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TR4/4A Want to buy tr4 tranny for my tr3a

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TS66693

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I interested to purchase a TR4 tranny to put into my TR3A to gain synchro in first gear! I was also told that the TR4 tranny is 1/2" longer than the TR3 tranny (added synchro rings I guess). Does the extra 1/2" in length necessitate any additional fitments/alterations when installing?
 
I do not believe that there is any difference in the length of those two trannys. I have made that swap in the past with no problems. What you may be referring to is the TR 6 tranny that has a thicker front housing. When using that swap one needs to use longer studs at the top of the bell housing. And possibly longer bolts the rest of the way around.

I may have a line on a TR4 tranny within a reasonable distance if you are looking for one. Let me know if you are interested and I will follow up with my source. The tranny is in your area not in California.
Charley
 
There is about a 3/8" length difference between the front flange and the rear mount, 3 synchro vs 4 synchro. You can elongate the holes in the rear cross member to accommodate the difference. Drill a new 3/8" hole right behind each existing hole, so the holes almost touch, then file out the metal between them to form a slot. On my 3A, I also had to bend down the flange on the back of the cross member, but that may vary from car to car. The driveshaft has enough travel, so no change needed there. And since your car is after TS50,000, you won't have any trouble with the starter bulge.

I did force it together on my first conversion, but for some reason the motor mounts never lasted very long :smile:
 
Thanks Randall! I wondered why the rear mount on my TR3A with TR4 transmission had been slotted toward the back. The rear flange on mine had not been bent back and that made for a tight fit and the mount seemed to be riding up on that flange. I recently took the cross piece off and bent the flange toward the back and welded shut the old original holes to ensure the cross piece was strong.
Regards,
Bob
 
TRMark said:
What is a TR4 transmission worth?
Click to expand...

It's a conundrum. In my experience... if you have a good one to sell it is worth very little but if you want to buy a good one it may cost you dearly.

When I put an OD in my TR4 I parked the old gearbox in the corner as I found I couldn't get more than core prices for it. I knew it was good but most buyers assume (quite rightly) that a used gearbox is a pig in a poke and expect a rebuild will be needed.

Personally, I see no great advantage in having a synchro in first. After decades of driving (TR3) w/o it, even now in my TR4 (which has it) I still shift as if there was no synchro there. I guess it is just simpler than thinking about which car I'm in every time I come to a stop.
 
TuffTR250 said:
I recently took the cross piece off and bent the flange toward the back and welded shut the old original holes to ensure the cross piece was strong.
Click to expand...
FWIW, I left the slots open on my 3A and the cross member was fine even after the accident that totaled the car and broke the front suspension. I kept it when moving the gearbox to my current TR3, just because it was easier than doing the mods again.
 
Geo Hahn said:
When I put an OD in my TR4 I parked the old gearbox in the corner as I found I couldn't get more than core prices for it. I knew it was good but most buyers assume (quite rightly) that a used gearbox is a pig in a poke and expect a rebuild will be needed.
Click to expand...

Exactly my situation
 
charleyf said:
I do not believe that there is any difference in the length of those two trannys. I have made that swap in the past with no problems. What you may be referring to is the TR 6 tranny that has a thicker front housing. When using that swap one needs to use longer studs at the top of the bell housing. And possibly longer bolts the rest of the way around.
Click to expand...

After thinking about this some more and reading the other replies, I realized that what I did was to put a TR4A tranny into a TR3B - a late TR3B that already had the equivalent of a TR4 tranny in it. Of course I had no problems with that swap.
Charley
 
Hi Charley,
Thank you for replying to my inquiry! If you could let me know more about the TR4 tranny that might be available in my area, I would be interested to look into it.
Thanks!
Barry
 
Quote from Randall: "[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]I did force it together on my first conversion, but for some reason the motor mounts never lasted very long :smile:"

i'll start another thread on this topic as I just replaced my motor mounts & have a problem:
it may have originated with the TR6 type A , OD tranny I had installed.[/FONT]
 
TRMark said:
What is a TR4 transmission worth?
Click to expand...

I swapped out my tr3a trans for a tr3b with the syncro also.As far as price,its been 2 yrs,but I got a totally rebuilt trans and o.d.,with dash switch and wiring harness,modified to keep oil dipstick in the top, from ebay seller Trbrad in Gulfshores Alabama for I think $2100+$75 shipping.Very Happy,althouth in hindsight I should have taken the later trans with thicker bellhousing flange since they both require modifying the rear mount.
Tom
 
Thanks Randall,
When I get into the installation, I will keep your instructions in mind! :smile:
I did not quite know where you were headed with your last sentence... did you mean that after installing the TR4 tranny, that your motor mounts wouldn't last, or wore out?
Cheers!:smile:
 
TS66693 said:
Thanks Randall,
When I get into the installation, I will keep your instructions in mind! :smile:
I did not quite know where you were headed with your last sentence... did you mean that after installing the TR4 tranny, that your motor mounts wouldn't last, or wore out?
Cheers!:smile:
Click to expand...
The first time I installed a TR4 tranny into a TR3A, I didn't know about the length difference and just assumed they were the same. That was around 1976 or so and I didn't even have a Haynes manual, let alone the Internet to steer me right. Not knowing any better, I forced the mounts into place, but that put a lot of tension on them. Both front motor mounts broke not too long after that.

A few months later, I also learned the hard way that a TR4 rear axle is wider than a TR3A axle.

It's like the old saying: Good judgement comes from experience. Experience comes from bad judgement.

Oh, BTW, I only paid $300 for the complete TR4, including working OD.
devilgrin.gif~original


Which, come to think of it, was more than I paid for that 3A.
 
TFB said:
althouth in hindsight I should have taken the later trans with thicker bellhousing flange since they both require modifying the rear mount.
Click to expand...
True, but the thicker flange complicates other things to some extent. I couldn't find studs the right length, so had to make some; and the clutch slave mounting will need to be modified. If you leave the mounting bracket on the back of the flange (as original), the thicker flange moves it back until the pushrod is too long.
 
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