Folks,

I recently did a C6 rebuild on my 78 4X4. After the rebuild, when I go for a drive, the transmission does not AUTOMATICALLY shift out of 1st.

1. I can shift MANUALLY from 1st to 2nd with no problem, but it never goes into 3rd in D. If it was a system pressure issue, I suspect that I couldn't engage at all?
2. In Drive it just seems to be in 1st the whole time no matter how high the rpm.
3. I checked the vacuum at the modulator and I get 18 in .
4. I have tried every color modulator band and have the black one in now.
5. During the rebuild, I cleaned the governor, so I don't think it would be jammed up since it wouldn't shift even when I first drove it.
6. During the rebuild, I cleaned the valve body.
7. I confirmed the kick down is free.
8. I get a hard shift in reverse and from 2nd to 1st, but when I go to Drive, and then second, I dont notice a hard kick. Could it be that I messed up the orientation of the front clutch seal? (I hope this isn't the case!)

Here is the last couple of things I can do, but I don't know if it can help.
1. Could the intermediate band be the issue if I can shift in manual if it's not shifting hard?
2. The mechanic said it could still be a governor gunked up, but I'm skeptical since it never worked after the cleaning.
3. The filter screen pan from the rebuild seems to sit higher than the original that has a pipe that hangs lower. Is this the suction or the return from the system. If it's the suction I can put the original in.

Is it bad to drive her in manual if I need to? Obviously I'll keep the speed low since I can't get into 3rd.

Can anyone of you wise soles out there help? When I air pressure tested the transmission before the install, everything engaged like it was supposed to and all of my clearances were solid.

*sorry for the long post, but I'm out of ideas*

 

When you did your air pressure tests prior to mounting the valve body, did you do the air pressure test on the governor inlet port, to hear if you got the flabby farting sound?

Valve Body - All check ***** back in place, all valve spools inserted in the proper directions and with springs on the proper sides?

All my trans info is packed away, so I'm going from memory of years ago... I'm pretty sure if you've got Manual 2nd, then your Intermediate Band IS capable of being applied OK, at least via the Manual 2nd fluid path. That checks out the servo and the band and its adjustment itself. It says nothing about whether the governor is being fed, or if the governor is stuck or assembled wrong, or leaking governor sealing ring(s) or valve body shift valve problems, etc.

The filter screen is indeed the inlet, not 100% sure if that is what you were asking.

Sorry, just to cover the bases, I better ask... there IS a thin pin behind the Vacuum Modulator... right?

 

Yes. It's been a month or so, but I recall it sounding like a propeller.Initially, I didn't disassemble the valve body (some gunk may have gone to the governor when I re ran it?). It was in its original state. I then took it out and cleaned it after I discovered that it wasn't shifting.

The servo and band checked out with the air check, but It felt a bit weak...I don't know how to describe it. Is this why my 2nd manual doesn't feel like a thump? I never adjusted the band, I just left the setting in it's original state. Is there a chance that it's slipping?
Is there any way to check the governor? Is the air test 100% accurate, or could it still be bad even if the test checks out?
I'm thinking it could be the pan. If it's true that it picks up at the tube, then I'm pretty confident that the new pan wouldn't be submerged with the normal dipstick marking. The pickup with the new pan is about an inch higher. I just don't see why it would run at all if this was the problem though
The pin is in there indeed. No worries, I can see how it can fall out and be overlooked. I feel pretty confident that the modulator is ruled out.

Also, I appreciate your time. This is a tough one. I'm just praying to god that I dont have to take out the tranny again.

 

Also, when I shift from 2nd to 1st, I hear a thump. When I shift from 2nd to D, I don't feel anything. It feels like it's going to neutral. I can then give it some rpm's and it will pickup. I don't know if that helps.

 

My hand-in-guts C6 experience was on the pre-1978 design, that did not have lipped seals, just square-cut. Behind early high compression 460s. The filter must be different on yours, mine had a rather complicated shaped thin housing held on by many screws, some of different lengths, and the actual fluid pickup point was an open square or something like that in the filter's housing. There was no tube extending down from the filter housing.

If you installed a new intermediate band, you should adjust it. The generic procedure is to loosen the locknut, then loosen the adjusting screw a few turns (don't get crazy over-loosening it, as the band could drop off the band holder if backed out overly far, at least on the earlier trans). Then tighten to 10 ft. lbs. On every Ft. lb. wrench I have, 10 would be way on the bottom of its range, not accurate, so I used an inch-pound wrench set to 120 in. lbs. instead.

Then, the procedure varies depending on the year/application. For mine, it was back off exactly 1 turn, then tighten locknut while holding screw still. Some others have you back it off 1 1/2 turns, need to check your particular application for proper amount of backoff.

