C6 shifts without vacuum

[vegas39]

my sons 86 with a c6 has been having a problem lately of shifting way too early. I thought it was a vrv adjustment but upon further investigation and unhooking the vacuum line, I discovered it shifts without vacuum and shifts way to early.
Can someone point us into what we need to check internally on it? Thanks.
He’s parked it for the time being

 

[riphip]

VRV will do this if it is bad or out of adjustment

 

[vegas39]

VRV will do this if it is bad or out of adjustment

I know but when you disconnect the vacuum line, the truck shouldn’t shift and if it does, it would be screaming before it did. His truck is quick shifting with zero vacuum. It’s an internal problem for sure

 

[Macrobb]

On my '87, with the vacuum line disconnected at the trans it wouldn't shift to 3rd. I forget whether it shifted 1-2, or was just stuck in 2 the whole time(in drive - the thing gets sticky at times)

 

[vegas39]

This one shifts as if it had full vacuum applied to it. You take off and 2-3 done. Lol that fast
So it’s doing this with zero vacuum applied
I just need someone who knows transmissions to tell me what might cause this so we can at least have somewhere to start

 

[riphip]

It is going to shift hard with no vacuum applied. Will end up tearing up tranny. Look at my Sig. Plenty of experience with the C6

You need a new VRV if this one will not adjust.

 

[Thewespaul]

Vrv is likely cracked and the diaphragm is stuck in the wide open position simulating full vacuum although you have none

 

[vegas39]

I don’t think I’m explaining this correctly. I have the vacuum line unplugged from the transmission and it’s shifting as fast as can be. Something in the transmission is allowing this thing to shift fast with no vacuum applied.
I discovered this after I fought with the vrv and discovered all was good with it.
I read something that a governer issue could let this happen, I just need to know where to go from here to fix it

 

[vegas39]

Anyone have any ideas? I read about valve body, governer, sticky this, messed up that. Lmao we may just have to find a shop that can look at it. I was hoping someone could talk me through what to check

 

[Thewespaul]

What’s the fluid look like? How long since filter change? I’d start by dropping the pan and giving it a gander if you’re positive the vrv is fine.

 

[vegas39]

What’s the fluid look like? How long since filter change? I’d start by dropping the pan and giving it a gander if you’re positive the vrv is fine.

I’m positive the vrv is fine. This thing shouldn’t shift like mush with the vacuum line disconnected.

 

[vegas39]

I know nothing about transmissions, so probably have to take it in. I know there has to be a few trans experts on this forum. Just wanted their input on what would cause it to do this

 

[franklin2]

I would pull the vacuum modulator out. It has a small pin that it actuates, maybe that is stuck outward, making the trans think it has high vacuum. I think there may be a spring inside the modulator also.

The trans uses the governor (road speed) and the vacuum modulator (load on the engine) and juggles both of these to determine shift points. The diesel setup is hokey at best, it goes more on throttle postion, not engine load the way they have it setup. The factory engineers did bandaid stuff sometimes.

 

[riphip]

Do not loose that pin. Vacuum modulator is a purple stripe

 

[Black dawg]

pull the modulator and pin, apply vacuum and see if it is stuck. I guess the mod could be stuck, could be whatever that pin actuates in the valve body.