TR6 TR6 "A" Overdrive fitted to a TR3A?

[bailee2]

have a opportunity to get a rebuilt "A" TR6 Overdrive for my 3. I was told once that this is not doable because the TR6 "A" has a slightly shorter input shaft. Can the input shaft be changed and then mount this trans to my engine? Are there clutch issues too? I have the older press on ring gear as well. Thanks in advance. Arlie

 

[Alan_Myers]

Hi Arlie,

I'm a little unclear if you are considering an A-type OD only and attaching it to your existing gearbox, or a gearbox/A-type combo and replacing your TR3's gearbox entirely. Let me try to address both scenarios.

I believe the A-type will work fine fitted to your existing TR3 gearbox. In my TR4 I have roughly the opposite: a TR3-era A-type fitted to a 2000 gearbox (essentially the same as TR6 gearbox). No fitting problems to speak of (see below).

Using your existing gearbox will mean installing the OD-compatible mainshaft into the gearbox, installing the mounting plate on the back of the g'box in place of the tailpiece (to attach the OD) and drilling and tapping the top cover for the inhibitor switches.

So, if you are re-using your existing gearbox, the input shaft is the same and it won't be a concern. Also, the clutch will be the same, and not a concern.

Now, if you were getting a TR6 A-type OD already mounted on a compatible TR6 gearbox, yes, the nose of the input shaft at the pilot bearing (in the rear of the crankshaft) is a bit shorter. It still works, though. I had that issue with the 2000/TR6 era gearbox in my TR4 as well. I plan to have a special pilot bushing made to compensate, or to just change the input shaft at some point. But I know of a cars with similar setups where nothing was done and they seem to get by fine (Note: putting a TR2-4 gearbox in a later car would be a problem! The longer input shaft would cause problems.). The short nose of the later input shaft still is about 3/8" deep in the pilot bushing on the TR4 crankshaft.

TR3A and earlier 3-synchro gearboxes themselves are slightly shorter than the later, 4-syncrho g'boxes, but the difference only really shows up at the driveshaft and that compensates just fine with the splined section. You might have to slot the holes in the rear gearbox mount a little, but that's easily done during installation.

There might be some clutch issues with a TR6 gearbox mated up to a TR3 engine. I'm not certain of this. The main thing I'd be concerned about is the later used a different diameter throwout bearing, and I think it rides on a different diameter front gearbox cover. However, these are external items that probably could be swapped around as needed. It's possible, too, to change to the later TR4A-TR6 type diaphragm clutch, if you wish. What's needed is re-drilling your flywheel since the later, lighter weight clutch is smaller in diameter. However, you can find plenty of reference to problems with this clutch in the archives, so it needs to be set up carefully. The TR2-4 clutch, although heavier, is pretty sturdy and problem-free.

There are some advantages to the TR6 gearbox, if that's what you are getting along with the OD. It has a heavier bellhousing flange that's less fragile than the TR2-4A gearbox. Also, a TR6 gearbox would give you synchro on all forward speeds. And, at some point, not sure when, the TR6 gearbox was upgraded a little internally.

Basically, the early and late versions of the A-type primary functional difference is that the early ones have a larger accumulator piston and will shift faster/harder into OD. The later A-types were slightly "detuned" to make them more "pleasant". The earlier ones are a little more desirable for racing. The really early TR2 and TR3 A-type had a slightly different arrangement at the solenoid, with a full cover protecting the actuating mechanism, but it is funtionally the same.

I think the TR6 A-type OD still offered 22% reduction, but I'm not certain of this. You should be able to tell for sure by the serial number, which will start with 22xxxxxx if it's that amount of reduction. J-type were 25% reduction and have 25xxxxxx serial numbers. Both of these assume no one has swapped around internals and changed the OD's reduction ratio at some point, which can happen, but is relatively rare.

