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Thread: TR3A 3-Synchro Gearbox Rebuild

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    TR3A 3-Synchro Gearbox Rebuild

    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.

    1st_20180225_173522.jpg

    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?

    Countershaft_20180225_175224.jpg


    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?

    Thrust_Washers_20180225_173703.jpg

    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.

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    Obi Wan Sarastro's Avatar
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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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:




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

    http://www.britishcarforum.com/bcf/s...earbox-Rebuild

    Best of luck!
    John

    1955 TR2

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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
    http://www.buckeyetriumphs.org/technical/technical.htm
    Bob

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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!

    Joel

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    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.

    David

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.
    Bob

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    Re: TR3A 3-Synchro Gearbox Rebuild

    You can also get Redline GL4 on eBay. Loads of people sell it.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: TR3A 3-Synchro Gearbox Rebuild

    Thanks
    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.

    David

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    Re: TR3A 3-Synchro Gearbox Rebuild

    Not only a smart a** but an imbecile too.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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
    2nd Good Dog Teeth_20180226_191035.jpg 2nd_Angled Dog Teeth_20180303_224828.jpg

    3rd Gear
    3rd_Good Dog Teeth_20180303_224846.jpg 3rd_Angled Dog Teeth_20180226_191049.jpg 3rd_Angled Dog Teeth_2_IMG_20180303_224907.jpg

    Top Gear
    Top_Good Dog Teeth_20180303_224937.jpg Top_Angled Dog Teeth_20180303_203145.jpg Top_Angled Dog Teeth_2_20180303_225029.jpg

    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?

    Reverse Gear_20180225_173630.jpg

    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.

    Joel

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    Re: TR3A 3-Synchro Gearbox Rebuild

    The asymmetrical dog teeth are actually original. Much later (during TR6 production), they went to symmetrical teeth.
    http://www.zeni.net/trf/TR6bluebook/index.php?page=85

    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.)
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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?

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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?!?
    John

    1955 TR2

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: TR3A 3-Synchro Gearbox Rebuild

    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:

    https://www.rauchandspiegel.com/prod...etrical-1slot/

    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.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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