Rover V8, Discovery diffs, AND overdrive??

[Scooby Jim]

I have managed to source an Overdrive for my Landy (will post pics when i get it), but what difference will it make??

I have a Rover V8 out of an SD1 so 9.35:1 comp ratio, changed the series diffs (exploded) to disco 10 spline ones, and am considering fitting the overdrive to that setup. What difference will it make in real terms, will there be any problems/difficulties associated??

I'll have to get used to driving the Landy anyways, as I have never driven her, so won't feel any different.

What you guys think??

Will be picking it up Thursday, here are the pics from the seller.

[missingsid]

If the diffs are 3.54:1 which I expect they are then I beleive that this plus the overdrive will be too much. People use either high diffs only or low diffs and overdrive I have not heard of both!

Well done for finding one as I have only seen high money for them? I would not mind changing mine to lower ratio diffs and an overdrive as this keeps the low ratio of the transfer box as it should be but the std low ratio diffs are weaker than the high ones as the crown wheels are thinner and flex, pegging would help.

High ratio diffs mean the handbrake has a tough time holding on a hill.

Marc

[Scooby Jim]

If the diffs are 3.54:1 which I expect they are then I beleive that this plus the overdrive will be too much. People use either high diffs only or low diffs and overdrive I have not heard of both!

Well done for finding one as I have only seen high money for them? I would not mind changing mine to lower ratio diffs and an overdrive as this keeps the low ratio of the transfer box as it should be but the std low ratio diffs are weaker than the high ones as the crown wheels are thinner and flex, pegging would help.

High ratio diffs mean the handbrake has a tough time holding on a hill.

Marc

When I get it I will say how much I paid

Would the V8 not have enough grunt, as to be fair it would only be needed on motorways, and its only an 88.

Or would my box carp itself??

[Josh NZ]

I think Nick (Snagger) has this issue. He broke his gearbox running a 200Tdi with high ratio diffs and OD. Discomikey runs this setup also with a tdi I think... Maybe they'll chime in for you! You may find the acceleration lacking a little

[Scooby Jim]

I think Nick (Snagger) has this issue. He broke his gearbox running a 200Tdi with high ratio diffs and OD. Discomikey runs this setup also with a tdi I think... Maybe they'll chime in for you! You may find the acceleration lacking a little

Was thinking more get up to speed then engage OD for cruising on the motorway. Hmmmm what to do lol.

[Team Idris]

I thought V8 plus rangy diffs plus overdrive was the to go. But an S3 gearbox behind a V8 will always have a reduced life span. That's why the 2A box was sought after back in the day; if you can live with syncro on 3rd and 4th only?

Personally I'd cock about with the 2 1/4 petrol. Because it is a diesel capable engine, you can go all out on tuning. Plenty of power without that damaging low-end torque.

[xychix]

I thought V8 plus rangy diffs plus overdrive was the to go. But an S3 gearbox behind a V8 will always have a reduced life span. That's why the 2A box was sought after back in the day; if you can live with syncro on 3rd and 4th only?

Personally I'd cock about with the 2 1/4 petrol. Because it is a diesel capable engine, you can go all out on tuning. Plenty of power without that damaging low-end torque.

What is the lifespan of a S3 gearbox on a series anyway? (with it's original 2.25Diesel engine and standard diffs and tyres.)

From what I read here and there Series III is only for the nerds whe like to rebuild a gearbox every other month..... my 70.000 km's series III is on it's second gearbox (just bought it, it was mounted 4.000 km's ago) so I'd expect a rebuild before ~ 130.000 km's...

[Team Idris]

It's not just the bearing life span either. Mine broke a spring in the syncro hub. The whole box out for some crappy plate springs!

[Josh NZ]

Although the OD for cruising only is fine in theory, you might find that inevitably you need to accelerate with O/D in and it will strain the mechanicals a little. It could also become be a bit of a pain to keep swapping in and out. If your engine is in great fettle, it will probably pull acceptably.

I would just see how it goes and if it's too slow then you know what to do

I'd hate to see you do all the hard work only to be let down Jim! I'll be following with interest

[Paul Woodward]

I used to run the 3.54 diffs and a Fairey overdrive in my V8 Series III. As has been said really only of use on the motorway. Also depends what size tyres you're running, I was on 235/85x16 BFG muds.

