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

Baron von Marlon said:
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.
Click to expand...

Should and does :mrgreen:

One thing I don't have photos of (yet) is of my P6 cornering hard, feels almost completely flat with the front suspension tweaks I've done 8)

The only issues I can think of with upgrading the standard differential assembly are the lack of gear ratio choice and the rear mounting plate, otherwise it's a full win situation apart from the costs! Rear mount can be beefed up easily as has been done before.
 
sowen said:
Should and does :mrgreen:

One thing I don't have photos of (yet) is of my P6 cornering hard, feels almost completely flat with the front suspension tweaks I've done 8)
Click to expand...
I'd be interested to see that! It's nice to get confirmation that my train of thought is along the right lines.
 
Baron von Marlon said:
sowen said:
Should and does :mrgreen:

One thing I don't have photos of (yet) is of my P6 cornering hard, feels almost completely flat with the front suspension tweaks I've done 8)
Click to expand...
I'd be interested to see that! It's nice to get confirmation that my train of thought is along the right lines.
Click to expand...

Specs are lowered 2-3" on custom springs with adjustable dampers and dual arb's, 15" wheels with 205/55 front tyres, front wheels sit at about 2-3 degrees negative camber. Getting photos of it going round corners so far has eluded me, I'd love to know what the wheels are actually doing! Just short of hanging a video camera off the front and going for a drive one day...
 
How much stiffer than standard did you go with the springs? I want mine to go round corners better, but I don't want to destroy the normal ride, which is stiffer than standard due to the adjustable shocks and the rear springs front and back, but it's still quite comfy. When the weather gets better, I need to measure where mine is at the moment, then work out where I want to go with it.
 
Baron von Marlon said:
How much stiffer than standard did you go with the springs? I want mine to go round corners better, but I don't want to destroy the normal ride, which is stiffer than standard due to the adjustable shocks and the rear springs front and back, but it's still quite comfy. When the weather gets better, I need to measure where mine is at the moment, then work out where I want to go with it.
Click to expand...

25% -2", but I'd go higher if I was to do it again. I found the dampers made the biggest difference to the ride, the springs just compress less for the lower ride height so it doesn't bottom out as quick as what it could do. I think the way Jaguar did their cars were stiff springs and soft dampers?
 
Sorry can you be clear on this. I understand the HD rears are 20lbs heavier than standard which is a bit more than 20% so where were you starting from when you go +25%, standard or HD?
 
PeterZRH said:
Sorry can you be clear on this. I understand the HD rears are 20lbs heavier than standard which is a bit more than 20% so where were you starting from when you go +25%, standard or HD?
Click to expand...

Custom made springs, spec'ed as 2" lower ride height and 25% stiffer over standard.
 
sowen said:
25% -2", but I'd go higher if I was to do it again. I found the dampers made the biggest difference to the ride, the springs just compress less for the lower ride height so it doesn't bottom out as quick as what it could do. I think the way Jaguar did their cars were stiff springs and soft dampers?
Click to expand...
I'm not sure how Jaguar do it - it's something I know I need to do a little more research on. When you say 25%, presumably that's from the standard front and rear spring ratings? I don't think that having the same rate front and rear on mine is doing the handling any favours, again, I need to sit down and do some calculating.
 
Baron von Marlon said:
I'm not sure how Jaguar do it - it's something I know I need to do a little more research on. When you say 25%, presumably that's from the standard front and rear spring ratings? I don't think that having the same rate front and rear on mine is doing the handling any favours, again, I need to sit down and do some calculating.
Click to expand...

I honestly cannot remember where I heard/read about the Jaguars, it was something about the plush sporty ride, though I may be wrong!

Yes 25% above the standard front/rear ratings. It was more of what the guy on the end of the phone suggested when I called, and from driving it works well with the adjustable dampers. I've had one car in the past with mismatched front/rear springs, it was horrid to drive, absolutely transformed by replacing all of the springs with a matched car set. If you've got adjustables already then you should be able to get the front and rear matched closer?
 
