Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board 72 Bonneville pops out of third gear

Moto;
Off topic but I use Yelp. Same easy operation. Same amazing searches. Without the annoying self promoting ads and notices.

Hi All,
Here are some pics:
she's up on the stand

the plunger end of my butterfly quadrant, looks kinda beat up

same thing from another angle

plunger quadrant

layshaft 3rd

close up of one of my plungers

visible wear on teeth on mainshaft low

not sure if it's bad or impolite to add too many pictures on one post so I'll let these go for now and add a few more later.If anyone would like to see anything else please let me know I'll take a picture.
Again thanks for all the help . I ended up using Flickr and will definitely try Yelp for searches.

Here are some more pictures. I think this time I'll put the captions below the pictures, I got confused reading my own post
overall I think everything looks in pretty decent shape. The wear on the butterfly quadrant concerns me. I'm also including a picture of my leaf spring which has where where it engages the shifter Cam plate. The dogs are all the gears look good to me, but I'm not sure what they'd look like if they were worn. If anyone wants me to include more pictures of the dogs or gears just let me know which ones. Back on the subject of speed, I found many inexpensive tachometers that I can use when I put my bike back together to verify my tach. It is also possible I miscounted the teeth on my countershaft sprocket as it was difficult to see it, but I thought I did a good job and had to count right. I'm starting to get lazy here and don't want to take the gearbox cover and 4th gear out because it feels fine, but I guess I probably should. My list of parts right now only includes gaskets and the leaf springs. Possibly the butterfly quadrant? What do you think?

it was hard to get a shot that showed the wear on the leaf spring.

this one shows the angle of the leaf spring relative to the cover. The leaf spring did engage the Cam very positively in my opinion

I think this is interesting as it shows where the case is relieved to allow the leaf spring to travel. I think it would be difficult to retrofit this case with the plunger as the case isn't very thick in this area.

this is a picture of the mismatch between my cases behind the pushrod tube. Just interesting, was this normal?

Yes. Sometimes just as bad in front or on the timing case. On my own engines I tend to grind to match.

SR

Does anyone have an opinion on the condition of the teeth on the plunger side of that butterfly quadrant? I'm thinking I should order one.

I wouldn't stress about those teeth, the selector engagement is pretty crude anyway. I have had a (admittedly 5 speed) new quadrant that was distorted - that took some figuring on a new build!

Hi everyone,
Roger thanks for the information!
Tinkerer, good news on the butterfly quadrant. This job starting to look expensive enough as it is.
The plot thickens. I'm told that the part numbers for the gears in this transmission should have started with a 57 prefix if they were the correct gears for the year. I believe that applies to four speed or 5 speed gears. What I have found is that I have a mix of T prefix gears and 57 prefix gears as shown below:
M high 57-3891 L high 57-3859 this gear may be a matched set to the layshaft
M 2 T916 L 2 T1085
M 3 T917 L 3 T 930
M Low this gear has no part number and may be matched to the main shaft
L Low T926
so it looks to me like whoever put this transmission together might have left the original 5 speed high gear in the transmission. When I took the transmission access cover off to look at the countershaft sprocket it looked very much like a factory bend over on the tab washer. It was so neat and clean and precise I thought it must have been done by some sort of a machine. Also the fact that the high gear on the main shaft and the high gear on the low shaft both start with the 57 prefix leads me to believe they may have both been from the original transmission. Not at all sure, certainly open to opinions and discussion. I'm being told the T prefixes are from an earlier transmission.
Also on close inspection almost all the dogs have some degree of wear on them and in particular I think my main shift third is possibly the worst.
Not sure how to proceed.

The numbers you give are for 4speed, BUT there were compatability issues between later and earlier gears. I have an Acrobat document on this, but can't attach it on this forum, but if you search on" Triumph-Gear-Interchange-4-speed", you'll find JRC have it. Beware that stamped numbers are for the bare gears, gears with bushes etc have different actual part numbers, usually one away from the stamped number. You can get a mixture of "T" and "57" if parts have been bought new, which can happen when someone is trying to create a cluster from bits.
I really hope this helps,
Mick.

