C6 transmission whining when hot and losing gears

[viven44]

Update... added more snake oil. Now the Bronco when hot has a persistent whine but no loss of driveability or power. I feel though I am under the gun driving with the persistent whine. Whine = metal to metal or whine = air in the system ? If its metal to metal, that is no way to continue business. If its air, maybe I'll give it more time.

[mat in tn]

they are extra cautious where their potential liability comes in. I have run into numerous cases of them not renting me a car hauler without "enough truck" when I had my excursion I had no issue renting. with e350s I had no issue. yet with my expedition they will only rent me a dolly.

[grumpin]

I have had the same thing happen in the past with U Haul.

They are prone not to rent to older vehicles too.

Never had a problem renting with the 3/4 ton Suburban I used to own either.

[viven44]

On a hunch last night, I dropped the pan. Found so much crap in it in just 100 miles. Filter pick up tube has a lot of debris. So it makes sense. The pump is starving after it runs for a little bit. After I turn off the vehicle and back on its back to normal.

I saw that if you change fluid on a sitting vehicle, the new fluids detergents will wash off buildup and all the years of scale and do just this.

Talking to the previous owner, he has no recollection of ever servicing the transmission.

[Gary Lewis]

That's U.G.L.Y!  But that doesn't mean the tranny is dead.  I would clean it up, put fresh fluid & filter in it with a quart of "snake oil" and give it another chance.  Cheaper than a rebuild.

[viven44]

Indeed!! I am just hopeful this is all the gunk. I have no doubts that it will improve in the short term, but if I am back where I was in another 100 miles, is it fair to call it 'rebuild time' ?

For insurance, I am reusing the 'skimmed' fluid I drained in hopes that all the detergent power from the fluid is used up .... else it becomes a chicken and egg problem

[Gary Lewis]

I doubt it is all the gunk. Some of it is in the torque converter if you haven’t drained it, and it holds about half the fluid.

How much does a full change of fluid cost?  Lots less than a rebuild. Maybe run the skimmed & filtered fluid a while longer then change to fresh fluid if it is acting better?

[viven44]

Good point, I will drain the torque converter again

Fluid change is quite cheap, probably less than $50 including snake oil

[viven44]

I poured back in the filtered fluid. It was about 12 quarts.

I drove it for about 30 minutes. No howling or complaints yet but the transmission does have some gremlins to be worked out (as it always has been). 1-2 shifts are too close together… 2-3 are normal. Doesn’t downshift to 1 unless I am dead stopped. I need the kickdown rod installed ASAP.

[Gary Lewis]

Progress!!!

Is the tranny full?  And you have how much snake oil in it?  It took some driving for one of mine that had sat for years to finally start out in 1st gear on its own.  But it did.

And have you tried driving in Reverse?

As for the kick-down lever, it really isn't needed.  It doesn't come into play except at WOT.

[viven44]

Yes I think it’s almost there, if not full. I’ll do a spirited reverse sometime soon here!

There was almost 2 bottles worth of snake oil in the old mix so it was potent!

Good to know the 1 will work better potentially as it’s driven more.

Big blue 2wd doesn’t have a kickdown and does excellent, but that is the only C6 I’ve seen do that. The 3 other ones I had all didn’t automatically downshift to 1 during slowdown but I didn’t drive them much either after they were woken up, before I sold them.

Personally my confidence level is low, let’s see what an old C6 is made of !!

[Gary Lewis]

The lack of a downshift to 1st at a stop appears to be typical of a C6 that has been sitting around.  I don't know why but it isn't unusual from what I've seen.

Good luck!  

[mat in tn]

the c6 is well known for shifting to 2 very quickly. fine tuning the vacuum modulator will help but wait til it's the last thing.

[viven44]

As unrelated as it may be, within 10 miles of turning the vacuum modulator ~1/4 turn in, I started having this problem. I am pretty sure it was mere coincidence that it happened.

[Gary Lewis]

I don't think 1/4 turn will make enough difference to tell.  But if the screw was already out too far and you turned it out, maybe.

[viven44]

I'm going to start experimenting with the vacuum modulator again. I need to space the 1-2 shift apart a bit more. It is almost not noticeable.

I have been trying to understand what would happen if the intermediate band adjustment was off, does that control the 2nd gear shift point relative to 1 and 3 ?

[mat in tn]

the band is there to grab the planet or drum. the valve body tells it when to do that. based on info from the vacuum modulator. the vacuum modulator is intended to "read " the load on the vehicle by how well the engine regains its vacuum after opening the throttle. in a loaded bog situation, the manifold vacuum is low, and the modulator will hold first gear longer. and with less load the engine will keep more vacuum and tell the trans it can handle second gear. in some cases, a lean carb can have an effect on the shift.

[viven44]

Thanks Matt! That makes sense. By having a good second gear I assume the band is alright.

What does the vac modulator 'screw' actually control ? Does it control the "rod" position or does it work as a controlled vacuum delay device of sorts?

Does the vacuum modulator also control the fluid pressure directly ? I mean by affecting the shift points, there is clearly secondary effects on fluid pressure but I was wondering if I would effect a global change in fluid pressure (while parked, idling, driving, etc).

[mat in tn]

the screw adjusts the preload on the vacuum diaphragm primarily altering the response to manifold vacuum as a result. the rod opens the ports in a variable action as a balancing act. the fluid pressure on one side against spring pressure in the modulator. the vacuum pulls with the fluid pressure against the spring. vacuum assist if you will.
 this is similar in a way to how the reversing valve works in a heat pump to change the evaporator into a condenser and vice versa.

[viven44]

Thanks! That sort of makes sense

I did a 1/2 turn in today. I am reasonably close to comfortable where the transmission is right now. I might do another 1/2 turn possibly as I don't want to lug the transmission with such a heavy vehicle.

I did change the tires to 31 inch and even prior to adjustment, the shift points are a lot better and the steering, throttle response, acceleration.... the 33 inch mud tires were awful.

I want to add a transmission fluid pressure gauge. Is the port right next (left of) the band adjustment bolt the correct place to install a pressure gauge ? Thinking a generic oil pressure gauge/copper lines should do the job but it might be in the way of the shift levers.... I added a tach today and it is already looking like a cockpit... but I really think I want to have a trans pressure gauge as well. A second/alternative might be on one of the cooling lines.