View Full Version : TR2/3/3A TR3A 3-Synchro Gearbox Rebuild

Joel M
02-25-2018, 11:11 PM
Hi All,

I'm a new member that is neck deep in the restoration of my late father's 1959 TR3A. Currently I'm working on rebuilding the 3-synchro gearbox, and am hoping to get some advice (mostly on acceptable wear) due to the fact that this is my first transmission rebuild. I would like to reuse components that are in good condition, but replace the ones that are out of spec, or that would be at risk of failing soon due to age and/or condition. Here are the details...

Gears: No broken gears, but some chipping on 1st. I think I won't be able to tell the difference if I replace with new, but I'm not entirely sure. Also not sure how 1st gear performed when last driven because it was over 30 years ago (I was only around 7 years old). All other main and layshaft gears looks good.


Countershaft: This gearbox has loose needle bearings, and there appears to be little wear on the countershaft. In fact, I really can't measure any dimensional differences across the shaft, but you can obviously see where the bearings rolled. I'm thinking it would be fine to reuse, but it seems that this part is commonly replaced. Not sure if the shaft shown in the picture has enough wear to warrant replacement. Thoughts?


Thrust Washers: I wouldn't have thought twice about replacing these because there appears to be some wear and even a little gouging, but I have seen information that the reproduction washers are inferior because they are not steel backed. Is the wear shown in the picture acceptable? Should I replace even if the new part is of inferior quality?


Bushings: 3rd gear bushing looks good and easily meets float spec. 2nd gear top hat bushing also looks good, but barely meets float spec. Top hat bushing seems to be another part that is commonly replaced due to breakage. Should I assume that it has been weakened and will fail sooner rather than later? I am thinking I should replace, especially since the spec is borderline.

Bearings: I assume replace all 3 bearings regardless, right? Not sure how to check them, but they do turn smoothly.

Countershaft Bearings: Should I also replace the needle bearings? They look good, but I assume go ahead and replace.

Synchros: 2 of the 3 were out of spec, so I will replace. Any advice on the standard synchros versus the premium ones?

Any other parts that you would definitely replace other than gaskets and seals?

Thanks in advance for any advice given. I'm sure there is a lot of experience here, and I am looking forward to contributing to the forum.

02-26-2018, 01:14 AM
1. I think first gear is OK. If you replace it, the new one will soon be in the same condition--they just get chipped in normal life.

2. I think the countershaft is OK. You'll always get some discoloration from use, but if there is no corrosion and it measures OK, it's fine.

3. If the float of the cluster gear is OK, I'd reuse the thrust washers.

4. I wouldn't replace the bearings without reason. A lot of the newer ones are much lower quality than the old ones. If you do replace them, get Timken or some other top quality. The original ones on my TR4A were British-made Timkens; probably yours had the same. They're good bearings.

5. Same story for the countershaft bearings; with no corrosion of the shaft, they are probably just fine. I think you have loose needles, don't you? The caged ones can be hard to remove.

6. I bought the uprated synchros; I don't know if they are much better, but they are not that expensive. British Parts Northwest had the best price, when I looked.

7. If the top-hat bushing is out of spec, it's probably a good idea to replace it. They do break, but it doesn't mean that yours will, or the new one won't.

As for other parts, do the checks listed in the shop manual, and you may find other parts that need replacement. If they meet the specs, I'd keep them.

Have fun! Transmissions, I think, are fun to rebuild. Not nearly as hard to do as many people assume.

02-26-2018, 09:58 AM
I agree with most of Steve's assessment.

The only exception is I would replace the needle bearings in the countershaft regardless. They are cheap and are usually the first parts to die, plus they are cheap.

Check the top hat bushing very closely in the corner. That is where they crack and eventually break. Most have cracks there, but if not, then re-use it.
Always buy the best synch blocker rings you can get. So, "yes", pay for the premium.

