[T2] 1978 VW bus "bucking"; SOLVED ? ?

[John Burneskis]

Yes, I believe it was the TS II.

I was able to drive from Key West to Key Largo, Florida, with some success
after I learned the idiosyncrasy of the "bucking".

I have a vacuum gauge at my glove box, reading the manifold vacuum.  I am
able to see this vacuum as I drive.

As long as the vacuum was in it's "sweet spot" all went well.

The "sweet spot" was between 7 - 17 in/hg.

So when I accelerated with a heavy foot, the vacuum would drop below 7
in/hg, and the bus would "buck"..  But when I let up on the fuel pedal, so
that the vacuum would rise above 7 in/hg, the bus would smooth out.


Pulling out from a dead stop, it seemed like a pantomime act!  I would be
jumping all over the place unless I was gentle on the pedal.  Getting from
1st to 3rd was a fun thing (not really).

But wait!  What about OVER 17 in/hg?  What was the issue there?

Glad you asked.  Did you notice that, while driving down the road, if you
lift your foot off the accelerator to slow a bit, what does your vacuum
read?  Why, 22 in/hg, {so that your decel valve opens}.  Vacuum jumps UP
when you are slowing DOWN.

And when you UP SHIFT, the vacuum jumps up to 22 in/hg IMMEDIATELY, and
then I get "bucking".

Ok, but "bucking" at the higher level only until my vacuum drops back into
the sweet spot.  Just 2 - 3 more jumps in the sweet spot and all is smooth.

So the bus runs great.  You just can't start or stop the bus, and cannot
accelerate or up shift.

Now that I think about it, my problem with stalling when coming to a stop
light or stop sign would have been as a result of the bucking.  As I
slowed, the vacuum would go over the 17 in/hg that was the top end of my
sweet spot, bucking would start, and I was only able to prevent a stall by
revving the engine in neutral to about 2200 RPM, while I was braking.

Wild times.

Well, I feel I have solved that problem, and now a new concern pops up: the
alternator light.

Maybe I have too much (or too little} electricity going to the alternator
idiot light.  Or something more 'Burneskis', like, my second battery
receives it's charge (through a relay) when the idiot light goes OUT (relay
is activated by sharing the regulator voltage feed to the alternator
warning light.}.

Over and out.

Barry sends (from Walmart parking lot WiFi in Bradenton Florida, headed to
more beach time and Fishers Buggies on Saturday)