Classic Revival Spring Rates Take #2
 

Howdy,

After testing Mike "The Magician" Murphy's rear bump steer kit and steering rack spacers, I am now ready to ditch the original springs I was supplied with and join the "B" club.:LOL:

To achieve uniform ride height my front off side spring is compressed almost fully, with the near side only about half. Are there any advances on the King springs that Classic Revival owners seemed to like in previous posts about this issue?

I am going to do both front and rear, and to be fair I do not intend to do much track work at all just yet, although have got the bug big time :3DSMILE:for some nice road cruising now I can drive without getting tension cramp in my arms!:D :D :D

Any advice specific to my Classic Revival will be appreciated.

Stuart.

eibach, 450 fronts 400 rear with keeper springs.

The rear bumpsteer has always been a problem but the B club have put a lot of effort in correcting the problem, Andrew (Tenrocca) set up a jig and measured the bumpsteer and tuned the new "raiser" for maximum effect, produced graphs for us to see.

Mike produced a high quality kit that is an almost bolt on solution, carefully machined and as always very resonably priced, (at twice the price it is still a bargin)

Stuart, it is good to see you are wanting to enjoy your car.

Thanks B club.

Phil

B club - is that like the Freemasons? :D

Nope, we are a top secret "Think Tank" with plans for world domination but we also do freelance Cobra technology development.

Stuart,

I am running the same Eilbach springs as Phil and they do the job very well. I have installed power steering and in the process lowered the steering rack, the front front end is now spot on. I am yet to deal with the rear end. The car is coming apart for painting very soon and I will attack the bump steer issue then. I have looked at Mikes kit on Leigh and Daves car and was very impressed. I have a couple of other ideas as well, so I will intersted to see how your car goes in cruise mode.

Rod

Sloth,

Good to hear you are putting some miles on your car. Mine has been puled apart a couple of weeks and I miss it!

I have yet to fit the Disco Mick rear end kit but everyone who has done the mods cannot believe the difference. I am looking forward to going to Wakefield with the right set up.

Ben

P.S. I am happy with my King springs

I rang the man at King springs to ask him what was available. I asked for a specific rate and he said that he didn't have a clue. I asked him about spring rate and frequency and he said all we do is use the oem dimensions and make them shorter for lowered springs, make them longer for raised springs. and just use a thicker wire for performance springs...no science just sell. I hope they have improved from that time. I'll be having my next set of springs made by Jubilee springs at gosford...they know the maths.

Rob.

There are very few steerers of Cobras that have the knowledge and track time to make some sense of what it takes to make a Cobra to go fast. That is why those pesky Queenslanders clean us all up!

If someone puts the time into a Classic Revival to make the most of it I think they will do well.

Ben

Oops, Double post

Ben
Iain Pretty done very well with a CR. Depends on the budget.
Cheers

From what I know, I think Ian's CR was an earlier version that had the VP Commonwhore IRS.

I have the same spring rates as Phil M, but have used King Springs with their keeper springs.
You will require spring ID, length and rate to order them but they can be purchased locally from any Bursons or similar store.

Come on guys,

More info on these bump steer kits. Need help keeping it on the road
Eibach on the front now, Ians springs on the back but bottoms out on bumpy roads, very little movement, possibly running out of shocks.
Cheers

I have the maths formulas for those that would like to waste a few months of their lives. These sums still leave some guess work as no body knows the actual frequency that a particular car oscillates at. Deep **** eh ?
I'm still building my car but test drives reveal a firm ride without bone rattling on railway track crossings and Newcastle rough roads. I'm about to fit the sway bars so that will provide another improvement to the ride.

Have a chat with Mike, you will not regret getting a kit (might have to wait till he is in the new shed though)

cobbindale,
You will find Ians springs do not have a short enough compressed length. That is why you are bottoming out on the rear, I have the exact same problem.

Phil

Hi Dale,

There's an awful lot of bump steer in the rear end of our CR Cobras. I don't know if it's in the chassis by design or something left over from the AU Falcon donor car. I became aware of it pretty quickly on my first outing in the car. I'm running 11" rear rims and was having problems with the tyres rubbing on the inside of the body tub. Initially I couldn't understand why it would rub there because it had heaps of clearance at ride height. I also found it felt very nervous decelerating from high speed at the end of the straights at Winton. The rear would squirm around under brakes and didn't inspire a lot of confidence. The only way to settle it down on the day was to wind all the shocks up to full hard (effectively disabling the suspension and making it a GoKart).

You will be able to see why from the graph below. I measured the bump steer on the standard setup and it was pretty bad. The measurements below are just from one side. From full droop to fully compressed there is about 40mm change in toe (measured from the OD of the tyre.) Add both sides together and that's 80mm of toe change. No wonder my tyres were rubbing.