Back to the diff. There's a reasonable consensus amongst people who have actually had them fail. They never fail on the crown wheel and pinion etc, ie the diff itself - except for a small number of cases where the crown wheel bolts have come loose and worked out until they have smashed the casing. Most common failure is the output stub shafts failing in torsion at the root of the spline. Next most common is the input shaft inside the extension failing in torsion at the root of the spline. The input shaft is easy to reproduce from a better quality of steel, and Alan at Classeparts has indeed done this. The output shafts are more difficult because they would need a very large diameter piece of bar stock to turn down to accomodate the large outer flange that the disc sits on. And that still leaves you with a non lsd. Alan has done a number of diffs himself with a bespoke lsd within. Not cheap though.

ALL cornering loads go up the driveshafts and into the diff, none go via the suspension arms proper. That makes the location of the diff very crucial and the Irish rally boys, who posted on this thread earlier, made up a neat steel tube diff bracket bolted direct into the shell to improve this when they were still running the Rover diff.

There's nothing fundamentally very difficult about mounting the Jag diff. Needs time messing about more than vast amounts of skill. I think I prefer the 5000TC solution over Simon Owen's, but if I were doing it I think I might think about modifying the floor of the base unit so that the diff could be bolted up directly to the base unit rather than messing around with lots of brackets. I'd be very interested to see how 808's diff is mounted....

I can confirm that the addition of a stronger front roll bar and commensurately stiffer back springs do indeed transform road handling. My own inclination would be not to go too stiff or too low even for a circuit race car. Given that the de dion takes care of things at the back rather well, no matter what the spring rate or roll angle, I'd suggest having a careful think about what happens in the front suspension geometry when the car rolls. It's very unconventional! Given that, I'd be inclined to allow an unfashionable amount of roll with a near standard ride height so that the rest camber at the front is near neutral. The roll then provides the negative camber that's desirable when cornering and the neutral rest camber allows you particularly impressive braking performance on the straight. Let aerodynamics be the sole arbiter of how low you want to go....

Chris
 
Incidentally, the front suspension geometry is officially known as "Modified Lawrence Link". Rover went to the trouble of buying out Chris Lawrence's patent..... Google his name and be prepared to be Very impressed....

Chris
 
Baron von Marlon said:
Looks like you're right about the Jaguar set up:
http://www.nsra.org.uk/newforum/showthr ... -rate-info

These are front rates, I haven't found anything about rear rates yet. I know that the XJ6 is a much heavier car than the P6, some 400kg!, so that will make some difference, but I'll need to do some maths to work out the optimum, based on those weights and the mounting angles.
Click to expand...

Not really a fair comparison, the geometry plays a big part and the Rover setup has a lot of leverage acting on the springs, more than the Jaguar I think?

Back on topic :LOL:

For reference here's a few pics I have of the output shaft, I don't have any of the extension tube or shaft to hand
 

Attachments

  • 100_1530.jpg
    100_1530.jpg
    110.9 KB · Views: 156
  • 100_1535.jpg
    100_1535.jpg
    99.9 KB · Views: 156
sowen said:
I think the way Jaguar did their cars were stiff springs and soft dampers?
Click to expand...

Baron von Marlon said:
Looks like you're right about the Jaguar set up:
http://www.nsra.org.uk/newforum/showthr ... -rate-info

These are front rates, I haven't found anything about rear rates yet. I know that the XJ6 is a much heavier car than the P6, some 400kg!, so that will make some difference, but I'll need to do some maths to work out the optimum, based on those weights and the mounting angles.
Click to expand...

Erm, stiff springs and soft dampers was the typical Japanese set up in the '80s and '90s, hardly a paragon of comfortable ride.
Just because you cannot compare apples and oranges, a spring poundage from an XJ6 might look stiff for a P6, but it doesn't mean that it was just as stiff in its original application. As you say there is some significant weight difference, and you don't even take into account the leverage on the spring and the suspension architechture in general.
 
chrisyork said:
The output shafts are more difficult because they would need a very large diameter piece of bar stock to turn down to accomodate the large outer flange that the disc sits on.
Click to expand...