I would recommend dressing your first gear with a dremmel and cut-off wheel to look like this when done:

https://i1082.photobucket.com/albums/j377/cjdurant/DSC02578.jpg (https://s1082.photobucket.com/user/cjdurant/media/DSC02578.jpg.html)

Here is a thread I did about wht wear is acceptable and not in a gearbox:


Best of luck!

02-26-2018, 10:40 AM
The Ohio Buckeye Triumph club has excellent technical articles on TR250 and TR6, including transmission rebuilds. Since the TR3 transmission is very much the same as the TR250/TR6 transmission, I recommend that you consult those articles for your rebuild

02-26-2018, 10:37 PM
I can tell you where I'm coming from--most of my gearbox experience is with Porsche "901" transmissions, which were used on the early 911s and 912s. With those, a set of synchros for ONE gear is about double the cost of the whole set for the TR4 box. So, a set of even the "expensive" sychros for the TR4 strikes me as a bargain. I once priced out a whole set of replaceable parts for a 901 five-speed box, and it came to about $3500. For that reason, we do not replace parts in those boxes unless they clearly need to be replaced. It is common, also, to move the top-gear synchros to lower gears, as the top-gear parts get little wear. Of course, this requires a lot of judgement, and I still favor summary replacement of certain critical parts, like synchro bands. So, I'm prejudiced toward reusing good parts.

Not only that, but I'm getting a little tired of low-quality and carelessly designed and manufactured components. This past week, I was seduced by the Lucas, five-vane water pump, and I tried to install a new one on my pump housing. I spent several hours doing what should have been a half-hour job. The pulley dragged on the pump body, and the nylon part of the Nyloc nut didn't engage the threads on the pump shaft. Also, the slot for the woodruff key was too shallow, so the pulley wouldn't fit over it. I had to grind off a bit of the body, repaint it, find a thinner washer, and grind down the key a little. Oh, and the shaft diameter was a little too great, so I had to ream out the pulley an extra mil; luckily, I had an appropriate reamer.

Joel M
02-26-2018, 10:51 PM
Thank you all for the advice. After reading your posts, I feel much more confident about being able to do a good job on the rebuild. I know I will have more questions, but in the meantime I'm going to start digesting all the information contained in John's rebuild guide, and further inspect each component. I really think this is going to be a fun project!


03-02-2018, 10:17 AM
There are also some good articles on the VTR web site:

03-02-2018, 02:27 PM
Any thoughts on oil for your rebuilt gearbox?

The book calls for 80/90 weight GL4 oil but GL4 is getting hard to find. My Ford Ranger manual gearbox uses ATF. I had to double check the hand book before I refilled it.
TRF has quarts of GL4 oil but I was hoping to find it locally.


03-02-2018, 05:39 PM
NAPA usually has StaLube GL4 85/90 by the gallon, or the store can order it for you from their distributor. At least they do in Raleigh.

03-02-2018, 08:28 PM
You can also get Redline GL4 on eBay. Loads of people sell it.

03-02-2018, 11:57 PM
The NAPA guy was a bit of a Smart A**. Said "well if you are worried about it wearing out don't drive it so much"
We do not have a local NAPA store locally. This one was about 40 miles away.

Had not thought of E Bay.


03-03-2018, 01:12 AM
Not only a smart a** but an imbecile too.

03-03-2018, 09:25 AM
Amazon Prime has GL4 for about $39.00 per gallon with free shipping if a Prime member. Tell the NAPA guy to think before he speaks, you're the customer, just because he sells parts doesn't mean he's an expert at anything. Looks like Amazon has good prices on MT-90 too which is what I use and really like.

Joel M
03-04-2018, 07:45 PM
So I was able to do a more detailed inspection and measurement of the gearbox components this weekend, and as a result have a few more questions:

1) Dog Teeth on 2nd, 3rd, and Continuous: Curious, but 8 continuous dog teeth (out of 30) on all three main gears appear to have retained their original shape with some rounding; however, the other 22 teeth on each gear look like they have been cut at an angle. After reading John's guide, I think I may be forced to replace. Based upon the pics, what are your thoughts?

