Overdrive or diff changes

[John]

I think on the old forum I read of the % step up in gearing of a overdrive or diff changes of other ratio's. Are these numbers some where on here?
I ask (OT question) as in a 86" I have a 2.5 petrol engine with standard S11 rear diff and gearbox, this seems very undergeared but I'm looking for a lower cost way to step up the gearing.
I have Rover 80 diffs to hand but is that the best route?

[Alan Drover]

The problem with higher ratio diffs is that all gears are affected. With overdrive standard ratios are retained with the option of a 5th gear or a very useful splitter between 3rd and 4th. The problem is expense. Roamerdrives are available but at a price because you have to deal with Roamerdrive direct as there are now no UK agents selling them and a good Fairey overdrive can be pricey too if you can find one.

[Adam1958]

Range Rover diffs made a world of difference to my 88. I was hesitant, so bought 1, chucked it in the rear in an afternoon and tested it in 2wd for a few weeks before deciding it was a winner. The caveat being the off-roading I do isn't challenging and I don't often tow a trailer. For £80 and a gasket it's worth a crack I'd say.

[John]

Are there any numbers to compare a fairly/Rover 80 Diff/RR diff?
I do agree that OD is the best option but the cost of a good one for my least used series seems perhaps just to much

[Peter Holden]

To find out the didd ratio if it is not in an axle case Mark 1 tooth on the crown wheel and count how many times you have to turn the pinion for 1 complete turn
Diff ratios that I know
4.88 to 1. Very early 80" land rovers (identified by the long nose diff casing
4.7 to 1 standard leafsprung S1,2 and 3
3.54 to 1 range rover
4.3 to 1 Rover 60
Other P4 rover cars also had a choice of 4.1 and 3.9

There may well be others

In the 70s and early 80s I ran an 80" with a 2l spreadbore engine as a daily driver.  It had rover 60 diffs and 750 truck radials on it.

The 4.3 diffs were probably equivalent to an overdrive and I really enjoyed driving it.

Peter

[John]

^^^ thank you
I think unless I find a good/cheap overdrive, which I doubt, its 4.3's as the best option

[Peter Holden]

4.3s work really well if you can find them

Peter

[John]

4.3s work really well if you can find them

Peter

Glad to say I have some in the shed

[NoBeardNoTopKnot]

With overdrive.... The problem is expense. Roamerdrives are available but at a price because you have to deal with Roamerdrive direct as there are now no UK agents selling them...

The way you see this, does dealing with Roamerdrive - direct - makes the product pricier or cheaper?

[Alan Drover]

Probably more expensive as an agent will be importing several units which will work out cheaper for carriage than one unit