The biggest disadvantage for me was that offroad low 1st was too high with the 3.54 diffs.

[timppl]

I found it very useful having the overdrive with defender diffs ( behind a 19J engine ) in my lwb ser 3 safari. It pulled acceptably from about 50 with overdrive in 4th ( series 3 box ). On a motorway run at around 60mph I would get about 45 mpg, dropping to about 40mpg if I was towing the caravan. As Josh suggests, you need to put it in and out of O/D a fair bit, but I was expecting this, so no problem. I have never driven a V8, but as it has more oomph than the 19J I would not expect any problem, unless you do a lot of offroad work and need the lower gearing.

O/D is off mine ATM for a rebuild, and it is quieter without it.

HTH

[Scooby Jim]

Are the Disco diffs that bad off road?? Knew there was going to be a difference, but is it that bad?

What would you say is best??

1. Disco diffs.
2. Series diffs and overdrive.

3. disco and overdrive.

Please bear in mind I probably never go too mad off road anyways.

[De Ranged]

Some thing else to consider.... there is a spline in the overdrive box that wears out, unfortunately my mate that has been dealing with this issue is on the other side of the world at the moment

I do know he has bought 3 overdrives (second hand, here in NZ) and all three were down to a knife edge of spline left... so was planing on spending $1500 for the new shaft and gear, guessing he'll be bringing it back from his holiday

Don't forget your tyre size.... it is critical to the above question

Ouch running late I'll put up some math tonight to show you how to calculate the effect in revs the change in gearing has

[Josh NZ]

If it helps any, I ran my Series 2a with standard diffs and O/D and i got it up to 85mph on a private road (wouldn't do it again mind you!). It was noisy, but the truck managed fine with the 2.25p.

I also ran my stage 1 v8 with the low comp 3.5v8 on standard 3.54 diffs and lt95 gearbox up 135kmh on the same road which I also wouldn't do again due to the wheel wobble. Your v8 is an SD1 type so should be around 155hp..? It will probably pull OD on standard diffs really well.

Another big point is that the truck is actually a little overgeared around town on 3.54s eg you will either be in 4th at 50-60 and will be lugging, or 3rd gear and revs are little high/noisy. I certainly found this with my stage 1.

So, I would say keeping your standard diffs and OD would be a really good compromise for what you want to do. But it's up to you ultimately!

Josh

[Cheesy]

I thought V8 plus rangy diffs plus overdrive was the to go. But an S3 gearbox behind a V8 will always have a reduced life span. That's why the 2A box was sought after back in the day; if you can live with syncro on 3rd and 4th only?

Personally I'd cock about with the 2 1/4 petrol. Because it is a diesel capable engine, you can go all out on tuning. Plenty of power without that damaging low-end torque.

The 2A probably isnt all that strong either is it? I managed to separate the drive dog off second gear pulling out of my driveway. I have never driven a 3.5v8 but my series

had a 4.1l straight six which should have been less powerful than the RV8 (its no where near the 4.5L RV8 in my rangy), even with the 3.54 diffs in it first gear was still a waste of time (750-16 SATs). I would have liked to have tried an OD on it but hens teeth comes to mine.

[Bowie69]

Are the Disco diffs that bad off road?? Knew there was going to be a difference, but is it that bad?

What would you say is best??

1. Disco diffs.

2. Series diffs and overdrive.

3. disco and overdrive.

Please bear in mind I probably never go too mad off road anyways.

My suggestion is, fit it all up and drive it some before you think about modifying it some more

Otherwise if you try to perfect it all now, it will never get finished.

Book an MOT, always a good incentive

[Scooby Jim]

Hmm conflicting things

What are the 3.54 diffs like off road??

[Josh NZ]

33% higher geared than standard across the range I think

[Pollywog]

I'm running 3.54 diffs, 235/85r16's and a fairey o/d behind a 200tdi in my lightweight.

I find it a nice drive, around town I'm mostly in 3rd, if it's a long straight at 30 I might pop it into 3rd overdrive otherwise I'm up and down from 3rd to 4th a lot.

