TR4/4A Adding OD to Standard TR4 Gearbox

[Burgieman]

Hi There,

I have several questions someone might be able to help me with regarding Overdrive on a TR3B

I purchased the car recently and it has an older TR3A gearbox in it without 1st gear synchro (someone replaced it at some point in its life) Originally it had overdrive but that is now gone. So I'd like to replace it... I do have some parts but would like to know what I need to complete the conversion. Here's what I have.

1) TR3 gearbox working fine in car
2) TR4 gearbox working not in car
3) rebuilt OD unit working not on a gearbox, Serial# 22 1374 005133 GB# 456007 (i purchased it along with 2 shafts and gears)
4) TR4 input shaft and gears
5) TR4 mainshaft and gears
6) adapter plate for OD to TR4 gearbox
7) extra TR4 gearbox housing

I don't know if the extra output shaft is for an OD or standard box. The owner couldn't remember. I can't see a part number on either shaft so I'm assuming its on the shaft under the gears. I read that the OD mainshaft is 1/2" shorter but I don't know what the length of the standard shaft or the OD shaft should be to measure the one I have here.

Questions:

How long is an OD mainshaft or standard mainshaft?
What do I need to add the OD to the standard TR4 gearbox I have?

I appreciate any help someone can offer.
Cheers,
Adam

 

[lbcs_r_fun]

Hi There,

I have several questions someone might be able to help me with regarding Overdrive on a TR3B

I purchased the car recently and it has an older TR3A gearbox in it without 1st gear synchro (someone replaced it at some point in its life) Originally it had overdrive but that is now gone. So I'd like to replace it... I do have some parts but would like to know what I need to complete the conversion. Here's what I have.

1) TR3 gearbox working fine in car
2) TR4 gearbox working not in car
3) rebuilt OD unit working not on a gearbox, Serial# 22 1374 005133 GB# 456007 (i purchased it along with 2 shafts and gears)
4) TR4 input shaft and gears
5) TR4 mainshaft and gears
6) adapter plate for OD to TR4 gearbox
7) extra TR4 gearbox housing

I don't know if the extra output shaft is for an OD or standard box. The owner couldn't remember. I can't see a part number on either shaft so I'm assuming its on the shaft under the gears. I read that the OD mainshaft is 1/2" shorter but I don't know what the length of the standard shaft or the OD shaft should be to measure the one I have here.

Questions:

How long is an OD mainshaft or standard mainshaft?
What do I need to add the OD to the standard TR4 gearbox I have?

I appreciate any help someone can offer.
Cheers,
Adam

You need an appropriate OD main shaft.

 

[TR4nut]

The output shaft is quite different for the overdrive - large splines on the end, and no threading for a nut to hold any kind of rear hub. I thnk you can forget about using anything out of the TR3 box, not much interchangeable there except maybe a bushing.

My advice first though is to study up on how to rebuild these units and I think you'll see if you are missing parts. Good starting points:

Nelson Reidels articles here.

VTR tech articles here.

Also, if you find you need an output shaft, you can get new ones here and other places for example. There are some differences in parts so you need to make sure the gear set / input shaft / output shaft are similar vintages.

Other parts that might be missing are the cam the drives the oil pump in the od, and the springs in the od since they would be loose once everything is torn apart.

 

[Celtic2]

You will want to add the two wiring harnesses, dashboard mounted OD switch, two limit switches and possibly a speedometer cable to your list.

Gary

 

[Marvin Gruber]

Adam
Sent you a PM with a guy's number that will build the trans for you

Marv

 

[TR3driver]

I read that the OD mainshaft is 1/2" shorter

Just curious, where did you read that? The difference in length is closer to 6" than 1/2".

I think everyone else has pretty well covered your questions, so I'll add only that this would be a good time to give the gearbox anything it might need soon, like maybe new synchro rings, thrust washers and seals. You (or someone) will be tearing it almost completely apart to change the mainshaft and add the isolator switches. There is a service bulletin that notes the correct location for the switches is not always in the center of the casting boss.

You may also have to change some of the bushings and spacers to get the right end float on the new mainshaft.

The wiring harness is pretty trivial, so you can make your own if you choose.

I would also plan on doing a pressure test on the OD before installing it in the car, no matter what it's history is.

 

[Burgieman]

Wow, thanks for all the responses. I know I read the 1/2" shorter thing somewhere if I remember or find it I'll let it be known. So the parts all came from a serious TR4 IRS daily drive/owner for 35 years. The OD came with all the springs and extra bits outside of the OD unit along with the adapter plate for his TR4. It looks like the serial was for later TR2-1964 TR4.

As far as the shaft he gave me, I now know it is an OD shaft (no threading and is 16 1/2 inches long) so that's pretty exciting. I'm glad nothing is worth using on the TR3 gearbox currently in the car. It allows me to just run that until I merge the TR4 box and OD unit. I'd love to tackle this myself... I've never dived into gearboxes before.. only heads and rear ends so if that experience isn't enough let me know now...

I'll snap some shots later on and post what I have, maybe an eagle eye will be able to spot more accurately what I have.

 

[TR4nut]

Take a good snapshot of your OD shaft - just guessing but there are maybe 3 variations of those out there (TR3 3 syncro, TR4-early TR6, late TR6?) and that will dictate a lot on how it will need to be put back together.

 

[TR3driver]

I'd love to tackle this myself... I've never dived into gearboxes before.. only heads and rear ends so if that experience isn't enough let me know now...

