C6 Transmission Issues

[dakotajeep]

I got the brakes fixed and took the rig for a drive of more than a few feet. It has fairly erratic shifts.

For example:

I have to run the shifter from D to 2 and back to D in order to shift into D. It also downshifts into 2nd kinda hard when I don't think it should.

I have heard of having to run the shift from 1 to 2 to D in oder to change gears but it seems just the movement of the shifter seems to help....might have to drive more to get better details of the issue.

Thank for any thoughts!

Thad

 

[icanfixall]

Your C6 needs imput from the vacuum modulater valve on the drivers side of the injection pump. Its adjustable. Also the throttle linkage has some kick down rods that helps the trans drop a gear. Many years ago it was called... Passing gear.... You step down on the peddle and the trans shifts to a lower gear and your off to the races. And boy o boy can those old v8 gassers scream up in rpms when this happens... Was a fun time back then....

 

[dakotajeep]

I failed to mention that the tach is intermittent ie it reads low if at all...

How essential is the tach and the sensor in the rear axle to proper shifting in the C6?

Thad

 

[IDIDieselJohn]

The C6 needs 0 sensors to operate. It is fully vacuum operated, no electronics, nothing.


Try shifting it manually to see if it shifts normally manually. Could be a problem with the VRV.

 

[Shadetreemechanic]

I do not think the tach is relevant at all in the c6. It is getting its signals from the two actuators icanfixall mentioned.

 

[dakotajeep]

Alright, i will give it a look in the morning.

Thad

 

[dakotajeep]

Well I just got around to test driving the beast again. It needed a little fluid...added a quart and still barely showing on the dipstick. I feel dumb now. Still a little more than a nickel width below the hash marks.

It won't shift to 2nd until 35mph or I manually shift it. With 4.10 gears it is winding up pretty high (not sure without a tach though). When it finally does it shifts fairly hard into 2nd. It won't shift into D until 45-50 mph.

Downshifts aren't anything to note.

I have not played with or tested the VRV at this time. If I had a vacuum tester I would have.

Where is a good place to pick one up? I have no idea if a regular parts store would even carry one (vacuum tester).

Thanks
Thad

 

[OLDBULL8]

There is a short rubber hose where the hard line connects to the tranny, they can be cracked and leak the vacumn, if it looks old replace it. Here is how to check/adjust the VRV. You can use a 1/2" bolt with a little electrical tape wrapped on it for the gage. Tape is .003 thick so it would take five wraps to get .515"

You must be registered for see images

 

[dakotajeep]

oldbull8,

In the link you sent it states that its only for the C6 with the 7.3? Mine is a 6.9. Never knew 7.3 with C6 was a combo...I guess I thought all 7.3's had the E4OD if they had and auto.

Thanks
Thad

 

[OLDBULL8]

I'll check tomorrow see if there is a difference in the shop manual. I wouldn't think so .

 

[icanfixall]

The trans couldn't care less what ingine its connected to. &.3 or 6.9 it wont matter. The only real differance between these two engines is the displacement. That wont change what the C6 sees.

 

[david85]

As John mentioned, the tachometer has no effect on the transmission.

The the only external inputs to the transmission are the vacuum regulator valve on the injector pump (your foot),
the shift lever,
and the kickdown rod.

Manual 1 allows 1st gear (not sure but this may be automatically delayed if a downshift is too high),
Manual 2 forces into 2nd (even at 0MPH - this is normal)
D allows all the gears to function automatically

The transmission is acting like the engine is at, or near full throttle all the time (which is often the result of a vacuum leak, or no vacuum at all).

The system works in such a way that the LOW vacuum signal means HIGH power settings on the engine. So LOW vacuum sends it into late, hard shifting. You can almost think of it like a C6 Version of the overdrive light blinking and I limped my C6 home a few times when the alternator belt flew apart. Whats nice about this, is the transmission goes to the safest end of its operational map in the event of a signal failure. Unlike the AOD for example, which defaults to early, mushy shifting if the throttle cable snaps.

I never bothered with the vacuum gauge for adjusting the VRV and just moved it to where I wanted it.

Just mark the current location before you change anything, and before you do that - check for any vacuum leaks. Unless its been tampered with, you likely have a cracked line somewhere. Don't suppose your power brakes are feeling a bit weak, are they?

 

[dakotajeep]

David,

Actually, the brake sdo feel mushy....will check the vacuum this weekend for sure!

Thanks for the info!

Thad

 

[mariner45]

It might be well worthwhile to replace the modulatr - the bit the vacuum hose fits on in the tranny. They are easy to change and are not too expensive - maybe $50 or so - the new ones come adjustable.

I had what I thought, were a few problems with my C6. I renewed all the rubber vacuum lines and put in a modulator and the improvements I got were very pronounced.

HTH

mariner

 

[dakotajeep]

Problem solved...

It was the VRV but not as you might think. The 'to transmission' or lower port on the VRV was broken off and was stuck in the rubber piece that slides onto the VRV. I pushed it out of the rubber piece and super glued (hold your flamings back!) the plastic back together and that was it. Most likely it was broken when the previous owner was working on the injector lines!!! Otherwise its kinda out of reach for most things to hit it.

Test drove it and it shifts into 2nd at 15-20mph depending on throttle application. It shifts into D at 25-30mph which is slightly early but it works for me since I am not wanting to rev the crap out of this thing.

My only real question is that it shifts real smooth now and I know on an E4OD thats not a good thing. Just curious if I should adjust the VRV now? (yeah the right answer is to vacuum test it)

Thanks guys so much!!!

I am loving my $400 rig more and more each day. Just installed a $40 window regulator and the drivers window works like a champ.

All I need now is to install my spare set of tires (with alignment!) and setup the glow plugs since they are not working at all...next weeks project.

Thad