Date: Mon, 31 Oct 1994 16:03:06 -0800
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: wabbott@townshend.Corp.Megatest.COM (William Abbott)
Subject: Re: Muir "How to Buy a VW" Question
> My question is, he says to check the differential and brakes
> this way: jack up one side of the car, block the
> other wheels, and run the car through all gears (this is on page 25 of
> my "15th" edition), is this possible? Won't the other rear
> wheel try to rotate too, with dangerous results? Has anyone
> done this test?
>
> Mark Janello
> mjanello@umich.edu
> University of Michigan School of Music
Mark,
Short answer. No, the other rear wheel should not try to rotate. If
it does, stop the test and don't buy the car. Any car should pass this
test, unless it has a limited slip differential, and you know what that is,
and want one.
Safety warning. I'd use a stand, not just the jack, when doing
this. But you only need to get one rear wheel off the ground to demonstrate
how the differential works, which is the point of this test.
Long answer.
The purpose of the differential is to allow the two rear wheels to
revolve at different speeds as you turn. There's a crafty arangement of gears
that link the two rear wheels together, but allow them to turn separately.
If you jack up both sides in the back, (engine OFF!) you can turn one rear
wheel one way and the other will turn the other way. Straaaange. Inside the
transaxle, engine power is passed to the differential. One wheel can go slower
than the other if the other goes an equal amount faster- that's why turning one
one way makes the other go the other way. The engine makes the differential
go, and the two wheels split that power however they need to.
I actually did this with a couple of cars I've owned- once on my
Rabbit after changing the transmission, once on the 914 to confirm that
the whining sound was associated with 5th gear, and to a lesser extent, 4th.
On the 914, you can't see the fan housing to turn the engine when
setting the valves, so I would put it in 5th, jack up one side and turn that
wheel with my foot, while watching the distributor rotor. The other wheel
wouldn't move, but the engine would, and that's how I moved each cylinder to TDC.
Bill
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