Axle conversion

[AndrewT]

Hello been thinking about changing my series 2 diff for a 3.9 one I have the 1098 engine fitted but at around 50 mph she's all out and high revving can I just change the diff into my casing or do I need to change the lot,if I can keep my casing am I ok to use my shafts etc? Many thanks guys or is there another diff that would help? I'm looking for around 70mph just to be able to use and not worry about using major road without it screaming many thanks

[Nickol]

I have a 3,9 fitted to a '69 Traveller and if I were to travel at (in world measurements) around 110 kmh, the engine and gearbox would also be screaming, albeit at about 10% less reva than before. At about 100, it is probably reving at 90 before so the difference is noticable but not a lot, I think you are perhaps expecting too much.

[AndrewT]

but surely it would help considering it's still running the series 2 diff

[pde2000]

I changed my series 2 diff for a 4.2 no problems. I will probably change back to the 5.3 though because the 803cc does struggle a bit 1098cc with a 4.2 would be sweet. You should uprate the brakes at the same time, at least with a servo, if not a set of discs.

[AndrewT]

Austin Healy/sprite 4.2 be alright? I know for one of these for £75

[pde2000]

I dont know anything about Healy, but assuming its a regular BMC diff then it would be fine. I see you also have a 54 series 2.

[AndrewT]

Yes 4 door came with a 1098 already installed but 45-50 and you need ear plugs so hoping to find a diff even if it's just to get 60 there's a Morris breaking near me which is a 1961 4 door do you know what diff that may have?

[pde2000]

Could be a 4.5, if the engine is 948cc. Just checked google and the healey uses the same type of diff.

[AndrewT]

Found a sprite/healey one which is 4.2 so I'd be better going for that over the 4.5?

[pde2000]

The 1098 was mated to 4.2 for higher road speed, compared to 948, so yes i reckon. You will have to use the breather hole to fill i think. When i replaced the oil i remember overfilling and getting oil onto the brake drums. My brakes are pathetic. I once had to make an emergency stop and had to stand on the brake pedal, still didn't skid but did stop just in time. When i used to drive a milk float the brakes on that was just as bad (and 6 tonnes loaded).

[AndrewT]

Il keep an eye on that one then if not would a 3.9/3.7 be better again? Yes I know what you mean I try my best to avoid needing to stop suddenly in the old girl

[amgrave]

With a 1098 engine a 4.22 diff will give you 60 - 65 easily, 70 if you don't mind a bit of noise but if you fit a 3.9 it will give you 70 easily but at the cost of being a bit sluggish up hills and struggle a bit in head winds at speed.

[AndrewT]

Im assuming I have a 948 box fitted would it help if I also fitted a 1098? Could I change the top selector of the box to still retain the wand gear stick?? Would I need to change my flywheel or clutch etc?

[pde2000]

Top gear is the same between boxes; 1:1

The series 2 box can be mashed up with the 948 box, but not the 1098

[AndrewT]

Is there a rebuild kit around for the 4.2 diff bearing seals etc just incase it needs doing? Also if this a easy job? I have tools,press etc

[pde2000]

Rebuilding a diff is not an easy job; the alignments have to be jigged or something. When i replaced the 5.3 it was because they werent available at the time, and there were only pinion and crown wheel sets, for about the same cost as a new 4.2. Replacing the diff is easy, just pull out the drive shafts, unbolt the prop, and swap the diffs. New gaskets for the diff and 1/2 shafts needed. brake hose flex is attached to diff.

If you need to refill through the breather you can insert a bleed pipe into the neck of a hypoid bottle and tape it up so that will fit the hole. The filler neck of a bottle of hypoid is too wide. The 5.3 diff has a level/filler plug in the side. I bet you can climb hills well with the 5.3 driven by 1098

[pde2000]

Is there a rebuild kit around for the 4.2 diff bearing seals etc just incase it needs doing? Also if this a easy job? I have tools,press etc

There are no bearing seals in the diff.

[Sleeper]

Input bearing seal...

John

[pde2000]

Input bearing seal...

John

oops

[philthehill]

Being pedantic as is my wont - the only (lip) seal in the Minor diff bears on the tubular part of the input drive flange which fits over the input shaft and therefore the seal is not connected to the input shaft bearing(s).
So to my way of thinking pde2000 is therefore technically correct in that there are no bearing seals in a Minor diff only an input shaft drive flange seal.

Replacing the input shaft seal is relatively easy.
Drain the diff oil and discard correctly and responsibly.
Torque the pinion nut and see what the torque reading is currently.
Undo the pinion nut (remove split pin if fitted) and remove the drive flange.
Prise out the lip seal and discard.
Smear the lip seal with LM grease.
Fit seal into the diff housing.
Fit drive flange, washer and nut (& split pin if fitted).
Torque to original setting.
Refill with correct grade of EP oil.
Setting the torque to original setting ensures that the collapsible spacer (between the input shaft bearings and which determines the preload on the bearings) if fitted does not collapse further / or is reduced in length.
If a non collapsible spacer is fitted the job is even easier but as you do not know what spacer is fitted it is better to check the torque of the flange nut before dismantling.

The factory torque setting of the pinion drive flange nut is 140lb ft.
See BMC wksp man section HH3 for details.
Phil