipe as an "anvil" to support the aluminum ear, while the mount was being hammered into place. (This is a 2 man job) The tranny mount bushing is now rock solid in the case, being a slight interference fit. The Moss tranny mount is definitely incorrectly sized, and could cause serious damage to the transmission case if not modified (machined) before installation is attempted. If Kelvin Dodd, or other Moss Motors staff is reading this, Please know that this part has ( and continues to have) a serious problem, and one that is of lengthy duration! Does Moss Motors ever intend to correct this potentially transmission damaging problem? What are people that don't have a metal cutting lathe supposed to do with a transmission mount that is too large to fit the transmission mounting hole? Cheers! Glenn |
Glenn |
M.J. If you think the part is sub standard, possibly post an article to Barney. http://www.mgaguru.com/mgtech/faulty/ft_parts.htm I've just purchased one of these myself from Moss UK, but not fitted it yet, so thanks. Cheers <MARK> |
Mark Hester |
I had the same experience as Glenn only I sent it back and ordered one from Scarborough Faire. I then machined a couple of bushings and pressed the new transmission mount in the aluminum tail shaft which I supported with one of the bushings to be sure and not crack the aluminum housing. Have a good day! John |
John Progess |
I really appreciate the information in this thread. I will be installing this bushing during chassis restoration work in the spring, and probably wouldn't have recognized the problem until it was too late. I consider myself a pretty good mechanic, but there's no substitute for the MGA experience you other guys have (this being my first A). The frustrating part is that you have to be suspicious of practically everything you install during a restoration, and even with a good mix of experience, commmon sense, (and maybe an engineering degree), you can still learn about a problem like this the hard way. |
G Goeppner |
Hi Mark. Barney Gaylord is already aware of the defectively oversize transmission mount bushing, and accurately describes the problem in his defective parts column. Barney also gives information on how to properly remove and install this bushing, as well as measurements the bushing's proper dimensions. To anyone planning a transmission mount replacement, this is required reading! Thanks again to Barney for providing such a useful website, and MGA resource for MGA owners! Cheers! GLenn |
Glenn |
Thanks a lot guys,especially Glenn, all this information and experience is invaluable and it's comforting to know other people have come up against the same problem. Since posting the thread I've been looking up tables of interference fits and for a 2" steel shaft in a steel hole the shaft oversize needs to be around 1.5 thou. It could be a bit more for an aluminium hole. However, the bush is normally assembled at garage temperature which around here at present is 10 deg C. As aluminium expands at twice the rate of steel the 1.5 thou can be wiped out if the gearbox temperature during running is 50 deg. higher at say 60 deg C. So perhaps the bush should be 1.5 to 3 thou more than the hole i.e. 1.878" for the 1.875" hole. Actually why should I worry about this - I think I'll do what John did and return it to Moss!! I've also been having trouble fitting a new Moss rear gearbox bearing to the third motion shaft and I've found the bearing hole is 3 thou undersize!!!!! But that's another thread. Happy Xmas Mike Moore |
m.j. moore |
Hi Mike. Of course the tranny mount bushing is not solid steel. It is a thin cylinder of steel, filled inside with rubber, and another thin cylindrical inner bushing. With the .001" interference fit, my bushing was very tight in the tranny case, despite being assembled with grease. However, an extra thou or two increase in bushing size likely wouldnt do any harm. Cheers! GLenn |
Glenn |
I had the same problem as above only I did not know any better so I decided to give it the college try. After a bit of jury rigging I initially gave up getting the bushing to fit in so I took it to a machine shop. I helped the guy put it in. Tight is way too loose of a term to say what that bushing is. I still can't believe that the mount did not crack while putting it in. Now the good part. After I finally got it in I come to learn that it is manufactured incorrectly. The metal tube rims are not in the correct positions so in order to use this, now tight, bushing I am going to have to shim the short side with a washer and grind off the long side to allow it to fit within the frame mount! This bushing came from Moss around Dec 03. I contacted Moss and they gave me a credit of $7.85. Yee ha. They have known about the problem for a long time and still unbelieveably have them on the shelf. INCREDIBLE. I am at the point now where I am deathly afraid of even trying to take it out and will do what ever it takes to just make it work! |
Ken |
I installed a SF tranny mount in August of this year. No problem what-so-ever. Fit perfectly. I use an arbor press to remove and install the mount. Of course, the tranny was out of the car and removed from the engine. GTF |
G T Foster |
At some time, Moss had it right. The one I bought in '97 fit. It was a tight fit but it went together. had it been off as far as some say, I know it never would have fit. I thought the natural progression for replacement parts for old cars was: first the parts are available from the car's mfgr; then parts are unavailable; then aftermarket parts are available with major quality and fit issues; then the aftermarket parts are made more closely to original parts. In this case it seems to be reversed. Chuck |
Chuck Schaefer |
If Moss is currently supplying faulty bushings, they are screwing up royal. Two years ago the center tube was too chort. 18 months ago the OD was also too large. I posted these notes on my web site, and Moss has known about the problems for a long time. For a while thereafter the parts were not available, as I think Moss removed them from stock pending reorder with correct dimensions. I hope they didn't accept another batch with the same bad dimensions. See here: http://mgaguru.com/mgtech/faulty/ft009.htm |
Barney Gaylord |
When I had my installation problem in early 2004 I contacted Moss and they acted like they knew of the issue. They did say they were going to pull the parts off the shelf until a suitable replacement was found. I do not know for a fact whether that was ever done or whether the one that mj bought is the same thing just slipped back onto the shelf or what. Could be that Moss draws from a different "shelf" for European sales, who knows. I do want to make any unwarranted claims about Moss without knowing all the facts but rather based my above rant assuming that mj had recently purchased the same thing. |
Ken |
This thread was discussed between 13/12/2005 and 16/12/2005
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