rear poly bushings on outboard end of CA

[blueovalz]

I have a few of them Mike, I'm obviously not using them

 

Any 240 transverse links?

[zlalomz]

Here is a variation of the John Thomas rear suspension. If you welded the rectangular tubing to the arms and had the heim joints on the inside you could also raise the inner pivots to change the roll center for a lowered Z, change the toe by adjusting the bearings and you have double shear for the bearings. If you raise the inner pivots some floor clearancing would be needed.

 

Or if you put the bearings on the outside there is less fabrication but you can't change the roll center. Both of these you have to disassemble them to change toe, unlike Terrys design.

[blueovalz]

Roll center adjustment at the rear: My take on changing the rear roll center would be a more permanent change by cutting the two cast extensions under the strut that connects the strut tube to the spindle pin boss, and then weld in a spacer of some sort. My thoughts were using 1/4" steel to extend this part of the strut assembly by whatever is needed (about 1" in my case). For the more adventuresome, weld up plates between the two severed pieces and fabricate something that allows some kind of adjustability (but this would seem to be a bit of overkill if you have a "set" suspension height and know what you want in regards to roll center). The extensions are not simple in that it is basically an short "H" beam with a large hole in the middle, but crossbracing, and proper design would make the longer extension as strong as is needed.

 

In essence, this would be the same method of roll center change as is used with the "bump steer" spacers commonly used up front. Simply an extension of the strut below the axle.

[JMortensen]

Kinda like this?

 

I know what it does and I'm impressed with that and it looks like it took some serious effort to design and machine it, but it seems way too complicated, plus it raises the rear roll center A LOT. Quite a bit more than a bumpsteer spacer does in the front, I think. Looks to be about 1.5" tall.

[tube80z]

I know what it does and I'm impressed with that and it looks like it took some serious effort to design and machine it, but it seems way too complicated, plus it raises the rear roll center A LOT.

 

Why wouldn't you make the inside adjustable? Then you could raise/lower the RC and play with antisquat/lift. Using something like Steve has in the pic above this looks like it would be a little easier to pull off.

 

For the amount of work in that spacer it would almost be easier to cut off the bottom on and weld on an entirely new piece. I'm making this double shear on my car by welding a tab from the strut tube down to where the spindle pin goes through and using a bolt instead of the pin. The front of the strut will be done in a similar fashion.

 

Cary

[blueovalz]

Wow! Very impressive.

 

The reason I sought to adjust the RC from the outside was because the inside bushings would be nearly impossible to raise, or at least much harder to raise, than to instead lower the outboard bushings.

[tube80z]

The reason I sought to adjust the RC from the outside was because the inside bushings would be nearly impossible to raise, or at least much harder to raise, than to instead lower the outboard bushings.

 

In stock form I agree. But if you create a subframe as in Steve's pics of JT's setup then you can make a bracket that bolts up that can be shifted up or down. And if you make the bracket wide enough you can use spacers to adjust within that range and if you need more you use the alternative holes for the bracket. I guess at some point you may need to be able to move both. That would be a seriously low car.

 

This is fairly typical on a lot of formular cars these days. Especially ones that are designed to use a couple different diameter of tires. I'm always happy to steal ideas from where ever I can

 

Cary

[zlalomz]

If the forward inner pivot is moved back from stock like in my hi-tech drawing, then you don't touch the forward pivot frame, you just raise the floor area behind it in the secret compartment area to clear the raised inner pivots.

Here is an electronic napkin sketch as Cary likes to call them of the clearance area and roll center adjustable spacers with high mis-alignment washers. The heims are horizontal 'cause Cary says they are designed to move that way.

 

[blueovalz]

Looks like it would work. What kind of stress increases are we looking at with the spherical bearings (rod ends) moved closer together? Lever action against the inboard pivots will increase with the decreased length between the bearings. I'm not looking for holes in a good idea, just considering all implications. Wasn't JT's car powered by the L6?

[zlalomz]

Oh yeah, you have gobs of torque. JT's Z is a Rebello L6 with I would guess 300HP. I was thinking out loud for my autocrosser which has even less muscle.

 

You could replace the stock subframe to keep the original width but I am talking about more work than your outside rear "bumpsteer" spacers. Cary will crash test his idea and then maybe share with everyone?

[tube80z]

Here is an electronic napkin sketch as Cary likes to call them of the clearance area and roll center adjustable spacers with high mis-alignment washers. The heims are horizontal 'cause Cary says they are designed to move that way.

 

Cool pic Steve. Heims will have lower friction when mounted this way versus trying to rotate the ball in the race. Just need to make sure that the range is appropriate, which it should be but one more thing to check.

