Differential upgrade

marnol74
Posts: 23
Joined: Thu Jul 16, 2009 8:32 pm

Differential upgrade

Post by marnol74 » Sun Mar 04, 2012 3:07 pm

Hello all,

I wondered what experience folk have had in raising the ratio of their differentials with the standard engine 75 fitted.

Dirk, you mentioed that you had done so. Does the vehicle pull adequately on hills and do you find yourself operating at wider throttle openings for longer periods? Is your fuel consumption favourable with the unit fitted?

Also, did you need to get the propshaft length altered or is it simply nuts and bolts?

Thanks for all your help!


Matthew

Paul Gregory
Posts: 114
Joined: Wed Sep 24, 2008 10:20 pm

Re: Differential upgrade

Post by Paul Gregory » Sun Mar 04, 2012 9:55 pm

Hi Matthew,
I don't have direct experience of running with a higher ratio diff but have certainly considered it in the past. It would certainly help to keep the revs down when travelling longer distances, but I have so far decided not to follow that route as I use the car mostly around Cumbria and the standard ratios seem to be very good for our roads, which certainly are not flat in parts.
If you do choose to go down the diff change route there are several ratios to choose from. The P3 has a long nose diff as standard, which I think is a 4.7:1 ratio (unless it is a 4.9:1 but I don't think it is). All the alternative diffs are short nose, and as a result would need a spacer adding between the propshaft and the diff (or prop and gearbox) to effecitvely increase the length of the prop. I cannot remember off the top of my head how long the spacer has to be but I seem to recall that it is something like a couple of inches. Your ratio options ( assuming you are going for a standard Rover diff) are 4.3:1, 3.9:1 or 3.54:1. P4's are fitted with a 4.3:1 in general, although I think at least some 60's had a 4.7:1 and the 95 (and some non-overdrive 90's) were fitted with a 3.9:1. I think most P5's are also fitted with a 4.3:1, though certain ones had the 3.9:1. P5B's were fitted with the 3.54:1 as were the classic Range Rover and many of the coil sprung Landies (Defenders).
Regards
Paul
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Dirkco
Posts: 142
Joined: Thu Oct 30, 2008 2:12 am
Location: USA
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Re: Differential upgrade

Post by Dirkco » Mon Mar 05, 2012 2:50 am

Hello Matthew,

I changed my Diff when I restored my 6 light to a later P5 MK 11 and I found that I now have first gear I can use. prior to the change 1st was so low that there was no point. I do cruise on the hi-ways here in the States and do find that I have to down shift on steep inclines and yes, I find that I use third more often around town. However I really wanted to keep the engine primarily stock and have resisted the impulse to upgrade the head to a early P4 and twins carbs. I have friend who did this and it really does add allot of power but....

I would never go back to the old diff ratio with it changed it is a use-able car anywhere and at hi-way speeds If I were you just do it! I did add a 1" spacer to the end of the transmission.

The 1 modification I did do was to add a brake booster to the front brakes. I found a small one on Ebay and it was easy to hide it under the intake manifold. I now leave the freewheel on all the time and never feel that I cannot stop in control.

I don't know about gas consumption as the original Solex was leaking so badly at the diaphragms that it could only improve with the rebuild of the carb. But I would say I am most likely getting about 18 to 20 mpg's maybe a little better but I am running the car lean.

I look forward to hearing more about your P3 and hope to see it at the National!

Dirk in the States
www.roveramerica.com

P3Steve
Posts: 123
Joined: Sun Sep 28, 2008 7:05 am

Re: Differential upgrade

Post by P3Steve » Mon Mar 05, 2012 11:08 pm

Dose the diff bolt direct into the case and are the half shafts a straight in fit?

marnol74
Posts: 23
Joined: Thu Jul 16, 2009 8:32 pm

Re: Differential upgrade

Post by marnol74 » Tue Mar 06, 2012 3:53 pm

Hi Dirk,

Thank you for your very detailed post. I suspect that I will try out a different differential ratio and see how it goes. I am afraid that it is a tall order to get it on the road for National but I am hoping to get there.

