What diff gearing do I have? Need OD?

[alaskajosh]

This is a two part question and I thank you in advance for your help--

The previous owner had the diff gearing changed at the same time that he got a Robert Davis 3.0 transplant. He didn't now exactly what they were.. he said 3.8:1 (??) or 3.9:1 (??) He didn't know and I don't either.

Do either of these sound right? It's Rover in the front and Salisbury in the rear.


Now for part two:

It has the aforementioned gears in the diff, a SIII tranny, and this 3.0l engine. Right off the bat I burned up the Fairey OD.. it was dry of oil and I didn't check before driving away.
Would you think, based on this combination, that I'd even need to replace the OD? It's geared pretty high as it is, don't you think? It will see a lot of road use as I would like to travel long distance in it.

I know you're going to ask, "Well how does it drive"? I coudn't really tell ya' as it's been torn down ever since getting it home and will be for awhile as I address many issues.

Thank you very much, gents--

[Mercedesrover]

Unless he started swapping gear sets your truck either has the stock 4:70 diffs or 3:54 diffs out of a coiler and there's a pretty big difference between the two.

You won't know if you need an OD until you drive it a bit. With 3:54 gears I would probably think not, depending on the size tires you're running. With 4:70 I would think yes.

jim

[scott]

i've 4.7s in mine. run 235x85x16 tyres, have a fairy o/d. in 4th the 2.25 screems in pain about 45 or 50 mph. with the o/d i can cruise about 55. all this would be on the flats top end on a down hill or with a good tail wind 70

[BackInA88]

I have the same set up as Scott and can cruise all day at 65/70 MPH.
Engine is running at about 3000 RPM and in pretty good shape with a 8:1 head.

I only loose speed on the biggest hills on the expressway.
I think my Weber is limiting me so what?
May buy a new Zenith?


Steve

[alaskajosh]

Yes, I believe he did swap the gears. I spoke to Robert Davis, who transplanted the engine and the gears, and he said they were 3.8 or 3.9 he couldn't remember. I'm hoping one of those is a possible choice that one of you recognize..

Thanks you

[badvibes]

apologies for the hijack

i've 4.7s in mine. run 235x85x16 tyres, have a fairy o/d. in 4th the 2.25 screems in pain about 45 or 50 mph. with the o/d i can cruise about 55. all this would be on the flats top end on a down hill or with a good tail wind 70

I don't know what Scott's talking about. He just told me that his 2A pushed his wife's LR3 all the way out to California at speeds up to 90 mph. I've followed him on the freeway as best I could with my truck, stock rebuild with a 1bbl Rochester, motor @ 6000 miles now and he always runs faster than I do. I just got back from the hills with a friend caravaning in his Dakota. On the flats on the highway he said I was running 60 pretty consistently. My speedometer isn't reliable at all. I have noticed that at 7000' and above my truck becomes an absolute slug though. So with a fresh motor I run 55-60 witout any trouble*.

Jeff

* as long as there are NO hills

[KevinNY]

GBR did indeed have a 3.9 gearset for a time.

[daveb]

3.9 diffs were used in santanas and rover p4's.

I drove robert's orginial 3.0 equipped 109 back in '96 or so and it had the 3.9's. it went quite nicely.

I'm hoping one of those is a possible choice that one of you recognize..

Thanks you

[TeriAnn]

GBR did indeed have a 3.9 gearset for a time.

I think Bill may still be offering a 3.9 & there is a 4.1 vailable.

I think the full range is: 4.75:1, 4.7:1, 4.1:1, 3.9:1 and 3.54:1