Difftastic?

[Pyoor_Kate]

So, my diffs developed a bit of a whine, it's not too bad at the moment but it is noticable on occasion. Presumably related to the (low) quantity of oil in there (my fault, forgot to check at the last service and it leaks).

I can also feel some 'slop' in my transmission - I've not yet looked to work out where, but I'm pondering that since it's 'recommended' that you have hardened half-shafts and so on with the 1275 - that perhaps it might be time to start thinking about a new diff and some hardened half shafts.

So, I was wondering - someone suggested that the 3.9 diff might be a possibility - presumably this'd drop the revs at motorway speeds (which'd be nice) at the expense of acceleration - is there anyone on here who's got this combination* and could give me an idea of what it's like?

How much should I be looking to pay for a s/h diff?
What questions should I ask a potential seller about it?
Is there anything in particular I should be looking for?

* 3.9 Diff / Standard 1098 Gearbox / 1275 engine

[Stig]

Hi Kate,

I got a s/h complete axle last year for £40, it was already off the car so I'd no idea how many miles it had done but I guessed on average it would be half what my car's done. Ideally you want to know something about the history of the car it's come from.
There's still a fair bit of slop in the transmission which must be the diff as the half-shafts looked fine -that's turning the propshaft round with the handbrake on. Less slop than before though. If anyone else knows how much slop is 'within spec' I'd like to know too.

I've since had to replace a propshaft UJ and still have a nasty vibration above 50mph but that may be a damaged gearbox bearing from running it with a knackered UJ. Straight after I replaced the axle there was noticeably less whine, it was a few weeks later that I got the UJ trouble.

Oh, that was for a 'normal' diff from a late 1000, higher ratio ones probably fetch a higher price.

[Matt]

1275 spridgets use the 3.9 ratio. They tend to go for £50-75 s/hand on ebay... (or at least thats what ive seen them go for)

[Willie]

Unless you are only interested in acceleration the 3.9 ratio would be fine
with a 1275 engine. The hardened half shafts are quite reasonably priced so,
I think, are worth it for the peace of mind.

[rayofleamington]

I've since had to replace a propshaft UJ and still have a nasty vibration above 50mph but that may be a damaged gearbox bearing from running it with a knackered UJ.

If it was the front UJ, then there is a high chance that the gearbox has been worn/damaged (extreme load from the runout will put too much load on the box).
This can be fixed by replacing the rear bearing (plain bush). However if you've done many miles then you may also find that the male part (on the propshaft) is worn eccentric.
This happened to me, and I had to replace the box but didn't realise the prop had also worn eccentric, so had to replace the next gearbox and the propshaft

[Stig]

If it was the front UJ, then there is a high chance that the gearbox has been worn/damaged (extreme load from the runout will put too much load on the box).
This can be fixed by replacing the rear bearing (plain bush). However if you've done many miles then you may also find that the male part (on the propshaft) is worn eccentric.
This happened to me, and I had to replace the box but didn't realise the prop had also worn eccentric, so had to replace the next gearbox and the propshaft

It was the rear one, the front one seems OK. I would've replaced both but damaged one of the new bearing races when changing the rear so used the second new one for that. I tried sticking a large jubilee clip on to balance the shaft but it made no noticeable difference even when I moved it 180deg. I really need to sort this out as keeping below 50mph down hills on A-roads (never mind motorways) is not fun! Any ideas on how to work out where the vibration's coming from?

p.s. Sorry for the thread hijack Kate!

[rayofleamington]

Stig28,
Sounds like a prize pain
My first recommentdation (although you may well have done this already) is to grab old of each end of the prop and give it a wiggle - this should highlight if the gearbox (or diff) bearings are nolonger holding it perfectly true. I'm not sure about the rear but there should be much less tham 1mm movement at the gearbox end (If you push the propshaft around, you'll move the gearbox in its mountings so it tke a keen eye to spot the relative movement).
If it is very sloppy you'll probably feel the slack - if it is this bad you need to fix it ASAP.
Vibrations at the gearbox or propshaft can lead to a lot of other problems
When I've had these kind of problems I used the rear viewm mirror as a measuring tool!. If the headlights of the car behind made a big blurry figure of eight then something was very wrong. If they only made a squashed oval shape then that was probably normal...