2nd Gear
52753 52754

3rd Gear
52755 52756 52757

Top Gear
52758 52759 52760

2) 3rd Gear Bush Float: Gear width was 1-mil under new condition at 1.216", so I guess there has been some wear. Bushing measured center of new condition at 1.224, resulting in gear float of 0.008 which I think is marginal. Would you replace gear? Maybe a moot point if the angled dog teeth necessitate new gear.

3) Countershaft: Diameter measured in spec, but about 1-mil less at needle bearing location. Needle bearings also appear to have lost about 1-mil off the original 0.118. I have decided to reuse the countershaft but replace the needle bearings.

4) Reverse Gear: I don't think it looks that good, and bushing has also lost about 1-mil resulting in clearance just out of spec. It is interesting that the new gears don't seem to have dimples on the bushing - I though this was needed for good oil flow. Should I replace?


5) Main Bearings: The current bearings are original Hoffmans. Are these considered good bearings?

If I do need to replace gears, any recommendations on vendors? A quick search show the cheapest prices from Rimmer Bros. in the UK. Does anybody have any experience with them? Are they quality parts?

Thanks in advance for any advice you can give.


03-04-2018, 08:27 PM
The asymmetrical dog teeth are actually original. Much later (during TR6 production), they went to symmetrical teeth.

The wear on 1st & reverse will make it more difficult to shift into those gears; but I would probably leave them alone. Replacing gears with new gets kind of expensive. Learn the trick of 'touching' 2nd gear (so it's synchro ring will stop the countershaft from spinning) before shifting to 1st or reverse.

The last time I ordered from Rimmers, fully half of the items I received did not fit properly. That was a long time ago, though. Before that, a friend bought a rebuilt transmission from them that kept popping out of gear. She returned it to them twice, before finally taking it to Herman to be fixed right. I buy from TRF if they have it (the stuff from Rimmers was for my Stag, which TRF doesn't cover very well.)

Joel M
03-04-2018, 08:55 PM
Wow, I would have never thought the gears were designed to have 8 symmetrical dog teeth and 22 asymmetrical. I wonder why they did this?

03-07-2018, 12:06 AM
Yeah, I had the same reaction. Porsche dog teeth are all symmetrical, so when I first saw the TR ones, I thought I needed new gears. A little investigation showed me that they were made that way. Transmissions for many other cars have asymmetrical teeth as well. I don't know why it's done.

I have mixed feelings about parts that are only a mil or so out of spec. I wonder how much that matters, especially if the choice is between a part that is a little out of spec and one of unknown quality that might or might not be better. It's not like the transmission won't work if one bushing is a mil short. I wonder, too, if the factory consistently met its own specs. I frankly doubt that it did.

03-07-2018, 12:41 AM
Well...it’s new to me. I have one single input shaft that has the asymmetrical teeth...and I thought they were worn that way. Other than that, and at least 3 dozen rebuilds of many marks, I have never encountered intentional asymetric machining of the dog teeth. I’ve been trying to come up with a possible reason it would be beneficial...but I can’t think of any reason?!?

03-07-2018, 11:59 AM
Just a WAG : During an upshift (by far the most common shift), one leading face takes most of the impact and wear. Making that face longer (at the expense of the opposite face) might make the shift easier, or make the parts last longer.

03-07-2018, 12:05 PM
Get's curiouser and curiouser. Apparently even Porsche switched to asymmetrical dog teeth in 1977, with the "915" transmission, which followed the 901 (the one I know about). I wasn't aware of that. Here is an example of the teeth that fit onto the gear, which is replaceable in the Porsche. It's pretty extreme:


Rauch & Spiegel (German for smoke and mirrors, if you can believe it--I wonder if that's a joke) is a major maker of aftermarket Porsche transmission parts.

