Working on my daughters 70 swb 390-C-6, and have noticed, when starting of in 1rst, you can increase the speed up to 10-15 mph, let off the gas and the transmission doesn't release, it actually starts barking the tires and attempts to stop the truck??
It doesn't do this if I start off in drive, only in low 1,
Could something in the tranny be stuck?
I've checked the fluid, It seem a little dirty, but not burned or terribly discolored.
I'm considering a tranny flush at our local oil change shop, but if this doesn't help, where do I go next????
Tom

 

the reason that it only does this in first is b/c the trans. stays in first therefore using the compression of the engine to slow it down no ther isnt anything wrong with it

 

I disagree. My C6 operates in 1st gear just like it does in Drive. Only difference is it doesn't upshift to second. It still lets the truck slow down and stop with the engine running without stalling or any hopping at the rear wheels.

 

yes it will run just like in drive only it will stay in first. but like i said earlier if u get the motor to lets say 2500 on a high comp. high displacement motor the motor wants to slow u down when u let your foot out of it this is normal. depending on gearing, traction, and type of suface that you are on when u do this depends on the type of reaction u get out of your truck. its fine

 

Let me clarify, this is a new problem, It didn't use to do this.
I understand compression, and the effects on the transmission.
This isn't the case.
Yesterday I drove the truck, and if left in first gear, any decelaration locks up the rear tire, if traveling over about 5 mph.
Tom

 

The problem may further on back. May be the ring or pinion binding in the rear. Have you raised the truck and free wheeled the rear end? Just a thought.

 

Mmm I am a bit rusty on auto trans theory but it could possibly be a sprag or one way clutch not releasing properly. Could be a sign of bigger problems on the horizon too. But thats all speculation on my part.