I have finally found time to offer some comments on this thread
The rack ratio and therefore lock-to-lock count is governed by the count of
teeth and the distance between the lock stops. Triumph Herald, Spitfire,
TR4-6 and Saloon racks have either 6 or 7 pinion teeth as standard. The
factory "quick racks" such as in TR's all have 7 teeth. Within the 1 length
of rack case used on all these cars, there have been 3 different rack
lengths, 5 different inner tie rod lengths, and 3 different lock stops, all
of which cater for differing chassis widths etc. If the rack length is
randomly changed so that the ball pivot on the tie rod no longer lines up
with the wishbone pivot, then bump steer is sure to occur. All
right-hand-drive TR's I have worked on, have a 650mm long rack shaft, which
I believe is identical to left-hand-drive TR's, as the pinion & case were
changed, not the actual rack shaft. The TR4 used a 170mm long tie rod,
whilst the TR4A, TR5 & TR6 went to 180mm.
According to road test data of the day, the TR4 originally had 2.75 turns
lock to lock and the later TR's, 3.25. The Car & Driver road test of the ex
Sebring Kastner TR4, gives lock to lock of 2.5 turns which may have been
achieved by thickening the lock stops as race cars rarely need the full
rack stroke for sharp u turns. Perhaps Kas still has some memories of what
was done and can comment further. The 6 & 7 tooth pinions can be freely
interchanged allowing "slow" racks like in saloons, to be uprated cheaply.
Some experimentation indicates a custom made 8 tooth pinion will not
successfully mesh with a factory rack.
Anyone wanting to sell me a "quick rack" for a TR would need to provide the
rack length, tie rod length, rack & pinion count, before I would
contemplate it.
Hope this proves useful
Terry O'Beirne
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