Dashpot Replacement

[oneohtwo 8]

I have been looking for a replacement for the dashpot on the throttle body recently as mine is knackered, and I am sure no longer properly doing it's job and contributing to poor running. I imagine this is the case for a lot of people given how old they are, but unfortunately the VR6 version is NLA.

However, by chance I stumbled upon a likely replacement from a Passat B3 and T4 that is still available:

Dashpot for VW T4 (volkswagen-classic-parts.com)

Part number is: 037 129 103

So I took a punt on it. It is not 100% identical, so not a direct fit, but the actual dashpot body appears to be identical to the Corrado version:

Corrado on the left and Passat on the right. as you can see the central section i.e. the actual dashpot appears to be identical. Same shape, diameter and length. The differences as I can see are twofold:

1) The plastic cam at the tip is a different size and shape. It is slightly longer which is OK as you can just wind it back a bit to get the correct contact. The end also is narrower and not flat so the contact patch isn't quite as good, but it still seems to be fine. I didn't risk trying to swap the caps over, but someone might want to try this!

2) The thread is different. The thread pitch on the Corrado version is much finer, not sure what it is exactly, whilst the thread on the Passat is 1.25mm. This is where you will need to alter the bracket on the throttle body.

This is fairly straightforward however, and all it requires is the old thread drilling out and Helicoil/V-coil inserts instead. It's about a 1.5hr job all in all. The inserts needed are:

M8 x 1.25 x 1D   (e.g. M8 x 1.25 x 1D V Coil - Fits Helicoil - Wire Thread Repair Inserts (QTY 10) 4022835072119 | eBay)

The 1D refers to the length of the insert, i.e. 1x diameter. The bracket is quite thin so the regular inserts in the Helicoil kits will be too long, but you will need the rest of the kit with the right size drill bit and tap, plus the handy installation tools. 

Caveat emptor: Once you start this process there's no going back... Once the thread has been cut for the Helicoil insert the old dashpot is done and you can't put it back. Make sure you get this bit right.

Once this is done though, hey presto:

Brand new dashpot!

I took a video of how the new compares to the old in terms of operation, but it hasn't uploaded. I will try and post that when I can but namely the spring back is almost instantaneous on the new so that it pretty well stays in contact with the roller constantly, where as the old was slow to respond. The damping is also stiffer.

It has had an almost transformational effect on driving the car at slow speeds, making it a lot smoother, particularly in first and second When you come off the pedal there's no longer the sudden jerk of deceleration. Gear changes are also smoother.

I say almost transformational, because whilst the stalling when coming to a stop seems to be fixed I did still get the odd occasion where the revs drop to almost stalling. I think this may be because I haven't reset the ECU so it hasn't got used to this, so I will do this and hopefully will all be good.

 

 

 

[fendervg 33]

Hey, that's some great research and tinkering there - this could be the solution. Will have a good read. Thanks for the effort and the sharing!

[Cressa 44]

Great bit of detective work 👍

[oneohtwo 8]

No problem. Wasn't much detective work involved... I can't remember how I stumbled upon it but think I was just googling "VW dashpot" and that popped up looking almost identical so I took a punt! Seems to have worked for me so hopefully it might help others out as well.