C6 Problem -- 88 F250 7.3L - Diesel Forum

LFDavidson · 11-17-2012, 06:24 PM

So searched threads here and found one close but not quite the same. My trans was working fine, no slipping and shifting smooth. Pulled a heavy 5th wheel just fine up and over mountain passes. Got into the truck one day last month pulled it forward and backed into my yard. Went to jockey it back and forth to hitch my 5th wheel and all of a sudden nothing out of the trans. Shift it back and forth through all gears and no engagement at all. Checked fluid level and it was fine. All of a sudden it started working, moved my trailer around and parked it. No problem. Moved the truck around by the street. A couple of weeks ago, I started it up. It pulled forward into a side street to turn around and all of a sudden nothing. Played around with it and again it started working fine. Moved it into my shop. Then today, went to put it up on ramps to change the fluid and filter. Started it up and moved it forward and back a couple of times (had trouble with a ramp sliding) then again nothing. No engagement of any gear. Played with it and it started working so I drove it up on the ramps. Pulled the pan and everything looks fine. Filter was not dirty at all..

Anybody got any ideas about what is going on??? It's like you throw a switch, works fine then nothing then back to working fine. I haven't driven it very far lately to see if it stays working on a long drive.

Thanks

NH2112 · 11-17-2012, 08:03 PM

The C6 is standard equipment on most makes of airport Ground Support Equipment, and I've seen what you describe many times. We send them out to be rebuilt, and each time it was the pump that had gone bad. I wouldn't say it's a common problem, but when there is a problem that seems to be what it is most of the time. I have no idea if there's a port where you can check line pressure. Just a month or so ago I had one rebuilt at a local shop and it only ran about $850 with a new converter, so that may be an option if you don't want to throw a salvage yard tranny in.

LFDavidson · 11-18-2012, 06:13 PM

Sounds like I will have to pull the trans then.... How hard a job is that to do?? How do you get at the top bolts on the bell housing??

chuckster57 · 11-18-2012, 06:31 PM

It's not that difficult. A couple of extensions, maybe a universal adaptor, and some grunting should get the bell housing bolts off. A C6 is light compared to some.

You may have to support the engine with a bottle jack. Use a square piece of wood to spread out the load on the oil pan. I like to use a 1X4 cut about 4" long.

Undo the battery cables, remove the starter. Them take the inspection cover off, unbolt the torque convertor from the flex plate and slide it back INTO the transmission.
Unbolt the trans and while supporting it, take the rear support out. Disconnect the linkage, reverse light, and speedo and you should be good to go.

I may make it sound easy, but that's because I have done lots of transmission removals. It's really not that hard if you have a good floor jack, or transmission jack and a bottle jack to hold the engine.

NH2112 · 11-18-2012, 06:36 PM

I either get them from the top with a wrench, or from underneath with several extensions and a U-joint socket. Pulling the granny isn't very hard, you'll just need to support the rear of the engine once the tranny is out. If it's not a 4x4, it's just a matter of disconnecting the driveshaft, removing the cooler lines, shift linkage, speedo cable, neutral start switch wiring, and modulator, and removing the 6 bellhousing bolts and torque converter nuts. Then slide it back and down.

IDIABUSE · 11-19-2012, 09:44 AM

I may be breaking the rules here, by exposing the root cause of your no go C-6.
the Valvebody Boost valve is jamming up in its bore, largest valve in the body, so it is easy to find.
http://www.sonnax.com/product-lines/...ion/parts/3128
Cheap fix and it is not necessary to remove the transmission.

Javier

chuckster57 · 11-19-2012, 12:08 PM

Not breaking any rules that I am aware of. If that fixes the problem, great! Dropping a valve body is a heck of a lot easier.

LFDavidson · 11-20-2012, 10:01 AM

Thanks for all the help. I did talk to a trans shop and the guy there suggested that there could be a little piece of grit causing the regulator valve to stick. That could cause the fluid flow to bypass the trans and simply dump back to the pan. Not sure if the valve you mention is the same one. How would you fix the boost valve? Replace it, change a seal on it, just clean it?

If I pull the valve body and then separate it, will all the little balls and springs stay in place in the bottom half? Never pulled one apart and I don't want to end up with a pile of pieces.

Can't afford to rebuild it right now (shop quoted me $650 to $700 which I didn't think is too bad. If I can easily do something with the valve body to get me through to next spring. I can have it rebuilt then. Thanks....

chuckster57 · 11-20-2012, 10:11 AM

Been a long time (2000) since I took my C6 out of my '86. Valve body comes out and IIRC, there is 2 or 3 balls. There will be a plate between the valve body and the trans that should come off and cover the passages with the balls. Just lift it off gently and make a note, better off take a picture of their placement. I don't remember if the balls are the same diameter.

IDIABUSE · 11-22-2012, 12:15 AM

the valve body is cake to remove and disassemble, if you are not in a hurry.

you may not have to seperate the VB to change out the boost valve, there is a clip that pulls out and the valve comes out, the Valve I suggested is the correct one and has o rings to help seal the worn bore, Most of the time if you seperate the VB you will see alot of sediment collecting in the passages and need a cleaning. not really a difficult job.
Plenty of info on check ball placement if you lose track.
Keep a nice camera around while you seperate the VB, should make it easy for you.

Javier

LFDavidson · 11-22-2012, 02:54 PM

So, thinking right now that I just want to pull the valve body down without removing the transmission (assume nothing will fall out) then bench clean the valve body and replace worn parts. Is there such a thing as a valve body rebuild kit or would that be the same as a shift kit? If so, are they all the same or is there a specific "heavy duty" one I should get for this truck (88 F250 7.3L Diesel 2WD)?

Thinking about downloading the Bad Shoe Productions video on the C6 rebuild.

chuckster57 · 11-22-2012, 03:04 PM

I don't remember that far back that good any more, but when I did my B&M shift kit on my '86 it seems like I remember drilling a hole a certain size in a particular spot on the plate between the valve body and the tranny. Maybe different balls too, been too long.

The valve body will come out easy enough without anything falling out. I would suspect that parts are easy to come by.

IDIABUSE · 11-22-2012, 03:07 PM

Yes just use the link below they have all the items needed to fix/rebuild your valvebody, be glad that the C-6 is so robust there is only a few parts needing replacement, I would just go with the boostvalve. Use Ebay and just copy/paste the part# and someone will have it available.
And for the RECORD I have no affiliation with SONNAX in anyway shape or manner, I dont want to get banned for suggesting a way to cheat a transmission shop out of a full rebuild...

Javier

Quote:

Originally Posted by IDIABUSE

I may be breaking the rules here, by exposing the root cause of your no go C-6.
the Valvebody Boost valve is jamming up in its bore, largest valve in the body, so it is easy to find.
Sonnax - Aftermarket replacement transmission, torque converter, and high performance automotive parts
Cheap fix and it is not necessary to remove the transmission.

Javier

LFDavidson · 11-22-2012, 11:13 PM

Great, thanks.. It won't be cheating the shop out of any rebuild since I will do that in the spring once I have the cash saved up.. I like the shop I was talking to and they will get the work in about April if I can get it to work well enough until then by cleaning up the valve body.

LFDavidson · 11-23-2012, 12:40 PM

Ok, finding it difficult to figure out what parts to get. I found this site to order the boost valve, FORD C6 Transmission Boost Valve SONNAX 36946-02K but what else do I need if I pull the valve body apart and clean it? Just a shift kit? If so, anybody have a link to the correct one to order?

Thanks...