question for the gearbox gurus!!
Turbo Mini Forums

i amgoing to rebuild the 'box in my engine ready for the turbo conversion. its a standard 998 a series box, what stuff do i need to rebuild and are there any mods worth doing while its apart, all i canthink of is comp diff pin and central pick up pipe anything else???
cheers in advance!
DAN :)

Minispares do a gearbox rebuild kit. Includes bearings, thrusts, shafts, baulk rings, etc, etc. It's pretty obvious, that's what I'm going for anyway. It's not cheap, but it is the way to go if you've got the cash to chuck around. (which I haven't-ish)

Bugger off, I'm getting there.

x-pin diff and a central pick up are worth it...

Also remember a 998 box has a different input nose bearing to a turbo... so you need a 998 transfer casing with the smaller bearing!

alex

AlexF

do you think you could explain the significance of the bearing to me? will the 998 one be able to with stand the punishment or should i shell out 350 for a rebuilt s/gt 1275 type box with 3.4 diff?
cheers!
DAN :)

The thing that always worries me about mini gearboxes is the resulting carnage if the gearbox DOES let go for any reason.......
A mate had a main gearbox bearing break up, the only thing salvageable from the engine was the cylinder head. The rest of it was scrap. Take into account a turbo on top, and it doesn't take much bearing debris to wreck an awful lot of expensive components.
Assuming you will have spent a fair bit of cash on your engine, I would suggest that not spending £350 on a reliable gearbox could turn out to be a false economy that might come back and bite you in the future.
Of course if you are handy with the tools you can rebuild your own box, but I would suggest that this is not something to undertake lightly, it takes a bit of experience of mini gearboxes to be able to tell what parts are worn, and what are OK to use. I personally gained this through class 1 autograss racing where engine and gearbox rebuilds were once or twice a season.
As for the increased nose bearing Alex mentioned....it is the bearing that hangs out of the side of the gearbox when the transfer case is removed. It seats into its outer race which is driven into the transfer casing. The Metro turbo one is bigger in diameter than the std Mini one, but is no wider. This increase in diameter does not give an increase in load capability, the effect is more to allow the bearing to run more slowly for a given shaft speed, hence increasing its life. I have personally never had a problem with this bearing before, even using the smaller mini one. All you need to make sure is that you have a matching transfer case for the size of bearing you do use.

Edited by Tom Fenton on 16th Oct, 2004.

A few points.
A 998 and 1275 A+ box is the same - except for FD variations. The 'nose' bearing (1st motion shaft) is the same on 998 A+ and 1275A+, but the turbo has a larger one (one more roller). Data from my bearing catolgue indicates this has a 30% higher radial load capacity than the stock 1275 bearing (but costs nearly 4 times as much!!!).
The 998A+ transfer case is missing a breather compared to 1275A+, but i'm sure is otherwise identical... or then again, isn't the crank main seal a different size? hmm - now not so sure!

Anyway! a 998 A+ box is the best start, with the 1275 transfer case - or the turbo one if you want the stronger bearing.

x pin diff (trannex, not minisport) is an excellent idea, as is central pickup.

just a quick question , as i was bout to post about this, is it possible to convert a turbo box, to use a non-turbo transfer case, as the transfer case i have here has a great many gubbed threads for the wok :S

edit, not my car, a mates :)

Edited by evolotion on 17th Oct, 2004.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

You can use whatever transfer case you want - but you need to make sure the ist motion nose bearing on the gearbox is right for the transfer case...

yes...

just change the bearing on the end of the input shaft.

Just make sure if you use a turbo bearing, you use a turbo transfer housing (or vise versa!)

I run a smaller nose bearing and it hasn't failed yet. The reason is my turbo bearing failed..







But I suspect that was my fault on reassembly! Still the smaller one in there is holding up fine after a few trackday miles



Alex

AlexF

Crank seal is the same on 998 vs. 1275 engines. s/Gt box is great, it is a so called "close ratio" helical box, well at least closer ratio than normal box. It has a different laygear and 1st motion shaft.

The big issue is the word "rebuilt". What has been done, what was replaced. I know of examples that were simply sidmantled, cleaned and assembled. Not really worth the money IMO.

Whichever box you use, make sure it is in top shape. Either do it yourself or have someone trustworthy do it.

