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I think I can finally report the beast is finished. It took a long time to sort the handling issues which turned out to involve a number of factors. Steering geometry was the most critical one - the attached pic shows the final setup at ride height. You'll notice the rod ends are dropped below the bottom of the steering arms. We spent a lot of time playing with different bushing lengths here to minimize toe change over full suspension travel, and this along with the narrower rack have eliminated bump steer. Dialing in the alignment helped a lot - in the front we ended up with 1 deg of negative camber, 2 deg of positive caster and .08 deg of toe in. The IRS setup also made a difference - there we have .5 deg negative camber and .15 deg toe in. With the wide tires and big wheel offset we were shooting for 4 or 5 deg of caster, but as you'll see from the pic we're maxed out at that 2 deg number. Finally, I can't say with certainty that the tie bar across the shock towers improved handling - we just made too many tweaks at the same time to know what to attribute the improvements to specifically. If nothing else the damn thing looks good so we'll probably leave it there.
Final judgement on the project is good. The beast looks great, goes very fast and handles better than my wife's XJR - due mainly to the lower weight I think. The car can be tossed around with confidence at high speed (finally), and braking forces are extreme with no fade (I'm afraid I'll be contributing to Michelin's profits for the foreseeable future). My biggest disappointment is that we didn't achieve the level of isolation we targeted. With all of the modern suspension and drive train mounts and dampening materials on the tub I thought we'd have a quiet, vibration free ride comparable to a modern car. I think the problem is due to some resonances inherent in the Mark 2's tub structure but I'm not certain. I'll be interested to know how Clyde's project with the Art Morrison chassis does in this regard, but then the 700 hp may negate any improvements in this area.
My heartfelt thanks to all of the folks on this forum who have helped me over the past 6+ years - I can honestly say I couldn't have completed this project without your help. Best regards to all. Doug Dooren
After months of trouble-free cruising the beast suffered a significant failure the other day - a broken rear shock rod. I was lucky that the spring simply jammed against the crossmember and was contained by the upper shock eyelet - the left rear dropped about 2 inches causing a slight tire rub on the fender lip with no damage. The rod snapped at the thread root where the upper eyelet attaches - the race boys tell me this is where they all break as a stress riser is created here. The concerning part is that I have no idea why this happened. The rod cross-section at the break suggests a clean snap, with an appearance of being sandblasted (no eddies). I can't recall the left rear ever taking a hit or seeing the kind of force sufficient to snap the rod. After removing the broken coil-over I installed another shock to check alignment - upper and lower bushings are perfectly neutral (no side loads when bolted up), and upper and lower mounting faces remain perfectly aligned over full lower control arm travel. Shock angles are modest (about 15 deg as I recall) and travel is set right in the middle of the specified range at ride height. My only thought is that a side load is somehow being induced on the rod, so I've ordered a pair of bearings to install on the lower mounts (if nothing else they can't hurt). Any other thoughts out there as to possible cause will be greatly appreciated.
Doug,
The Strange shocks on my chassis have heim joints top & bottom. Spacers called "hats" are used on both sides of the heim inside the mounting to prevent bind.
Cheers.
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If it looks like a clean snap, without any distortion of the surrounding material, this implies a fatigue failure after a large number of load cycles.
It would be interesting to look at the fracture surfaces because you can usually see "beach marks" as the fatigue damage propagates.
A structural overload would result in the surrounding metal being distorted as it yielded before breakage.
I think you would be well advised to inspect the other shock absorber for cracking.
Thanks Bruce. I did look for beach marks - this is what I referred to as eddies as in eddy currents - but none were present. Unfortunately the broken components are off to a rebuild shop, otherwise I would take a closeup shot of the surfaces. I did have some old boys at the local race shop (I call them the cheering section) inspect the damage and they didn't see any evidence of fatigue cracking either. They likened it to the kind of failure they see after wheel contact on the track. Unfortunately I can't think of any time the car has seen a pothole or similar. Despite this I'm concluding that fatigue cracking is the most likely cause, so hopefully the spherical bearings will mitigate this. I appreciate the heads up - I'm removing the other shock now and will take it to the race shop as I know they have dye penetrant for checking for cracks in chassis welds. Will let you know if I find anything.
Hi Doug, I'm wanting to do a project . I've got a Mk2 Jaguar body and I'm wanting to modernize it so I'm looking at either a Jaguar XKR2003 or a 2007 XJ8 Sovereign. I have been looking at the discussions on what you have done. It seems to me that there are more options on the later car. I was also looking at using the front suspension from the donor car, gear box, diff etc. Your thoughts please.
Hi Doug, I'm wanting to do a project . I've got a Mk2 Jaguar body and I'm wanting to modernize it so I'm looking at either a Jaguar XKR2003 or a 2007 XJ8 Sovereign. I have been looking at the discussions on what you have done. It seems to me that there are more options on the later car. I was also looking at using the front suspension from the donor car, gear box, diff etc. Your thoughts please.
Fifty - I see Beacham is now using a later engine and drivetrain than the X308, so that's certainly an option. I know people have grafted the later front suspension carrier into the Mark 2, but that poses some major issues. Foremost for me is the safety of the installation - cutting and replacing the frame rails and carrier is certainly possible but I don't have the engineering expertise to attempt it. The other issues include a wheel track that's much too wide for the car, a spring rate that's much too high for the car (the Mark 2 is roughly 1000 lbs lighter that the later sedans), and steering geometry that's inappropriate for the Mark 2's much shorter wheelbase. It can and has been done but I'm guessing that what you'd end up with wouldn't be very pleasant to look at or drive.
I'm driving my beast every day (except when there's snow on the roads) and thoroughly enjoying it. Other than a recent shock failure it's been very reliable, but I'm guessing there will always be something to deal with given the number of modifications involved. As far as a project is concerned, be advised it takes a lot of time (thousands of hours) and a lot of expensive materials and parts to do it right. Dave on this forum is doing a Daimler coupe restomod, so hopefully he'll weigh in with his thoughts. Good luck.
02-02-2020, 07:36 AM