Since it sounds like you're not getting beyond 1st gear in Drive, there is another use of the governor that you could try out. The governor helps prevent engine overspeeding when attempting to manually downshift from Manual 2nd to Manual 1st.

How it SHOULD work -- Manual 1st and Manual 2nd have 'holdback", that is, there is no overrunning clutch effect. Letting off the gas in either, the vehicle's momentum will spin the engine, like a manual transmission.
So if someone is driving along say 40 MPH in Manual 2nd, and they move the shift lever to Manual 1st, if the trans complied and did the downshift right then, engine revs would shoot way up, the sudden engine braking effect would slow the rear wheels so abruptly they could go into a spin if rainy or on a curve.

So instead, when they move the lever to Manual 1st, the governor output pressure is looked at to judge road speed. If the road speed is too high, the trans stays in Manual 2nd, until the vehicle slows down enough to the trigger point, then the actual shift to Manual 1st will occur. It will be abrupt and unexpected. The road speed of the governor-controlled Manual 2nd to Manual 1st downshift depends on the vehicle, engine, tire size and rear end ratio, etc. but is in the range of say 17 MPH up to maybe 30 MPH, depending on the application.

So if you were going at least 40 - 45 MPH in Manual 2nd, then move it to Manual 1st and take foot off of gas, nothing should happen until it slows down to the trigger point. Don't do this on a curve, wet road, or with somebody behind you! Seatbelt ON!

If there is the delay until it slows down, then it downshifts, then I think that shows the governor is working, and at least part of the valve body is working.

If the governor pressure is low or zero instead, that would make it look like low road speed, and it might do the downshift to Manual 1st immediately, at the too-high road speed I would think. So if the rears stay locked and it dry skids, head back up to Manual 2nd!

 

Oh, about this... assuming you're moving when you are doing all this, the thump from Manual 2nd down to Manual 1st is the driveline shock caused by mismatched engine vs. road speed via the holdback effect of the Manual gear positions (see above post).

When you shift from Manual 2nd up to Drive, if in Drive it is really sitting down at first gear due to the problem, it will overrun (there is no holdback effect in Drive like there is in Manual 1st or 2nd). Until you bring engine revs up enough to exceed present road speed, only then would it start to pull.

Just another indication that the trans is not automatically upshifting from 1st like it should.

 

i wonder if the downshift mechanism is somehow locked in pass inside the trans?
if you put it in drive, speed up, and then let off the throttle, will it upshift, or just stay in first?

 

First off, Thank you for taking the time. I know that you could be doing a million other things, but you chose to help a stranger. That's pretty impressive!I ended up dropping the pan and swapping the filter yesterday. The transmission shifts a bit harder (in manual) since I've done this, but the problem is still not resolved.
I agree that this needs to be done simply out of principle. I'll knock it out this coming weekend. I was told that if I can shift to second, then the band shouldn't be the problem. What do you think?
So, just to be clear, under no circumstances do I ever get an upshift in auto. I tried to rev it up high in D and let off the gas, and nothing happens.

Today I moved from 2nd to D, at about 35 to 40 and it did as you said. It simply dropped to 1st, but wouldn't react/pull until I have it enough RPM.

When I moved it from 2nd to 1st, there was a short delay, about 1 to 2 seconds max, and the engine would break it to the point that my wheels squealed. I dont suspect that it coasted down. I'm not sure what my speed was as my speedo cable has been disconnected/broken for some time now. It's in the mail.
From what I'm hearing, it seems like it's likely the governor or the valve body? I'm just disappointed that I cleaned both and everything seemed to be just fine when I put them back together.

I hear a sputtering sound every once in a while like either there is air in the system (like slurping from a straw at the end of a soda) or like a ball is rattling around. It happens at first start up while in park and I think I can hear it when I'm accelerating, but it's hard to tell. I'm sure it's not normal, but what could this be?

 

You're welcome! My wife says I'm an "explainer" type of person. I think sometimes she doesn't want to hear it

I agree.


If you were still doing, say, 35 MPH when you shifted from M2 down to M1, and the delay was only a second or two for it to actually drop down into M1, then the very short delay was just the normal command to actual shift time. In other words, there was nothing preventing it from doing the actual M2-->M1 shift at too high of road speed. Leading back to governor, or valve body

One easy thing you can check, just to verify it isn't the problem, is to check the main shift valve positioning. The main shift valve is the one that the shift lever on the side of the trans engages. When in "D" at the column, the shift lever should be solidly in the trans's detent for Drive. Disconnect linkage down at the tran's shift lever. Click the lever through all trans positions to get the feel of it, then leave it in Drive position. Then be sure the column shifter is solidly in "D". Then check back at the trans, do they match? If the linkage is off, it is possible that the column will be in ITS "D" detent, but the trans main shift valve itself will not be centered in its own detent. If the manual shift valve is not centered, then pressures will be off, and I can't say all what may happen. Probably not your problem, but it is easy to check, to eliminate.

