Butler Cobra with Mustang II IFS

[RallySnake]

Hey Guys,

I have to speak up here for a minute in defense of the MGB suspension. Sure the kingpins are old technology, but is that a bad thing?

I remember vividly the first time I drove a new MGB in 1969. The steering was amazingly precise and direct. Ron Butler has built a lot of race cars and if he didn't have a lot of faith in the MG front end he would have changed it when he took over the production from Steve Arntz.

Things do wear out, though. I had a similar problem to Tom's. After years of driving, the car wandered a lot and was all over the place when I braked hard. I pulled the body off and started trying to "bumpsteer" the car. I worked on the steering angles for hours before I leaned against the brake caliper and the upper a-am moved forward 1/2 inch! The lever shock bushings were completely worn out. I bought some second hand shocks and took them apart to remove the levers and pistons. Then, I drilled and tapped them to install grease fittings on both sides of the horizontal shaft. I bought the hard "racing-type" polyurethane bushings for the outer pivot points and also for the lower arms.

The lower arms were a problem themselves. The bolt holes (under the kingpin) had worn down more than a quarter inch from their original position. I bought new ones from Moss for less than $20.

I then started checking the bump steer and it was very near perfect without any adjustment. I did change the castor angle. Brett Butler (Ron's son) suggested this. With the MGB suspension bolted to the Arntz chassis, the angle is about 6 degrees. This makes the car run VERY straight on the freeway, but VERY hard to turn while parking. I used spacers under the front mounts to reduce the angle to 3 degrees.

After putting the car back together, the transformation was amazing! The car tracked straight and true even at really high speeds. I could steer within an inch of an apex. The steering remained straight under hard braking (even though the engine often dies). I do have about a dozen grease fitting to hit a couple of times a year and I am running KYB shocks meant for the rear of an early 'Vette. The kingpins show no wear or play and they are at least 40 years old.

I did replace the calipers with rebuilt ones ('74 Dodge Dart). I had the rotors turned and installed Porterfield pads. Since then, I've probably driven 50,000 hard, fast miles and it's still working great.

Paul

[lal Naja]

Paul, you make a good point. There are thousands of satisfied MGB's and other cars around the planet doing just fine with king-pin type technology. However there have been a number discoveries and improvements in suspension design and geometry since the creation of the MGB.

The reason for wanting a change, is to take advantage of newer technology. Also, a fully adjustable suspension gives you the opportunity to fine tune the car's suspension based on the driving conditions. Multi piston caliper brakes would be good to.

Form and function appeals to me.

I spent a lot of time rebuilding and modifying the MGB setup. I installed an Aluminum/Nylatron bush kit made by Global West Alignment in the inner lower wishbone pivots, a well engineered setup. I also welded two 1/2" id x 1" od x 1/2" thick Shaft-bushes to the lower wishbone arm outer pivots. This will prevent the elongation of the 1/8" thick metal of the wish-bone. I replaced the MGB bolt with a grade 8 bolt 1" longer. The bolt can be locked in place with the shaft-collar set screws. Now the pivot will never wear out. I also installed needle thrust bearings at this outer pivot point, similar to all the XKE Jag rear-end pivots. The upper-outer pivots for the lever shock has been replaced with Nylon pivot bushes. And much, much more! But after all that, it will still be 50tees technology.

Ron is a great engineer and fine gentleman. He built a great car. I don't want to modify his frame. I'm hoping to develop an bolt-on replacement that could switch back to the MGB should anyone ever want to do that.

Look for my updates,

Arthur

[migge]

If you just want a bolt on solution try:

http://www.hoyle-engineering.co.uk/

Cheers
Migge

[arntztype4]

For a bolt on front end replacement for your MGB front end, go to "fastcarsinc.com". This guy builds them for the MGB set, but it looks like a nice piece. I spoke to him a while ago, he sells them for $3750.00 plus shipping.

[lal Naja]

Migge, thanks! Unfortunately the Hoyle unit still uses the 50tees king-pin technology. This limits the caster adjustment to no adjustment. Plus nothing else can be adjusted either. I guess it's okay if you want a fixed setup, but I want a system that can be fully adjustable for various tracks and driving conditions. I also want to be able to obtain parts easily in the US for future rebuilds.

Thanks for your comments.

Arthur

[lal Naja]

Thanks for the tip.

Arthur

[lal Naja]

Hi Paul, one other comment about shimming the crossmember to decrease caster. If I were to guess why 6 degrees caster? The original MGB designers did not know about anti-dive. And even if they did, the British car industry was so distroyed by the labor unions, that they had no money available for fine tuning and improvements. They were struggling to stay alive.

I'm also guessing that Butler knew about anti-dive and designed in into his chassis by tilting the crossmember. This provided for the new anti-dive technology, but increased caster. In a non-adjustable older setup you can have one or the other only. If it works for you, great. I will be doing some track driving so I'm looking for all the technical attributes to help my driving skills. Arthur

Seems like my guessing in the last paragraph above was wrong. The Butler Cobra and the MGB crossmember bolting geometry is the same. Tilting 10 degrees up to the front. Does anyone have any futher comment?