More great info, Thanks Mick!
My brother just picked up two used 4 speed gear clusters that are supposedly from the mid 60s. I will study all this and find a way to put together a working gearbox from these parts and info. I have a new leaf spring assembly coming, and more and more people are encouraging me to go to the plunger, but I think I'll hold off on that for right now.

The plunger is probably the single best improvement you can make. And one of the cheapest. I understand the jig used to drill the hole went missing, surprise, surprise, but is not totally needed. Bill Getty flopped my 72 on it's side in the mud of his yard and just eye balled it. It's been working just fine for over 30 years. The tap to do just one hole will be spendy.

Wow, that was a leap of faith! Glad it worked out! OK as far as I know at this point there is a metric thread plunger assembly for the bottom of the gearbox and an American thread plunger assembly for the bottom of the gearbox. Does anybody know off the top of their head what the thread size is for the American thread plunger assembly? I don't hear anybody saying that those gears look particularly bad, although after looking at the pictures again they're just not that great. It very much sounds like everyone is still leaning towards the leaf spring being the main culprit here. I already have a new leaf spring coming so I will try it first, but if it doesn't cure the problem right away I will switch over to the plunger assembly. I'm going to post a much more detailed picture of my mainshaft 3rd and the main shaft low gear which is splined to the main shaft. Any opinions on the conditions of these gears would be appreciated.
[img]https://www.flickr.com/photos/[email protected]/52678484512/in/dateposted-public/[/img]
[img]https://www.flickr.com/photos/[email protected]/52679429585/in/dateposted-public/[/img]

Well I'm not sure what I'm doing wrong this time. I have two great photos of these gears and I can't seem to get them to load into the text box.
Wish I was in technology challenged

Try again

I like this better

No sure if it has been mentioned but remember that bad shifts can also be from Over or Under shifting (of the pedal can travel too much or not enough between the stoppers) and you sort of wend up in an in between gear then jumps out. There is a service bulletin on how to fix this (building up the stopper essentially) Ill try to dig it out.
Cheers

Thanks BigBars!
Anyone else? I need to order parts in the next couple of hours and I have weather for the next week that would allow me to assemble the bike and take it for a test ride which is unusual for Pennsylvania this time of year. I know I can get these two gears brand new if I have to, but if this is just normal wear and tear I'm going to try that new leaf spring, before I go to the plunger. But I honestly don't know myself if this is normal wear and tear, or if these gears have seen better days. Anyone's opinion is appreciated. If I can get this transmission out of the way this coming week I may be able to fit in a top end before the riding season starts. Thanks!

Having never seen a set of new gears I don't know what they are supposed to look like. I have seen the gears in my bikes many times. I have about a zillion miles on my 72 and the gears don't look as chipped up and worn as yours. Hopefully someone with more knowledge than me will chime in soon. If you don't know if it's broke or not, how do you know if you should fix it?

While there's a reason they reverted to a plunger after just a few seasons, the leaf spring isn't all bad news. If you got hold of new spring I'd just go with it. If your bike get used at around the same frequency and mileage as most other old bikes on here, it'll last your lifetime.
Your heirs may perhaps get to use it on 4th of July or at closed rallies were they're allocated a gallon of alcohol or some other useless potion to run it on. Under supervision of course.

SR

i ran an original leaf spring for 40,000 miles in my 72. swapped out for a plunger and noticed no difference at all.

maybe if the leaf spring goes bad it would be an improvement, but the shifting is the same on mine

but assembling the gearbox and getting the indexing correct is vastly improved, and the conversion is worthwhile if only for that.

Hi, is there any method to the jumping out of gear, mine only ever jumps out when shifting up, which led me to the discovery of this over shifting problem. I stuck a timing disc on the gear change shaft with double-sided tape, and with a wire pointer could measure how many degrees up and down I was shifting. I was clearly shifting more up than down.