No idea, but if its not been heard before...
Only noise I have heard is on first startup after complete rebuild, similar to that sound. I forgot to hook up the vac hose to the modulator. So I think with no vacuum, the Throttle Valve Pressure probably went to maximum, just as if I had the accelerator floored. Which probably would have prevented any upshift if I would have driven it. But I heard the sound and figured it out (and also did not remember connecting the hose!)

You said that you cleaned the governor and valve body. Do we assume that you have a book that shows the governor parts with enough detail that you had a pic to re-assemble to?

And did you take the valve body all apart, upper, lower, separator plate and gasket, plates at the ends of the valve body, took out all valve spools, springs, check ***** etc. , laid them out in order on a clean place, cleaned them, cleaned the passages in the valve bodies, lubed all parts with ATF on reassembly, all spools moved without sticking on re-assembly, on and on? That is a critical job, and easy to mess up. I used a piece of thin white cardboard, which I fan-folded back and forth many times to make a sitting place for each valve bore's guts, all laid out along the cardboard groove in order.
Also, the torque for all of the screws holding it all together is important. Too loose, something leaks internally. Too tight, can distort a valve bore and pinch a spool inside.
IIRC, there were some different-length screws in certain positions so I make a paper template with a quick drawing on it to push the screws through.

Unfortunately, I'm running out of ideas. Might be good to think through step by step everything you've done, to possibly ID an error.
I was cleaning a valve body outside by spraying solvent through it every which way, and after cleaning the valve body, I was back inside looking at all the parts laid out to go back in. Uh oh, there should be a check ball HERE, and there isn't! What? Oh, wait a minute, when spraying solvent there was a "splut" noise for an instant, was that the ball? Oh noooo! I'll NEVER find it! I found it laying in the gravel right where I was cleaning out! Lucky!

 

Torky, thanks again for the detail. I tried driving down the road while moving the shifter up and down in the D position to see if itll move the spool. As you can imagine, no luck.

Im trounleshooting an electrical issue that keeps draining my battery. Im going to get it in the garage and bite the bullet. Im going to pull the governor off once again and clean it. I had used the book to put it together, so it should have been good. I didnt use atf when putting it back together, I just assumed that it would automatically lubricate when flooded at startup. thats the valve and the governor. is there an exploded view of the c6 valve? Ill want to take it apart and make sure this time. Last time i found some pics online, but ill want to be sure.

 

Ok, today I disassembled the governor and found something interesting...

I am missing this cylinder in my assembly. This bad boy likely ran off during the initial build and was swept up with oil dry and saw dust.

Is it possible that this was the cause in the issue? I would think that this mass wouldn't be the issue on shifting. I would think that the mass on the left is the centrifugal mass that looks at output shaft speed. Because the spring is on the left of the valve on the right, I can't see how it would impact the up shift control.

At any rate, I'm sure it does something. Is there anyway to get a hold of this somewhere, or is my better option to buy a new governor?





Governor

 

This is gonna be long!

The part may not have ever been there. The 1970 C6's did not have that spacer. The 1977-vintage diagnosis book I have does not show it there either. Instead, the spring fit directly into the cup on the spool. Put the spool, spring, and the keeper plate back in, then shake the governor housing, while watching the spool. Is there slack between the spool and the spring? If not, if the spring exerts pressure against the spool, then I doubt that anything is missing.

I found the box with my books! The fatter spool governor is the Primary Governor, the smaller one is the Secondary Governor.
"The Primary Governor valve prevents governor pressure from building up under 10 MPH. The Secondary Governor valve functions as a balanced valve to furnish a pressure in proportion to output shaft speed."

"When the transmission is in neutral and the car is stopped, there is no pressure of any kind at the governor. The primary valve is held IN by its spring and the secondary valve is held OUT by its spring.
Suppose now that the driver shifts to any forward gear, but the car is still stopped. Control pressure from the "F" passage (forward clutch) is now routed to the governor. This pressure first acts on the face of the secondary valve's large land and pushes the valve IN. Moving the secondary valve IN opens a connecting passage to the primary valve and control pressure is directed to a dead-end between the primary valve lands. Now we have full control pressure against the outer end of the secondary valve holding the valve against its spring."

"When the car speed gets to about 10 MPH, centrifugal force is enough to overcome the primary valve spring. The valve moves OUT and relieves the connecting passage to sump. With this pressure relieved, the secondary valve can move OUT and crack the control pressure line to the governor pressure port. Now the secondary governor valve becomes a balanced valve - governor pressure acting IN is balanced against the sum of the spring force and centrifugal force acting OUT. Increasing the car speed now will increase governor pressure."

