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TR2/3/3A TR 4 transmission in a TR 3A.

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J

John_Progess

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My 1960 TR 3A project has a TR 4 transmission, serial number CT 53541. Is this a TR 4 or a TR 4A transmission and does it make any difference when it comes time to order parts. Thanks and have a good day!

John
 
John
I think it is a TR4 trans. Have you followed the overdrive thread here, it has some good information in it. There are are couple of changes to the trans from TR4 to TR4a.

Marv
 
Marv,
I forgot to mention that it is not an overdrive tranny. From reading that thread I decided to go out and check to see what tranny I had and discovered it is a TR 4 tranny but I didn't know if there is a difference in the basic 4 versus 4A model. I want to be sure that I order the correct parts. Thanks and have a good day!

John
 
What is the commission number on your TR3A (over or under TS50000)? I ask as some 59s ended up being sold/registered as 60s and TS50000 was a significant gearbox/engine change point (starter bulge).
 
I believe CT53541 would be a TR4A trans. They only made 40,000 or so TR4s, so CT numbers higher than that have to be 4A.

The only important difference in the transmission itself (that I know of) is that the front cover (where the throwout bearing carrier rides) got shorter by about 3/8" or so. This is required to use the 4A clutch. But supposedly the shorter cover still works fine with the TR3 clutch.

The Moss catalog shows that the 4A used the later narrow bushings for the clutch shaft; but either type will fit and work. My preference is for the earlier, wide brass bushings (and adding a way to grease them from time to time). There was also a change to the shift rail detents during TR4 production; but again either setup will work. As I recall, they changed from using a ball to a pointed plunger, which gave notchier shifts but covered up a tendency for some units to jump out of gear on overrun.

Of course, I'm comparing TR4 to TR4A. There were a whole lot of changes between TR3A and TR4, mostly to accommodate the synchromesh on first gear. Even the housing is different. If you haven't already, you'll need to elongate the holes where the rear motor mount bolts to the rear crossmember, to allow the extra length. You can force it together without slotting the holes, but the motor mounts won't last very long (BTDT).
 
My car has a 69000 commission number and the engine number is about the correct vintage. So should I fit a TR 4 clutch and TO bearing set up to the car? I have no idea how the car functioned as it was apart when I got it. Thanks for the help and have a good day!

John
 
John-

Do you still have the old clutch setup? If so duplicating it would be the easiest route to take. My guess is your flywheel is likely original, which means its likely you have a TR3/TR4 clutch setup. To use a TR4A clutch the flywheel would need to be redrilled as the 4A pressure plate at 8.5" is smaller than the TR3/4 pressure plate at 9".

The pressure plate for a TR3/4 car is a three-finger style, like this: https://www.rimmerbros.co.uk/Item--i-GCC127
For the 4A, it is a smaller diaphram style like this: https://www.rimmerbros.co.uk/Item--i-GCC228

Of course, with the 4A gearbox, you may have a 4A flywheel as well but I'm going to say its less likely. Unfortunately, I don't know the mounting hole dimension differences which would be a good way to check if your clutch is completely missing.
 
I agree, by far the easiest course is to use the clutch that matches your flywheel.

The mounting circle for the TR3-4 clutch is very close to 10.5". 4A is about 9.75"
 
There is a clutch attached to the flywheel. Right now the tranny is attached to the engine which is in the frame for weight while I was doing the body repairs. I don't know if it is the clutch that was on the engine when it was running but I will put the engine on a stand this weekend and let you know what type of clutch it is. Thanks for the help and have a good day!

John
 
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