When you get your wheel alignment done they set the toe at ride height. Say for example they set 2mm of toe in. When you drive out of the shop and put your boot down your rear suspension compresses and your 2mm of toe increases to 20mm or more depending on how much your rear squats. This isn't so noticeable since the tyres are planted and the thrust of both wheels is pushing towards the center line of the car. However when you lift off and put the brakes on the rear end unloads and lifts and you suddenly have a heap of toe out. The wheels are pointing out and are pulling the car left and right depending on which tyre has the best traction.

http://www.clubcobra.com/photopost/d...0/Bump_Kit.JPG

The B Club have been discussing these suspension issues at length and trying different things. I went as far as designing and building a whole new rear suspension system to correct this and a few other issues I found. Andrew (tenrocca) found that raising the pivot point attachment on the suspension upright dramatically improved the bump steer. The problem we then ran into was due to the angle of the pick up point on the upright, the higher you went the closer the pivot point got the the brake disc. We did a bunch of measurements and found the ideal height to near eliminate the bump steer couldn't be achieved with the existing clearance. The other issue was raising the pivot by using a longer bolt and spacers was putting a lot of extra leverage on that bolt and there was a real danger of failure.

The solution was a clevis setup that raised the pivot point to the right height without the danger of a long bolt and spacers fatiguing and failing. It's also machined at an angle to maintain clearance to the disc rotor. The kit includes 2x clevises 2x tubular chrome molly track rods with left and right hand threaded ends, Chrome molly rod ends, machined spacers and bolts to suit. All you need to do to fit it is drill out the tapers in the suspension upright to 5/8" for the grade 8 5/8" UNF bolt that attaches the clevis to the upright.

As you can see from the graph there is still a small amount of bump steer left even with the kit installed but the more dangerous change when in droop is almost eliminated. The only significant change is when the suspension is approaching full compression but it is still significantly less and I doubt you will notice the effect.

I'll try to post a pic of the kit tomorrow as I think I have a one on my work PC.

The bottoming you're experiencing may not be coil bind. It may be the top rear suspension arm hitting on the chassis rail. This was another shortcoming I found with the rear end design. There's usually a rubber bump stop in the shock that should soften the hit when you bottom the rear end out however with my chassis when you fully compress the rear shock the arm hit the chassis rail before coming anywhere near the bump stop. It might be worth while pulling the spring off the shock and pushing the rear suspension through it's full travel and see what hits first. When I designed the tubular arms I made an allowance for it. It gives a full 170mm of travel at the wheel. You can see the curved upper arm here:

http://www.clubcobra.com/photopost/d...spension_3.jpg

This may not be a problem for you as I went for shocks an inch shorter in the rear. I did this as I kept the lower mounts inward a bit more to make clearance for the 11" rims.

Cheers

I found this pic of the kit installed on my rear suspension setup. I was developed a version to suit Mando's CR as he had some 2" shorter control arms made up for his rear (same length as mine). The basic design is the same as the regular width rear end kit but some of dimensions are different.

http://www.clubcobra.com/photopost/d..._Steer_kit.jpg

Cheers

Cobbindale,

Mike's Rear end kit is a must if you still have a stock CR rear end. It has transformed my car ito a machine that i can now drive with confidence on the street (one handed even...). I had the local engineering shop drill out my tapers to 5/8 and that left the hardest part for me to do being removing the hubs.

Thanks for the info fellas. I will go with the eibachs. Looking forward to catching up with some of you soon.

Stuart.

Just a bit more background to this and a few other things to consider:

Identifying the need to raise the outside mounting point was actually pretty easy, and dissapointing the manufacturer had not taken the necessary steps to design the rear better. Basically I jacked the car up on a level surface, took the shock off and raised the suspension through the full range of travel from full droop to full bump. I started with 0deg toe at full droop, and at 20mm increment while jacking up the suspension, wound the toe arm in or out in order to maintain 0 toe, keeping track of the revised toe arm length.

I drew this all up in a cad package, and from each of the points on the arc created by moving the suspension up and adjusting the toe arm, drew a series of arcs, that intersected at a point approx 35mm below the inboard mounting point for the toe arm. Unfortunately due to the design there it is difficult to move the inner mounting point down the necessary amount, so moving the mounting point on the toe arm up is the easier solution.

I took a slightly different approach with mine, and machined the top of the toe arm at right angles to the brake disk, so the riser stayed vertical and doesnt interfere with the disk. I think an advantage of this is that with a bolt and spacers I can fine tune a little down the track - I plotted a similar chart to Mikes above and got slightly different results too. As no two CR's seem to be the same the ability to fine tune might be advantageous. Either way though it is a bloody easy fix to get a 90% improvement.

I have also found on the rear I have too much negative camber even at full adjustment of the top arm. Again a symptom of the cabbage patch kit syndrome. I think down the track I will make some tubular lower arms like Mikes to allow for a better adjustment there as well. Im curious if anyone else has the same issue on the rear of their CR's?

Cheers