The V8 Owners Forum -

Hi guy's
Hope you all had a good Christmas. I bought a reliant scimitar axle to go on my 4.5 humber sceptre , I'm on my 3rd diff now and not got any more so I thought it's about time to upgrade, so I bought this axel the guy told me it was a 3.54 ratio but when I got it and started to stop it I noticed it was a 3.33 ratio . So has my car stands now it's a rover 4.5 with the rover p6 3500s gearbox which is a 3.54 ratio but my sceptre different ratio is 3.7 ... so has it stands I don't use first gear at all . But now it's time to upgrade but I was wondering if I get a a cwp wheel from the reliant scimitar to match my gearbox I guess it would be a straight swap ? My question is is there a company that supplies cwp sets ?
Cheers Dave

Look for something from the jags which use the same central axle. You will be able to upgrade to LSD as well if you wanted. It's far from being a straight swap through and takes a bit of work with shims and engineer's blue.

Thanks for that info I will do a lot more research I think they use them on the mk2 jags

They use them in a few models, there are a few scimitars with the complete IRS backend in them if you really wanted a project.

Hi Dave

A little unsure by what you mean when you say, "the rover p6 3500s gearbox which is a 3.54 ratio "

I have a Rover P6B ( V8 ) and the gearbox in top is 1:1 ratio, with a diff ratio of 3.08. (The standard 3500S that is, mine's an LT77 now).

What are you trying to achieve here, is the car for road use or are you racing it?

Richard

Hi Richard
You've got me thinking now I've Google the ratio of my gear box and I seem to get is its a 3.54 when I first did my engine swap my different was 3.89 and was no good to drive on the road which it is used for and the odd drag strip so then I put a 3.7 ratio different in which was better but 1st gear is not used ,so I tHoughton if I could match the gearbox ratio it would come back to be normal in every gear ,well that's what I'm hoping also the rootes diff don't last long all so I've just found out that the mk 2 jag used a 3.54 crown wheel 46x13 cwp so that should be a straight swap in theory hahs

Hi Dave

I think you're getting a bit mixed up with ratios

The original gearbox would "probably" had a fourth gear ration of 1:1 same as the Rover box. The differential (diff - final drive) ratio on the Humber may have been 3.54:1, and the diff ratio on the P6 3500S was 3.08:1

Just to give you some idea, the P6 at 70mph with the 3.08 diff, would be spinning the engine at around 3,000 RPM. If you changed the diff to 3.54:1 it would spin at 3,450 RPM, which will be a tad noisy on the motorway, and rather thirsty too. (Your car may be different to this as the wheel and tyre sizes change it).

I am going to fit a Jag diff with a 2.88 LS Diff, which will drop my RPM to 2,800 RPM at 70mph, and of course the 5th gear on the LT77 will drop to 2,340 RPM. This will make it quieter on the road, more economic on fuel, but sorry to say, not as much fun at the drag strip.

Richard

Hi Richard
Your right it's a nightmare lol so has my car stands now with the 3.7 diff at 70 I'm doing 4500 revs so the 3500s gearbox I have is a 3.08 . So the axle I have got fit is a ratio of 3.33 so it's closer to the 3.08 I need to natch my gearbox I think I'm just going to fit it and see what it ends up with if it's makes any sense to you

There's no such thing as a 3.08:1 gearbox Dave, the Rover gearbox is a 1:1. It used to be connected to a 3.08 Diff when in the P6.

You need a high geared Diff, the highest you can get so you can bring that rpm down.

2.88 would be the best one with a vehicle like yours, but a 3.07 would suffice if that's all you can get (both Jag ratios)

Hi Richard
It all makes sense now thank you for that I've been going wrong for years ... I will let you know how I get on ... happy new year

If you do decide you need a different ratio set then I have plenty of 4HU (Jag) gear pairs available in just about all the ratios from 2.88 to 4.55 which will fit your axle. I rebuild the IRS diffs for the Cobra fraternity (and own a Scimitar coincidentally).

Hi guys update time I've put the 4ha axle from a reliant scimiter with the 3.3 ratio it's better but not right I need to go lower I will try a 3.08 next , am I right in thinking that all the CWP are inter changeable? Russell do you have any cwp for sale ?

I'll have to check what I have 'in stock' but pretty sure I'll have a 3.07 pair. I'm in the workshop tonight - I'll have a look.

As for interchangeability - it does depend on year a bit but usually it's only the 2.88 ration that isn't an easy swap. The input pinion is so large that the crown wheel flange is moved across on the carrier to give it enough room in the case. (Even then, you can sometimes get away with removing shims and machining the end off the bearing spigot on the carrier to get it to fit without any real issue - it'll stick through the main bearing inner race on the crownwheel side too far to go into the case otherwise)

Must admit to surprise the P6S four speed handles the torque from a 4.6. I managed to break a few with a 3.5. Is it not possible to fit the 5 speed SD1 box? That is direct in 4th and has an overdrive 5th. So would reduce the revs with the same axle.

Unfortunately, a quick check seems to suggest I don't have a 3.07/3.08 (or 2.88 actually) gear pair loose or in a complete diff. I'll have a better look at the weekend but I don't think I can't help - sorry.