I tend to put it into 4th overdrive at around 50 and it will happily cruise at anywhere between 50 & 70 and probably more!

With the original diffs I used to be in 4th by 20mph.

The only time it seems to struggle is pulling away from a steep junction with a lot of steering lock on. I don't get any wheel spin anymore.

I've had it off road a couple of times since fitting the diffs and the rise in low ratio gearing is not an issue for me, yes it is slightly faster but still very acceptable in my opinion. If you were using it for trialling every weekend then probably stick to the standard diffs but if it's only the occasional jolly then I dont think you'll have any issues with it.

On the subject of how series 3 boxes cope with all this mine was all well and good in my old lightweight then I took it out and put it into this one with the 200, after a month or so it started to jump out of first, it had rattled the mainshaft nut loose and still jumps with a new one correctly torqued. I think the synchro is going also starting to think the same about 3rd. It also recently chewed up a shim on the transfer intermediate shaft which caused a terrible noise, and the speedo drive has stopped working.

Lt77 is on my shopping list!

How all that relates with the differences between the torque of a 200tdi compared to the high revving v8 I don't know.

[Scooby Jim]

I'm running 3.54 diffs, 235/85r16's and a fairey o/d behind a 200tdi in my lightweight.

I find it a nice drive, around town I'm mostly in 3rd, if it's a long straight at 30 I might pop it into 3rd overdrive otherwise I'm up and down from 3rd to 4th a lot.

I tend to put it into 4th overdrive at around 50 and it will happily cruise at anywhere between 50 & 70 and probably more!

With the original diffs I used to be in 4th by 20mph.

The only time it seems to struggle is pulling away from a steep junction with a lot of steering lock on. I don't get any wheel spin anymore.

I've had it off road a couple of times since fitting the diffs and the rise in low ratio gearing is not an issue for me, yes it is slightly faster but still very acceptable in my opinion. If you were using it for trialling every weekend then probably stick to the standard diffs but if it's only the occasional jolly then I dont think you'll have any issues with it.

On the subject of how series 3 boxes cope with all this mine was all well and good in my old lightweight then I took it out and put it into this one with the 200, after a month or so it started to jump out of first, it had rattled the mainshaft nut loose and still jumps with a new one correctly torqued. I think the synchro is going also starting to think the same about 3rd. It also recently chewed up a shim on the transfer intermediate shaft which caused a terrible noise, and the speedo drive has stopped working.

Lt77 is on my shopping list!

How all that relates with the differences between the torque of a 200tdi compared to the high revving v8 I don't know.

Very interesting, Id imagine the torque is higher on the derv, and torque will kill things. Plus Id imagine the V8 would deliver the power smoother than a turbo??

[Scooby Jim]

As for tyre size one of 3 (as I have 2 already) 235/75r15, 7.50x16, or 31x10.50r15 (255/75r15). Or some 16 in the similar size.

I'm not going to go large in tyres, as I think they look daft on a series,and I want the "standard" look. And from experience with my last 4x4 a Sportrak, it suffered badly if you went over a certain size as the acceleration went from normal to epically slow, and off road it got stuck, and nearly broke things. By keeping the wheels around standard size, but maybe a tad wider, will be what I want to do.

So maybe fitting the OD when I have given it an overhaul, and if I don't like it I can always sell on as I will NEVER lose money.

[FridgeFreezer]

I've just skimmed this so haven't caught all the arguments.

But I ran 3.9 V8 + Series box + Overdrive + RR Diffs (well, RR front, Stage 1 rear, but 3.54:1 gearing) for quite a while (years) and it was fine, and the gearbox etc. then went to TheRecklessEngineer who put it behind another V8 and abused it for quite a while longer until it died.

Off-road the 3.54:1 diffs were a tad high for my liking, only on hill descents though.

Gearbox lifespan is a function of your right foot and servicing.

