18 replies to this topic

[1977 Loud_Mini]

Hi all, i have just split my 998 engine to inspect the gearbox as it sounded as if i had straight cut gears or straight cut drops. Anyway it has neither but does have some cracking it seems in the casting, so would it be ok to put this gearbox on my tuned 1380. I have added pictures of my 998 gearbox looking fairly clean and a 1275 gearbox looking dirty and i don't know what condition its in thats why i'm asking this question.
Any help would be much appreciated.

Evan.

[TopCatCustom]

Unless it's had a whack or two I'd be suprised if either were cracked- probably just casting marks. Maybe check the part numbers on both cases to see if they are the same, how clean the oil is is normally the best way to see how well it has been looked after in the past, in which case the 998 one may be the wiser choice- but without trying each you can't guarentee how good the syncros will be. Count the number of teeth on each crownwheel and pinion (tipex one tooth and count round) as they may be different ratios, then you can decide what ratio you would rather have depending on what you want the car to do.

Hope that helps!

TC

[1977 Loud_Mini]

Unless it's had a whack or two I'd be suprised if either were cracked- probably just casting marks. Maybe check the part numbers on both cases to see if they are the same, how clean the oil is is normally the best way to see how well it has been looked after in the past, in which case the 998 one may be the wiser choice- but without trying each you can't guarentee how good the syncros will be. Count the number of teeth on each crownwheel and pinion (tipex one tooth and count round) as they may be different ratios, then you can decide what ratio you would rather have depending on what you want the car to do.

Hope that helps!

TC

Thanks fo your help. I just thought it looked to be cracked in two places but needed a second opinion. So you think it may be ok, but why did it make a whining noise with no straight cut gears, thats why i thought the appeared crack maybe causing stress on the bearing (the crack in the middle support part of the gearbox) and causing the noise, I used the 998 gearbox on a tuned 998 with 266 cam, 12g295 head etc and regulary changed the oil and it still be seen inside the box. I will count the teeth when i get a minute. Do you know which teeth count would give which final drive?

[pikey7]

yeah, as above they'll be just casting marks.

No reason why you couldn't use it, but you'd better give it a good rebuild and replace all the bearings and mainshaft/layshaft to be sure, plus the baulk rings, and inspect the synchros and replace if in doubt. oh, and make sure you get a centre pickup pipe.

You'll want to possibly change the final drive too, depending on what you have in there now.

Not a cheap job, but then why spend loads on the engine and have the box fail?

[1977 Loud_Mini]

Exactly right, Yeah that sounds like a good idea,i know the syncros where good as i drove the 998 with that gearbox for a fair while and there wasn't any rumbling noises or anything, just the whining noise.
How can you tell which final drive a gearbox has then, just by counting teeth as TC (C4NNON) said?

[pikey7]

yip. go onto guess-works.co.uk (or maybe .com.. don't remember offhand!) and you can see the possibilities and variations.

[1977 Loud_Mini]

yip. go onto guess-works.co.uk (or maybe .com.. don't remember offhand!) and you can see the possibilities and variations.

Thanks, will do.

[1977 Loud_Mini]

Guess-works site doesn't seem to be working for me so will check it out tomorrow or sometime.

[TopCatCustom]

Final drive ratio- just divide the number of teeth on the crownwheel by the number on the pinion, eg 60 on the cw and 20 on the pinion is 60/20=3 = 3:1.

[1977 Loud_Mini]

Final drive ratio- just divide the number of teeth on the crownwheel by the number on the pinion, eg 60 on the cw and 20 on the pinion is 60/20=3 = 3:1.

Thanks for that it's much appreciated. Will check the final drive on the 1275 box tomorrow and then split the 998 again to check on wednesday.

[pikey7]

if your box is from an "E" model, then it'll likely have a 2.9 FD, which will be too high. good for motorway speeds, but a bit too tall for town/backroads. You'd be better off looking for a 3.4 or 3.7, but it depends on what cam you are using aswell. you don't want to "fall off" the cam... which is basically when you change gear, to drop to such low revs that you are no longer in the peak characteristics. But then again, you don't want to go too much (3.7 *may* be too much, and anything above that) and you'll be changing gear every 3 seconds and be at 6000rpm at 65mph on the motorway, which will get very unfunny very quickly.

[1977 Loud_Mini]

if your box is from an "E" model, then it'll likely have a 2.9 FD, which will be too high. good for motorway speeds, but a bit too tall for town/backroads. You'd be better off looking for a 3.4 or 3.7, but it depends on what cam you are using aswell. you don't want to "fall off" the cam... which is basically when you change gear, to drop to such low revs that you are no longer in the peak characteristics. But then again, you don't want to go too much (3.7 *may* be too much, and anything above that) and you'll be changing gear every 3 seconds and be at 6000rpm at 65mph on the motorway, which will get very unfunny very quickly.

Not sure if its from an E model. I have a 296 camshaft i will be running when the engines buil but don't want to be thrashing it on motorways etc. I think southy on here has a 296 cam and a 3.2 final drive and he says it's not too bad.

[Guess-Works.com]

Yes sorry, upgrade work on the network means the website is down..

Looking from the pictures the 998 (upper) gearbox seems to be in relatively good shame, there's little evidence of chipping on the 2nd gear dog teeth, and as a rough guess the pinion looks big enough to be a 2.9... simple thing is to count the teeth... 20 - 2.9, 19 - 3.1 or 3.2 ( unlikely a 3.2 ) and 18 - 3.4 which looks like what you have in the second gearbox..

Apart from that the two gearboxes are exactly the same, there is no difference between an A+ 998 gearbox and an A+ 1275 gearbox, apart from 998's are usually in a lot better condition.

[1977 Loud_Mini]

Yeah i thought the 998 gearbox seemed to be in good condition, thats not saying the 1275 one is bad, its just really mucky and needs a damn good cleaning. Do you think the 998 box would be ok to use with the casting or cracking defects? I'll count the teeth on both gearboxes and post my findings. I currently have a 1275 possibly MG metro engine and it seems to have a better top speed than the 998 box, revving less so maybe my 1275 i have at the moment is running a 2.9 final drive, but as i'm using it i can't dismantle it to check on the teeth.

[Guess-Works.com]

They're not defects, it's just where the different parts of the cores join together to make the mold...