03-07-2018, 12:34 PM
I can understand making all the teeth asymmetrical to improve fast upshifts at the track. I have trouble understanding only making 2/3 of the teeth asymmetrical though. Maybe the engineers figured 2/3 of the shifts are up, with only 1/3 down?? Maybe Triumph wanted to emulate the German idea, but were non-commital?? If it improves upshifts, then why not make ALL the input shaft dog teeth on the input shaft asymmetrical, since they only see upshifts??

Boggles me.

Joel M
03-08-2018, 12:05 AM
I found a technical paper on asymmetric gear teeth design that does a good job explaining their purpose in the introduction:

"In propulsion gear transmissions the tooth load on one flank is significantly higher and is applied for longer periods of time than for the opposite one. An asymmetric tooth shape reflects this functional difference. Design intent of asymmetric gear teeth is to improve performance of the primary drive profiles at the expense of the performance for the opposite coast profiles. The coast profiles are unloaded or lightly loaded during a relatively short work period. Asymmetric tooth profiles also make it possible to simultaneously increase the contact ratio and operating pressure angle beyond the conventional gears’ limits. The main advantage of asymmetric gears is contact stress reduction on the drive flanks, resulting in higher torque density (load capacity per gear size)."
DIRECT DESIGN OF ASYMMETRIC GEARS: APPROACH AND APPLICATION*Alex Kapelevich, AKGears, LLC, 316 Oakwood Drive, Shoreview, MN 55126, USA

Based upon my understanding of the above, I would guess they used 22 asymmetric teeth to increase the load capacity for the gears during drive, but kept 8 teeth symmetric to maintain an acceptable level of performance during coast. If that's the case I think the asymmetrics are a better gear, but also probably more expensive to manufacture (which may be why they switched to symmetric gears at a later date).


03-08-2018, 12:35 AM

03-08-2018, 01:00 AM
Interesting article Joel. So the asymetrical is to reduce loading in drive, but at the expense of coast. I’m not sure I would rate that as a “better” design, but more of an attempt to prolong a gear that is designed at the edge of it’s limits. In other words, it sounds like an attempt to stretch a stock box enough to hold it together in performance applications.

I used to build rock crusher muncie M22’s behind 1200HP motors. That was a box designed from the ground up for performance. All teeth were symmetrical, and we even ground off every other tooth to speed the shifts. We effectively doubled the design loading on the dog teeth, and then hit them with 3 times the stock horsepower.

03-08-2018, 04:10 PM
It would be interesting to interrogate (think bright light or water boarding) a Triumph engineer that was responsible for the design of some of the components used on the TR6. Lack of replaceable cam bearings, 180 deg thrust washers on the crankshaft, fine thread studs that hold the hubs to the aluminum trailing arms,lack of drain plug for the diff,no tap on the later radiators, and a change to symmetrical gear on later transmissions. I suppose many of the decisions were related to cost.

03-08-2018, 04:31 PM
Oddly enough, everything you mention except the fine thread studs is a change from earlier cars. So I'm guessing you are exactly right about trying to reduce costs.

Some of those decisions obviously weren't the best; but it's worth remembering that we are trying to keep these cars running long after their design lifetime is over. The factory's primary goal was to keep them running past the warranty period (!) and ten years was a pretty good design lifetime back then. Especially for a "cheap" car.

One other point, I know from experience that such decisions are very rarely made by engineers. Every engineer would rather make the best product possible. Cost reductions always come from management (often in the form of people whose only purpose is to cut costs). Engineers are much more often on the "do this or get fired" side of the equation.

Symmetric gear teeth are stronger and, as mentioned in the TRF article, that change came in when the V8 Stag gearbox was "rationalized" with the TR6 (again primarily with the goal of reducing costs). The Stag still kept it's more expensive roller thrust bearings on the countershaft, but most of the other parts were made the same between the two.

Joel M
03-08-2018, 10:43 PM