Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Three part numbers for trans outer cover?

I might have to replace a transmission outer cover. The filler plug hole thread is buggered. Fixable -but a tap costs more than another cover.

It looks like T3760 is used from '69 up to at least '72 which is the year of my engine. T3628 looks like it fits only 1968. There are a lot of used covers available under the part number T3753, but I can't confirm what model/year uses that number. This needs to be a 4 speed cover.
Thanks
Al

The 57-3753 I see listed on Ebay say '68-'72 four speed. Although the number of speeds does not matter for the bare cover, only if the shift block is installed.

I search three parts supplier sites and none listed 57-3753.
My '72 parts books (both models) lists 57-3760 as the outer cover. As Dave says, the cover is the same for 4 and 5 speed models.

I search three parts supplier sites and none listed 57-3753.
My '72 parts books (both models) lists 57-3760 as the outer cover. As Dave says, the cover is the same for 4 and 5 speed models.

Don't give up with your existing cover. I have successfully chased the thread using a smaller tap of the same pitch, just run it round the threads applying quite a bit of pressure. Also note that the earlier covers (pre-67?) didn't have the filler plug hole as it was on the top of the gearbox and the clutch cable fitting was different. T3753 might be the casting number for the cover.

Hi All, There is a lot I don't know, but I'll tell you what I know about the outer trans covers.
'67 & older has no trans filler hole, so obviously they are out for your bike.

1968 has filler hole. Part # T3628. The cover has Whitworth, CEI threads or whatever, but not American threads in hole for clutch cable abutment & the other threads for clutch lifter & the guide plate. The shifter shaft has smaller oring ring groove. Has a vent hole for trans near top front guide plate stud.

1969 has filler hole. Part # T3670 (70-3760) Threads changed to Imperial (American) threads throughout. Has a vent hole. Shifter shaft has smaller oring groove.

1970-72 part # T3670, but there were changes... Still has American threads throughout. On the examples I've seen vent hole was eliminated as now trans vented via clutch push rod to primary case breather. But... is that actually correct as I've not seen that many examples? Groove in shifter shaft was enlarged. Oring wall thickness enlarged.

57-3753 is a casting number for the raw casting of outer cover. This casting number continued to the end of the right foot shift T140.

The T140 70-3760 are viable covers for you if you swap over your 4 speed shift parts. They are coveted for 4-5 speed conversions & not so easy to find. T140 covers do not have vent hole drilled.

Your bike may or may not blow oil out vent hole if you get '69 cover. You could always put a small screw in vent hole with some sealant or loctite.

The cable abutment for '68 is apparently the same thread for clutch cable, even though threads into cover are different.

So end of day you can use 1969 or later even if you must plug vent hole. The skinny oring for shifter shaft is very hard to come by in correct wall thickness. Swap your later shaft over if it's still ok.

1970 or later is best bet if possible.

I just looked over ebay. Very sad offerings for covers at the moment. I didn't see any I'd want to use. But this one shows some promise??

https://www.ebay.com/itm/314222722286?hash=item4929223cee:g:9WEAAOSwIQRjau5Z&amdata=enc%3AAQAHAAAAsJVg2azlvUEcbSAL%2BhSqbCPiiWOTBmQI%2Fo%2BlQtZK6udKK%2BfFS%2Fd5cNanXaemVGhQt9ltnhuXkRtGKuUTbH0ugMmoDUO20NS%2BpuY%2FQrmP4p4Aa7cMEC4Xc59i9%2FhU23Gm03EezN2CXPTkXbJ92wymSiAVHfbm1eQcVH9bG4sJG1RzJbbLq8Tec3JQ0TC0SCGUP2XGkrqBTHTYDsESNYUV%2BU7brGZybH64xenaILqrfv6N%7Ctkp%3ABk9SR5CXy4mMYQ



If you look at this cover, very right side of last photo you just barely see the vent hole.

https://www.ebay.com/itm/255819727061?epid=1611885164&hash=item3b900b40d5:g:vN0AAOSw2b1jbD39&amdata=enc%3AAQAHAAAAsJrWd5PYroJV41za4OwlKXHYKxDJ3yaaAiczwfz4Hz785l73PziO%2FcTO%2BdUmAcr3O7DM84PVwJO6yu%2B27gDzwFR2%2FSINchbi5iPrLIrDMnGDMW%2BCKY8gQh0OxKktgDPGRFmz8sMBk%2BonlKBWF%2BES%2FcnbDPfz%2FZgdUsG9qNaWi9h1kx%2FZDCa1miCiyzue2WevsqfeB8%2FCgHdmNaI3GxziN9uKlplhItRP3NIGlmrlVsKC%7Ctkp%3ABk9SR-ywlYeMYQ

Getting good covers is getting harder by the day.
Don

Hi Al, Please look at your outer cover. Does it have a vent hole? Thanks.
Don

Hi Al, Another thought. Large taps are quite cheap from China. I'll have to check & see the thread size. Maybe somebody knows it?
Don

I followed tiger cub's lead and used a 3/8-16 BSW tap to scrape the threads. There were only two bad threads but actual damaged extended about a third way around. It went well and before I thought it would the plug screwed right in.
I'm sick today, just a sore throat cold, but after fixing the gearbox cover hole I cleaned all the holes and threads and went ahead and sanded it in prep for polishing. Now I'm wiped out, achy and sore. Maybe I'll get back out there later today.
Thanks very much!
Al

Hi Al, Sorry you're not feeling well.
I know everybody has a way to refurbish the polish on covers. A ton of work for sure! I don't have a big polishing wheel. I must do by hand.

