Yet another Rear control arm design

[jeromio]

Or maybe just a parts list and some rough measurements. Actually, if you could gather up the parts, do a line tracing on some craft paper and package it up, I'd buy it.

 

"Cut here, length of square tubing cut at this angle, weld here, bracket welded here, drill here...etc"

 

I have an extra set of control arms and I could make my own leveraging your research and parts sourcing (which I've found to be a PITA). You could add sufficient mark-up to make it worthwhile.

[MONZTER]

So with this new rear design, could you lower the rear inner control arm point, thus increasing the anti-squat

[blueovalz]

I don't believe you would be able to do this any differently with these arms than with any OEM arm. The pivot point is still based upont the OEM location that the OEM arms use.

[tube80z]

So with this new rear design, could you lower the rear inner control arm point, thus increasing the anti-squat

 

Certainly. We didn't do that yet but it was in the back of our minds as something we'd want to be able to experiment with.

[tube80z]

"Cut here, length of square tubing cut at this angle, weld here, bracket welded here, drill here...etc"

 

You're assuming I make any two items the same Since that hasn't happened yet I can only show you what the mockup looked like, which is attached. I did add some info to the picture that may help. I will be building a couple more that may be a little different but will try and take a few more pictures.

 

These were made reusing as many items as I had around the shop. We needed a longer arm to fix CV binding and something stronger than the AZ arms we were starting to have a number of issues with. And this allowed us to test out this idea to make sure it held no nasty surprises. The end goal is to make tubing versions of these arms and a diff cradle that lets us move the inner points too. This is the first step and so far has been a success. More testing is needed.

 

Cary

[JMortensen]

I'm resurrecting this one as I'm in the planning stages, trying to figure out how wide to make the control arms. I measured stock at 14.5", and I have the 300ZXT CV axles. I will be running seriously low ride heights, so I'm thinking at least 15" wide. I'll also have flares (which I anticipate having to widen already) and I have 15x12 wheels for the back with 4.5 offset. Anyone have any input on control arm length, specifically as it relates to CV binding?

 

After hemming and hawing and buying the wrong parts twice, I finally ended up deciding on a 1.125" OD, .935" ID, .095" wall DOM tube. I wasn't going to do this at all, but after seeing all the CV binding posts a couple months ago I decided it would be worth it for that aspect, not to mention the freedom of motion and reduction of stiction.

[74_5.0L_Z]

Jon,

 

My control arms are 14.5" long when adjusted to their minimum length. I also have the adjustable aluminum/delrin inner pivot bearings adjusted to give me the widest spacing of the inner pivots. The rear camber plates are adjusted as wide as possible to minimize my static camber. With my rear suspension set up this way, I can go through the entire range of motion without binding the CV axles (specifically the passenger side).

 

If I were to use inner pivots that were centered on the inner mount, then I would add 0.375" to the minimum length of the control arm. So, I would make the minimum length of the control arm 14.875".

 

One way to alleviate the CV binding without lengthening the control arm is to lower the differential to the point where the minimum length of the CV axle occurs at full droop. Lowering the differential is on my to-do list. I may actually finish it some day....

[JMortensen]

Jon,

 

My control arms are 14.5" long when adjusted to their minimum length. I also have the adjustable aluminum/delrin inner pivot bearings adjusted to give me the widest spacing of the inner pivots. The rear camber plates are adjusted as wide as possible to minimize my static camber. With my rear suspension set up this way, I can go through the entire range of motion without binding the CV axles (specifically the passenger side).

 

If I were to use inner pivots that were centered on the inner mount, then I would add 0.375" to the minimum length of the control arm. So, I would make the minimum length of the control arm 14.875".

 

One way to alleviate the CV binding without lengthening the control arm is to lower the differential to the point where the minimum length of the CV axle occurs at full droop. Lowering the differential is on my to-do list. I may actually finish it some day....

I was thinking it would require more than just 3/8". I can't say for sure, and I can't do what I tell everyone else to do and put it together and check for bind, so I'm a bit screwed. I was thinking 1/2" or 3/4". I did PM mayolives, I know he had custom CV axles made, I was thinking if I made the control arms longer by the same amount that he made the CV's shorter, that should do it.

[74_5.0L_Z]

Making the control arm too long can put you in a situation where you won't be able to dial out enough negative camber. With my set-up and ride height, I get 2.2 degrees negative camber at static ride height with the camber plates adjusted as far outward as possible. If I lower the car the minimum negative camber increases at the rate of about .74 degrees per inch.

 

I would not make your control arms any longer than 15" or you not be able to adjust your suspension to give you less than 4 degrees of negative camber at ride height. If the control arm is a little short when it is adjusted to minimum length, then you can increase that length with the rod ends. But if it is too long at its minimum length.

 

I'd err on the side of being too short at minimum adjustment. That is why mine are stock length at minimum adjustment. But hey, that is just me.

