So the fun begins. You may remember me from such recent threads as "Thoughts on this truck", where I picked up a 1970 250 camper special for the sweet sum of $999.

The truck has been great so far, as in driveable, but this morning things were different. I noticed the transmission (C6, I think) wasn't shifting as I'm cruising down the highway. I gave it some more gas and a rattling/grinding type of sound happened that I haven't heard before. It stopped when I got off the gas pedal. I turned onto a side road and the car still wouldn't shift right. I got it back home and tried to shift into park and then back into drive, took it around my block and it seemed fine. Is there a chance the gear selector was stuck in between settings?

I also noticed tranny fluid leaking from near the oil filter. What would that be? I will take some pics/video when I get home but curious if anyone has heard of this happening before.

 

Yep. I remember the $999. 1st thing is I would check the tranny fluid. The trans fluid has to be warm when you check it. Tranny in Park or Neutral. Engine idling. Does it look and/or smell burnt? Fluid at the correct level? Only Type "F" has been added to it, correct?
A leak by the oil filter would prolly be from the P/S system. Which also takes Type F.

 

Yep, checked it when I first got it home while warm, idling, and level. Was about a quart low so I filled it up. Has held at full the other few times I've checked. Thanks for the info on the power steering. I assume that is the leak I am seeing. I'll get under there after work and take a look. Have you know the gear selector to cause shifting issues? Is is possible to adjust? I think the selector was between N and D while I had my issue earlier, but it's hard to tell. I can drive around the hood later and do some experimenting.

 

I suppose if the stars were aligned right but the shift lever wasn't it could cause it. If the tranny was trying to do 2 things at once. I've never experienced it, but possible. Make sure you "feel" it go in to the Drive detent through the shift lever.
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EDIT
You didn't answer about the fluid. Look brownish or smell burnt?
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A C6 when working properly rolls out of 1st very quickly, give it a lot of gas pedal and it will stay longer. Shifting out of 2nd depends on gas and load. More pedal longer to shift. My guess when empty and not under stress it should be in 3rd by 45 at least or close.

There can be a number of things that can cause one not to shift. Did the truck sit for a long period?


John

 

Thanks for the info, John. The truck didn't sit for longer than a few months at a time as far as I know. Perhaps that was enough to cause this issue?

 

Shouldn't, but there are too many other factors. What does the fluid smell like (fresh or burned)? We can give you a few tips but without access it's a guess.


John

 

Just got home and took it for a drive. All is well. I'm guessing I had the gear selector in a strange in between position that caused the issue. I did notice some dark fluid (bad if it's tranny fluid) dripping from where the transmission cooling lines curve. I'll need to hunt down the source of the leak and it could probably use a transmission fluid change. Thanks for the input. I hope this continues to be a non issue.

 

My first thoughts were a possible tranny vacuum line leaking to the modulator if not shifting right.

This vacuum line comes off the rear of the intake manifold goes down the firewall to the trans and into a little round module can.

And when the modulator diaphragm leaks it sucks tranny fluid into engine that causes it to smoke out the exhaust pipes an not shifting right.

Orich

 

[QUOTE=orich;16664495]My first thoughts were a possible tranny vacuum line leaking to the modulator if not shifting right.

This vacuum line comes off the rear of the intake manifold goes down the firewall to the trans and into a little round module can.

And when the modulator diaphragm leaks it sucks tranny fluid into engine that causes it to smoke out the exhaust pipes an not shifting right.

This makes me worried now....

 

[QUOTE=72CC428;16665286]Easy enough to check the modulator. Put a hand-held vacuum pump on it, pull a vacuum and see if it holds. If the vacuum won't build up then there's a major rupture in the diaphragm. If it slowly bleeds off there's a small hole in it. If it holds a vacuum, it's good.

I was going to replace the modulator on my C-4, when I was working on it recently. I checked it with a vacuum pump and it held a vacuum so, I didn't see any point in changing it out since there was nothing wrong with it.

 

[QUOTE=ultraranger;16665306]I'd think you would have changed it out Steve, as it's cheap insurance of trouble free miles. And not wait till it fails.

Orich

 

[QUOTE=orich;16665457]I have faith it will be ok. --if it should fail, I'll replace it.

With my wife having recently been laid off for four months, that extra $17.00 bucks was better spent elsewhere getting the C-4 back in my truck.

 

Usually if it's bad, You will find tranny fluid when you remove the rubber hose off the vacuum modulator. On C4's and C6's there is an exact length pin stuck in them in the tranny side of the modulator. Putting different length pins in them changes the shift a bit. They are called Throttle Control Rods. If a person changes the vacuum modulator out and forgets this pin it won't shift correctly. It's basic part number is 7A380.
Hey Bill, can you please post 64/72,illustration section A76, page 9?

 

What is the adjustment procedure for that pin in the Vacuum modulator?