I have a Tremec T5 in my 65. I replaced/rebuilt everything related to the speedometer. It worked great for almost 2 years and 5000 miles. Well recently it started bouncing some at highway speed.

I'm having a hard time believing that anything wore out this quick. I did check the speedo gear and it looks fine, its not chewed up or anything.

Does anyone have any suggestions?

I also noticed that some of the speedo gears have a longer snout on them. What is the purpose of this?

 

it's the speedo cable. make sure there is no bend in how you routed it, keep it as straight as possible. disconnect at speedo and pour a bit of gun oil down there (the cable). should cure it

 

I put drop of wd40 on indicator bearings and C4 fluid in the cable a few years ago. Still runs smooth today. Not sure what maximum bend of cable is.

 

The longer snout on the gears is designed, IIRC, to damage them directly unpon installation so you have to buy another one and try to figure out what happened to the last one. I guess its a marketing strategy....

For example the 21 tooth purple gear (I think that was the tooth count...it is purple though) has the long snout on it. This snout will actually butt up against the t5 internals on installation. The plug that seals into the trans does not fully seat and finally when the bolt is torqued down the entire load forces that snout into the t5 case effectively jamming the gear so that it cannot spin and the gear is destroyed instantly by the drive gear when the two attempt to spin.

The fix is to cut the snout to the same length as the original gears.

-Gun

 

Back when i worked in the dealership, i saw car only 2-3 years old get the speedo bounce, so it is entirely possible that its the new parts wearing out. I like the others said most of the time its the cable. I did see a few that it was the gear. On these i saw small ridges on the shaft, the ridges were so small i almost couldnt feel them with my thumb nail. The shaft had a very slight oval shape to it.