2.8-1 Differential Poll

[johnwp5bcoupe]

Poll put forward by stevew to change the Differential to 2.8-1 from 3.54-1, for the benefit of lower revs and less fuel consumption.

Plus the price you would be prepared to pay? sensible answers on this one! as steve is talking to a diff supplier.
Take into account the tooling costs, building (setting up) postage etc in the price.

[Deleted]

I just bought the p5bcoup from ebay the SLEEPER with a poor gearbox that had a 4.5 litre upgrade to the tune of 30k from dak autos.God knows how they spent that much ,but its not the gearbox its the diff knocking so im looking for something myself.
The wheels are off the very latest jensen ,not my favorit.and yes she revs to high with 14inch wheels and 55 low profile tyres .Seen the post with the cherokee wheels ,not bad .But what else fits chaps .Im more of a Track basher than a wheel man own www.tanks-alot.c.uk 100 or more Tanks and military vehicles.probably why i like the rover.
Nick

[Deleted]

Been told a landrover/rangerover diff will fit and will gear it up any views on this ,i cany be the first to try.Got to do something quick mines clunking badly

[johnwp5bcoupe]

Having played around with 4th gear see members section, IMHO the standard 3.5 with BW35 will struggle with the 2.8-1 diff under load conditions low speed, hills etc.

I think the LR ratio is something like 4.1-1 so you would be going the wrong way!

[colnerov]

Hi, the Range Rover diff ratio is 3.54 the same as the P5b and is a direct swap.

Colin

[johnwp5bcoupe]

I know the series 2 LR is 4.7-1 Colin, and the early RR was 3.54-1 but didn't the spline count change 10 to 24 on the later models?

[colnerov]

Hi, yes John. But no clear cut off date and not for all. It depends on whether considered heavy duty or not I believe. If buying secondhand and they are usually 10 spline, if not vendor usually stresses the fact they are 24. Salisbury axles are 24 spline but not relevant in this case.

Colin

[stevew]

Received an email out of the blue that crownwheel and pinions are now available 2.8 to 1 ratio to fit p5's from the supplier I was talking to when this poll began. He did want a minimum order so am a bit puzzled.

[Deleted]

Interesting wonder what the price will be .Happy with my joj though, seen it coming along expect it will be finished by the weekend .
Pleased mine will have the semi floating powerlock diff from the 5.7 L jensen stops wheels spinning with the tuned 4.5L sdi engine i have and good in snow to.
When i get mine back i will give some indication on the change in gearing when its motoring for everyone.
Nick

[stevew]

I took the opportunity today in taking some measurements with the standard 3.54 diff ratio to compare later when the axle is changed for one with a 2.8:1 Bizarrely my speedo is in direct comparison with the sat nav which makes easier.
tyres are 215 70 15 with radius of 26.8 rolling circumference 84.2inches

MPH RPM
30 1650
40 2000
50 2400
60 2750
70 3150
zero too sixty ten seconds
Obviously these rpm measurements are taken from the car tacho and are as acurate as possible

[johnwp5bcoupe]

A near as dam it RPM measurement Steve on 185's is 2-1 ie 3500 at 70 and it should be linear sadly as the components age and they are not accurate anymore I had left over from my kart racing days a programmable standalone counter that picks up inductively from any lead so I could be sure of my findings for my project

Good luck with the conversion

[Deleted]

Some technical stuff on here but is this the oil I need for my original 1971 diff? This seems to be the closest to the oils specified in the handbook and is for Spiral bevel diffs. I haven't changed the oil for a long time.

www.classic-oils.net/Product-187/Oils-by-Manufacturer-Brand/Penrite/Penrite-Hypoid-85W140

[johnwp5bcoupe]

That will do Richard that or straight SAE 90!
Be prepared for the Smell

[Deleted]

Thanks John

Smell from the old or the new?

