more GTI info (NAC)
Scott_Fisher at intuit.com
Wed Jul 18 10:34:19 EDT 2001
>The current owner installed a short-shift kit (don't know which) relatively
>recently. The forward gears are "vague" but the real worry is reverse...
>car "bucks" a lot in reverse.
Bucking in reverse MIGHT be a tranny issue, but in my experience it's more
likely a transmission or engine MOUNT that allows the linkage to
tighten/release/tighten/release as the car winds up in the opposite
direction to the usual torque loads on the engine/drivetrain. Especially if
the car has a mechanical (cable) clutch, which is normally tight only when
you push on the pedal and loose when you don't. Good engineering designs a
linkage so that normal engine torque while driving twists the engine in the
"right" way to keep the clutch from disengaging while driving. (Better
engineering uses a hydraulic clutch to avoid the whole mess in the first
place, but that's another story.)
Reversing, however, by its nature twists the engine unit in the opposite
direction from that induced by forward motion. If the engine or
transmission mounts are soft or worn, reversing can twist these soft/worn
mounts just far enough that the clutch cable pulls tight when the clutch
engages, causing the clutch to slip and the car to slow down; this in turn
reduces the twisting on the soft/worn engine mounts, which loosens the
cable, which causes the clutch to grip, which causes the car to go, which
increases the twist on the mounts, which tightens the cable, which -- you
get the idea.
Audifans who know me from Another List Far Away (heh) might recall my
description of another car I owned, on which this was the problem, as
resembling an overamorous kangaroo when reversing. Same problem, different
engine orientation. Oh, and I've previously owned two GTIs, so I've had
some experience of what Doug speaks.
Internal transmission woes usually result in a continual absence of motion,
or in the car popping out of gear, rather than the on/off bucking you
mention. Even if the shift linkage were worn, you'd be more likely to get a
tendency for the gear lever to pop into neutral when driving in reverse (as
in one of my cars from Another List Far Away).
And as several other people suggest, putting a short-shift kit on a car with
worn bushings will result in a car that shifts short and sloppy. So this IS
a problem, but still less expensive than a transmission rebuild.
Oh, and by the way, this rocking on soft engine mounts can also lead to
premature exhaust-system wear as the downpipe is continually flexed between
the header and the main exhaust system. VW has used some pretty clever
slip/flex joints over the years, but it's another reason to check the engine
mounts (and another thing to look at -- the exhaust) before your nephew
actually agrees on a number to put down on the check.
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