Single shocks on Jag rear

[David Hodgson]

Don't know if this has been discussed previously, has anyone had/got thoughts or opinions on just using one coil over unit per side on Jag rear ends?

Seems most guys I have talked to that are using Spax shocks have the rebound screwed mostly to the lightest position.

I'm currently using one Spax and one "dead" shock per side and have the Spax set at 8-9 turns out of 14 for rebound and the dead shock is just to carry the other spring.

I see in 302Cobra's gallery he has only 1 set per side and obviously a stiffer rate spring.

Would there be any rotational forces applied to the lower control arm, given it was originaly balanced by one each side?

[302cobra]

Yes I am only using one shock per side. I am running a Qa1 Shock with a Carrera spring, it is fully Adjustable for ride height and tension settings. I have 12 levels of adjustment and I think I have it set on about 6 or 7. It is not 100% necessary to fit twin shocks, I think I will get a ride that is just as good when the car is on the road.

[Bryan Wilson]

I feel that the Jag rear end beind designed for twin shocks and only having a shock on one side would put a twisting load on the lower swing arm.
Just my $.02 worth.
Cheers,
Bryan

PS I run dual shocks.

[NASSTY]

I know Python Cobras run a single shock Jag rear end. IMHO if the donor suspension manufacturer spent $$$$ trying to get it right why change it? I know of people who are using either one adjustible shock combined with a non adjustible shock or using two adjustible shocks. I'd check with an engineer first before proceeding.

[BMK]

Used the QA1 shockers also - photo in my gallery. Having used a full live axle 9" I was able to get away with the single.

I have noticed numerous Jag. rears under Street Rods and other vehicles at the race shop where I built my Cobra. All have had the four shocker coil over set up.

The spring set up will need to be calculated or checked with someone here to get the right spring for the new lighter set up.

I agree with Bryan also and would run four in the Jag. rear end.

Bernie

[Rebel1]

I agree with the 4 shock setup.

There is absolutely no way would I use one shock a side. If one was looking at improving the ride then it need be done in other ways than removing a shock/spring from each side.

Lets put it this way. Jaguar have spent mega-dollars over the years and essentially their system has not changed. Do you really think they would keep 2 struts a side if they could SAFELY save one set of springs and shocks?.

Don't expose yourselves to possible litigation fellas. A smart litigant will have a big win one day and I doubt if the manufacturers recommending single springs/shocks will be the ones footing the damages bill.

The spax shocks I have were part of a shipment from RMC which were supposevely re-valved to suit the RMC.

[302cobra]

The guy who I bought my jag gear off is extremely "clued up" about jags, and seems to think 1 shock is OK. I have also had it checked with an engineer and he thinks the same.

Saves on cost too, I would have doubled the price for my rear shocks if I went with dual ones!!!!! Now I can spend that money somwhere else!!!!!

[Rebel1]

Whatever makes you feel good 302cobra.

We were asked ....we told

[Aussie Mike]

I reckon you could do single shock on a Jag rear. The way I'd do it is to put the shock mount in double shear.

I'd make a brace linking the pivot points at each end of the dog bone. The pivot bolt would run through the brace as I'd be reluctant to weld anything to the forged steel end of the dog bone. I'd then have a cross brace welded to the steel tube of the dog bone (welding to the tube would be safe enough). Then from the brace to the shock original shock mount I'd make the double shear mount.

The advantage of this is since the shock mount is in double shear there is little to no twisting loads on the dog bone.
The other big advantage is the braces wold stop the ends of the dog bones pulling forward under hard acceleration and back under hard braking. This along with a set of trailing arms will just about eliminate any change in toe under braking and acceleration.

I've drawn a little picture to show what I mean. I hope it makes sense.

[Rebel1]

That sure would remove any twisting of that lower arm mike.

Now...If I had yours and Bernies money..this is what I'd like to do with my rear end.

Note: can run one coilover right in the middle or one either side of center like the originals. Might do without my trailing arms too.

[Aussie Mike]

There's probably $300 woth of aluminium plate in those lower arms before you've even touched them with a mill cutter.

My way has about $30 worth of steel tube and plate.

What do you mean "yours and Bernies money"? I'm working on a shoe string. I try to make all my stuff cause I can't afford to buy it.