Nose bearings are a pain since you need to be careful with transfer cases. Back when I was doing the engine swaps some 20 years ago a "new engine" was fitted, well read assembled from leftovers. Anyway, the transfer case would not fir properly no matter how heavy the mallet. Turns out the nose bearings were of different size, I had a bigger inner race but too small an outer race. Well they dont exactly mate together... Remember that we are talking about late 60´s stuff. Themoral is to check everything, not assume. Nowadays I simply buy a new nose bearing just about everytime I rebuild a box. Unless I know for sure (boxes that I have rebuilt myself) when it was replaced the last time. The bearing is cheap enough compared to e.g. a new /used transfer case.

Sorry guys, should have read the topic title. The word guru has nothing to do with me.

Apologies.

Sorry Jukka, but you must have had a blow to the head! The term is pretty close to the truth for yourself in my opinion!

D

thanks for all this help guys, i am begining to get it now, keep the advice coming!
cheers
DAN :)

if i do decide to rebuild the box my self are there any specific tools i am gonna need?
DAN :)

Haynes Metro workshop Manual.
The usual imperial socket set.
1.5" AF deep socket for mainshaft pinion
socket for 1st motion shaft; the one that holds the bottom idler gear on (it's either 1 1/6" or 1 1/8" or 1 1/4"AF) LOL!
Breaker bar/windy gun
0-50lb ft Torque wrench
150lb ft torque wrench
Large internal circlip pliers
Feeler gauges
Brass drift and hammer
Thin pin punch or similar (approx 1.5-2mm dia) for removing the 2nd/3rd gears from mainshaft
Bench vise / workmate for supporting mainshaft in above operation
A set of heel bars (£15 machine mart) is usefull for removing the mainshaft bearings, but improvisation with an old screwdriver is possible.

ISRT MOTION SHAFT NUT IS 29MM IN METRIC TERMS.

always looking for them bigger bunches of bannanas

right does this lot sound alright?
-mini spares, central oil pick up
-gearbox rebuild kit, less the diff stuff.
-s/gt close ratio conversion kit
-tools etc as dave's post
-4pin diff (tranex)
if that lot is put together properly will it handle up to 100bhp?
what can i do with the drop gears, (i cant afford straight cuts)
what options are there? is it just a case of rebuild it all with new bearings and do it properly or can i uprate anything while its all off
cheers again! keep the advice coming!
DAN :)

I'm not sure if the S/GT conversion is worth the money, as the ratio increase is only slight...


What diff you proposing? If the stock item, replace the diff pin and the fibre thrust washers as a matter of course.

he's got a 4 pin on his list dave

I used to have a box with the S/GT ratios in it, I used to love it as it basically had a longer 1st gear, and then the rest were all closer together. Especially 3rd to 4th was nice and close.

Having said that, that was back when I used to have a 1300 n/a engine with a peaky power delivery........I would think with a turbo torquey delivery there wouldn't be that much benefit though.

use std drops if thats all you can afford!

But if you don't know what to look for in terms of wear or in how to set them up then get a pro to help you :)

st8 cuts are fine but noisy and I am yet to break a set of std ones with 150 lb/ft of torque.

Alex

AlexF

Yes definately. If you can't afford s/c drops then you need to make sure your helical ones are set up 100%. So that means checking the size of the bushes in the primary gear, checking the size of the crank nose where the primary gear sits. Also the endfloat of the primary gear is important. As is the endfloat of the idler gear, this needs to be set up to the correct tolerance as well. To do this the haynes manual details a method using wax washers to determine the clearance, or do it with the gearbox seperated from the engine using a new gasket and a set of feeler blades. Either way, you need to measure accurately (e.g. with a micrometer) the thickness of the thrust washers you have, and then order the oversize ones you require to get the float correct.

if i don't really need the s/gt conversion then i can strecth to a set of s/c drops.
i like the nois of s/c gears and drops! i don't know about long journeys though!
if i am really stuck while i do this is there anyone in the hampshire area that would be willing to help, beer/money would be paid..
also what brand do you guys reckon is best for s/c drops? anyone had good results with any particular make?
cheers!
DAN :)

Where in Hampshire...

I'm in Newbury...

Alex

AlexF

winchester so just down the a303 from you i think.
DAN :)