Most liked posts in thread: Sprite Race Gearbox Rebuild

Ok, so here's the difference between a smoothcase or Morris Minor gearbox and the later ribcase - BugeyeDave bought this transmission from Vicky Brits already rebuilt over 25 years ago. At that time it was just a street driven car and didn't become a full on racecar till much later in it's life - that's when it blew third gear to bits! So either they put smoothcase stuff in this ribcase case - which was not uncommon way back when as the case is a lot stronger too - or like I said, it's a MM transmission.

So Clancy had dropped of another transmission earlier for me to rebuild but frankly I though the case was suspect - it had clearly broken and been rewelded and while it looks fine, I don't know that I would trust it to be straight and true. We decided to rob the mainshaft from it to use in BugeyeDaves trans, so I stripped down the new mainshaft so I could change the gears from helical to straight cut.

In the first pic you can see it uses the same pin and plate arrangement as the earlier gearboxes, but when you get that plate off you can see a row of needle bearings - that's the big difference.




That and there is a boss machined in the later mainshaft for the 2nd and 3rd gears to ride against that the earlier trans doesn't have, instead it relies on a brass plate between the gears.



Once 3rd gear is off, I flip the shaft over and take out the harder plate - it has two pins, and some small half moon plates that ride under the pins and fit inside the plate on the top.



It's a lot of bits to juggle around when it goes back together - but I've developed a secret way to get them off and on now. I use some assembly lube to hold the needle bearings in place on the shaft while I carefully slide the gear down over them.

Then there's a pic of the mainshaft to show the assembly all done.


Last pic shows the input shaft and laygear installed, however, to put the mainshaft in the case you have to pull the layshaft out of the laygear and let it drop down into the case so the mainshaft gears will clear those on the laygear. Once the mainshaft is in place then you raise the laygear back up and slide the layshaft into it, making sure not to drop the end washers out of place, cause they can bee a bugger to get back in with all the gears in place.



After all that the next phase is to get all the detents and springs in place - I counted 5 pins and 2 balls that have to be put in the exact right place for them all to work correctly. Once those are all done, I'll put the tailhousing on and shim the rear bearing, then install the shift linkage and lastly I have to shim the front cover bearing too. Before I put the sidecover on I have some plates I made to hold the detents in the case while I shift it thru the gears to make sure they all work. If they do the side cover goes on and it's done and ready to race. Still a ways to go on this one.

 

Clancy got me another gearbox, so I stripped it down and now have the right mainshaft to build Bugeye Dave's gearbox. More as it happens.....

 

Much better, this one won't break unless he does something wrong....

 

I finished his race box today and he'll pick it up and put it in the racecar before the next event in mid-September.

Today I also started on the last of the three boxes, this one for a guy in Houston. He'll be at the September race too but I think this is a spare gearbox for him.

This box is in very good shape, 1st gear isn't even roached up badly so it should be a fairly straightforward build.

First thing I did after getting it disassembled was to remove all the studs, chamfer all the holes, tap all the threads and clean off all the gasket mating surfaces. After that, into the tank for a thorough cleaning in the solvent and a good blow dry.








Next - disassemble the mainshaft - always a "fun" job.





Once that's done, all the bits go into the tank for another cleanup, I'll wire brush the threads on all the studs and bolts, clean all the little plungers and such and get it ready to put back together. I think I spend more time cleaning than dis-assembly and re-assembly!

 

This one went together pretty smoothly, I got the gear assembly into the case with no issues, but when I went to install the shifter I noticed it didn't want to move - it was locked up with a big mud dauber nest! I took the back plate off and dug out the mud, cleaned it all up and now it shifts well.



although it wasn't completely roached like most of them, I did put a new first gear in this one too along with a new shift fork. You can't but a shift fork or shift sleeve for 3rd/4th....all you can get are used ones and hope to find one that's not too bad. The owner had a new hub and shift sleeve made in Australia (or was it new Zealand?) and while the sleeve was good, the hub did not fit the shaft, I don't think the splines were cut correctly.....the sleeve is the part that wears out anyway, so I did use it.

I cleaned up all the studs and bolts - I always use new nuts and lock washers as they get grungy and are difficult to clean - new ones are not expensive. Still have to tap all the threads in every hole to get a good clean assembly tho, can't skip that step or you pay for it later when something won't tighten properly.



So this one is ready to go back to Texas.....there is a race at Eagles Canyon in mid Sept, that Clancy will go to and the owner will be there that weekend too, so Clancy will transport it for him.



Looks like there are two more coming in over the next couple of weeks.....it's getting to be almost routine now, tho never easy, but at least there are fewer mysteries with each one I complete.

 

Another Sprite race gearbox rebuild, and another third gear stripped - but this one is a straight cut gearset so I was surprised to see this. He said the last three events he had to hold it in 2nd and 3rd till 3rd finally gave up. I don't think I've seen one destroyed quite this badly...