[De Ranged]

I'll keep this simple and quick lol I'm tired

I'll use mine as an example... I'm a wee bit different being that I'm fitting a new motor and box but this will give you the idea

With my motor & box combo it originally came out with 4.11 diffs and 31" wheels as standard.... now I'm looking at running landrover 4.7 diffs so....

lets start with diffs since I'm increasing the ratio I'm going to end up with more revs on the same wheel 4.11 into 4.7 = 1.14 times so...

if 100km/hr was originally 3000rpm it is now (x 1.14) 3430rpm for the same speed

If I had gone for the rover 3.54 diffs (4.11 into 3.54) = 0.86 so that times 3000rpm = 2580rpm for 100km/hr

Now this is just looking at open road speed, you also have to consider other gears like offroad decents in first gear.... you have the advantage that your truck is running to get an idea drive it in these gears at those calculated revs and see if you like the way the motor performs.... does it accelerate happily on the open road, how about holding power on a hill ?.... remember there will in your case be a bit more drag from the increased speed, and there won't be as much power to accelerate due to the taller gearing but it gives you an idea

Lower gears and how they perform are a bit harder to replicate...

Since your not changing tyre size... tyres will not cause/solve any issues lol

But in my case with the 4.7 diffs I can solve the over rev'ing by increasing my tyre size 31" to a 35" (31/35) = 1.12 so this just about counters the change in diff gearing

Hope that gives you some idea to work on

[Scooby Jim]

Tbh guys don't worry too much about off-road, as the chances of it seeing anything technical is going to be negligible.

Having never driven the Landy I'm sure its just something I will have to get use to, with the diffs. And the Over Drive I can fit it, and if I want I can either remove, or only use occasionally. OR I can always fit series diffs. I will probably get a set and see what they are like, and if I am planning to go properly off road I can plan in advance and change the diffs. This is not going to be used a lot, as I have 2 other cars, so mainly cruising around, or driving in the snow. Daily drive it is not.

Braking wise I have changed from the standard 10 inch single line system (non servo), to 11x3 twin leading shoe fronts and 11x2 single leading shoe rears now twn line and servo assisted. So I'm well over specced in that department.

Hmmm can see me having to change gear a lot to make sure the engine doesn't try and rip the box to bits, but driving vehicles with 12 manual gears it should be ok lol.

Only way i could see the tyres helping is if I went to small wheels, which isn't going to happen as it would look bloody stupid. Just means that I am slightly more limited in getting larger tyres, but as I don't want to go bigger than they are standard just wider I should be ok.

As for holding speed going up a hill, I can only imagine that the V8 will have the torque, but if needed I could always change down and add OD?? Same as dropping 2 on the truck and adding a half gear (1 back up) if that makes any sense??

Why didn't I just fit series diffs?? lol.

[discomikey]

I think Nick (Snagger) has this issue. He broke his gearbox running a 200Tdi with high ratio diffs and OD. Discomikey runs this setup also with a tdi I think... Maybe they'll chime in for you! You may find the acceleration lacking a little

Thanks Josh, yes i do run an overdrive and 3.54 diffs, also with 235/80R16 which have a rolling radius of around 15-16"

i find for motorway cruising and everyday driving, its not far from ideal. although for motorway towing is is a little less ideal. its set up so i get peak torque around 60-75mph which is bang on. if im towing through a long 50MPH section (like the bleeding M1 J28 upwards etc etc ) then i could do with top overdrive being a smidgen shorter, as im below the main torque band but its a bit revvy at 50MPH top no overdrive.

thats not a common occurance though to be honest. and overall im happy with it. on the plus side the road speed is 152% of the speedo indicated speed. whereas the conversion from miles to Km is 160% working out if i used a kph speedo it would be reading 1.05% road speed (albeit with the wrong units but we can ignore that) i.e. indicated 80kph would be 76mph road speed.

if anyone has a kph speedo (for a SWB geared for 6.00 tyres) i want it

yeah when towing right up at my limit, i have to drop it into low box to set off up a hill sometimes, but i dont find that an issue and i have found the weakest link in my drivetrain is the rear diff, not the gearbox although now thats an ATB so probably the shafts.

if i were to consider changing the gearing, i may think about very slightly shorter diffs, not much shorter though. but to be honest i think i would leave well alone as i know this setup works well and 90% of the time my gearing is right.