[johnwp5bcoupe]

The old Richard it stinks

[Baldrick]

The new stinks too... And avoid getting on clothes as the smell is washing detergent proof!

[stevew]

It's going in

2.8:1 Ratio crown wheel and pinion


Actualy it's 2.8333333333333335 :1
And your correct EP 90 does stink, Iv'e had it up my nose all day, YUK

[stevew]

3.5:1 CWP

SAT
NAV
MPH RPM SPEEDO READING
30 1650 30
40 2000 40
50 2400 50
60 2750 60
70 3150 70


2.8:1 CWP
SAT
NAV
MPH RPM SPEEDO READING
30 1200 25
40 1250 35
50 2000 42
60 2220 50
70 2500 59

[johnwp5bcoupe]

Looks ok Steve my only concern on a standard engine is under heavy load conditions I know from my own experience as I can duplicate changing the rear axle ratio that the gearbox changes very late and the strain on the gearbox/torque converter concerns me

Perhaps Harvey the gearbox guru will come in on that angle

[enigmas]

Nice set of gears, and the figures look convincing on paper but I'm with John on this one, a 2.8:1 ratio is too tall unless it's all freeway driving and there's a 351ci engine under the bonnet. A 3.5 litre engine will struggle. OZ P76 cars (4.4 litre engine ) came factory fitted with a 2.9:1 ratio but these had greater torque (longer stroke at 3.5") than the early Rover 3.5 V8. An overdrive gearbox would produce better all around performance and economy.

Fitting the biggest cubic inch Rover motor available would make it viable

www.roversd1.nl/sd1web/capacity.html

[harvey]

I've said right from the moment the idea was first raised that I think that a diff ratio that high will lose everything it gains during high speed cruising by the loss of performance from a standstill. I haven't been bothered to calculate the overall gearing in first with both diff ratios, but I see it as though you will be pulling away with a ratio closer to second than first, and although Rovers always had second gear start it wasn't meant for quick getaways, rather for lazy driving, and other than where second might be better in poor traction, I can't see the point when you've got full auto mode anyway. It will be the converter taking the strain, and that will mean extra heat to get rid of.

[redsunbeam]

Well done Steve. Is it much work to do? Has it made any noticable difference to the acceleration?

[Welsh Warlock]

Very interested in this as I have a 3.9 engine built for torque by V8Developments and Harvery's friend rebuily my gearbox a couple of years ago.

My car is suffering from a rumble/vibration at 65+ mph which I suspect is either the propshaft or the dif.

I took the propshaft off last night and ran the car up to 100mph in the garage and the rumble didn't appear so it must be in the transmission. No apparnt lateral play in the UJ's (they are sloppy in their intended range of movement but no play as such). I do need to look at the centre bearing though as I ran out of time last night.

I have had the rear axle clunk a few time on pulling away and there is some play in it so.......

Can we find out the cost and some feedback on the performance from the standard engine with this plase.

[enigmas]

Eastmidsrep, I'm not sure of the configuration of a 3.9 engine but generally longer stroke engines produce greater torque at a lower rpm. The 3. 5 is an oversquare short stroke engine. (ie. The bore is larger than the stroke) The 4.4 P76 is a 'square' engine...bore and stroke both at 3.5". Older British cars were traditionally undersquare (for tax reasons) producing lots of torque at low rpm. A big inch undersquare engine would be the go.

[Deleted]

Well picked up the rover today with the jensen back axle fitted drove much better will check the rev to speed ratios with my sat nav over the next few days.Pulled out of the filling station a bit hard to check the limited slip diff, seem to do the job ,only one wheel span for about a second then it locked up nicely.the car seems responsive not at all sluggish .but it is 4.5L not 3.5L that may give it a bit more torc.can get more jensen axles with the disk brakes and calipers still attached.have one handy but the calipers are missing .my local garage will do the whole job for £500 thought it pretty reasonable,handbrake,reweld all the axle mounts,redo brakepipes fit a balancer and sort the prop.