TR2/3/3A TR3 Transmission Differences

[RedTR3]

I have seen references to "early" and "late" TR3 transmissions (standard not OD). Can someone fill me in on the differences in the early or late units? Thanks, Tim

 

[TFB]

Tim,
early no syncro first,late,full syncromesh.These are the only differences I am aware of,but anxious to here if any others,as I am contemplating upgrading.
Tom

 

[TR3driver]

There was another significant change, at approximately TS50K. A bulge was added to the bellhousing, to accomodate the later starter drive. The dipstick was deleted, and a fill plug added to the side.

There were also some minor internal changes I believe, but I don't recall the details offhand. I vaguely recall some of the bearings were changed, and maybe the washer that goes against the circlip on the mainshaft. Few other minor details, like early top covers were always drilled and tapped for both the OD switches and a reverse light switch, while later ones were not drilled unless required. (Not all of these changes happened right at TS50K either.) I've got the details at home, so let me know if this is what you want.

But the starter bulge is the big deal, because you can't use a later starter with an early transmission. (Although the aftermarket gear drive starter will fit, so that is one alternative.)

PS, synchromesh on 1st gear didn't come in until the TR4 and TR3B. (Don't recall offhand if the first run of TR3B had it or not, but the second run definitely did.)

 

[Don Elliott]

The pilot diameter was smaller on the very early TR2s.

 

[TR3driver]

The pilot diameter was smaller on the very early TR2s.

You mean where the input shaft goes into the pilot bearing in the crankshaft? There doesn't seem to be any mention of that in the SPC ...

But if you are talking about where the mainshaft goes into the input shaft, then that is part of the bearing changes I was talking about. The bearing inside the input shaft changed as well.

 

[White79MGB]

Hi Randall,

I think you covered what I need; my car has an early starter that still works - so apparently I can use either an early or late transmission as a swap. But I kind of like having the dipstick however.

 

[Geo Hahn]

If the dipstick is important to you (and esp if you havbe the old gearbox) I think you can swap on an early cover onto a late gearbox and have the dipstick.

If you do use a late gearbox on an early TR you will probably have to 'massage' the sheet metal of the tunnel a bit to make room for your the bulge.

 

[vivdownunder]

The TR3A 3 synchro gearbox changed at car TS26825.

Different input and mainshafts. Needle roller bearings replaced plain bearings.

As already covered, the next changes were at TS50000 to accomodate the new starter motor and delete the dipstick from the top cover. Thereafter the oil level had to be checked through the gearbox side plug. Backward step really.

It had been much easier (and safer) to home check the oil level through the tranny tunnel. Thereafter, apart from needing to work under the car, the side plug was a pig to get out.

Viv.

 

[TR3driver]

If the dipstick is important to you (and esp if you havbe the old gearbox) I think you can swap on an early cover onto a late gearbox and have the dipstick.

Yup. But if it's a 4-synchro box, then you need to swap the shift forks and rods from the later cover into the earlier cover.

I've got a dipstick top cover and shift lever mounted on a late TR6 box (with early TR6 gears and a TR4 OD).

 

[Don Elliott]

I have a friend who owns two TR3As and 2 TR4s. On one of his TR3As, he removed the 3 speed synchro g/box and put in one with an overdrive attached and which had come out of a TR-250. Since none of his TRs had the top dip-stick for checking the oil in the gearbox, when he saw the dip-stick on my 1958 TR3A, he drilled a hole on the top of the boss for the shift assembly from the TR-250 to accomodate a dip-stick.

 

[RedTR3]

OK, is it possible to swap the top cover from an old OD tranny with the dipstick to a non-OD? I assume that it is the same top cover and shift forks?...

 

[TR3driver]

OK, is it possible to swap the top cover from an old OD tranny with the dipstick to a non-OD? I assume that it is the same top cover and shift forks?...

Should work fine, as long as your new tranny is still a 3-synchro box. The shift forks and shafts changed for the 4-synchro (TR3B-TR6) box.

BTW, if you do use the side fill plug, IMO using a hex socket plug makes it somewhat easier to deal with:

 

[Geo Hahn]

And/or open a hole in the tunnel (the one with the rubber plug) for easier access:

Admittedly easier with the cardboard tunnel.

 

[RedTR3]

How about just drilling a hole in the top cover to accept the dipstick?

 

[TR3driver]

How about just drilling a hole in the top cover to accept the dipstick?

Should work, but you want to be sure the dipstick can't get into the gears. IOW the hole needs to be long enough (and the stick snug enough) to keep the dipstick from moving sideways very far.

 

[sail]

I drilled mine out with good results.

 

[bartu]

Does anyone knows what need to be done (changes) to fit a 4 synchro TR3B to a "TR3" (not an A ? Is there a number in the housing to identiy a 4 synchro transmission form a 3 synchro? Any info would be appreciated.

Thanks,

Joe

 

[Andrew Mace]

Does anyone knows what need to be done (changes) to fit a 4 synchro TR3B to a "TR3" (not an A ? Is there a number in the housing to identiy a 4 synchro transmission form a 3 synchro? Any info would be appreciated.

I'm not positive, but I suspect that a true 3B box would carry a "TSF" (or possibly "TCF") prefix serial number.

 

[TFB]

Hey Joe,what I learned from the forum pre purchase of my 3b trans w/od islarge bulge on left rear of trans indicates 1st gear syncro.
the 3b has a thin bellhousing flange like the non syncro,while later years TR250=6? have a thicker bellhousing flange.

I had to relocate the rear trans mount to the rear about 3/8-1/2",which suprised me because I have the thin bellhousing flange.I suspect that the later ones added the thickness to backside of the flange,and any full syncro trans requires relocating the mount.Drill 2 new holes almost tangent to the old,and you have to bend the heck out of the upright at back to get the mount to sit flat in new poition.I welded up old holes but probably not vital.
Also after all the great info I got I had the vendor install the dipstick cover.
Tom

 

[TR3driver]

I suspect that the later ones added the thickness to backside of the flange,and any full syncro trans requires relocating the mount.

Yup, just so.

Does anyone knows what need to be done (changes) to fit a 4 synchro TR3B to a "TR3" (not an A ?

You will also need to massage the sheet metal in the trans tunnel, so it will fit around the larger starter bulge on the later gearbox (which is also a problem for early 3As).

With my later TR6 gearbox, I had to install longer studs and modify the clutch slave mounting; but that should not be an issue with your early 4-synchro box.