Rear Caster Alignment SPEC?

[TexasPettey]

I've had issues with the fit on my delrin bushings. I ended up needing to put in a number of shims to get the fit right without play. I'm going to take the car into an alignment shop to see how far off the alignment is. I've got specs for everything except for the rear caster. What are those specs?

 

[dave6666]

You don't say what vehicle. My '01 GTS...

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[TexasPettey]

'95 R/T. I use it for both track and street.

 

[dave6666]

My software don't go there.

Sorry.

 

[RAYSIR]

Tell me how you measure rear caster when caster is a swing on turn in and out measurement. It is the measurement of the upper to lower ball joint front to rear and measured on swing.??? Dang, been doing alignments 30yrs and never heard of this one. Please enlighten me.

 

[TexasPettey]

Tell me how you measure rear caster when caster is a swing on turn in and out measurement. It is the measurement of the upper to lower ball joint front to rear and measured on swing.??? Dang, been doing alignments 30yrs and never heard of this one. Please enlighten me.

I had the same discussion with a friend of mine who owned a shop for years. Neither of us could figure out why there is a spec for rear caster, yet it exists.

 

[got one]

Chris, do you have a shop manual? IF not, then come over, I have one that should cover thsoe numbers.

 

[GTS Dean]

Tell me how you measure rear caster when caster is a swing on turn in and out measurement. It is the measurement of the upper to lower ball joint front to rear and measured on swing.??? Dang, been doing alignments 30yrs and never heard of this one. Please enlighten me.

It is practically impossible to do a conventional caster sweep on the rear of a Viper. The only way to carry that out is to pop the toe link, install the donut spare and go with maybe 10 degrees instead of 20. Then, there's the whole issue of the halfshaft pivot axis to consider as well.

Dodge does indeed have recommended caster settings for the rear, and they vary by Gen. The Viper Service Tools include an inclinometer that attaches either directly (via magnet) to the Gen1 knuckles or by means of an adapter bracket (Gen 2&3). The Gen 1 unit is a simple gravity inclinometer. The later models are electronic and feed directly into a DRBIII with an inclinometer/gas analyzer module on the back. The bottom line is that a dealer visit will be in order.

If you do an alignment and don't get caster at least EVEN on both sides, you WILL have strange handling on power-down out of curves.

 

[GTS Dean]

I've had issues with the fit on my delrin bushings. I ended up needing to put in a number of shims to get the fit right without play.

I hope you spaced the shims equally to center the wishbone in the frame ears. That will DEFINITELY affect the caster.

 

[TexasPettey]

I hope you spaced the shims equally to center the wishbone in the frame ears. That will DEFINITELY affect the caster.

Nope. I wish that I could have. Unfortunately, my ability to fab is pretty limited. The manufacturer only sent me two shims, one for each side up front. He hasn't returned any of my calls over the last couple of weeks. So, I had to fab with what I have available at HomeDepot, etc. There was only minimal gap on the bottoms, so I'm hoping that the effect is minimal. It's far from an exact sience. The big gaps were on the upper front a-arms. I figure that that's one of the more adjustable areas. I can also easily move the shims around or add another shim on the opposing side. I'll find out when I get to the alignment shop.

The big issue I have is that I don't know what position the a-arm was in when the alignment was done. So ..., even if I evenly space it, I could still have messed up the alignment. This whole issue has me quite disgruntled: $600 for bushings not built correctly & install that didn't catch it. On top of that, the ends of the frame ears were bent during the alignment process.

 

[TexasPettey]

Chris, do you have a shop manual? IF not, then come over, I have one that should cover thsoe numbers.

I may take you up on that. I've got a shop manual on the way, since I'll be doing more of my own work.

 

[RAYSIR]

What I'm thinking now is that they are measuring the centerline, or stud, between the upper and lower ball joint. Seems you would have to have both wheels off and measure the degree the upper ball joint is tilited rearward from the lower to get the positive caster. Upper would be to the rear of the lower 1 degree. I am going to talk to my freind who is a Hunter rep here and see if he can find a better answer but I think this is it and it is not a swing angle but rather a measure front to rear of the ball joint angle from 0 being striaght up and down.

 

[GTS Dean]

I would guess that the newer infrared target-based 4 wheel alignment machines might be able to determine the caster angle by interpolating the movement from droop to jounce, and looking at the effective wheelbase lengths side-to-side.

A determined individual could spend hours trying to do it on his own, or with the help of a neighborhood alignment shop. I've thought about it a LOT, and decided it was more important to cultivate extremely good relations with my Dodge dealer to be able to borrow their specialized tools over the weekend. Despite having trained Viper techs for 13 years, my dealership has never done a single Viper alignment, but I've probably done 40 in my garage.