Pretty basic problem, my C6 won't shift down at a stop. I can drop it down to 1st, and it shifts up to 2 and 3 fine, but I'm waaay up high in 3 every time I take off from a stop.

The kickdown linkage isn't hooked up, but the vac modulator is.

What are all the possible causes of this problem?

AleX

 

Even though you know the vacuum modulator is hooked up, do you know it is working? Lack of vacuum or I believe they can get transmission fluid in them and will make them act funny.

 

Well, I guess I don't know that the modulator is functioning, but I can tell you that it's new, within about 6 months (when I completely overhauled the trans), and that it worked fine before i took the truck off the road at the end of summer to replace the engine. Also, the engine pulls about 21 (mm in Hg???, whatever the units on a vacuum guage are) at idle.

 

I can downshift manually aaaanytime no trouble at all. It's a combination of vac modulator and governor that downshifts you at a stop right? Is there anything else?

 

Sounds like the Governor is sticking.

Josh

 

My idle is also pretty high at the moment, about 1400 in park, and about 900-1000 in drive with brake, could that be an issue?

 

No, my 428 idled, for the most part, 850-900 in gear.

Josh

 

Just back from a second test drive. Let the whole truck get nice n cold for this one, to see if that made any difference, and no, it still didn't downshift, not even the first stop sign, about a half a mile down my street.

Going to pop off the hose now and check for vac at the mod., and see if there's any fluid flowing through the mod. at the same time.

If I come to the conclusion that this is a governor problem, I can't deal with that right now timewise. Am I doing any damage whatsoever by shifting it full manual?

 

Be sure to check the condition and color of the transmission fluid. It can tell you a lot about what's going on, specifically if the clutches are burning up.

I would lean towards the governor, and then the valve body. I highly doubt you're problem is the modulator. However, it would nice if it is, cheap and easy to fix.

Josh

 

I had the same issue so what I did was pull the tail shaft(about 4 quarts in here) and take the govenor off and cleaned the piston up with some very fine emery cloth and pour some fresh transmission fluid in it and bolted it back on. What happens is all the junk you would see in your pan the fine metal gets into you govenor and then the piston won't move proper causing it to not downshift do to the piston being sticky takes about 2 hours at the most to clean up. I would also drop the pan and filer and change the fluid and put some lucas trans conditioner in it and with in about 100 miles she will be shifting nice.

Can you hurt it if you continue to drive it? Possibly but as long as you shift manually you should be fine you just don't want to be taking off in second all time as it will heat up your transmission. Also you can rent a video on youtube made by Ken Collins at bad shoe productions which will show you how to do a full rebuild on the C-6, I purchased it recently and it is a great video.

D

 

Ya, I have the BadShoe video, liked it very much, and I have a 4X4, but that is true, I could access the governor fairly easily actually, by popping of the T case. I'll think about that.

AleX

 

I'm having the same issue. I thought it was the modulator, replaced it.. adjusted it several times,,it's not solving my issue... From what i'm reading, I think i'll have to take it to the shop.
I don't think I can handle such a job..for it to down shift while driving I gotta floor it or manually down shift it.
If i am at a dead stop it'll down shift.. At times when i let off the brake, I feel a thump like slop in the steering / front end, But i think that it's down shifting once i start to roll a tad.
whatchy'all think ??

 

accidental double posted.. Delete this one..