bushing modification question

[BRIAN]

Question about using rubber bushings. I hate poly stuff, with that said I am going with rubber. Poly bushings are supposed to reduce bind with that in mind would rubber bushings benefit from the serrations removed so that they would move freely. They would retaing their softer feel but act like a poly or Global bushing. I know it used to be trick on drag cars to loosen up the front end. I would think with stiffer springs,shocks, and bars the serrations wouldn't be needed. I know somebody will set me straight why this wouldn't be beeficial???

[David Pozzi]

Polly and Delrin bushings have an inner sleeve, the A arm bolts are tightened to grip the sleeve and the Delrin or polly wears on the bushing OD.

A ruber bushing with serrations cut off would have to be slightly loose to allow movement, I'd think the bolt would come loose or even egg shape the bolt holes in the frame after a while. The rubber bushing flexes in twist and might add 10 lbs per inch to the wheel rate, but that's just a guess, it would be nice to measure it.

there are cheaper "Lightweight" nylon/glass circle track bushings that can be used.

10 lbs / inch at the wheel is not insignificant.

[Norm Peterson]

If you allow the sleeves to move freely about the bolt you are reducing the accuracy of your suspension slightly. How much is roughly by some function of the clearance between the OD of the bolt shanks and the ID of the sleeves and the spindle height. These small movements mean that you'll lose a little camber while cornering and caster could wander around a bit under braking relative to leaving the OE bushing sleeve teeth intact. Since these movements require very little load, you could end up with about 0.5* worth of free play in your camber as you steer from left to right.

You also change the method of load transfer between control arm and chassis from interference between the serrations of the shank and the gouge marks on the chassis bracket to pure shear across the bolt. This may be OK in a dedicated track car, where things like that should receive frequent attention, and in the case of the drag car, where they see miniscule lateral loads anyway (unless there's an immediate issue with directional control present). I'm very uneasy about this in a car that's apparently intended to see mostly street duty, as even with the best intentions, its inspection & maintenance is likely to be spotty at best.

All that suspension stiffening, plus the assumption of hard cornering with grippier tires, has the effect of attracting greater loads through these things, so if anything you need a better grip on holding that bushing centerline location in position.


David - I think it was either on Corner-carvers or over at the Corral where somebody actually had taken the trouble to measure the wheel rate effects of OE bushings for a Mustang. As I recall, it did fall in the 10 - 15 lb/in range. By comparison, the OE wheel rate due to the springs was 120-ish.

Norm

[BRIAN]

I had to read that several times to get it all but THANKS! I guess I am just trying to avoid the poly deal as they just do not fit properly and yes they do bind and work the stock bolt out of the arm with real street driving. Vette brakes used to sell with the tube a little longer which made fitment more accurate with some filing. But the last set I bough was about 15years ago. I am giving Marks' Pole Position with larger stud ball joint set up a try (If I ever get the rest of the parts) and they have rubber bushings. If I remember one of the mfg's used to list a harder compound rubber bushing for the lower arms?? I do not want to mix and match so I am stuck with the rubber lowers. I actually do not mind a little give as I live in NY and the roads are ROUGH to say the least. Would rather have give than have broken parts. What do you guys feel about mixing different upper and lowers?? Global West lowers?
On another note David I would like to thank you for your site. Between being hear and reading the info on your site I waste 1/2 my day. Great info. I am not big F body guy and apprecaite the help.
The PP arms are a lot heavier gauge stuff then you would think. I have used Mustang 2 tubular arms plenty of time and am actually impressed with the PP arms in terms of heft. As of now the only problem I do see is no mtg for bumper? I am probably going to use the opened spring space for a modified easy to adjust weight jack set up. Maybe a bolt on upper shock mtg where I can make a tool with a mated end on the adjuster to adjust from the top. Thanks Brian