[ROVERNET - UK] 3500S Rear Ends

Vern Klukas vern at inkspotco.com
Sat Sep 11 18:38:12 BST 2004

>Hi Vern,
>All good points.  The SD1 suspension isn't a true
>torque tube setup anyway.  A Panhard rod would do in
>place of the Watts links.
>What really concerns me is the business about the
>spring and shock mount posistions.
>>  Even if you could make use of the existing trailing
>>  and leading
>>  links, the current spring and damper position would
>>  be too far
>>  forward to allow adequate control of the added
>>  sprung weight of the
>>  live axle.
>The spring mounts for the P6 are in the same relative
>position as on the TR7/8.  I admit that I've never
>designed a rear suspension, so if you have the time,
>tell me something about the issues related to shock
>location.  It may all come down to a definition of
>"adequate controll."  Certainly the P6 rear suspension
>is much better at controlling road wheel movement than
>any straight axle setup could possibly be.

Hi Kent

Just to be clear, while I've assisted I've never designed and built a 
rear suspension on my own. I do have a pretty good understanding of 
the basics though.
I think if you were to measure proportionally, you would find the TR 
spring pan quite a bit closer to the axle centre than the P6 arm. 
Three things at play with the springs and shocks, all more mechanical 
than geometric; bending moment of the trailing arm, sizing of the 
springs and dampers and the entire system's natural frequency of 
You could reinforce the trailing arm, which of course would increase 
unsprung weight even more, though not to any huge degree.
The dampers would have to be larger, and mounting points reinforced.
I would see the biggest problem as the where the new natural 
frequency lay (If you can imagine, the trailing arm from the spring 
pan back to the axle acts like a leaf spring with a weight on the 
end, which will vibrate at a certain frequency when excited. More 
importantly, the trailing arm and axle entire will vibrate at another 
frequency, determined by the road spring rate.). You may end up with 
terrible axle tramp and hopping problems at certain speeds.
Certainly the handling of the car would be greatly affected 
regardless, but towards oversteer or understeer I have no idea.

>  Also, using the leading links would mean
>>  the axle will
>>  rotate as it moves, greatly complicating the watts
>>  linkage attachment
>>  to the axle.
>Again, we're not re-inventing the wheel, just
>transplanting SD1 pieces.

My point was that you might find that the SD1 linkage would bind. If 
we want to keep it Rover, a P5 rear axle may be a better starting 

>>  A deep extension would have to be added on one side
>>  of the P6 to
>>  accommodate the lower link of the Watts linkage.
>Now THIS is an issue.  Although I prefer the Watts
>links, a Panhard rod might be easier to fit but you
>still have the problem of where to locate the rod end
>mount at the body end.

A Panhard would be a much easier proposition, and adding a mount for 
that fairly easy I would think. A bonus would be that you could 
attach the Panhard at about the same height as the existing rod, 
which would keep that part of the geometry the same.

>  >
>>  Finally, the brakes. Changing to drum rears would
>>  mean, at a minimum,
>>  a new master cylinder and probably the addition of a
>>  residual
>>  pressure valve.
>Residual pressure and front/rear proportioning do need
>to be considered, but the M/C should do quite well. An
>adjustable proportioning valve is an easy fix for the
>front/rear problem.

I'm not sure about the M/C working, Any drums would need much more 
fluid movement than the Girling rear calipers with their tiny 
pistons. I really think you would find the M/C short on capacity.

>Keep talking, Vern.  By the way, I have your heated
>rear screen out if we can figure a way to ship it.

I've been meaning to e-mail you about that. I had set aside that idea 
after I heard of your move, figuring I didn't what to add to your 
suddenly more complex life. I'll e-mail you about it soon, as I was 
recently thinking you must be settled in by now.

>Kent K.
>>  Yours
>>  Vern
>>  >Hi Randy,
>>  >I've considered this many times, but never gotten
>>  >around to it.  Almost any rear end used would have
>>  to
>>  >be narrowed (even the TR7/8, I measured), but using
>>  >the existing leading and trailing links by cutting
>>  and
>>  >welding the relevant portions of the bracketry onto
>>  >the axle tube should locate a straight axle fore
>>  and
>>  >aft.  Because the P6's use a torque tube already, I
>>  >think I would narrow the SD1 axle and use torque
>>  tube
>>  >and the Watts links, welding brackets to the base
>>  P6
>>  >base unit where necessary.  Rover actually used a
>>  P6
>>  >base unit to test the SD1 suspension, as I recall.
>>  An
>>  >added plus...you keep it all "Rover."
>>  >
>>  >Let me know if you pursue this as I am quite
>>  >interested.
>>  >
>>  >Roveroversimplifiedly,
>>  >Kent K.
>>  >--- NOBLIOUS at aol.com wrote:
>>  >
>>  >>  With Hurricane Ivan looming and nothing better
>>  to
>>  >>  do, I was wondering what would be the
>>  possibility of
>>  >>  changing the 3500S rear end setup (primarily the
>>  >>  differential, inboard discs, De dion tube)to
>>  >>  something simpler and stronger.
>>  >>
>>  >>  Years ago they used to race 3500S in the UK (and
>>  >>  Australia?), so I was wondering which rear end /
>>  >>  differential was used. Was it the original one?
>>  Has
>>  >>  anyone converted the OE rear end to a live rear
>>  >>  axle?
>>  >>
>>  >>  Thanks for your input.
>>  >>
>>  >>  Randy - Miami, FL
>  > >>

Vern Klukas                             I'm a little . . .
Inkspot Type & Design
vern at inkspotco.com

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