Two transmission and O/D questions

1) Would a non-crash 1st gearbox on a TR3 be considered an "upgrade" or would that detract from the value of the car?

2) Any issues with adding an A-type O/D to a later TR6 box. I know I'll need ot take it apart and use the main-shaft that is correct for the A-type O/D requirements, but are there other issues to be aware of?

Thanks guys!

Unless it's a very correct restoration otherwise, I can't see a 4-synchro box detracting from the value. Besides, you'd have to either drive the car or jack it up to see the difference (if you keep the TR3 gearshift).

There were several different gearsets & mainshafts used during the TR6 run; some of the later ones never came with A-type ODs. You might be able to get a custom shaft made to suit (I believe ORS in the UK can do this). I switched to an earlier TR6 gearset instead.

The OD adapter plate also changed, the early plates won't fit the later boxes without modification (although later plates will fit early boxes). If you're getting a new one, Quantum Mechanics offers a beefed-up plate that is worthwhile IMO (the original ones frequently distort enough to leak oil at the joints).

Otherwise, the conversion is straightforward.

Some indirect issues to be aware of:

Late TR6 boxes had a much thicker front flange. You may need longer bolts & longer studs in the engine block. On my TR3A, I also wound up making a little bracket for the clutch return spring, to get it's length right. Didn't move it to the TR3, now I need to go back and do so.

For TR3/A before TS50k, the later gearbox will hit on the tunnel (the starter bulge is longer). A little quality time with a BFH will solve the problem, but it makes a lot of noise if you leave them touching.

The 4-synchro boxes are about 3/8" longer than the 3-synchro (independant of the increased flange width). Best IMO to elongate the mounting holes in the rear crossmember so the motor mounts aren't strained (otherwise the mounts don't last too long).

It is possible to rebuild the early top cover with the 4-synchro shafts & forks ... I didn't want to lose the dipstick. If you use a later top cover, you may need to drill it out for the cross-bolt used with the TR3 shifter.

TR3driver said:

I didn't want to lose the dipstick.

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I read dipstick would not have room above heater box but it does.

How about the reserve - a non-synchro first in a later TR4A? Any thoughts/issue on that?

well dono value but first is not really needed since the car would pull most anything you would want to steal off its bolts. [not recommended for your average user} could have lost 1rst and added 5th.

tdskip said:

How about the reserve - a non-synchro first in a later TR4A? Any thoughts/issue on that?

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Tom-

For Christmas, I think I'm going to send you a certain book by Mary Shelley - I can see you hooking up all sorts of bits together, plugging in a big charger to get some sparks, and shouting "It's alive!" when it fires up!

If its an early non-syncro box with the old style starter you might have some headaches with the flywheel or clearance in the bell housing, but I'm guessing it could be done.

Randy

Looks like I have some digging to do into the details here - thanks for the caveats guys!

Another thought on using an early box - don't they have a longer input shaft? If so, perhaps that causes some interference issues when mating up to the input shaft bush/ crankshaft.

The aftermarket gear-drive starters are an easy solution to the early box/late flywheel issue as either starter will fit in either bellhousing. I've also seen people just cut a hole & let the starter drive stick out. Not as elegant, but seemed to work fine.

The part of the input shaft that extends into the pilot bearing is longer on the early boxes (sticks out beyond the face of the bellhousing), but I don't see that being a problem on the TR4/4A as they have the same pilot bearing.

Shelley would have been proud of the gearbox currently in my TR3 : late TR6 case, early TR6 gears, TR4 overdrive, TR3 top cover. Works a treat.

sail said:

I read dipstick would not have room above heater box but it does.

Click to expand...

Heater?
We don need no stinkin heaters!

sail said:

first is not really needed since the car would pull most anything you would want to steal off its bolts.

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FWIW, the later TR6 boxes actually had a taller 1st gear ratio, which mitigates the "stump pulling" effect. It's also more important if you go with a lightened flywheel. And I plan to convert to 3.45 final drive, which will make 1st even more essential.

Edit : stock TR3 1st gear = 3.38
TR6 to CC89816 = 3.14
Later TR6 = 2.99

tdskip said:

How about the reserve - a non-synchro first in a later TR4A? Any thoughts/issue on that?

Click to expand...

I did this with my TR4A initially to get overdrive and I must have lucked out and gotten a late TR3 transmission since I don't recall having any issues with it up to point where I had a tooth chip on the layshaft (which is where I rebuilt the original TR4A transmission with an overdrive mainshaft and acquired an A-type overdrive adapter plate and used the overdrive from the TR3 transmission). From other posts here, it sounds like I must have changed the front cover to the TR4A one due to the clutch differences (and probably did it when I replaced the oil seals).

I of course was going for functionality and not worried about value and having the overdrive outweighed the non-syncro first for me (plus my wife's 1968 Spitfire MkIII still had non-syncro first so I was used to it).

Scott