Front bump stop pads.

[tbburg]

This is probably only a problem with the Jeep style front 4-link suspension.

Because the bump stop is mounted on a pylon in the middle of the spring, it has little lateral support, and a fairly long "lever arm" acting on the bump stop. When you hit the stops, there is no way the bumper is always going to be perpendicular to the pad when it hits. Because of this, the bumper is always going to try to slide off the pad, putting all the lateral force on the pylon mount. The harder you hit, the worse it is. Because we spent so much time smashing the bumps at speed, the desert/JeepSpeed/prerunner crowd sees a lot oof damaged stops, spring buckets, and other various suspension components.

What if, instead of a flat bump pad, you had a cup shaped pad, maybe 3/8"-1/2" deep in the center. Then, most of the lateral force acting on the bump stop would be forcing it toward the center of the bump pad, and not to one side.

What do you guys think? Way off base, or worth further thought?

 

[crazyjim]

The though behind the idea is valid, but the major problem I see with it is that you'll NEVER hit center. Think about it, the axle swings one way as it compresses, therefore, in a big g out even hit on the front end, both sides will be hitting the sides of the cups, and as you said trying to force them back to the center. But the trac bar will win that battle, and will bend the mounts just as easily as they do when they're flat, if not more so.

Also on side to side hits. The cup will be contacting the side of the bump stop, again pushing it to center, but is this really a good idea?

 

[tbburg]

I'm not sure, that's why I brought it up. The thought was; With a flat pad, eventually the bump stop pylon is going to bend far enough that it no longer hits the bump stop pad on the axle. The bumper slides off the side of the pad and hits the spring.

With a cup shaped pad, if it bends at all, the force will tend to push it to the center of the pad instead of away to the edge. I don't know. We screwed up the front of the 7118 truck at Parker last year and rammed the antisway bar end links through the fenders. Would like to see it NOT happen again. As they now allow air bumps in 7100class now, it may not even be a problem any more. 'Just thinking out loud and bouncing thoughts off (hopefully)people with similar experience.
A quick sketch of what I had in mind:

 

[jeeperjohn]

Seems like it would help reduce lateral forces applied to the bumpstop. I think it would be helpful.

 

[XJRunner]

seems logical to my too.

 

[grandrunner]

i thought of this too. but what i thought about more was even if the bump hit the outer part of the curve it would be forced to the middle, wouldnt that also possibly cause a bent coil tower too with the force pulling it in??? just a thought because most of the jeepspeed/ prerunners will be hitting straight on and in the drawing you did it looks like the axle is articulated, and that may work better for crawlers because it would hit an even surface and not at a high rate of speed.

 

[tbburg]

Agreed rock crawlers do more side to side articulation, but they usually don't hit at high rates of speed. It's more of a hit and bounce back off. When a race car bottoms out, the chassis usually wants to keep going in the direction it's headed(normally forward and down) and you pushing the whole weight of the car, plus momentum, against the bump stop pylon.
There are plenty of places on race courses where the cars really work the suspension side to side. Also, I'm not just talking side to side. The side to side case was just easier to picture. I think it would help fore/aft too(remember, I said cup-shaped, not U-shaped) After all, in our case, when the bump pylons on the truck bent, they bent forward.

I'll be honest, I don't know if this would work. At the least, I'd have to very carefully figuring what curvature to use on the pad.

 

[VAhasnoWAVES]

sounds logical to me as well. though i think after some testing you might find that the depest part of the concave wouldnt be exactly in the middle of the pad. it would really depend on the rig.

now, on a JS rig does the bump consistently hit in the same spot or no? i would imagine joined with hydro bumps it may increase the life of the front uniframe rails... :dunno:

 

[crazyjim]

The problem is you can't get the cup off center, it'll always be worse in 9 out of 10 situations. So to help that one perfect hit, you'll be destroying it faster the other 9 times it doesn't hit perfect. The main issue here is that the axle swings as is compresses, therefore the bump stop will be hitting the side of the pad.

 

[tbburg]

yeah, that's what I'm trying to figure out. Is there a way to get a "sweet spot" centered under bump stop for straight up/down hits, and curved correctly to catch the side hits.

Looking at your version of the drawing, I think I have the axle movement pictured the wrong direction. I think(if I can use that term )the bump stop actually hits on the outboard end of the bump-pad when just one side of the axle goes up(duck walk) The way I pictured it originally might make the situation worse.

Well, I do have a dead Cherokee in the garage. I suppose I could put it on stands, pop the springs out, and play with it. Only way to know for sure, really.
'Project for one of these weekends when I'm not too lazy to move.

 

[zoomy97acr]

Since it would hit on the edges of the cup, the lateral forces would tear the mounts from the spring cup, i think. Remember it split the sheetmetal right behind the spring cup. the whole upper structure moves with every rebound that involves the bump stop. thinking of another style strut brace that incorperates the bump stop their by alowing the load to be passed along at more points, and using Fox's internally "bumped" shocks. BTW this is an issue, because i will be converting it from 7100 to 7300 class when i get home.... there is no way to keep up with the mini trophy trucks.