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Transmission Interchangeability

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Matthew E. Herd

Jedi Warrior
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I believe that I may have recently destroyed my transmission in my '76 Midget (w/ 1500). I was wondering what the transmission differences are between 1500's and TR-6's. I know that there is a gearset offered by Quaife that is a close ratio set for TR-6's, but wasn't sure if it would be compatible. Also, I had read somewhere that GT-6's and Spits ran TR-4 transmissions in factory racing efforts, which would seem to indicate that the transmissions for larger cars may be compatible. Just looking for any thoughts. Thanks!

Matt
 
Hey Matt,

I'm not sure about the transmission swap, but just noticed you are an RPI grad. I am also, class of 78, Mechanical Engineering. I never used my degree as I was in ROTC and went into the USAF as a pilot. The school definitely looks different than when I attended, but Troy still looks like heck!! Nice to see another RPI grad into LBC's. Good luck!

Mark
1970 Frame Off TR-6 Project
 
Hey, thanks for the input! I'm always amazed at the number of RPI grads I meet. I've met two at autocrosses in the Philly Region just last summer alone! Maybe someone will know the answer to my question, as well ... who knows?

Matt
 
Sorry, just wanted to say one of my best friends graduated RPI, class of '92, mechanical engineering also. He's now living in Shaghai (yes, china), got transfer there from his firm in northern NJ about a year ago. The guy my wife dated before me also went there, small world, you RPI people are everywhere!
 
Matthew, what you are wanting to swop out will be a real pain, but the Midget or Spitfire transmission from '75 on will fit and if you could find one with overdrive even nicer. The Spits had the shifter for the overdrive on the gear knob, not sure about the Midget. Wayne
 
Actually, the transmission that I believe I destroyed was definitely from a Spitfire. I already know they're interchangeable (except for one small detail which caused some trouble). However, I was wondering about the larger TR series cars, as I'd seen that their transmissions were used on the smaller GT6 and Spitfire racers from some GT6 page I'd read. I have no interest in overdrive because it would involve cutting my transmission tunnel. If I were to go so far, I'd rather change transmissions altogether, but for the time being I'd rather simply research stronger replacements or alternate gears in the same case (as I was wondering about the quaife gears).

Matt
 
If I'm not mistaken, the GT-6 has a 2 litre version of the TR6 engine, therefore the TR6 (TR4) trans should bolt right up, although you may need the plate that bolts to the block. I don't know if you can do that with the spit (midget) engine. However, all the Quaife gearsets I've seen have straight cut gears. They are alot stronger, but noisy as heck. They would be unacceptable (IMHO) for a street car.
 
Well, this isn't much of a street car. It's basically an autocross car lately, although I enjoy street driving now and again. Thanks for the input, I wish I had some pictures of TR6 Engines/transmissions, etc. I also have a friend who did a spit/gt6 conversion, so perhaps he can help. He ended up using the tr6 crankshaft, so it's really a 2.5 liter motor in a spitfire chassis. Theoretically he'll finish it this year ... sure /ubbthreads/images/graemlins/smile.gif
 
The 1500 Midget uses a single-rail BL trans that was used in the non-OD Spit and also in some Austin Marinas (an even rarer car in the US). There is an older Spit trans that will fit the engine, but has a different driveshaft connection.
The TR-7 4-speed looks very similar, but has a different part number (maybe due to different gear set).
The trans that intrigues me is the 5-speed TR-7 trans. It The actual gearbox looks about the same size and I've always wondered if it will fit the 1500 bellhousing....maybe.
If you're curious about this (or any other Triumph stuff) you might try sending a note to Rimmer Brothers. They also have some good pictures of Triumph transmissions on their site.

https://www.rimmerbros.co.uk/
 
Are you sure about the different driveshaft connection? I'm reasonably sure they're the same, although I couldn't verify that. My transmission had the correct output flange, but the pins which locate the shifter (and prevent it from spinning round and round) were reversed, as I believe is the case with spitfires, for unknown reasons. Since I was using a Midget shifter in a Spitfire trans (I'm 99% certain it was originally from a spit), I had to (very painfully) switch the little pins.

I had thought, previously, about exploring the 5 speed TR7 option, but haven't found much information as of yet, and I don't have one to measure.
 
The TR7 4-speed case looks very different than the 5-speed case. The 4-speed is a rectangular box with a separate, flat top cover. The TR7/TR8 5-speed transmission (yes, the same 5-speed was used in the TR8) is in a curve-sided, single-piece, cast case without a separate top cover. The cast top of the 5-speed case slopes upward toward the rear and has a different rear bell housing shape and transmission bolt pattern than the 4-speed.

The Moss TR7 catalog is also the Spitfire catalog. Therefore, you might be able to compare the transmission parts numbers and drawings for the two cars in the same catalog to see the similarites and differences.

Sorry I can't give you dimensions of the cases or bolt patterns--don't have the 5-speed out of the car and don't have a 4-speed at all. But, when it comes to buying TR7s, the general advice is "avoid the 4-speed." /ubbthreads/images/graemlins/nonod.gif
 
Well, it would seem I may have overpowered mine with my diminutive 1500 and some sticky Yokohama race tires ... too bad the 1500 4 speed just fits in the transmission tunnel. It's very unlikely that the 5 speed would fit in the same location, as I'd guess it's higher. Also, you would need to customize the bellhousing because the bolt patterns are pretty clearly not the same between the TR7/8 and the Spitfire. I'm unsure whether a TR6 transmission would fit either, as the design is clearly not the same. The bellhousing, from the Rimmer Bro.'s site, seems to be cast as one piece with the case.
 
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