My M21 in my 66 vert was rebuilt about 6 years ago and has 10,000 miles on it. I bought the car 3 months ago. I have an issue with down shifting. The transmission shifts perfect going through the gears. It does not come out of gear and I have no grinding. It has a Hurst shifter. It down shifts to 3rd and 1st fine. It will not down shift to second unless you put it in first and then pull it back to second. Any ideas on what the problem is? Could it be the shifter adjustment?

Mark

 

You have a shifting adjustment issue. All these transmissions, whether they are Muncies, T-10s or Ford Toploaders have interlock devices that prevent the tranmission from going into two gears at once and that is the problem. On Fords it is a interlock pin that is internal and sits on the shift rail between the 3/4 detent. On Muncies, everything is situated in the side cover which is much, much easier to deal with, especially if it needs to be repaired.

Examine the position of the 1/2 and 3/4 shift rods, levers, and the shifter levers themselves. Make sure something isn't loose, bent or out of adjustment. My guess that the problem is there and not internal. You may want to start at the beginning by using the alignment tool in the shifter itself and check the position of the arms relative to the shifter/tranmission levers.

 

To align the shifter you can use a .25" drill bit for a gauge. Put the trans in neutral and then disconnect your linkage rods at the end with the adjustment.

Slide the drill bit through the shifter case as well as all the internal plates. Then take the shift rods and reinstall them by lengthening or shortening them until they slip in with no problems.

Remove the drill bit and check the trans out, hopefully this will cure your shifting problems.

 

Thanks for your help, an adjustment is sure easier than tearing down the transmission.

Mark

 

See post 11 in this thread for a pic of the adjustment slot. On 64's you could use a drill bit but 65 and up used a flat tool into the slot in the top pic.

http://forums.corvetteforum.com/c1-a...uge-lenth.html

Don

 

I believe all Hurst shifters use a .25" drill bit.

 

Right on John, missed the Hurst part.

 

The shifter is adjusted perfect. I had it checked yesterday by a transmission shop. The problem is inside which is not wotth fixing just so you can down shift. Thanks

Mark