Try this, and see if you can access the file.

https://drive.google.com/file/d/1gn9dKRsMBqHaCrqhOK2anriluoYuuKAp/view?usp=drivesdk

Thanks again everyone,
BigBars I was able to download that service bulletin and most certainly check my shift lever travel in both directions!
After much deliberation I've decided to go ahead and order a new mainshaft third gear and I'll have to wait for that to show up till about Wednesday or Thursday. It's gonna drive me crazy to wait that long because it's going be beautiful weather all week. However I want to give the new leaf spring every chance I possibly can to work properly. I have put the transmission together several times now using the method mentioned in hermit's posts, and I have indexed the gearbox with the leaf spring several times in first gear as was recommended in Mr. healeys's discussion I believe. Indexing goes well every time, and I'm able to shift through all four years with no problems and shift back down to 1st. I believe I pretty much have it down at this point. Now it's just a waiting game for that third year. I should be able to get it put all back together fairly quickly and a good test run in before we lose this warm weather. If everything works well I'll probably try to tear the top end down this winter. Incidentally that is a new leaf spring and a new helper spring that goes in under the leaf spring that was installed. Again thanks to everyone for their input and all the fantastic links with great information. I'll let everyone know how the test ride goes as soon as I can.

HI everyone,
I'm sure I'm overlooking something here but I need someone to sanity check me. My brother picked up two used gear sets in Wisconsin and ship them out to me. One gear set is in very good condition but a completely different set of gears. Wider teeth different dogs towards the primary side. Not sure if it'll work with my current shifter Cam. Didn't really want change everything out and start from scratch either. The other gear set appears to be very similar to my gear set but worn just like my gear set is. That is with the exception of the main shaft and the main shift low gear that is pressed onto the main shaft and does not have a number on it. This mainshaft that my brother picked up is in better condition overall than mine. But more importantly the main shift low gear that is press on to that main shaft has the teeth cut differently to allow for a bigger pocket that Dmadigan justified in an earlier post when I questioned why there was so much slop in the engagement of my lay shift second gear to my lay shift high gear. When sliding my main shaft third gear which is a T 916, 24 tooth onto that new/used mainshaft, I get the bigger pocket of engagement between the two gears or what I described earlier as slop, but here's where it gets very interesting. My main shift third gear engaged with that new/used mainshaft low gear is a much more positive engagement despite the larger pocket or slop as I described it.If I take my original mainshaft and try to twist off my third gear as soon as that gear backs off about an eighth of an inch it wants to fly off of that low gear. On the new used shaft from my brother, my third gear stays on that main shift low gear for a full 1/4 of an inch before it will actually release and pop off simulating the action of popping out of third . I've attached pictures of both main shafts and both low gears below . I'm beginning to think this might be the actual issue here, because the difference between the positive engagement of the two is so extreme . Anyone have any opinions ?


all of my final parts are coming tomorrow morning and I wan't to put this thing together. I'm thinking I want to use the shaft from my brother.

Hi Moto96, I do not know the answer for this. Here is a gear chart. Will it help you?
Don

https://www.jrcengineering.com/technical-support/triumph-650-4-speed-gear-interchange/

Hi Don,
Thanks for looking. I think Mitch sent me a link for this earlier but I had forgotten it had shaft dimensions on it as well! I have since done some measuring and comparison on the two shafts and all of the threads are the same, the diameter of the shafts appear to be the same, it appears the only difference is the length of the long splines. The long splines on the shaft from my brother extend about 1/8 of an inch further down the main shaft. It appears to me like it won't cause any problems. I'm going to fully assemble the gearbox with this shaft and see if there are any problems with indexing and getting all four gears to engage smoothly. I also need to make sure the clutch basket is gonna sit at the same dimension as it did with the other shaft so that my primary chain is aligned properly.
Craig

Sounds like a good plan.
Don