Gearbox top cover.

[Charlie D]

Hello All,

 

The 40 year long rebuild of my ’59 TR3a is progressing, and I have got to the stage of cleaning up the gearbox and am about to fit it.

 

Over the years bits have come and gone, so I don’t have a clue where this box came from. All I know is that the serial number is:

 

CT700xx

 

And the OD serial number is:

 

22/61759/0038xx

 

I read that this makes it a TR4/4a box. Probably a 4a because of the quite high number. (I’m guessing a bit here…)

 

Now the odd thing is that it is fitted with a dipstick.

Am I right in saying that from the TR4 onwards there was no gearbox dipstick?

 

The obvious answer here is that someone has swapped the top cover with an earlier one, which did have a dipstick.

 

But…

 

BOTH the OD switches are stamped with “4/66”, which I am taking to mean “April 1966”

 

Which again ties it into a TR4a.

 

OK, someone could have fitted the switches to an earlier top cover, but why? One might have gone faulty, but not both at the same time.

 

The dipstick hole looks very professional (Not the sort of butchery that I would have done…), so I guess it was always there.

 

I don’t think any of this matters too much, just curious about it’s origins.

 

However…

If it is an earlier top cover, from a 3 synchromesh box, is it OK being fitted to a 4 synchromesh box?

 

I like the idea of a gearbox dipswitch. It seems sensible.

(But you can’t beat the old Rover P4 idea of pressing a button on the dash and the petrol dial turns into an engine oil level indicator.)

 

 

Charlie D.

[Lebro]

I would not have expected a 3 synchro top cover to work with a 4 synchro box.

 

Bob.

[Guest ntc]

I would not have expected a 3 synchro top cover to work with a 4 synchro box.

 

Bob.

It does, Roy Talbot fitted me one to a six A type gearbox

Edited July 23, 2017 by ntc

[Fireman049]

Charlie D ~

 

Here's the top cover from my 1960 3A. No dipstick hole. The gearbox is a four synchro.

I believe that the dipstick was fitted to the TR2 and possibly the TR3?

 

Hope this helps.

[BlueTR3A-5EKT]

My TR3 has a 4 synchro Stag internals gearbox with a dip stick. I drilled the top cover to accept it. At C&B I used to do this job for customers and also made dipsticks.

 

Peter W

[Ian Vincent]

My 1959 TR3a had a dipstick fitted in the top cover but it was a non O/D box.

 

I acquired a 2000 saloon box which was fitted with O/D and a spare cover from a TR which came complete with a dipstick hole (but no dipstick) and was drilled and tapped for O/D switches.

 

I rebuilt this spare cover to incorporate both a dipstick and the necessary O/D switches and it now works perfectly on my saloon 2000 O/D box. In other words, as far as I can determine, all the parts are interchangeable.

 

Rgds Ian

[Don H.]

I almost fitted an earlier dipstick style top cover to my four-synchro 'box when we added O/D. Decided not to in the end, but it would have been easily done.

[Lebro]

Seems I was wrong in my assumption, quite surprised that the selector forks are in the right place given the different construction of the 1st / 2nd gear selection hub.

 

Bob.

[BlueTR3A-5EKT]

Seems I was wrong in my assumption, quite surprised that the selector forks are in the right place given the different construction of the 1st / 2nd gear selection hub.

 

Bob.

I would guess the trick is to change over the selector forks from the 4 synchro to the dip stick drilled 3 synchro. Reverse also being a most obvious candidate.

 

Other issues would be the design of the spring and how the gearstick is held in place. It changed in the TR6 era to a bayonet fitting retaining cap, instead of the long bolt through the stick.

 

Peter W

[Charlie D]

Thanks for all the replies and comments.


It’s prompted me to look deeper and I have discovered that the dipstick ended at TR3A TS50000.

Also the parts book shows that although the main casting is the same on the 3 sync and 4 sync, several of the other parts differ between the two.

So I guess it is possible to swap them over, so long as the relevant parts are fitted as well.

Because I have the switches dated 4/66 I would guess that it is all original TR4A, and someone has simply drill the hole for the dipstick.

(I hope they did it on the bench, and not while it was still attached to the gearbox…)


Regards,

Charlie D.