Rover P6 Diff - How Strong is it? Other options?

RoverAlex

RoverAlex

Active Member
Browsing around the forum as you do and I came across this comment here: viewtopic.php?f=5&t=5053&p=28823&hilit=r380#p28823

Something else that you may like to consider. The series one Rover 3500 differed from the later series two 3500 along with the 3500S in that a number of modifications were made to both the suspension, final drive unit, rear axle flanges, drive shafts and propeller shafts. Apart from any increase in component durability, all were balanced to a higher degree.
Click to expand...

I have a Series 2 so Is the Series 2 diff much better or just mildly? So how much power can the diff take? Would it take a mildly tuned 4.6 V8? How about a 4.6 Mildly tuned supercharged V8?

I am fairly new to investigating this and have been enthused by the responses from a few certain Rover P6 owners to push my build and research more. I know many fit a Jag rear end but I am not too keen on this and I just sold mine to get other bits for the P6. If the P6 diff won't take much power then is there a relatively straight swap to something more powerful? Are diffs from later Rovers perhaps the SD1 more suitable?
 
Hi,

We heard horror stories about diff strength when we first started using our car as a historic road rally car, historic road rallying involves doing autotests as one of its disciplines so potentially really sore on diffs. However in the 3 years we competed with the Rover diff in place we had no issues at all, I accept that although we were fully committed while competing we were never brutal with the car.

What you’ve done with the engine is only one side of the story, the diff can only get as loaded as the rear grip will allow, once the rear tyres let go you’ve reach and exceeded the maximum loading on the diff. I note that you’ve gone for in your words “proper wheels and tyres” this probably has a greater effect on diff life that your big engine.

We eventually went the Jag route, full IRS conversion rather than just the diff, this very much suits the events that we use the car for. It was prompted by a desire to get an LSD in there cheaply rather than chronic diff strength issues.

What are you planning on doing with the car once done?

Tim
 
Dunlop CR65 Race Tyres - they are pretty wide and pretty sticky hence thinking the diff will be the first thing to let go. A lot of chopping to the car to get them to fit! These ones: http://www.longstonetyres.co.uk/page/65 ... acing.html

The plan is to get the 4.6 on the road without a charger, that will come at a later date. Get the engine bedded in nicely on the road (fresh rebuild) and then go to autosolo, track days and drag racing as well as keeping it as a road going car.

Alex
 
That's the general train of thought I know.I'd much rather the idea of not having to fabricate a load of things to make the jag diff fit - I don't have those kind of facilities any more. I am also very keen on having an LSD, I suppose you might be able to find someone to make stronger internals (been told the input and output shaft is the weak point) but not a lot of point in doing that and then ending up with an open diff.

Trying to get ahead of myself and at least have a plan for when the diff does break.
 
I've done about four diffs in my P6B. One was due to faulty material which broke one tooth off (car still drove for a couple of years) the rest were broken stub axles although my first failure had the broken axle also twisted two splines (as was its partner) and the torque tube shaft about 1.5 splines. the other two weren't so bad. Broken shaft showed zig zag cracks to the centre from each spline so I put it down to bad spline design/machining quality. Racing diffs would normally have these radiused and polished to remove the stress risers. Personally I've always preferred the Rovers ride and handling at high speed to the jag, particularly when you have two wheels on the dirt, the de dion seems to deal with bumps better.
 
There are a few folks that have made a cradle to hold a different make of diff (normally Jaguar) and retain the De-Dion assembly, it's not
an all or nothing swap. At the end of the day it's down to your abilities and the ratios available to you for choices.
I know a bloke who fitted an Alfa Romeo Afetta/Giulietta trans-axle in his P6, but that was a race car, so the inconvenience
of losing the rear seats to the clutch housing of the trans-axle was irrelevant.
 
I don't want a Jag rear end I would like to retain as much of the rear end as I can. There are talks about other developments here and there I am sure a few of you will know.

There is also the option of a Quaife LSD....but there needs to be 20 of us with orders for them to make it.
 
A way of getting around the linkages of the other build would be to make an extension tube to the same dimensions
with the prop shaft running inside it and mount it to the gearbox, then all you need to do is pick up the mountings.
 
I've been having a think about this and it occurred to me that the P5B diff runs the same 3.54 ratio that the 2000 does. Given Leyland's penchant for sharing parts between models, it is entirely possible that the crown wheel and pinions are the same design, meaning the 4 pinion P5B centre would fit the P6 case; giving the lower ratio in the stronger V8 centre. It then follows that the Land Rover diff centre, being similar to the P5, might be usable in a P6B casing. Unfortunately I don't have enough bits to check this theory out as it would simplify the LSD problem. Won't fix the stub axle issue though. Any ideas?
 
