On Sun, 29 Jun 1997 11:34:25 +0800 "Jerry Causey" <reecau@whidbey.com>
writes:
>I rebuilt the rear leaf springs on my '67 MGB GT a couple of years
>ago, and in
>the process, modified the rear geometry, a la Fred Puhn (How to Make
>Your Car
>Handle). They are de-arched, with extended rear hangers, and Koni tube
>dampers.
>This left the rear sitting a bit over 1 inch high. I just recently
>bought and
>installed a set of 1.25 inch lowering blocks which levelled the rear
>of the car
>perfectly, but introduced a very unsettling movement of the rear end.
>When I
>suddenly let off, or jump back on, the throttle the rear end twitches
>(to one
>side off, other side on). Nothing appears to be loose or incorrectly
>installed.
>Could this be due to the change in pinon angle caused by the lowering
>blocks,
>and will shimming one end of the blocks to restore the original angle
>eliminate
>the twitch? Any other suggestions for a cure?
>
>Regards,
>Jerry Causey - 1967 MGB GT
>Whidbey Island, Washington, embraced by the Puget Sound
>(fairly close to Seattle, and the rest of the USA)
>
Jerry,
The cause of the darting to one side on acceleration and the other on
deceleration is the rear axle is not aligned to the chassis. That is, the
axle centerline is not 90 degrees to the center line of the car.
Imagine if you will a simple axle across the centerline of the car. If
the axle is not correctly alinged, when you apply thrust (mash the
throttle) the drive force instead of being parrallel to the center of hte
car, forces the rear one way or the other. Conversely, when you let off
the drag is in the opposite direction.
Correction is simple. Loosen the U-Bolts on each spring and using a
small "bottle jack" on the side that is more forward, between the axle
and the bulkhead (base of jack against bulkhead) move the axle slightly
reaward. Retighten U bolts and try it out. Repeat as needed.
Or the shorter, but slighlty more expensive solution. Take the car to
a good alignment shop, one with a 4 wheel alignment machine. Tell the guy
you want to check the "Thrust" alignment. Most times you'll get a neat
print out telling you which way the axle is off. Adjustment is as above,
but with fewer repeats.
Been there done that. The Midget took 2 trys to get is right, the B only
one.
good luck
Rick Morrison
72 MGBGT
74 Midget
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