1985 6.9 C6 problems HELP!!

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Mar 4, 2013 | 02:59 AM

weezer4117

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1985 6.9 C6 problems HELP!!

1985, 6.9,l 4x4, unknown miles

The other day my transmission started to loose power, ended with no power. I could feel the truck wanting to move and it would but not much. pulled it into low lock and seemed to move more but still not rite. Fluid level was good. Dropped the oil pan, fluid was black/red didnt really smell burnt (unknown age of fluid). I have suspected that my vacum pump was going bad as i could hear hissing while truck was running, does have noticiable vacum to the C6. Would a vacum pump failure cause this? Im afraid the C6 is fried but I really dont know how to tell based off of these symtoms. I know the words tranny fluid and black dont go well together but i have SOME hope!!! Please help advise based off of these symtoms... Thanks

Mar 4, 2013 | 06:16 AM

hairyboxnoogle

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Vaccuum will cause it to not shift right, but it will still move just fine. Sounds to me like you have no line pressure, but i dont know my **** from a hole in the ground when it comes to autos.

Mar 4, 2013 | 10:40 AM

84-6.9L

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From: Princeton MN

Pull the modulator vacuum line at the trans and see if there is fluid in the line, if so replace the modulator, with zero vac to the trans (i.e. vac line removed) you will have full line pressure with the black stuff in the fluid had to come from somewhere, probably the clutch packs, does it just not move forward? How is reverse working? If they are both bad that would point to a bad pump or converter, if it backs up fine your forward clutch went out.

Mar 4, 2013 | 12:29 PM

weezer4117

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reverse works flawlessly. looks like im in for a rebuild!! Anyone advise the going rate to have a C6 rebuilt? I can remove/replace the trans but I will have to have someone rebuild it.

Mar 4, 2013 | 03:50 PM

IDIDieselJohn

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From: Ottawa, Ontario

I had my C6 rebuilt by a shop (I took it out and installed it my self) and it cost me 600$.

Reading on here, i've seen full rebuilts from 300-800$ for a C6. Someone who knows what their doing, can have a C6 apart, and fully rebuilt in 2 hours.

Mar 5, 2013 | 01:28 AM

weezer4117

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$600 doesnt sound bad, i had a ruff quote of $500 w/ a shift kit installed. Time to get the wrenches out, not looking forward to this as ive never done any trans work. Oh well, you live and you learn!!

Mar 5, 2013 | 10:37 AM

84-6.9L

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From: Princeton MN

The shift kit isn't a bad idea, because the 2nd to 3rd shift needs to be firmed up a bit. My rebuild was 1100 because it needed alot of hard parts, it had the 3 disc forward clutch instead of the 5 disc, it also sent all the shrapnel through the pump. And when you get a converter get one with a drain then you can do a complete fluid change.

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Mar 6, 2013 | 09:02 AM

84-6.9L

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From: Princeton MN

Not all converters had drains, if it does its a little pipe plug on the front of the converter

Mar 6, 2013 | 01:00 PM

#10

IDIDieselJohn

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From: Ottawa, Ontario

The C6 in my motorhome didn't have a drain either.

Heres how I flush out all my auto trannies. No fooling around with the TC drain.

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Reinstall pan, fill back up to capacity.

Start 'er up and let 'er run for a couple minutes. Shift through all the gears a couple times.

Now get a 5 gallon bucket (or any good size pan) and a piece of rubber hose.

Disconnect the trans feed line from the radiator (or aux cooler) and shove on the rubber line on that and aim the rubber line in the bucket. Tape the line to the lip of the bucket so it doesn't come out while it's flushing.

(to find the feed line, disconnect both lines to the radiator and start the engine for a second, witch ever line squirts out fluid is your feed line.)

Give a couple shots of compressed air through the radiator (or aux. cooler) to send all the old fluid and crap out.

Put a good funnel on the transmission dipstick tube.

Now prepare at least 10 *OPEN* quarts of ATF ready, at easy hand reach.

Fire the engine up, and start pouring the ATF down the dipstick tube, and don't stop! As much fluid will be coming out as you are putting in.

When the fluid coming out and dumping into the bucket looks as nice and clean as the fluid you are dumping in, stop the engine.

Reconnect the feed line to the radiator (or aux. cooler). Make sure BOTH lines are well connected.

Start up engine and check level. Add as needed. Make sure level is correct.

Go for a good drive, when you get back, check level again and your done!

It's a good idea to be 2 people doing this, one sitting in the drivers seat of the vehicle waiting for commands by the person doing the work outside, just incase something happens that you need to turn off the engine quickly. You don't want your transmission to run dry.
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