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TR2/3/3A Will this Tranny fit my TR3 ??

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Will fit with just minor changes. The wire is for the backup light, just leave off. You can find TR3 trannys used for alot less money.

Marv
 
I agree that is a lot of dough for a non-OD unit. When I replaced my 4-speed gearbox with an OD I found that the good gearbox I had removed was just about worthless to the market, put in the corner for a spare.

<span style="font-style: italic">I should clarify -- that is probably a fair price for a rebuilt TR6 gearbox -- just seems a lot of money to still have a non-overdrive unit. BTW, Quantumechanics sells a rebuilt TR6 4-speed for similar money, but you would be dealing with a well-known rebuilder who is proven to stand behind his work.</span>
 
The cable is from a reversing light switch fitted from TR5/250 onwards.

Longer bolts are for the thicker flanges on later gearboxes.

Later all synchro boxes were slightly longer, so need the rear mount reworked.

Later gearboxes were mated to a diaphragm clutch, but 3's have the old spring pressure plate clutch. Each type had its own clutch release bearing set.

While the gearbox is out it's worth renewing the clutch fork locating pin. These days high tensile pins are supplied which aren't prone to snapping.

Viv.
 
As I recall, that top plate didn't come in until very late TR6 (75-76). If it is late enough then your speedometer will be inaccurate after the swap. TR2-early TR6 all used the same drive ratio for the speedo cable (cable turns at 2/5 driveshaft speed), but that scheme was changed in 1973 to have the cable always turn at 1000 turns per mile. The difference is around 12%, meaning that with your speedo reading 65 mph (assuming it is accurate otherwise), you will actually be doing over 70.

I have a TR6 box in my TR3 (formerly in my TR3A). In addition to the changes noted above, I had to install longer studs, and then wound up trimming them to the exact length required. If they are too long, the tail flange fouls on the driveshaft tunnel during installation. (At least I think that was it, I don't recall exactly, just remember having to stop and cut the studs during the gearbox installation). I don't know of a source for the studs already cut to length, so you'll need to buy some threaded rod or longer studs and cut them yourself.

Possibly less than "minor" modification : the rear crossmember (plate that the rear motor mount bolts to) has to have new holes drilled to accommodate the extra length of the 4-sychro box. It's only about 3/8", but if you force it together without moving the holes, motor mount life will be much shorter. On my 3A, I then had to bend the flange at the rear of the crossmember so it would clear the motor mount.

The thicker flange moves the mounting position of the clutch slave closer to the lever. I had to make a shorter pushrod, the original didn't have enough adjustment.

I wound up also making a little tab to restore the length of the return spring. Without it, the clutch slave would sometimes stay partially extended, which put the clutch release point closer to the top of pedal travel. Not a serious problem at all, but I found it annoying, especially when trying to do a smooth start from a stop light.

There are some other minor differences, but they don't seem to hurt anything. TR6 input shaft is shorter, so doesn't engage as far into the pilot bearing. And the TR6 front cover is shorter, so might not support the throwout bearing carrier as well. Those have not been issues for me (but I am also running a TR4A-6 style clutch).

Oh, one last thing, you will likely notice that the first gear ratio is quite a bit 'taller'. That isn't necessarily a Bad Thing IMO, the TR3 has a "stump puller" 1st that isn't much use, but it is a difference.
 
The reason for changing it in the first place is the syncros. The tranny in there is rebuilt and has 1200 miles on it. Problem is it seems the wife (or maybe me) chipped a tooth so if were gunna pull it out I figured we'd put in one with less potential of damage.
 
OK, let me first of all make it clear that I have no idea what I'm talking about here. My father in law, who built the car has three questions

#1- Does the clutch need to be changed from borg/beck to a diaphragm?

#2- Does the throw out bearing sleeve need to be changed?

#3- In regards to the shorter push rod, can we just thread it more and cut off the excess?

Thanks
 
#1- Does the clutch need to be changed from borg/beck to a diaphragm?

No you don't have to unless you want to - changing to a diaphram style would mean redrilling the flywheel.

#2- Does the throw out bearing sleeve need to be changed?

No if you stick with the old clutch, then stick with the old throw out bearing assembly - but you may want to swap in the front nose piece on the gearbox that the assembly rides on. The TR6 I think is shorter, the TR3 is longer and they should be interchangeable.

#3- In regards to the shorter push rod, can we just thread it more and cut off the excess?

You might not need to do anything - you could attach the slave mount bracket towards the front of the car, and the slave on the rear side of the bracket (if that makes sense) - and you should have the geometry about right. I think TR6's pretty much had it that way as well.
 
In regards to #2, yes you will need to swap the nose-piece-with-the-3-finger clutch because the 3-finger clutch is a different height than the diaphram pressure plate. If you decide to change the flywheel to a leter TR4 flywheel, then you can swap to the diaphram clutch and use the TR6 nose piece.

Just keep the nose piece with the associated clutch together and swap as an assembly.
 
I still believe that changing the front cover (aka nose piece) is optional, but it certainly won't hurt. As Randy said, it is a direct replacement. In fact, the factory didn't even change the part number! The difference in length is only about 3/8". Be sure to do something to seal the 4 bolts though, as they penetrate inside the gearbox and gear oil will find it's way along the threads. The TR3 used lead washers, I forget offhand what the TR6 used originally. I use copper washers on mine (kit from HF) along with a smear of Hylomar, they seem to work well and can be reused. Also be careful not to let the splines damage the seal as you reinstall the cover.

The problem with attaching the bracket at the front is that now it crushes the flange on the cover. The TR6 is different in that area, it doesn't use the cover with the rolled edges. However, yes, it is easy enough to cut down the old pushrod. You might not even have to cut more threads.

And BTW, the diaphragm clutch was introduced on the TR4A. All TR4 used the 3-finger B&B clutch same as TR2-3B.
 
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