What a difference a Diff makes

[warb21]

For any who may be interested….

See other threads about this for the background but I got hold of a 3.9 diff (thanks, you know who you are!) for my 1098 Traveller daily driver, because I do a lot of motorway/dual carriageways. Had it fitted this week(thanks YOU know who you are!), and WHAT a difference! Even my family who are not very car-aware have noticed it's 'smoother'.

But there's a twist. Turns out I actually had a 4.55 diff under there, so no wonder…

First still feels like first, just slightly less nippy; second lasts longer, third lasts longer still - am sometimes driving at 30 in third now - and fourth, strangely doesn't FEEL that different once I get up to about 60. But that may be just my perception because it also turns out the speedo was previously reading too fast - suspect it was never calibrated for the 4.55 diff - and now it's reading much more accurately when I test it with a GPS speedometer app(which I never did with the 4.55). I've no doubt that steep hills will be slightly more work, but I'm not likely to encounter those day to day. I'll miss the yappy-dog acceleration of the 4.55 but the engine is generally not having to work as hard, which might have a fuel economy benefit.

Are 4.55 diffs in demand? And which cars would they originally have been made for?

[aupickup]

vans and pick ups and early mogs for the 4.55

[philthehill]

The people looking for a 4.55 ratio are usually looking to replace like for like but quite a few people like your self raise the diff (or lower it to be precise) ratio exactly for the reasons you quote.

The ATA carrier assy and 4.55 ratio fitted to the Minor 1000 - 948cc is more than serviceable but the BTA carrier is better and has stronger webs around the sun and planet gears.

The carrier to use with the 4.55 ratio is the BTA but quite rare and the assembly is Pt No: ATA 7093.

[bmcecosse]

I too found my 1098 Trav had been fitted with a 4.55 final drive. The change to a 3.7 was quite dramatic!

[warb21]

The people looking for a 4.55 ratio are usually looking to replace like for like but quite a few people like your self raise the diff (or lower it to be precise) ratio exactly for the reasons you quote.

The ATA carrier assy and 4.55 ratio fitted to the Minor 1000 - 948cc is more than serviceable but the BTA carrier is better and has stronger webs around the sun and planet gears.

The carrier to use with the 4.55 ratio is the BTA but quite rare and the assembly is Pt No: ATA 7093.

I'm lost on what ATA and BTA mean! Loving the learning curve though. 6 months ago I didn't know what a diff was.

And - BMC - I'm now wondering what a 3.7 would be like...

So, anyone want/need a 4.55 diff?!

[bmcecosse]

My 1098 engine is uprated - and pulls the 3.7 easily. I do think it would be too low for a standard engine - unless living in a v flat area with no hills.

[warb21]

Now wondering whether to sell/offer the 4.55 diff or keep as backup...

[bmcecosse]

Just hang on to it - it's not worth much......

[Roni]

Store the diff with the nose pointing up to keep any contaminants/dirt from getting into the front bearing. A small bucket works well.

[bmcecosse]

Hardly anyone will want a 4.55 final drive. Most are doing as you are doing - upgrading to a lower ratio final drive in search of economy and (hopefully) some peace and quiet.....

[jaekl]

You'll need it if you decided to put 20 inch rims on.

[bmcecosse]

[POMMReg]

Apols for hitching a ride on this.....

Is there any way to tell the difference between an 803cc rear axle and that of a 948/1098?

Cheers

[bmcecosse]

I think - only by checking the final drive ratio.....

[warb21]

Store the diff with the nose pointing up to keep any contaminants/dirt from getting into the front bearing. A small bucket works well.

It's currently wrapped up in bubble wrap, in a bag, in a box. Like pass the parcel! Reckon that will be ok?