Sprite Race Gearbox Build

Started by MiniDave, June 22, 2021, 11:19:18 AM

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MiniDave

I now have 3 of these to do for various people, so I'm going to incorporate all of them into one thread, and try and document every step of the build. All will have tall, close ratio straight cut gears and regular synchros.

I'll be starting these sometime next week, so stay tuned!

In the pic, the black one is done and ready to be picked up this Friday, and another one is on the way to me from out of town.

(Yes, I need to sweep the leaves out of the shop!)
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#1
Black gearbox picked up today, I hope he never has to use it because he has a dogbox in the car now, but if he does it's ready to go.

I got a call this morning from another racer who is also sending me a gearbox to do, I think I need to raise my prices!

Edit: Third gearbox showed up today, so I need to get some parts on the way for it. I'm planning to do these one right after the other.....
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

Wow, 2 more Sprite gearboxes have shown up today for straight cut gear sets......I'm getting to where I can do these in my sleep!   8.gif

I think I need to raise my prices!  ::)
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#3
Wow, this first gearbox is an absolute mess.....it was partially disassembled when it came into the shop and when I finished taking it apart I found all sorts of things wrong, detents in the wrong place, balls instead of plungers - the wrong springs used, parts missing.....I hope I have enough left over scraps from other boxes that were junked to build this one. Some of the little parts I need are just not available anymore.....

I can always tell when someone has been working on one of these - or on a Mini engine - things like nuts removed with a hammer and chisel, RTV squirting out of every joint and of course, things put together wrong. I'm surprised this one even worked - if it did!

The bearing plate is supposed to have a round hole with a peg in it to locate the plate in the correct orientation - I'm not sure how I'm going to fix that....I may have another plate but I know I don't have the peg, and those are not available.

One interesting thing I found - the splines on the input shaft (where the clutch disc rides) are the same as the splines on the output shaft where the driveshaft slips into the gearbox - so I use a driveshaft yoke to hold the shaft so I can tighten or remove the big nut on the shaft - instead of using a hammer and chisel like they did on this one.

Just got the email from DHL on my Mini parts, it says Wed delivery - which usually means Tuesday so, the race is on! I think the parts from Virginia will get here first, but the ones from California might get beat by the ones from England!
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

In the pic above the hole the peg is supposed to fit into is damaged, and I found the missing plug buried in the case. I also found another plate and plug so I won't need this one, but I'll keep it just in case. The old plug is damaged, but i think I can save it by working it over with a file, and I can redrill the hole in the plate that it fits into. It won't be prefect but then it only has to locate that plate....there's no force on it once it's all together.
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#5
Some misc bits I've found that were not right or just messed up...

In the first pic the springs on the left are what I found in the gearbox in various places, the ones on the right are what's supposed to be in there. A couple of them look like they came out of a ball point pen or something!

In the second pic - I had a lot of trouble getting the shift rods out of the forks and the case, the middle screw shows why. The tapered end fits thru the shift fork and into a hole in the shift rod. the two outer ones were screwed into the shift rod so hard that they deformed the hole in the rod, so it had to be driven out of the shift fork. The middle one missed the hole but was tightened up anyway, mashing the end of the tip - I'll replace that one. The other two are usable but it's not necessary to screw them in so tight.....there is a star washer under the locknut - you want them tight enough that the fork doesn't move on the shaft, but that's it.

I've got everything cleaned up and ready to go back together now, I'm just waiting on parts to show up - same with the Mini gearbox. Once those get here I can crack on with both jobs - we're trying to get the Sprite gearbox done in time for him to make a race Oct 8,9,10 at Hallet, so as soon as it's done he needs to grab it so he can get it installed in his racecar.
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#6
I think the reason they thought they had to use so much RTV on this gearbox is because they used a hammer and chisel to take it apart - I found some more damage to the case where they drove a screwdriver or chisel between two pieces to get a small cover off.

I also found a lot of stripped threads, I've re-tapped all the blind holes and I'll use blue locktite on the studs that go in them to make sure they hold OK.

Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

94touring


MiniDave

#8
Yes, it is....... :(

Especially when you just finished putting something together and realized you forgot one little tiny bit and you have to take it apart again. And then you take it apart to put the tiny bit in and it won't go, so you have to take it apart further to figure out why that piece won't go in - then when you do figure it out and fix it, then you have to put it all back together again, only this time it doesn't want to go back together, where it did easily a minute before....   :-[

BTW, Moss Virginia won the race, and I think between what they sent and what I have on hand I have enough to finish the gearbox, so he should have plenty of time to put it back in the car and get it run in.   4.gif
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#9
So.....this one is done - sort of. Everything inside is finished and it shifts beautifully. Clancy brought me a front cover - he has a guy who machines them and puts a lip seal inside so they don't leak oil thru the mainshaft. Originally, they have a sort of reverse thread that's supposed to scroll the oil back into the box, but the front covers wear and the gap gets big enough that they leak thru and it gets on the clutch, this helps eliminate that.