"UPSHIFT - Governor pressure is first directed to the ends of the shift valves. A force is exerted on the shift valves to move them to the upshifted (down) positions, when the force is great enough to overcome the forces holding the valves up."

"Beyond the shift valves, governor pressure is also effective against the ends of the cut-back control valve and the coasting boost valve."

"CUT-BACK CONTROL VALVE - On the way to the pressure booster valve, throttle pressure is routed through the cut-back control valve. Throttle pressure exerts a force on the cut-back control valve that holds it UP against governor pressure.
an important note here -->At some point between 10 and 30 MPH, governor pressure overcomes throttle pressure and shifts the cut-back control valve DOWN. With a light foot on the throttle, the (cut-back) shift occurs at 10 MPH when the governor cuts in; with a heavy foot, at a higher speed. In most cases, the control pressure cut-back occurs before the 1-2 shift comes in.
When the cut-back control valve shifts, throttle pressure is cut off from the upper passage to the pressure booster valve, and the control pressure decreases."

They mention that even if maximum TV (throttle valve) pressure exists (like a stuck TV rod or missing vac hose on modulator), an upshift WILL occur in a road test if driven fast enough. This is to verify that a TV issue is not the problem, so on to the governor test.
This will look for the cut-back of control pressure. It will verify whether the governor is acting like a governor or not:

GOVERNOR TEST
Rear wheels both clear of the ground (jack stands).
Requires a vacuum source with gauge (a hand operated Mity-Vac with gauge is perfect) connected to the modulator input instead of the engine vac line (plug engine vac line off).
Requires a pressure gauge with hose and suitable adapter to screw into the control pressure take-off port at the left front of the case (forward of the control levers).
Hoses need to be long enough, as you are looking at speedo and working the gas pedal and gear shift.

Start engine.

Light Load Test - Apply 10 inches vacuum. Slowly accelerate in M2. Watch for pressure cutback between 10 and 20 MPH. Record road speed at which cutback occurs.

Heavy Load Test - Apply 0 - 2 inches of vacuum. Slowly accelerate in D range. Watch for pressure cutback at between 30 - 50 MPH. Record road speed at cutback. *** Do NOT EXCEED 60 MPH*** this is the usual warning of an non-limited slip rear end, where if only one wheel spins under engine power, it will spin at twice usual road speed, 120 MPH! But the speedometer would read 60 MPH in that case. They worry about tire explosion. Same as some goofus spinning a wheel excessively on ice!

So... the way they test the governor is to look for the cut-back. I might be able to find some typical speed numbers tomorrow, I have a 1970 spec book, may be in there. Either way, this test should show for sure whether the governor is working or not. If there's no control pressure cutback, then the governor isn't working, zero governor pressure to cutback valve.

 

Folks,

The transmission is complete!

There was no weight in my governor to begin with. I confirmed by buying one off ebay for $17. It assembled the same way as mine did.

I cleaned the governor valves on my original governor and lubed them this time. I gave it the shake test and the big valve moved freely. The smaller, pressure valve, moved freely with a small amount of force from a screw driver.

As a side note, its may have been installed originally backwards. Im not sure if it was this or gumed up valves.

I installed it, assembled it, and took it for a spin. Success!

Thanks for everyone

 

Ok,

Everything was going well untill...About 3 weeks ago, I lost pressure in my transmission while driving around.

When I pulled over, I found a substantial leak coming from what appeard to be the pump seal.

I had a slow leak at the cooler that I was getting around to, but I needed the truck for a couple of jobs before I could repair it. I think this leak may have been worse when the fluid heated up. Also, I noticed that my cooler lines were slightly pinched between the frame rail and body. Long story short, I think the fluid got low and hot causing the pump seal to fry. When I put fluid in the transmission, it shifts and drives like a champ until it leaks out. I just tried it out so that I could get it in the garage.

I think my pump seal is toast but my friction should be ok. Does it make sense to just redo the seals, or to do a full rebuild again?

I'm afraid I know the answer...

 

Ok, just read this whole thread, and the original - I feel pretty edumicated at the lowest levels - my issue, not anyone elses. . .

So, I have the same initial symptoms - D won't automatically upshift; Selecter to 2 gets the upshift, but stays in 2, and back to D gets me to 3 but only when warm.

The only tempting contributing/external factors were my son said it was running hot (within the normal range, but at high end), and the neutral indicator switch was replaced by a new mechanic.

I haven't dug in yet, but am hoping the latter scenario is likely - I'll attempt an adjustment of the linkage and switch this weekend and let ya'll know what happens.

Long story to ask this question - is it possible the overheating was related to the "pump" seal breakdown (described above)? Or the reverse - could a lack of proper fluid level contribute to the shifting weirdness?

Finally, thanks all for the prior dialog - truly, makes my newb world much more clear!