car slams into reverse. help!!

[stcos85]

Just got the car on the road after a year and a half laid up.

When I put the car in either of the forward gears it is fine but when I put it in reverse it really jolts the car with a big thud. Don't know how else to describe it.

I have a copy of the bentley manual but this issue is not described in the fault finding section.

I haven't touched it yet as I was hoping someone could explain on here in simple terms what I might be able to do to cure it.

Any help would be appreciated.

[bookwus]

Hiya stcos,

Most likely you have the small hose from the control valve hooked up to the wrong port on your carburetor.  In this configuration the vacuum signal from the carburetor is so strong that one is unable to even adjust it softer with the control valve adjustment screw.

I would suggest that you try drawing the vacuum from another carburetor port.  Ideally, what you are looking for is a port which draws its vacuum from above the butterfly.  It's sometimes hard, just looking at the outside of the carb, to tell from where a given port is drawing its vacuum.  If you can trace the vacuum source for a port by studying the carburetor body - fine.  Otherwise, simply try moving your small vacuum hose from one port to another until you notice a difference in the shift action.

When you do find the correct vacuum source you will definitely notice a difference in the shifting action.  And from that point you may wish to refine the shift action by turning the adjusting screw atop the control valve.

[stcos85]

thanks for the advice. I will take a look one night during the week.

How many ports do you think I will be able to find as I am not sure exactly what I am looking for other than a brass pipe?

[bookwus]

Hiya stcos,

You know, that will really depend on the type of carburetor you have.  I think (DON'T take this as gospel) you should probably find at least three on most 34PICT3s and 30/31s.

Yes, you DO want to look for those little brass outlet ports.  Unused ones will be sporting a plastic (usually black) cap.  Don't be fooled by the position of the port on the body of the carb.  That is, some think that if the port is located higher on the carburetor body then it must draw its vacuum from above the butterfly.  Not necessarily so.  Try them out till you do notice a difference in the shift action.

[68AutoBug]

Hi,
Yes, I agree with Mike... as i have this problem all the time in Low and reverse... although its probably worse in reverse...
it really thumps into gear... I adjusted the control valve on the LHS of the engine bay,
but all it did, was made it thump slightly slower than before...
As Mike said, the pipe being used for the control valve may be the wrong one... it may have been a vacuum advance pipe...

My problem is a weber carburetor.. with too much vacuum...
I have to drill etc another port in the carby one day...
and OK on the port location Mike, I never really thought of that before.
that the location of the pipe, isn't always the location of the port in the throat of the carby... I'll keep that in mind...

Best of luck..

Lee Noonan  68Autobug  Australia

http://community.webshots.com/user/vw68autobug