Adjusting Caster via Radius Rods

[Whittie]

Hi All,

 

Just to set the scene: I just put new TTT rear control arms and Roll Centre Adjusters on the car. I previously have fitted TTT Radius Rods.

 

When I took the car to the shop that does my setup they adjusted a fair bit of caster into the front of the car by winding out the Radius Rods. I only have the standard Lower Arms with Elliptical bushes at the cross member to get some negative camber. The arm is now so far forward that the front wheels rub on the guards when turning.

 

I didn't pick up the car personally so I didn’t get to speak to them and get their input so I couldn't ask them about it, but I am going to take the car to them on Saturday and get the full setup measurements just for my own info.

 

Now, when I searched I found reference to a few people with the same radius rods and using them to adjust caster, However, I would have thought that this was a pretty bad way to adjust caster as it will just put some crazy bending forces into the lower control arm and the joint on the cross member. If there was a rose joint on the arm at the cross member end then there would be no binding, but with a standard joint I can't imagine this is doing anything good for it. I just put the Rear Control Arms on the rear because I was using elliptical bushes to adjust toe in and I wore one of the self lubricating bushes out in about 2000k's.

 

I don't like doing things dodgy so if someone with a little more knowledge than me can give their input please that would be greatly appreciated.

 

 

**UPDATE**

 

Just spoke to them and he's wound in 4 Degrees of caster on the front. He rekons the arms looked like they could handle it, but I wouldn't have thought so personally...

Edited May 13, 2010 by Whittie

[JMortensen]

Exactly right!

 

The "right" way to do this is to put the control arm on a rod end so that the angle of the LCA doesn't create a bending moment on the arm or the crossmember. Probably the worst thing to do is use the camber adjust bushings in front, because they don't allow for ANY angularity of the arm, even that which it would normally have as the suspension goes through its motion (caster sweep). When I put adjustable T/C rods on my Z I had poly front bushings and after adjusting the caster to where I wanted it I realized the LCA bushing was bound up pretty tight, so the next mod was to put rod ends on the control arms. I suggest you do the same.

 

FWIW, the rears that we have here are aluminum and delrin and are not self lubricating. I used to lube mine once a year and finally removed them to put something better on, not because they had worn out.

[Whittie]

Thanks Jon,

 

Delrin, that's the stuff. I was told they were self lubricating, or at least didn't nead oiling when I bought replacement bushes but I decided to stop being a cheap-scate and get some proper arms on the rear instead of instaling them just to have them wear out again.

 

I've not had an issue with the caster in the front before, a differant guy at the shop did the adjustment this time and thought he was doing the right thing. Back to the shop it goes

 

**EDIT**

 

I didn't wanna do it cause shipping is gonna be a killer but I'm probably gonna order some TTT front arms. Would have been so much easier to just buy some new front arms when I ordered the rears....

Edited May 13, 2010 by Whittie

[74_5.0L_Z]

If you have aluminum/delrin bushings on the stock lower control arms, then you should be very careful about how much you add caster via the Tension/Compression rod. The aluminum delrin bushing are made to rotate about a fixed axis (the bolt at the crossmember). When you move the outboard end of the LCA forward to get more caster, you need a joint at the inboard side that can pivot in three dimension (a spherical bearing). The aluminum/delrin bearing will bind if the control arm is too far from perpendicular to the centerline of the car. So, if you want to get caster from the T/C rod, you need spherical bearings at the inner pivot of the LCA.

 

Dan

Edited May 13, 2010 by 74_5.0L_Z

[Whittie]

If you have aluminum/delrin bushings on the stock lower control arms, then you should be very careful about how much you add caster via the Tension/Compression rod. The aluminum delrin bushing are made to rotate about a fixed axis (the bolt at the crossmember). When you move the outboard end of the LCA forward to get more caster, you need a joint at the inboard side that can pivot in three dimension (a spherical bearing). The aluminum/delrin bearing will bind if the control arm is too far from perpendicular to the centerline of the car. So, if you want to get caster from the T/C rod, you need spherical bearings at the inner pivot of the LCA.

 

Dan

 

Cheers Dan,

 

That's what I thought but it's great to get another opinion. I have booked in for it to be adjusted back to neutral next week.

 

Tom.

[tube80z]

 

I didn't wanna do it cause shipping is gonna be a killer but I'm probably gonna order some TTT front arms. Would have been so much easier to just buy some new front arms when I ordered the rears....

 

You can go the old school route and used a captured spherical in place of the stock lower control arm bushing. I'd bet someone locally does those and it should be a lower total cost.

 

Cary

[260DET]

Yeh there is not much room to push the front wheels forward to get more caster, adjustable strut tops will help and are not as alignment disruptive. My S30 had spherical bearings fitted to the inner LCA, its not hard to do and works well. Really what the S30 front end needs is some Ackermann and say 8 degrees caster, which you won't get with the standard parts.

 

See you at the Bathurst FOSC in 2011 W

[Whittie]

Thanks for all the input guys.

 

Well due to an unfortunate incident I had some credit with Gabe at Techno Toy Tuning so I thought "Why not?!!" and ordered some Front Control Arms. They are on their way as we speak I believe.

 

Good to hear you'll be there Rich! I'll be in my new improved Zed (see my build thread if you haven't yet) and looking to do a 1:4x lap =D