So I got my supercab running pretty decent. Your answers to my posts helped a lot, the trans is good now and engine has never sounded better now that I have vacuum leak solved and carb adjusted much better..Moving on I have a 79 regular cab with the c6 trans. It needs alot but is driveable. Transmission thumps if I hit gas hard starting out (is that drive shaft?) Its kind of a shutter like not letting clutch out right in manual trans then a thump. Thats not the main issue though. Second gear....right before it engages theres a horrible sound like a tractor trailer stopping with loud brakes and then a clunk when it engages. Theres no issue once its in second it stays and the second to third is smooth. Anyone know what this sound is? Seems like its coming front end but other than that i am cluless. Given the age I can only assume this one needs a rebuild too but I hate not knowing what makes this horrible sound. Appreciate any answers, thanks.

 

Sounds like the valve body is sticky and that you have metal to metal contact in one or more of the clutches. The thump on acceleration may imply that you also have a problems with the vacuum modulator. You may want to drop the pan. I suspect you'll find metal and chunks of friction material.

My usual test for driveline trouble is to pay very close attention to the coast to acceleration transition and vice versa. There shouldn't be any banging but a bit more or less noise out of the rear end is OK.

Michael

 

Thanks Mike. Is there anything I can ad to fluid to help valve body? I did drop the pan, fluid wasn't great, lots of black sludge on bottom of pan. Not really and chunks of metal. Fair amount of fine matetial that I could barely feel between fingers. I found just a couple larger tiny flakes of metal. I drained torque converter as well and refilled with synthetic fluid and 2 bottles of Lucas anti slip. Does shift slightly better but has same symptoms.

 

The black sludge is probably the remains of the friction material in the clutches. The metal flakes are from the direct metal to metal contact due to the friction material having worn off. There is no permanent cure other than replacement which isn't that hard but does require attention to detail and a tool you can make or buy for under $35. If there is no other damage and you don't need to replace the converter, a quick rebuild, meaning just friction, steel and seal replacement, shouldn't cost more that $100 in parts and take you a few days if you take your time. I spent north of $400 on my C6 late last year but that included all new bushings, new converter, new plate style cooler, seals, steels and frictions. I also replaced the cooling lines as I couldn't get the can of cooling line flush to flow through the old ones. And I might have bought a tool or 2...

The tolerances in the valve body are very tight. There "may" be something you can add to the fluid to free it up but nothing will compete with taking it apart and cleaning it by hand. There are very finely machined components and a number of springs but it's not rocket surgery. If you are a tinkerer like me, it might take all afternoon and several bottles of root beer. If you do it for a living, it's an hour at most. Just pay attention to where things came out and what length bolt came from where as there are several different lengths.

Michael

 

So when I started messing with this truck again I discovered that with the vacuum line unhooked from modulator the truck drives great manually. 1st and 2nd no third. Syptoms are totally gone, no horrible noises. Now this is more or less a farm truck but I would like to take it on road sometimes. What if I were to change out the valve body or rebuild it and put in a full manual kit so I can also get third gear? Does the fact that it drives good like this narrow down diagnosis? When I rebuilt my supercab c6 I put in a Transgo shift kit ( the automatic one 67 1 &2 I think), and I believe they have a fully manual kit too. It may make more sense just to get a new manusl VB if it doesnt costmuch more.
Is it bad to drive without vacuum on trans? Is there a heat issue? Should I ad a second oil cooler? Or is this altogether a dumb idea? Will the trans likely deteriorate anyway or is this a reasonable fix at least for a good while? I really dont want to rebuild the whole thing unless I have to and I would probably just park it for a while. Input is appreciated greatly.

 

What the vacuum modulator does and when is outside my ken but while you might get 3rd back with a full manual kit, I would just pull the valve body and give it a good cleaning.


If it sat for a long time, it may have corrosion binding some of the valves. I actually had rust on some parts even though I drove the thing 4 or 5 times a year. I now drive it at least twice a month. Not only does it run better now, it leaks less oil than it used to.


Once the wear starts to set in, it will get worse. There is limited travel in the pistons that make the clutches work and once the frictions and steels start to wear, there will be less and less clamping pressure and more slippage.


I used to think that I'd like to put a shift kit in one of my vehicles but at 56, I'm no longer as excited about getting messy if I don't have to!


Michael

 

Yeah I hear ya. I think I will pull the valve body and clean it first and see if that helps. My knowledge of transmissions is limited but it makes sense that the valves are hanging up. I'm hoping that the lack of metal chunks in the pan means the inner workings are still in decent shape. Thanks

 

I've decided to go ahead and rebuild the c6 in my regular cab too. I don't have a lot of money to spend on this one. Any recommendations for a decent kit around 100 bucks? I will replace torque connverter too. Also I need to make sure I clean the valve body real good.....should I take it all apart and soak it or just spray it. Id the a particularcleaner I should get? I assume anything petroleum based will work. Thanks for the input

 

The kits I looked at all seemed the have the same brand parts unless you were looking at racing/drag strip use then they got fancy. Quickly.