RoverAlex said:
Browsing around the forum as you do and I came across this comment here: viewtopic.php?f=5&t=5053&p=28823&hilit=r380#p28823

Something else that you may like to consider. The series one Rover 3500 differed from the later series two 3500 along with the 3500S in that a number of modifications were made to both the suspension, final drive unit, rear axle flanges, drive shafts and propeller shafts. Apart from any increase in component durability, all were balanced to a higher degree.
Click to expand...

I have a Series 2 so Is the Series 2 diff much better or just mildly? So how much power can the diff take? Would it take a mildly tuned 4.6 V8? How about a 4.6 Mildly tuned supercharged V8?

I am fairly new to investigating this and have been enthused by the responses from a few certain Rover P6 owners to push my build and research more. I know many fit a Jag rear end but I am not too keen on this and I just sold mine to get other bits for the P6. If the P6 diff won't take much power then is there a relatively straight swap to something more powerful? Are diffs from later Rovers perhaps the SD1 more suitable?
Click to expand...

The P6 Diff is purportedly made of a combination of Blu-Tack and Swarovski Crystal, however I've hadn't broken mine despite a reasonable amount of punishment over the years.

The most common breakages are from careless selecting drive from reverse without coming to a complete stop.

I doubt one would survive a decent burnout and side stepping the clutch should be avoided.
 
I've done a lot more research now and I don't think it is a case of the crown wheel and pinion or carrrier being made of butter so much as poor qulity control or low standards. Some break some don't. I've had a good look at the broken ones I've had or received and the gears generally break in a colloidal fashion, that is they appear to fracture along a fault in the metal (with little deformation) rather than by overload. the shafts tend to let go after cracking along the spline bases, very close to the sharp lip machined just before the turnout portion. I suspect that removing the raised area and bringing the spline into a single piece would alleviate the cracking there; it is also a case that some axles fail and some don't under the same or similar conditions so again I suspect the quality of the production run is the main issue.

With regard to the earlier and later changes the biggest change is mounting the crown wheel onto the carrier; diffs suffix D onward use 3/8" bolts while A to C use 5/16" with two specific fitted bolts.

My research also indicates that neither land rover components nor SD1 components fit the P6 housing however I haven't covered all possibilities yet. main problem is that it is a very small unit and uses 12 bolts to mount the crown wheel, an unusual combination.
 
mikecoombs said:
I've done a lot more research now and I don't think it is a case of the crown wheel and pinion or carrrier being made of butter so much as poor qulity control or low standards. Some break some don't. I've had a good look at the broken ones I've had or received and the gears generally break in a colloidal fashion, that is they appear to fracture along a fault in the metal (with little deformation) rather than by overload. the shafts tend to let go after cracking along the spline bases, very close to the sharp lip machined just before the turnout portion. I suspect that removing the raised area and bringing the spline into a single piece would alleviate the cracking there; it is also a case that some axles fail and some don't under the same or similar conditions so again I suspect the quality of the production run is the main issue.

With regard to the earlier and later changes the biggest change is mounting the crown wheel onto the carrier; diffs suffix D onward use 3/8" bolts while A to C use 5/16" with two specific fitted bolts.

My research also indicates that neither land rover components nor SD1 components fit the P6 housing however I haven't covered all possibilities yet. main problem is that it is a very small unit and uses 12 bolts to mount the crown wheel, an unusual combination.
Click to expand...

Great information Mike and do post back if you get more findings on your investigations. So (pending me getting the car working again)....perhaps I should try to break it to add to your research :D
 
Thats a very interesting picture youhave there! You can see the load on the near side tyre as you straighten the wheel while the rear wheels are still flat on the road. As i understand the rear suspension to work it looks like it is actually pushing that wheel down while lifting the rear offside of the body. That would go a long way to explaining the roll behaviour!

I'm currently looking at manufacturers that might be interested in making a limited slip diff centre, input shaft and stub axles. At the moment Quaife are the top of the list but they have a minimum order of twenty at between $1000 and $2000ish. Hollinger are second but they prefer to alter their unit to fit the rover space - sort of the reverse of a jaguar install. New diff centre was about $5000 Which is a lot.

If anyone else is interested int he Quaife option please Pm me. I only need another 19...
 
As I understand it, it's the front suspension geometry that causes the unusal roll behaviour, not the rear. The rear suspension is configured so that the tread of the tyres remain parallell to the road surface under roll conditions, which I believe is down to the way that the de-dion tube works.

It is an interesting picture, as it tells me that with an upgraded anti-roll bar, and a bit of negative camber on the front wheels, a P6 should corner exceptionally well.
 
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