I'm pretty sure the press on ring gear will work, too. In fact, didn't Triumph go back to a press on ring gear on the TR250/5/6, after switching to a bolt-on gear midway in TR3 production and up through at least the TR4A? One question is what starter you are using or if any changes are planned there. The TR6 gearbox can accomodate the later style of starter, but that would mean reversing the ring gear so that the teeth are oriented properly, if it's currently installed for the early TR3 starter. (Note: with a modern "gear reduction" starter, the change wouldn't be necessary)

You can get OD conversion/fitting kits and the gearbox mainshaft from John Esposito at www.quantumechanics.com, by the way. He would also be a good person to discuss all your concerns with in more detail.

Hope this helps!

/ubbthreads/images/graemlins/cheers.gif

 

[Geo Hahn]

[ QUOTE ]
...There are some advantages to the TR6 gearbox, if that's what you are getting along with the OD. It has a heavier bellhousing flange that's less fragile than the TR2-4A gearbox...

[/ QUOTE ]

Which means using longer bolts and studs to attach the gearbox to the block.

 

[Marvin Gruber]

Have put a TR6 "A"type o/d on a couple of TR3's and TR4's with no problems. Currently have a 56 smallmouth TR3 with the "A" type o/d, I have have this car for a couple of years. Haven't ever tried the "j" type on anything other than a TR6. You will need to replace studs at the top transmission mounts. I like to put pne long one on anyway to help align the transmission, slips in and not as much strain on the back when reinstalling the trans.

 

[Alan_Myers]

Hi again Arlie,

I took a quick look at Spare Parts Catalogs to see if I can identify any major differences between TR4 (same clutch setup as your TR3) and TR4A (same diaphragm clutch as used on TR6). I don't have a TR6 spares catalog to compare, but the following might help:

In this case, even the input shaft (constant pinion shaft, actually) numbers are the same: 204215. So the only change to TR6 was the shorter nose that was used with the different crankshaft. (Note: I would expect this number to change on TR6, but I can tell you it's still usable on TR4, in particular, and thus should work on TR2-3 too.)

The gearbox front cover are the same, too: 100157. There was some sort of change after TR4 CT23846, but the part number remained the same so I have to assume they are entirely interchangeable.

The clutch operating fork remained the same (106022) along with it's associated parts. The clutch shaft was the same on late TR4 as all TR4A, when Triumph went to a non-greasable version along with wimpier bushings in the bellhousing. I'd strongly recommend retaining your earlier one, that is the same except that it can be greased and enjoys larger and more durable bushings (a good retrofit for later cars, too).

The throwout bearing and TO bearing carrier are different, of course, to accomodate the change in the clutch pressure plate and spring method. But, because the underlying parts didn't change, it appears as if it would be okay to use a TR3 TO bearing and carrier on a later gearbox, which is what you'd need to do (unless you really wanted to update your clutch assembly too). Note: the popular Gunst TO bearing *cannot* be used on the TR4 and earlier clutches. But, the earlier clutches aren't prone to the problems that led to the development of the Gunst bearing, anyway.

As I said above, I don't have TR6 spares catalog. If you can get one (or maybe look on Rimmer or TRF websites) you might be able to compare the part numbers above with a TR6 gearbox, too.

Marvin's point is a good one I sort of glossed over. Yes, the bolts and stud need to be changed, too. Not a big deal and maybe a good opportunity to upgrade to Grade 8 bolts!

 

[bailee2]

Alan and Marvin,
Wow! Thanks for the fast reply. I would replace the entire transmission since I don't have all the crossover components. I will do some more research and get back to this subject. My other option is the 5 speed conversion which is a another topic. In St. Louis there are a few Healeys with the conversion and are top rated.
I do like the idea though of looking more more stock.
I am impressed with this site as I just found out about it and noticed some Healey guys I know. Thanks again as I am sure this forum is the neatest thing yet.

 

[JFS]

Arlie, I put a TR6 A type OD in my 58 TR3A. I kept the 3's clutch, but changed the flywheel to a TR4 for starter-header clearance (later changed to the smaller gear reduction starter). I did have to change to the longer input shaft (TR3, if I remember correctly) and slot the tranny mount. Alan pretty much has covered everything quite thoroughly and well. I never had an OD before and the improvement is fantastic! So is the fun factor! The 1st gear synchro is much appreciated as well.