What set the price was which parts came in the kit. The cheapest were just seals and gaskets and it went up from there. I got my parts from Oregon Performance Transmission, partly because it was closer to Seattle than the outfit in Florida and partly because I liked the web site. He emailed me several times to verify I was getting the right parts and in the end, I did get the right parts first try so that was good.

The valve body shouldn't need parts other than a gasket and filter which will come in the kit. It needs to come apart to properly clean all of the valves. Lay out a big area of paper towels and line up all of the bits as you take them out. It will save you a lot of grief later. And try to keep track of the ball checks and springs.

I used the cheapest brake cleaner I could find, cheap acid and chip brushes from Harbor Freight and a lot of elbow grease. Plus a late night trip to the coin-op carwash. No sandpaper or other abrasives.

Michael

 

Sounds like band adjustment, modulator adjustment, and linkage adjustment are in for a preliminary examination. I say you can have a brand new from ford c6 and with poor tuning, and poor adjustment, it wouldn't work either. First is adjust the shft linkage, second is adjust the modulator and or rod, third is kick down, fourth is verify proper vacuum hookup and no leaks for modulator, and finally adjust the band. good luck. I would recommend these things before doing a overhaul. but do as you wish.

 

I ended up getting a kit and torque converter from O Reillys only because it was in stock and I had a few free days to do it. It turns out that the forward clutch was totally fried. The friction plates were unrecognizable and there were deep groovesin the steels. I cant believe it ran as long as it did. Im pretty sure sticking valves were the problem. I cleaned the governer and valve body very well and very carefully did the rebuild folliwing the Bad Shoe video. The hardest part by far was getting the transmission lined up and bolted back in place perfectly. Patience was definitely helpful there.....Anyway I got it all back in and prayed all would go well. It drove like new, shifted strong and I was giddie like a kid on Christmas morning. And then.........after driving probably 40 miles, i was on my way home and the transmission started "jumping" slipping from third to second and back again. As i drove it started getting worse fast...i pulled over and was in absolute shock. I imagined that a snap ring popped off and the inside of trans was ruined. My friend who was rideing with me jumped out and saw fluid spraying from under front of truck and said hey I think a hose came loose.......there was a line of fluid behind the truck ad far as i could see. A hose had slipped off a secondary trans cooler that I hadn't touched for a long time. I fixed the problem and had a friend bring us more trans fluid....I had lost almost a gallon on the highway. In the end thats all it was and the trans works perfectly. Im guessing putting in the rebuilt transmission made the pressure in lines greater and caused that rubber line to come off. What ever caused it, it scared the crap out of me big time.

 

I ended up getting a kit and torque converter from O Reillys only because it was in stock and I had a few free days to do it. It turns out that the forward clutch was totally fried. The friction plates were unrecognizable and there were deep groovesin the steels. I cant believe it ran as long as it did. Im pretty sure sticking valves were the problem. I cleaned the governer and valve body very well and very carefully did the rebuild folliwing the Bad Shoe video. The hardest part by far was getting the transmission lined up and bolted back in place perfectly. Patience was definitely helpful there.....Anyway I got it all back in and prayed all would go well. It drove like new, shifted strong and I was giddie like a kid on Christmas morning. And then.........after driving probably 40 miles, i was on my way home and the transmission started "jumping" slipping from third to second and back again. As i drove it started getting worse fast...i pulled over and was in absolute shock. I imagined that a snap ring popped off and the inside of trans was ruined. My friend who was rideing with me jumped out and saw fluid spraying from under front of truck and said hey I think a hose came loose.......there was a line of fluid behind the truck ad far as i could see. A hose had slipped off a secondary trans cooler that I hadn't touched for a long time. I fixed the problem and had a friend bring us more trans fluid....I had lost almost a gallon on the highway. In the end thats all it was and the trans works perfectly. Im guessing putting in the rebuilt transmission made the pressure in lines greater and caused that rubber line to come off. What ever caused it, it scared the crap out of me big time.

 

Good. Glad you got it fixed. I do believe that this could have happened (the burning of clutches) if someone ever coasted or towed it with driveline intact the transmission was turning and I believe these transmissions will be hurt in that matter without fluid pumping. Might be what happened, glad it got fixed

 

That makes a lot of sense. (That someone towed truck in gear) I am no expert after only 2 rebuilds but the friction clutches were so trashed there was nothing left but very thin mangled medal. Seems to me it had to be something pretty severe and not a gradual wear. I appreciate everybody's advice. Next item on both my trucks is probably body mounts and weather seals and then some body work and hopefully paint if I can afford. Ive considered trying the paint myself ( on farm truck first to see how it goes)