On AAR /T/A E‑bodies: Do you know the effective steering ratio on those cars with the longer Pitman and idler arms used to get “fast ratio” power steering? The standard Mopar power steering ratio of those years was 15.7:1. The faster ratio on those particular E‑bodies would be a lower number. I looked on the I‑net but could not find that data. My understanding is that the AARs & T/As had a stock ratio box and merely used a longer Pitman arm. As I recall, Chrysler “cheated” the arrangement and didn’t even use a longer matching idler
arm but not sure about that. I’m interested in knowing the effective overall ratio with the longer arm and hope to package longer Pitman and idler arms on my ’64 Sport Fury 540 CI Hemi /T‑56 6‑speed restomod currently under construction. I’ve subscribed to and read your magazine for many, many years and highly value your contributions to the Mopar hobby. I retired as a senior manager from Chrysler Engineering in
‘06 after 37 years. Of interest, one of my early student rotating engineering assignments in the fall of 1969 was building the first AAR ‘Cuda program car. Jim Thornton was my boss at the time shortly before he left Chrysler. I also have a numbers matching ‘69 Hemi Road Runner.
You’re right about the “cheating.” Yes, the Ackermann geometry was less than perfect. (By the way, the actual inventor of this geometry, which allows the inner wheel to turn tighter than the outer, minimizing tire scrub, was actually Georg Lankensperger. His agent was Rudolph Ackermann, who patented it in England in 1818 for horse‑drawn carriages!) The Chrysler engineer who created the fast‑ratio power setup, Larry McLeese, was told to spend as little money as possible on the project, so he just lengthened the Pitman arm and moved the stops in the chuck. A standard idler was fitted. McLeese related that the poor Ackermann was only noticeable on very tight turns, so he just let it go, as he was instructed by the bean counters.
Just a heads-up: Fast-ratio power was optional on ’70 AAR and T/A cars, also on ’71 E-bodies (all). It was never standard equipment on any Mopar.
The number that comes to mind is 12:1 (overall), but that’s just from memory, and I have found no published spec on this—ever. So, to confirm (or not!) my fast‑fading memory, I simply measured up a standard‑ratio Pitman vs. a NOS fast ratio arm. (As you know, all Chrysler PS chucks had an internal ratio of 15.7:1, and most platforms had an overall ratio of 16:1).
The standard arm measures 5⅜˝ (effective working length), the fast‑ratio version comes in at 6⅝˝. Therefore, the fast‑ratio arm has a 27% ratio gain, the new overall ratio calculates to 11.7:1. Since my measurement technology was about apprentice-carpenter grade, I’d say the 12:1 overall number is correct.