 

[bailee2]

Thanks JFS,
I still have the bullnose starter whch was NOS in 2001 when I restored my 3. It has a nagging whinning sound recently and I am considering a gear reduction starter as well. So I will hold off buying the starter until I am sure that I have the flywheel and starter issue worked out. Big problem is that I just had my header and intake chrome ceramic coated and just got it all back together. But I am getting faster at R and R these days.
Arlie

 

[Alan_Myers]

Hi again Arlie,

I've not driven them both, but some TR folks have tried the 5-speed conversion and not really liked it (Many others love it, so I'm really not knocking it). I think a reason for this is that the TR gearbox is pretty darned good, especially the full synchro like you'll be installing. Triumph did a good job setting up the gears and the OD is like the icing on the cake.

A lot of folks look to the OD to give them more pleasant cruising rpms, which it will do. Others like it for the fact that it works on 3rd and 4th gears, at least, and even 2nd gear if set up that way. So, in effect, you end up with a 6- or 7-speed. Cool! For "spirited" driving all those gears can come in very handy, with a little practice.

Roger Williams in his books "Improving TR2/3/4" and "Improving TR5/250/6" talks a lot about the J-type and encourages folks to choose it over the A-type. I respectfully disagree and side with John Esposito who feels the A-type is much more robust. J-types are a bit less prone to leaking (run on lower oil pressure) and are generally less expensive.

I guess it all depends on how you end up using your OD. Someone wanting lower rpms on the highway will be happy with either and might actually prefer the J-type for its softer shifting. Someone who avoids highways to spend their time on twisty windy two-lane roads would probably prefer the A-type.

BTW, if you look at changing your flywheel, you might want to consider a lightened one. It's also a good opportunity to switch to the later, diaphragm clutch, if you wish, too. There's a bit more weight savings with it, too.

Have fun!

 

[bailee2]

Alan,
I appreciate your suggestions on the overdrive. I have a TR4 flywheel I can use so I will take a look at it for service, if it looks good I will have it machined. I like the idea of the aluminum flywheel too. I have to do some of these changes under the radar so if it is too costly I wait.
I am getting excited about the Triumph overdrive now since it does not sound like it will put the car out for long.
I am planning on taking it to VTR. I made the Branson TRA last year and did ok but driving would be easier with the overdrive. I assume the stock TR3 OD switch and wiring will be ok. I will look at both 3 and 6 wiring diagrams to be sure.
Thanks.

 

[JFS]

Arlie, if you aren't concerned about maintaining a stock looking dash, you might want to consider using a shift knob switch. I have one that I was told is from a Stag. It has the correct shift pattern scribed on it. I think Spitfires used the same switch knob. My TR3's shift lever is hollow, so I drilled an exit hole at its bottom and ran the wires through the lever. I find it much more convenient to use than a dash mounted switch. My overdrive is wired to work on 2nd, 3rd & 4th gears, giving the effect of a 7 speed if I want to play. /ubbthreads/images/graemlins/driving.gif

 

[bailee2]

Thanks JFS, (BTW, In the aircraft industry JFS means Jet fuel starter) it is a small gas turbine engine used to provide bleed air to start the main engine. Thanks for the comment. How did you find the Stag switch, Vicky British, ebay??? If it is a Spitfire switch I might have a better chance of locating one.
I like that idea since the original position is not that ergonomic, or better put driver friendly. What did you do to prevent the wires from chaffing the shift bottom hole?
That is a neat idea! I need you and Alan for our club Tech Sessions.
/ubbthreads/images/graemlins/iagree.gif

 

[JFS]

Arlie, I got the switch from a guy named Chris Mills who runs a local LBC salvage yard. Although the Spit uses the same switch knob, I think it is scribed with a different shift pattern. I used some shrink tubing in place of a grommet to prevent chaffing; I've been running it for a number of years with no problem. Jet Fuel Starter, eh? I like that -- good alias. /ubbthreads/images/graemlins/smile.gif