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7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

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Old 07-24-2012, 01:04 PM   #1 (permalink)
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Exclamation c6 transmission gears not engaging

HERE'S THE SCOOP, I HAVE A NEW REBUILT TRANSMISSION, NEW TORQUE CONVERTER, NEW VACUMN MODULATOR, FRESH FLUID, AND THE TRANS. WON'T ENGAGE.. I'M WONDERING IF IT IS BECAUSE I FILLED IT WITH DEX MERC., INSTEAD OF TYPE F FLUID... WOULD IT MAKE THAT MUCH OF A DIFFERENCE FOR A NON-LOCKUP TYPE CONVERTER??? I'VE READ DIFFERENT THINGS, SOME PEOPLE HAVE NO ISSUES WITH DEX MERC., BUT APPARENTLY TYPE F IS BETTER FOR TOWING... MY TRUCKS AT A STANDSTILL, FOR WHO KNOWS WHY... LINKAGE IS MOVING FREELY, AND PROPERLY SETUP FOR SELECTING EACH GEAR, BUT TIRES WILL NOT MOVE... LOL! @ ME! WHAT A STUPID PROBLEM TO HAVE. CERTAINLY DON'T WANT TO YANK THE TRANS. FOR SOME SMALL ISSUE... WHAT A PAIN IN MY NECK.. MY ONLY OTHER GUESS IS REPLACING THE VRV.. YET IT SEEMED TO HAVE VACUMN, ALTHOUGH I HAVEN'T CHECKED IT WITH A GAUGE TO VERIFY AT LEAST 20" OF VACUMN.. I DUNNO.. SHOULD I JUST T INTO MY VACUMN PUMP, AND CALL IT GOOD, OR DO I NEED TO STICK WITH RUNNING THE TRANS. VAC OFF OF THE VRV ON THE IP??? THANKS
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Old 07-24-2012, 01:44 PM   #2 (permalink)
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Vacuum isn't your problem. Even with no vacuum the trans will engage and operate, it will just shift at high RPM.

Dex/Merc isn't your problem, either. If the friction materials were designed for Type F instead of Dex/Merc the trans will operate normally except all of the shifts will be long and slippery.

Here are a few things that I can think of that will cause no engagement.

Low trans fluid
Loose/missing internal filter
Torque converter not seated on the pump
Bad/missing internal clutch seals
Bad pump
Linkage not connected to the manual valve
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Old 07-24-2012, 02:56 PM   #3 (permalink)
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Quote:
SHOULD I JUST T INTO MY VACUMN PUMP, AND CALL IT GOOD, OR DO I NEED TO STICK WITH RUNNING THE TRANS. VAC OFF OF THE VRV ON THE IP??? THANKS
Don't do that..The modulator valve shifts the trans based on vacum increase, so if it's hooked to a constant source, it won't work right.
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Old 07-24-2012, 11:36 PM   #4 (permalink)
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Cool got her figured...

Hey... Thanks a lot for your input... I had removed the valve body once before, come to find out, the pin wasn't connected to the likage lever.. too funny... I am going to fiddle with the vacumn modulator a bit in the morning.. but now it works.. I have the brb turned all the way to the firewall and I'm sure I will figure the fine details afterward.. thanks again.. any suggestion on stick out for the modulator.. I tried it flush to the nipple, but some people say run it out further for towing, and firmer shifts.. I know they sell longer pins for it as well. Yet again, these are fine tuning issues.. right now I have great throttle response, just smoking too much for the neighbors because of the 2 stroke I mixed in to help seat and protect the freshly built motor...
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Old 07-25-2012, 10:18 AM   #5 (permalink)
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I have no help for you on tuning a C6. I know a lot about electronic transmissions, and just the basics on a C6.
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Old 07-25-2012, 10:27 AM   #6 (permalink)
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I had a C6 in my '86 F250 and IIRC there are different color modulator valves. I had a shift kit in mine so I didn't mess with the screw on the back side of it. hauling my fiver, I could get firm enough shifts to shake the dashboard. IIRC backing out would result in softer lower RPM shifts, but I would set the VRV first.
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Old 07-25-2012, 06:42 PM   #7 (permalink)
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Exclamation

Well... I appreciate the input, but i'm turning 2,000 rpms and barely moving, so something is definately wrong somewhere else I guess... Bummer... I have no other ideas... Tranny is just slipping! Can't get it figured... The whole thing was in great shape internally, and the torque converter appeared to be brand new as well... I pulled apart the valve body twice, and I couldn't seem to see any clogs, or visual damage anywhere... I also installed brand new pump gears, and I'm positive that they were done correctly... Just can't seem to wrap my head around it... I assumed that it was a vacumn issue... But who knows..??? It's a pickin'
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Old 07-25-2012, 07:43 PM   #8 (permalink)
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Disconnect the vacuum line and try it. That will put more pressure on the trans.
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Old 07-25-2012, 11:17 PM   #9 (permalink)
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Cool right on...

Thanks man.. ill try that out.. I'm kinda nervous I dropped the 2-3 shift ball out of the valve body...
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