The last several years I've started using Wet/dry paper. I use lots & lots of water the entire sanding process. Unless scratches are super deep I try not to use coarser than 320. It can take longer to sand out the scratch marks from too coarse of paper than work down the aluminum with a finer grade to remove the scratch. I also try to avoid making a flat spot or dip where a scratch was. I try to work around the scratch. Really these are more like gouges.

I often work in garage sink under constant trickle of water. Allowing sanding dust to build up can ball up & gouge the metal. My primary cover got a fairly bad gouge a few years ago when it was hit by the guts of a muffler that fell out of bike I was following at 65 mph. My leg healed itself, but the case took work. Plus cover had many small defects from stones etc & from toe of boot, pressing on brake pedal etc. So the entire cover needed work.

After working the gouge area down with 320, I worked that area down until it looked smoothy with sanding scratches. Then progressively worked area with finer grits until scratch marks were nearly gone. Again going ever finer paper, always flooding with water. I worked the minor scrapes, scratches down and at the same time worked on the deeper nicks, but none were very deep. As needed I would go back & use a little coarser if needed on a nick or scrape.

Very soon I'll be into the upper hundreds of grit. Occasionally I'll go into 1000 grit to get a better sense of how it's going as you can't always see the marks under the paper scratching. Finally I'll work my way to 1000, 1500, 2000, 2500, 3000. Now the flaws will really start to show. I'll go back & work any areas that don't look good. Then go over it with 3000 again. You can go finer if you choose. Amazon sells a nice paper assortment for about $15-20 I try to get individual large sheets from autobody supply store that is local to me. When you get to 1000 working up a step at a time on grit works well & saves time.
Finally I polish with Mother's Mag/Aluminum polish. That's my favorite, but any of these fine metal polishes work as good. Autosole, SemiChrome, Flitz. I have all on hand. The key for less work is do your careful inspection & smoothing with the wet/dry. Then it's super fast & easy to bring the matt finish of 200-3000 to a very high gloss. Too high of gloss for my preference, but I've learned to bring it to that super high gloss. Then allow it to dull slightly to a more pleasant sheen to my eye. There after routine maintenance is very fast & easy.

Polishing cloth. An old soft worn out white cotton T shirt cut into squares works really well. The soft microfiber polishing cloths work really well also. Flip a coin?? Both are good. I tend to polish with the T shirt, then buff with micorfiber cloth. For routine maintenance a used microfiber that is blackened from buffing & a tiny bit of new polish works very well, then a light final buff with clean microfiber.

It takes me about 2 hrs. To renew the finish on a pretty beat up trans cover like what you see on eBay.
Occasionally I'll peen the high spots at sides of gouges back closer to shape. Occasionally take a like new clean singe cut file to remove metal from a deep gouge, but I try to avoid it. I've wondered how thick the covers are?? I've not worn through one yet. I've removed some dents by cold driving on inside of primary covers. Most weren't horrible though. My Cub cover was dented very bad. A tiny crack. I straightened & epoxied on inside. You can't see crack & no leaks. You can't tell it was dented.

Unless patent plate is missing its ink, I always put masking tape over patent plate. The ink is so thin even light coat of polishing paste can wear it through.

This is nuts... I find bringing the covers back to like new is fun & kind of therapeutic. To my eye even on bike with old fading paint, polishing covers & chrome, cadmium parts best you can makes bike look better. Some like the original found it in a barn look & would never polish anything. Personal taste it is what each should do.
Don

I search three parts supplier sites and none listed 57-3753.
My '72 parts books (both models) lists 57-3760 as the outer cover. As Dave says, the cover is the same for 4 and 5 speed models.

A note on polishing - I have big polishing spindles (but not a lot of skill), but the sand cast earlier cases have a coarse grain structure, exaggerated by corrosion. Just using polishing mops lifts the grain boundaries, so you get a mottled finish on your nice shiny covers. IME you have to go down Don's route first, which although it takes forever, is the only way to get a smooth shine (you can finish using soft mops and compound). Proffessional polishers cannot do this, it takes too nuch time (money).
Luckily, later Triumphs used die castings for most stuff, though I think the gearbox outer was an exception?

Hi, We know 57-3753 is a casting number. Once drilled the actual part number we see in parts book is assigned.

Looking at photos on the web, the '67 & earlier spoke type does not have a casting number, at least not in same location.

But.... The one year only 1968 cover T3628 cover has the Whitworth, CEI threads.

It appears the 57-3753 is the casting number with cover that has filler hole.

Then factory drilled, threaded it. When they changed to imperial threads the part number became T3760 (70-3760).

It makes sense parts sellers do not list 57-3753 as it's just an unmachined raw casting. The eBay sellers list everything they can to get a hit on the site, no matter if it fits or is correct. They don't care so long as they sell it.

Don

In looking up gearbox covers on ebay I noticed almost no one gave info about the bike/engine it came off. Let the buyer beware. I am quite relieved that I was able to fix the cover I have. And at no expense. (My budget for the Project is getting low, and I sorta want to have a little cash on hand for the next job in the garage!).