 

Terry, I'm not quite following your question. Do you mean the stress goes up because we've reduce the lower suspenion arm mounting distance (closer together)? Or is it something else.

 

This would look real trick integrated into that AZ billet stuff in another post.

 

Cary

[tube80z]

Cary will crash test his idea and then maybe share with everyone?

 

I'm looking very forward to being able to write about the first drive in anger. Hopefully nothing breaks ... but it will be shared good or bad.

 

Cary

[blueovalz]

Do you mean the stress goes up because we've reduce the lower suspenion arm mounting distance (closer together)? Or is it something else.

 

Yeah. It may be inconsequential, but here is what I was trying to say in a nutshell:

 

[tube80z]

Yeah. It may be inconsequential' date=' but here is what I was trying to say in a nutshell:

 

[img']http://www.fototime.com/5F650A3F1F42963/standard.jpg[/img]

 

It's early and I haven't had any coffee just yet. But isn't the torque created by the traction proportional to the lever arm from the outside to the inside at the front and rear pivot? I don't see where we changed that distance. If you were talking about lateral force I could see where that went up due to a change in leg angle but it wouldn't be a factor of two. And what we're talking about here is just shortenning this by only a couple of inches at most.

 

Cary

[zlalomz]

Here is another abomination submitted for your much appreciated comments.

 

 

Besides the shorter length between pivots (if JT doesn't break I won't with my anemic motor) would this twist or tear apart somewhere?

[JMortensen]

The only concern I have with this type of mount is that the range of motion of the rod ends is going to be pretty limited. If the idea is to have adjustable inner pivot height, then you might be asking a lot of those rod ends. If the CA were perfectly flat than the rod end would have the maximum amount of motion up and down. So the higher the roll center the less droop you'll have available. Might need Cary's favorite: droop limiters. Your gusseted design looks plenty strong to me though...

[blueovalz]

And what we're talking about here is just shortening this by only a couple of inches at most.

 

True, and that is why is think this may be inconsequential.

 

zlalomz:

 

It was mentioned earlier about the angles needed for full articulation with the "flattened" bearings. Normal movement on a race-preped car would most likely stay within the restrictive field of acceptable misalignment angles (14º to 24º for most rod ends) for the ball. 24º = ~6" of axle movement.

 

When jacking up the car, you'd want to ensure the misalignment angle never was exceeded, or you'll risk damaging the bearing. I know that on my steering rod ends (1/2"), that this limit does get bumped at full droop, which in a worst case scenario, could cause the threaded rod or the bearing to fail, which would not be good.

[zlalomz]

Thanks. Looking at the Chassis Shop catalog even with the mis-alignment washers or the high priced mis-alignment bearings it looks to be 22 degrees max.

Here is a vertical bearing napkin sketch.

 

 

Another way to get a less coarse adjustment would be to slot it vertical and use the flat serrated washers like the 510 guys do in the Hotrod Datsun book.

[tube80z]

The only concern I have with this type of mount is that the range of motion of the rod ends is going to be pretty limited. If the idea is to have adjustable inner pivot height, then you might be asking a lot of those rod ends. If the CA were perfectly flat than the rod end would have the maximum amount of motion up and down. So the higher the roll center the less droop you'll have available. Might need Cary's favorite: droop limiters. Your gusseted design looks plenty strong to me though...

 

On my car, which has longer arms than normal I have 9 inches of movement before the rod ends touch, and that's mocked without misalignment washers. What I read in my catalog claims 22 degrees of movement with them.

 

On the back of my race car I typically only use about an inch to 1.25 inches of droop. I found it seems to work best by setting the rear limiter at the point where the spring just slightly touches (maybe 20 pounds preload) on a 450 pound spring. And for bump I have about 3 inches but it's really only using around 2. I think these numbers could easily be doubled and you'd still have no issues with clearance. But using some form of mechanical stop would be good so that you don't break the rod end. If that happens the outcome will not be pretty.

 

These are all good things to think about though. And I think this only makes sense on a race/track car.

 

Cary

[JMortensen]

Thanks. Looking at the Chassis Shop catalog even with the mis-alignment washers or the high priced mis-alignment bearings it looks to be 22 degrees max.

Here is a vertical bearing napkin sketch.

 

 

Another way to get a less coarse adjustment would be to slot it vertical and use the flat serrated washers like the 510 guys do in the Hotrod Datsun book.

I've had my front crossmember slotted for years. Never had the LCA slip, and it enabled me to dial in the bumpsteer just right.

 

I've been thinking over my TC rod modification thread that was going to use a very similar vertical bolt with spacers type setup with the horizontal rod end. Thinking now that I might be better off making a stronger than stock TC rod box and slotting it. Still need to do some testing to see if I can get full articulation out of the vertical bolt. If not I'm going with a slotted box.