[Alec]

Hello Kate,

we have a 3.9 differential on our Traveller, with a 1275 engine (Cooper pistons, 'rally' camshaft, single 1 1\2" S.U. and three branch manifold)
It pulled this very easily so much that I now have fitted an overdrive gearbox as well. It seems to manage that OK also so there is sufficient power\torque.
Still on standard half shafts also.

Alec

[Pyoor_Kate]

Oooh, ooh. What overdrive gearbox did you fit? What was involved?

I've been pondering overdrives for a while, and wondered what was available in that direction too.

[chrisd87]

I know the Triumph overdrive can be fitted somehow. Don't know how much work it involves, but it'd be quite a nice 'period' alternative to a 5-speed.

[Alec]

Hello Kate,

I originally fitted a Marina gearbox with the 1275 engine, and saw on E-Bay an overdrive gearbox taken from a 1000, which I bought. It is originally a Triumph gearbox but it is the same basic unit as the Marina. (Normally known as the single rail gearbox.)
Basically I had to relocate the gearbox cross member further back for the Marina box and then further cut and reinforce it for the overdrive due to it's much larger diameter. A modified propellor shaft is required as the gearbox has a flanged output and the gearbox cover was extensively modified to fit over the bulkier gearbox and slightly different gaer lever position. All in all, a lot of work but I'm very pleased with the result.
I much prefer an overdirive to a 5 speed as instantaneous changes can be made with the flick of a switch. Third gear overtaking, in particular, is enhanced as a quick flick of the switch and a higher gear is the result.

Alec

[wanderinstar]

Kate,
would you not be able to fit the 3.7 diff from Wolsley 1500 or Riley 1.5. Would have thought the 1275 would pull it ok as the 1098 pulls the 3.9, just.

Have got a 3.7 to go in mine, but as I only have 1098 have worked out that if I put 13" wheels on it should be ok. However, since I got the diff I have now fitted Cooper head at 9.5 C/R,1.75"carb and w/h manifold so it may not need 13" wheels.
Hope this has been of some help.
Ian.

[bmcecosse]

Wolseley diffs are harder to get than Wolseley brakes !
What are 'Cooper' pistons, Alec ?

[Pyoor_Kate]

Alec - cheers - sounds a bit more work than I'm likely to be able to afford; perhaps one day.

Wanderinstar - I'd not thought of that, I'll keep an eye open, although I imagine that as BMC says they're not that common... If anyone sees one, in good nick, give me a shout eh!

[Alec]

Hello Bmce,

pistons that are used in 1275 Mini Coopers, basically higher compression than the Marina ones.

Alec

[Matt]

Re 3.7 diffs the last few years of spridgets used them, so if you can find a late spridget you could use the diff

[ianselva]

Kate,
would you not be able to fit the 3.7 diff from Wolsley 1500 or Riley 1.5. Would have thought the 1275 would pull it ok as the 1098 pulls the 3.9, just.

Have got a 3.7 to go in mine, but as I only have 1098 have worked out that if I put 13" wheels on it should be ok. However, since I got the diff I have now fitted Cooper head at 9.5 C/R,1.75"carb and w/h manifold so it may not need 13" wheels.

I ran a 1098 Traveller on 3.7 and 3.9 diffs for years . The engine was standard apart from high lift rockers and it pulled the 3.7 quite easily although it was mainly used one up and would have struggled with 3 passangers etc.

[bmcecosse]

Re-Cooper pistons - unless you had a 'low compression' Marina, then all the 1275 engines used the same pistons - except the MG Metro engine which had slightly taller pistons (still dished) to raise the CR slightly. Cooper engine was exactly same as standard 1275 Mini engine - although some think it had the bigger 1.75" carb - i'm not so sure. Certainly head/cam/pistons etc all the same.

[Alec]

Hello BMCE,

I can't remember all the figures but I know that these pistons gave me about a 9.5:1 compression versus the standard 8.5? They were selected using one of David Vizards books, but as I say the details are now a bit hazy.

Alec

[Stig]

Back to my thread hijack I found the cause of the vibration was a loose nut of the front of the diff. Must have been shaken loose when the propshaft joint went and got gradually looser. Quite impressive when it's supposed to be tightened to 140 lbft! I dread to think what that's done to the pinion bearings but I can now go over 50mph without the car shaking to bits!