However....

He brought me the wrong one - he brought one for a smooth case gearbox, and the bolt hole pattern is different.

So I have it all done save for that. He was supposed to get it on Tuesday so they could put it in a car for the races at Hallet, if they can work out the pick up schedule OK they still have plenty of time to get it in the car.

All I have to do is measure the cover so I know what size shim to put in it and bolt it on, won't take 15 minutes once I have the right cover. In the meantime I have a small bracket bolted on to hold the input shaft bearing in place.

With this one done I can now get back to work on the Mini gearbox as all the parts are here for it. I'm hoping that the various machine shops will be done with their work on the engine block, head and crank by tomorrow afternoon, but I have plenty to do in the meantime.....

Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

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.

Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

#11
This is the gearbox that got locked in first gear at CoTA, he dropped it off at the shop today and just as expected the problem was that the gear had gone too far and the detent balls had locked it in place. It was a bugger to get apart as the fact that first gear was out of place meant it was almost impossible to get the main cluster out......the only way to get it out was to release the detents (into the wild - they go everywhere!) so I could move the gear back into place. Once the cluster was out I had to disassemble the entire thing to replace the detents and springs. I have it all re-assembled now and ready to go back to the racecar.

The cure to this problem is pretty simple, a 2mm thick washer on the shift shaft keeps the gear from being able to overcenter the detents by limiting how far the shift sleeve can move the gear......simple and fail proof.

He said the issue with the overheating was a bad water pump, he replaced it and now the engine seems to be right as rain again!

His next race is later this month at Hallet. March 18-20th

Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

Ran into a further problem with this gearbox, it was difficult to get it to shift into second on the bench, and as I took a closer look I found out why - 1st/2nd gear operating sleeve was cracked!

I dug around in my box of old retired gears and found 2 to choose from, one was still in really good shape so I disassembled the mainshaft yet again and swapped it out. Changing one of these involves three little springs and detent balls that usually go flying around the room as you try to assemble it. I have a tool made to do this but could never get it to work - Paul came down with a part he'd made for me (more on that in a minute) and we messed with it and he figured out how to get it to work! Yay! no more tiny steel balls launching themselves into warped space never to be found again!

The gearbox went back together with no further issues and shifts smoothly now, so he picked it up and will put it back in the car this weekend sometime.

Paul brought me a fixture that he 3D printed to allow me to ream the rear bushing in the tailhousing. Our first attempt at this device wasn't too good as I apparently did not give him accurate measurements to work with, so he took another crack at it and this one worked perfectly!

It simply mounts to the tailhousing to help keep the reamer square to the bore - it works well but I'm going to see if I can find someone with a proper milling machine that can maybe do it for me. The one that is in the pics is a junk housing that's cracked where the bushing fits in so I didn't expect a good result, but it proved the concept for us.
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

After the disappointment of our weekend at Austin, Corey took 2nd this weekend at Hallett!

Next race weekend will be the end of April at Eagles Canyon, west of Dallas.....
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

MiniDave

After doing so many of these, I'm still learning new things!

I've finally learned that you can't really rebuild a 948 or 1098 engined gearbox with straight cut gears, unless you put all 1275 "stuff" in it. The case is the same, everything else is different. I've also figured out how to tell a 1098 box from a 1275 without tearing it all down.....pull the side cover off and if you spray a little WD40 or carb cleaner, brake kleen or something in between the 2nd and 3rd gear you can see the washer that separates them - if it's brass (or bronze I guess) it's the early box and you're stuffed. If it's shiny steel, you're good to go.

The reverse and 1st gears are part of the problem, they don't play nice with the straight cut laygear......they fit just fine but make a terrible noise as they rotate. They look the same, have the exact same number of teeth and are the same diameter, but something about they way the teeth are cut or something made makes it a bad match. Of course you also need the 1275 mainshaft and all those associated bits, cause they are unobtanium thru any source that I've been able to find. I can buy the gears (getting spendy now) but none of the bitsas that put it together

Anyway, I'm trying to get out of building these, I'm doing the last one today (I hope) as a favor to Clancy for a guy who's sponsoring his grandson in a Bugeye. I was building them a straight cut race box to use after he gets thru driving school and gets his license, in the meantime he blew up the stock box in the race car - well blew up might be overstating it a bit......it locked in 2nd gear and wouldn't come out. When I took the side cover off it was dry as a bone inside - I've never seen one that dry, there usually is some oil left on the gears, but not this time. A couple of the gears were blue and the 2nd gear synchro was "welded" onto the gear.

I found him another 1098 gearbox to use in the short term, then once he's thru driving school he can put the race box in and go for it.
Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers

94touring

This is the last one about a dozen later?  :grin:

MiniDave

Complete failure at retirement - but getting better!

1972 Mini Racing Green
1972 Mini ST hotrod
2017 Audi Allroad - Glacier White - His
2018 Audi Allroad - Floret Silver - Hers