Cheers

[Rebel1]

Ermm....well Mike...The way I figure it is.

All that money you're saving making stuff yaself can be given to me to buy my alloy lower arms.

Fair's fair ya know

[BMK]

I'm flippin burgers to make ends meet here also..

Bernie

[boxhead]

LOL @ Bernie the burger flipper.

I am just pictureing Bernie with the big red shoes flippin those burgers over.

[Chris D]

Guys
RMC did it (One Koni and a heavier spring mit nothing on the other) as an extra cost option. Perfectly OK recalling the rear end weight of a Cobra. Mine was built that way and has had 7 years on the road with no problem. Ride is, if anything, too soft so could do with additional 50 lbs in the spring.

Makes for less room.

Mikes mod looks good and is reminiscent of Concours West's rear end.

Hope it helps.

Chris

[David Hodgson]

Hey guys, thanks for all that input, Robnell had an option similar to that alloy set up.
I'm impressed with your "little picture" Mike, a nice simple solution to two potential concerns. Do you think there is measurable for/aft flex in the dog bone without a trailing arm? I would have thought the weak point would be the inner pivot bracket that bolts to the diff housing, though retaining a tough tie bar across lower pivots should help. I believe RMC also trialed these rears without a trailing arm.

Chris D.. Do you know what your current rear spring rate is? I've been trying to calculate my rates but as I mentioned I've got one adjustable and one slave(three position height adjustment only) each side and with both seats in the lowest posi the springs are compressed to different lenghts. With the 255/60 tyres its sitting very high in the back.

[NASSTY]

The original dog bone tube is 3mm thick. My dog bones have been cut and shut and this centre tube has been replaced with a 10mm thick tube. Laurie Bongailas did this b/c he found out (the hard way) that at high hp the original 3mm tube would split along the shut weld. Bracing along the sides of the dog bone will reduce for/aft flexing but it will not stop twist through the centreline of the dog bone. An engineer has tested the 10mm tube and found it to be 2-1/2 times stronger than the 3mm tube. So it reduces for/aft movement as well as twist (from braking and accellerating).

It's also worth remembering the the original Jag rear end was in a sub frame that was rubber mounted. Most cobras would have the diff mounted directly to the chassis. Consequently, if using the jag trailing arms which use a rubber mount, their effect on reducing for/aft movement would be nil because of the movement in the rubber mount; the rubber will move more than the dog bones could. In a Jag, they would reduce for/aft movement because the whole rear end is rubber mounted so the whole rearend would move within their mounts.

Hope that makes sense.

[Aussie Mike]

You could use teflon lined spherical rod ends on the trailing arms.

I agree with Al, you need to do something to beef up those lower arms if you're going to put lots of power through them. Either add a brace or use thicker tube.

I've seen a few pics on this forum of broken lower arms in Cobras and the drastic results. Not worth taking any short cuts on in my opinion.

Cheers

[David Hodgson]

Mike
Were these breaks on shortened dog bones only? or std as well.
I've used the narrower "S" Type shafts and arms without cut and shut. I see that accel and decel forces would act to about the hub and induce twisting on the dog bone. I also use a radial trailing arm anchored at the chassis in line with the lower inner pivots with a rose joint and at the dog bone with nylon bushing. In some Kits this arm is a hinderence to achieving a suitable seat hieght.

[Rebel1]

I totally agree Gentlemen. (Ok..I'm bein nice today )

As Mike said, the archives contain heaps of history about failures, some catastrophic (sp) of failed Jag rear ends.

Whilst in the Jag ( a much heavier car) it is all rubber mounted. All that rubber does is wash off some of the stresses. In the cobra we solid mount them so that stresses are immediated and not cushioned. Not a good thing in my book.

Also on my RMC the coilovers are mounted about 70mm either side of center of the swinging arm. This to me would increase any twisting forces applied to the arm in the case of a single coilover system.

The case that RMC did (in the later part of their involvement) use single coilovers, I'm not convinced that is a valid reason to do so.

I make reference to the fact that RMC front top suspension mounting points were twisting off is sufficient justification to suspect any manufactures recommendation.

CWI also make a tubular moly swing arm for the Jag. I don't know if this is any stronger than the Jag setup but it is said that trailing arms are not requited for this setup.