What if someone machined the shaft and the flange from two different parts, and then welded them together with that "friction welding" method? I am not sure how this is really named (or if it is at all applicable here...) but i am talking about the method that one part is spinning fast on a lathe, pressed against the other stationary part, and eventually the two parts are fused together from the heat through friction at the contact area.
 
Hi, yes, it's friction or inertia welding. It has quite widespread use. The tell tale sign of it
can be left as they do on axles or machined off as they do on valves.

Colin
 
Chris you are quite right about the rear suspension looking after itself, my point was that the action of the watts linkages on the outside tends to lift the rear outside corner under heavy load which causes the opposite front to dig in; The shot in question has the front wheel pointed pretty well paralell to the car so the car is just exiting a turn but the roll is still occuring. I am coming to the view that an ATB diff would even out the force and reduce that motion.

There are a couple of reasons I don't want to go for a Jag diff. Replacing just the carrier unit is a lot simpler if something is available, the rest of the car stays the same, the MOT guys aren't going to burst into tears when they see it (coz they wont) and I have plenty of spares, the only jag parts I have is a couple of windscreens which aren't much use in a diff.

With regard to the axle shots, the breaks occur where chris says, youcan see where the spline wear stops that is pretty much the point. I suspect that machining the ridge down to a smooth curve instead of a sharp lip and grinding the base of the splines to an even curve would greatly reduce the likelyhood of breakage, however the unknown is going to be whether the original product was good enough in the first place. My first break saw one axle twisted three splines, its unbroken mate twisted two splines and the input shaft twisted one and a bit splines but no twist on the pinion spline. That is the worst I've ever seen. Other diffs just broke one axle without any noticable twist anywhere. no amount of work on the existing axle will work if the original product was near defective when orignally made. I wonder if jag axles could be made to fit.? Or we could go all modern and make them from Carbon Fibre!
 
Part of the issue is there is nowhere for the shaft to absorb the shock loads, the only answers are bigger diameter or an exotic material. The Jaguar parts are renowned for being up to the job and are significantly larger in size, and also a pair of tapered roller bearings in a bolt on assembly rather than the single ball bearing of the Rover.

Out of the box thinking would be to make up a heavy duty bespoke output shaft assembly conversion based on using an alternative diff centre fitted into the original casing?
 
You are quite right Simon, the bearing does take a lot of side load, but then to get to it the load has to pass through the needle roller bearings in the drive shaft universals which are far smaller. you can get side load ball races, or deep groove ones which would fix that issue. so far I haven't come across a diff centre that comes at all close to the rovers small size and has twelve mounting bolts. Hence the Quaife option looks pretty attractive once the twenty units minimum is reached as it would be a straight bolt in. I'm uncertain what Alan at Classeparts starts off with. there are quite a few manufacturers who will make bespoke stub axle shafts including quaife. they buy blanks which are machined to your requirements. The Splines are also rolled on rather than cut so are much stronger than the standard shaft.
 
The Rover ball bearings are upto the job, it was just an observation that the Jaguar had a full paired bearing assembly in it's installation with provision for pre-load adjustment.

One thing I would say is that if the diff was to be upgraded then the chances of greater power and more enthusiastic driving going through it would be so much greater that there almost becomes little point in trying to make each individual part backwards compatible with original if going all the way and fitting an LSD.

If that was the case finding a suitably small centre that could be mounted within the Rover casing, then having an adapter ring turned up for the ring gear and having output shafts manufactured to suit?



This is why it is so much easier to weld up a frame, bolt the Jaguar differential assembly underneath and fit custom length propshaft and driveshafts :mrgreen:
 

Attachments

  • 100_1541.JPG
    100_1541.JPG
    110.6 KB · Views: 91
You must log in or register to reply here.
Back
Top