Check out the links that Randy posted above. Both series of articles are great.

If reading those, or the prospect of building some simple tools for yourself, doesn't scare you off, then IMO you will do fine. It's not especially tricky, there are just a lot of details that have to be checked and gotten right.

FWIW, I picked up a cheap digital fish scale for checking the various forces. Seems to work OK, but you have to have a steady hand to use it because the update rate is so slow.

And of course, if you have questions, you know where to ask!

 

[TR3driver]

Take a good snapshot of your OD shaft - just guessing but there are maybe 3 variations of those out there (TR3 3 syncro, TR4-early TR6, late TR6?) and that will dictate a lot on how it will need to be put back together.

There are more than that; at least two different ones for the TR3 box, two (oops, I looked it up, there are 3 of these) for 4-synchro w/A-type and two (or is it 3) for 4-synchro w/J-type.

To complicate matters even worse, it is sometimes possible to swap them around along with other components. For example, my current gearbox has a later TR6 housing, but an early TR6 gearset & OD mainshaft. (Plus a TR3 top cover and a TR4 OD ) So don't be too surprised if you find things don't fit quite as expected.

 

[MDCanaday]

Sell it all on E-bay, take the money and do a 5 speed with an Eaglegate conversion.I have done several it is THE answer,all else is questionable.
MD(mad dog)

 

[hondo402000]

and while you are at it sell the engine too and buy a crate motor and install that. heck if you go that far sell the car and buy a BMW Z3, Just kidding, send it off and have someone rebuild it, its worth the money and they can do all the up grades like new syncros, and layshaft bearings replace all the chipped gears, and put the OD back to like new condition with better friction material on the clutch, unless you like doing that kind of thing. but if you have to pull it out again and go back thru the tranny or OD you will have lost all the money you thought you would save by doing it your self. Just my opinion and just because I have done projects and ended up doing them again and in the end letting a professional really fix it right.

Hondo

 

[tdskip]

Hi Adam - welcome.

Lots of wisdom and good advice here - as you have already found out.

I know the guy Marv is going to connect you with - good guy. There are several places in CA that can rebuild these as well. And of course Quantum in CT is a go to as well.

What my preference as been is to start with a factory OD unit rather than trying to "make" one. Parts is parts so it can be done but adjusting for homework / changes as Randall and others have pointed out / and cost of getting all the bits correct sourcing a OEM unit is usually viable.

Not having a syncro on 1st gear isn't a big issue in my opinion - nice to have but not a deal breaker by any means.

Keep us posted!

 

[HerronScott]

When I restored my TR4A, I had picked up a used TR3 overdrive transmission as having the overdrive was a big plus over not having syncro first. I was also used to non-syncro first from my wife's 1968 Spitfire as well. Unfortunately in the first 6 months, I lost a tooth on the laygear so I ended up sourcing a TR4 mainshaft and overdrive adapter plate for my original transmission, rebuilt it with new bearings, syncros and transferred the overdrive unit and top cover with switches over from the TR3 transmission (I think that I had to switch parts in the top cover to match the syncro first if I recall correctly).

I had never done anything with a transmission before and I didn't recall finding it that difficult except for removing the mainshaft circlip. After a lot of work with several screwdrivers and some colorful language, I was able to get it off though. I was certainly nervous but it all went together well and I was very happy with the result. I didn't have any issues with the transmission or the overdrive and I put another 70,000 miles on it. Note this was pre-Internet so I only had my Bentley and Haynes manual and a copy of someone's handwritten notes on how to do it. You have a lot more resources available to you now including the Buckeye Triumph guides and some really smart and experienced people in this forum so if you aren't afraid to tackle a suspension rebuild rebuild or certainly an engine rebuild I would say go for it.

Scott

 

[tdskip]

Scott is more talented with a wrench than I am! (but not saying much - ha)

 

[HerronScott]

Tom,

HA, I doubt that! I was 24 and had little spare money so I was limited to doing everything mechanical myself or it didn't happen. Bodywork and paint and of course machining for the engine work was farmed out.

Being broke definitely forces you to do things you wouldn't tackle otherwise.

Scott

 

[TR3driver]

had little spare money so I was limited to doing everything mechanical myself or it didn't happen. Bodywork and paint and of course machining for the engine work was farmed out.

Being broke definitely forces you to do things you wouldn't tackle otherwise.

BTDT

But in my case, anything I couldn't do myself, didn't get done!

The "pros" also don't always get things right the first time either.
And honestly if something has to go sour, I would prefer it was something I did, because at least that way I will learn not to do it again.

But then I also enjoy knowing it's something I had a hand in building. Driving a car that someone else built just isn't the same.

I'll also say that virtually everything I've tackled has turned out easier (in retrospect) than I expected. Once you get past that fear of the unknown, none of it is rocket science; just old fashioned attention to detail.

 

[cheseroo]

If I may chime in, I'd say the most important thing I did when I rebuilt my trans was to put all the gears/washers/spacers/etc on a coat hanger as I took it apart. Several appear very similar but the mic showed them to be of different sizes. I regret having put new synchros in as the old ones spec-ed out okay. The old synchros worked better.

 

[HerronScott]

Rich,

Good advice as I did the same thing to keep things in the right order. I've heard others still reporting issues with new syncros. They were still selling original British Leyland ones when I did mine in 1982 so no issues with those!

Scott