Pontiac Owners Club UK

The gear change has been progressively getting worse recently. Shes basically not changing up and when she finally does, it almost snaps your neck! The revs build and build and sometimes it wont even go into second gear. If i come off the throttle and back on again, its as if im in neutral and she just revs.

I can get through gears by starting in Low for first, then into Sport for second then Drive for third, but thats only if the revs are high enough for it to change. Recently returned from the US so made another visit to Summit Racing and bought a filter kit for the box. My mate changed the filter and oil last weekend but its not much better. Did a bit of searching on the interweb and all forums point to the Modulator Valve being the cause as this is what tells the box to change gear. So got a new one on its way from Summit as we speak. Fingers crossed this cures it.

Paul.

Have a word with Richard Alders of Alders Automotive, a club sponsor, sure that he will be able to assist.

There are 3 things to check here and one of them is the modulator. However, the governor is what control up shifts on the turbo hydromatic box - if it is sticking it can cause late shifts and harsh shifts. It's located on the drivers side of the transmission at the back near the output shaft. Remove it and see if the valve moves freely on the spool shaft. You should be able to hear it rattling if it's free, there is also a plastic gear on the end of the weighted shaft and it can get worn out - will be easy to see if it is worn out.

Thirdly, the kickdown cable can cause issues if not adjusted correctly. If it's in the downshift position when it shouldn't be then it will cause the transmission to shift late, but I doubt it would cause neck breaking shifts, only late shifts. My money would be on the governor first and modulator second.

Governor....

Cheers guys.

Going for the modulator valve first as most Chevy forums point to that. If I give it the berries then it does shift up which they suggest is not the governor as it would never shift at all if it was. Also kick down works fine too. Good news is the mod valve has arrived at customs so hoping to have it here in the week. Will keep you updated!

Paul.

Happy days! It was the modulator valve after all.

Bought the adjustable one so after a few adjustments and test drives, she's changing gear spot on.

Paul.

Well done! Cheap fix is always good.

Well would you believe it! Turns out it wasn't the Modulator Valve after all.

After cleaning her yesterday, I took her for a short spin around the block just to check and it was back to normal, revving all the way up to 4000 rpm before she would slam into second and break your neck! So had another look today and thought to myself, where does this vacuum pipe go to? So found where it gets it feed from the inlet manifold and look what I found!!! Air filter housing was crushing the rubber pipe blocking the vacuum. Fitted a new straight piece of pipe and spot on! Always something simple!!!

I'm one happy Taffy!

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Paul.

That's a nice and easy fix! but at least you know the whole vacuum side of things for the box works ok now.