On further teardown I found parts missing, and parts lying in the bottom of the case that definitely don't belong there!



and finally I found these broken synchros, which I've never seen one do before.



My speculation is that the box was assembled incorrectly and went into two gears at once - at speed.
I have all the new parts, and it's going to pretty much take everything to fix it! about the only parts I'll reuse are the mainshaft and reverse gear. It's a bit worn but you use it so rarely on a racecar that it shouldn't matter.

 

Moving along on this gearbox build, I was able to find in my box of old gearbox parts a 1st gear, and 3/4th shift hub and a 3/4 shift fork to replace the damaged ones, I still need a 1/2 shift fork and I have one on order from Moss. Some of these parts have become virtually impossible to find.....case in point, the 3/4 shift hub is pretty much unobtanium new now - I did find one NOS in Va for $275 but I didn't buy it as I found a good used one in my spares. But, I may buy it anyway for a future build. The same place also had some 3/4 shift forks used but good for only $25 - I may buy a couple of those too.....no one has those for sale new anymore that I can find.

So I got all the pieces parts cleaned up and ready to go back together.

I started by putting 3rd gear in place as there's only one pin to address there, once that was on I flipped the shaft over and put 2nd on - which is VERY fiddly and takes usually about an hour!

With that done I assembled the shift hubs - there are three springs and detent balls that have to go together to allow the outer part to fit over the inner. I use a hose clamp as I find its the easiest way.....it holds all three balls in place, then I smack the outer down over the inner and is shoves the clamp off as it fits in place. works a treat but it's a little tricky the first few times you do it - it's a good idea to encase the hub in a shop rag in case it doesn't go together - springs and balls flying everywhere if you don't!

Old first gear, and new first assembled on the mainshaft






After that I put the new bearing on the input shaft and installed it - it goes in from inside the case, then the retaining clip goes on the outside, and you push it back down into place. After that I put the layshaft in place with it's two washers and measure for end float - it was spot on. With that done the box is ready to reassemble.





I need that shift fork before I can finish it up tho.....

all the detents, springs and other bits that have to go in yet.

 

Mostly back together now.....I found a 1/2 shift fork in my spares that looked almost new so I was able to go ahead with the assembly....



I've bought gasket sets from three different sources and they all must get them off the same machine with a worn out die, cause this one gasket never fits worth a crap. I wind up using my little grade school hole punch to modify the holes so it will fit.

 

Yeah, one of the detents was sticking - probably some tiny bit of errant swarf I didn't get completely cleaned out even tho I cleaned the living crap out of it - works fine now.

 

The race car is running twin HS4's, those are right in Kent's wheelhouse - his favorite carb setup so he'll be tuning it.

Both Jesse and Kent have extensive experience tuning Webers, and a BIG box of jets and such - which is essential to getting them tuned right.

Today I'm starting on gearbox #2 while all the pitfalls of the first build are still fresh in my mind, and I'll do the third one right after that assuming Moss gets the last bits I need delivered in time.

That will be it for gearboxes this year. Well, for Sprite gearboxes anyway.....I have two Mini gearboxes to build too. They mostly just need synchros but of course you have to disassemble the entire box to get to them.

 

Got the case stripped out and cleaned up, there was a lot of corrosion on the gasket surfaces so I removed all the studs and counter sunk the holes a bit, then took a large flat file tot he surface, lastly a twisted wire wheel brush in the angle grinder cleaned off all the corrosion.





I also disassembled the mainshaft and got it ready to rebuild. I'll be gone tomorrow so may not get back to it till Thursday. When this one is finished it's going into the little white racecar - he thinks it might be good for 1-2 seconds a lap just from having better ratios. Not to mention the straight cut gears are a whole lot stronger so he can bang on it harder if needed to get past a competitor.

 

I threw a coat of paint on it - I wouldn't normally paint one white but that's what color it was when it came to me, so......



Just heard from one machine shop - block, pistons and crank are done for the Mini engine, I'll go get them tomorrow.

 

Yeah, they're pretty easy once you remember where they all go!

I have all the forks in now, ready to shim the rear cover, then add the shifter housing.....should have it done this afternoon sometime.

 

You can find the odd one-off part made by somebody, but the costs are pretty high. MiniSpares has done a fantastic job of keeping the Classic Mini alive and on the road. You can buy just almost anything you need from them.

Thanks for all the nice comments too - only they may have been premature - I had to take it apart again this morning, couldn't get it into 2nd gear. It seems there's a sticking detent somewhere. The good news is the only deadlines for me to complete these are in my own head.

 

The next one came to me in chunks - it's on the bench now ready for teardown, I have all the new parts tho there could be the odd bit missing - he says he has everything I might need tho.

I believe him - he has a two car garage FULL of crap! so much so that he has to work on the racecar in his driveway or in his trailer if the sun's too hot.

 

You're probably right!