[JMortensen]

Making the control arm too long can put you in a situation where you won't be able to dial out enough negative camber. With my set-up and ride height, I get 2.2 degrees negative camber at static ride height with the camber plates adjusted as far outward as possible. If I lower the car the minimum negative camber increases at the rate of about .74 degrees per inch.

 

I would not make your control arms any longer than 15" or you not be able to adjust your suspension to give you less than 4 degrees of negative camber at ride height. If the control arm is a little short when it is adjusted to minimum length, then you can increase that length with the rod ends. But if it is too long at its minimum length.

 

I'd err on the side of being too short at minimum adjustment. That is why mine are stock length at minimum adjustment. But hey, that is just me.

Tom was nice enough to respond to my PM, his shafts are 7/8" shorter than stock. I'm not so sure about the 4 degrees neg camber though. I was able to run less than 2 degrees camber in the rear previously and I didn't have the Ground Control camber plates adjusted all the way out. How much camber do you figure adding say .75 to the control arm will add? I seem to remember that the camber adjusting bushings adjusted about 1 or 1.5 degree in the back, and I don't have a set to measure the offset. I know it was different front and rear, but I want to say the front was about .5" offset, and I think I ran them towards the outside of the range...

[Mike Mileski]

I had a pair of Mike Kelly's tubular LCAs and they were about 3/4" shorter than stock, when everything was screwed in all the way. I spoke with him because I am currently making up a new set for myself and he indicated, if doing it again, he would only go about 3/8" shorter. If you lower your car don't you gain negative camber, which means that you would want to pull the bottom of the wheel in, meaning a bit shorter arm, to get you back around zero degrees camber?

 

Mike Mileski

Tucson, AZ

[JMortensen]

I had a pair of Mike Kelly's tubular LCAs and they were about 3/4" shorter than stock, when everything was screwed in all the way. I spoke with him because I am currently making up a new set for myself and he indicated, if doing it again, he would only go about 3/8" shorter. If you lower your car don't you gain negative camber, which means that you would want to pull the bottom of the wheel in, meaning a bit shorter arm, to get you back around zero degrees camber?

Depends on what tire you're running and what you're doing. I'm road racing and autoxing with slicks, so I had figured that I'd probably need between 2 and 3 degree neg camber in the back. That's an estimate and what I actually do will depend on what the tire temperatures tell me.

[tube80z]

The arms I made ended up about 3/8 wider than stock to get the CV axles to work. We ended up modifying the arms to where they are maybe stock or an 1/8 wider. The axles still have some room to move.

 

The rear arms are very close to flat (as in the pics I sent) and you have to watch droop or you'll start to loose free play in the axles. We moved the upper pickup point for the plate out to get camber in check. The hoosier radials don't seem to like a lot of negative camber (-1 in this case).

 

The key as you mention is to find an axle and then build everything around that. And you have to decide if you want a narrow or wide car.

 

Cary

[JMortensen]

I'm struggling with this one. I don't want to run the threads too far out on the rod ends, even though they are 3/4" rod ends... I'm thinking I may go 1/2" wider than stock, and then I can thread the ends out another 1/4" without worrying if needed.

[heavy85]

Can you mock up a LCA out of rebar and eye bolts or threaded rod or wood or something just to get the length you need to prevent CV bind while getting desirable camber? May take a little effort but could save a lot of effort in the end.

 

Cameron

[JMortensen]

Can you mock up a LCA out of rebar and eye bolts or threaded rod or wood or something just to get the length you need to prevent CV bind while getting desirable camber? May take a little effort but could save a lot of effort in the end.

It's the fact that the car is on the rotisserie still that makes it a bitch to check.

[WizardBlack]

Rebar would probably bend, though, no?

[JMortensen]

I went ahead and made the jig 15". I won't have all the parts ready for another week or so, so if you have a good argument to change it I'm all ears.

 

I have another idea which I'm not sure is worth following up. I could move the bottom of the strut back 1/2" or so. I don't think I have room to move it forwards just because the tires would be pretty close to the fenderwells, but back is a possibility. I think this would make the spring rate and shock damping more progressive because as the shock compresses it gets more straight up and down, so I'm thinking that's probably the end of that idea. It is possible with this type of arm to do it and not bind everything up.

[tube80z]

I have another idea which I'm not sure is worth following up. I could move the bottom of the strut back 1/2" or so.

 

Not that it matters on track days but if you autox some people get fairly pissy about wheel base changes. Given that I'd opt to do the change up front for more caster.

 

Are you just wanting to center the wheels in the wheel well or is there some other reason driving this?

[JMortensen]

Not that it matters on track days but if you autox some people get fairly pissy about wheel base changes. Given that I'd opt to do the change up front for more caster.

 

Are you just wanting to center the wheels in the wheel well or is there some other reason driving this?

No reason at all, just trying to figure out what effect it would have and whether that could possibly be beneficial. Or, to say another way, I had the spacers in place from the old control arm when I made the jig. Putting the spacers in there made me consider the effect that the spacers had (keeping the strut perpendicular to the control arm), and also that this is no longer necessary. So then I thought what would happen if I made the control arm so that the rod end was further back?