What type of brake booster have you fiited? Is it a remote servo similar to those fitted to the p6?

thanks again.

Matthew

Paul Gregory
Posts: 114
Joined: Wed Sep 24, 2008 10:20 pm

Re: Differential upgrade

Post by Paul Gregory » Tue Mar 06, 2012 8:35 pm

I believe the diff is a straight fit into the axle casing, and the halfshafts will fit. I seem to recall that some later classic Range Rover diffs use a different number of splines so the halfshafts wouldn't work on them, though I may be completely wrong on that, and cannot be 100% certain without doing some digging. Certainly the P4 & P5 diffs will be a direct fit into the casing, and will just require the propshaft space to make them work. Changing the diff ratio will of course make your speedo read incorrectly unless you get it re-calibrated.
I think you will find there is info about changing Diff ratios available within the P2 / P3 workshop manuals available through the RSR.
Oh, the other thing is that the diff from a P6 is very different and would not fit.
Regards
Paul
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deckell
Posts: 86
Joined: Mon Mar 05, 2012 11:12 am
Location: Bundaberg Queensland Australia

Re: Differential upgrade

Post by deckell » Sat Jul 25, 2015 4:41 am

Hello matthew i am about to attempt to replace my 4.7 diff centre with a 3.9. and i wonder if you could give me a head start on what to do and what to avoid on this endeavour. any hints or tricks would be appreciated. thanking you in anticipation best regards Derrick.Smith.

RobHomewood
Posts: 320
Joined: Tue Oct 22, 2013 8:04 pm

Re: Differential upgrade

Post by RobHomewood » Sun Jul 26, 2015 7:49 pm

I understand that the diffs have remained basically the same in the LandRover until almost current times. I was offered a big range of ratios when I got my diff refurbished recently by the local Landrover specialist and slightly regret sticking with the original 4.7:1 of my P2 (to avoid changing the transmission shaft length). By the way there is a great U tube of the refurbishment process on Ashcroft Transmissions website

jefflee
Posts: 105
Joined: Sun Mar 04, 2012 4:35 pm
Location: ROTHERHAM S. YORKS

Re: Differential upgrade

Post by jefflee » Thu Jul 30, 2015 11:46 am

Gearing up the diff ratio is the best mod. you can do to old Rovers.
Oil seals and gaskets available from Landrover dealers.
It is reasonably easy and I have done this quite a few times on P2s.
Axles before 1939 are different fitting and wont accept later p2 p3 p4 or 4x4 diffs.
I think all P2 6cyl are good with 3.9 and all 4cyl + 1599cc 14 are good with 4.3.
From 1939 all diffs are interchangeable through to early Range Rovers!
(must be 10 spline with a filler plug, some 4x4s had filler in axle).
From 1939 the axles on models except 10 hp were increased width by 2"
so on my 1936 14 ss I first fitted a narrow track 1946 10 hp axle, then higher ratio p4 diff.
This model is the hardest to do because it doesn't have the large lift out seat pan
it has two small rear seat cushions and the frame covers over the top of the diff.
Different models require different prop shaft length's the 14 needed extending 1-3/8"
I had a new prop tube made and balanced local for £80 cash.
This gear up makes the car much more drivable & economical.
Forget the speedo calcs.& tyre size arguments, just do it you wont regret it.
And if you really want the best ad Mike Evans excellent overdrive unit.
Jeff.Lee
1937-20 SS _ 1938-20 SS _ 1946-16 SS _ 1947-16 saloon

deckell
Posts: 86
Joined: Mon Mar 05, 2012 11:12 am
Location: Bundaberg Queensland Australia

Re: Differential upgrade

Post by deckell » Tue Aug 04, 2015 10:47 am

Thanks for the information i now have the diff fitted and waiting for a spacer to be turned and then i will be mobile again regards Derrick Smith

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