Sorry for the long post, thought more info would be better.

I am having trouble with a C6 I just rebuilt for my '79 F150 - 2wd. I have just put it in the truck. It will go in reverse fine, but not in forward. It will move slightly if I rev up the engine, but barely. I searched this forum and found a similar post, but his was a busted forward clutch drum. I think this is a different problem. I am hoping someone can help me out.

I had bought a used C6 that had been previously rebuilt with a wide ratio gear set in it. I completely disassembled both transmissions and put the wide ratio set into my original transmission. I installed a complete rebuild kit, replaced all the piston seals, discs, thrust bushings, etc. Also installed a new TCI torque converter and purchased a rebuilt pump.

This is my first transmission rebuild, so I may have done something wrong. I did go through it all very carefully and made sure everything was well seated, fit well without force, etc., all the way through. In addition to the Haynes manual there is a great post on the Full Size Bronco forum with about 100 pictures of a C6 rebuild - which was very helpful.

With all that being said, I feel fairly certain it went together right. Has anyone had experience with the wide ratio gear sets - is there something I may have mixed up there? I used the low/reverse and the forward clutch set that came with the extra trans that had the wide ratio gears. I used the original high/reverse, but the two look identical. The only difference I am aware of is that the wide ratio had 5 disks in the forward set, the original had 4 plus a wave ring. The kit had 4 disks, so I used those and the wave ring. THe snap ring set tight. I don't race or pull with the truck. Just drive it to work on occasion so I was not too concerned about the 4 disks not having enough grip - it worked fine for the first 150k miles.

Only thing I did not re-build was the valve body, I used my old one. It may have been a mistake, but the original trans ran ok, was beginning to slip in first. It shifted fine and did not ever fail completely. I even replaced the radiator at the same time, so the trans cooler is new.

I checked the shift linkage, it runs through the gears fine. I have not had the pan off yet.

There is 13 quarts of fluid in it, dip stick reads slightly above the top arrow - although I have not been able to warm the trans up except sitting and ideling.
With it moving some with engine reved up it seems like it is trying to engage.

Does anyone have any suggestions for what to start with? I am at a loss.

Thanks in advance for any help

 

Gotta ask... how did you go about installing the torque convertor and transmission in the truck? Essentially, outline your procedure.

Josh

 

Also is the vacuum modulator connected?

Did you remember to reinstall the modulator pin?

Josh

 

when you put the drums together with the new clutches in, did you air check every thing to watch & listen for the clutch to apply?,Gerry,how much clearance did you leave in the forward clutch?

 

Thanks for your responses - this forum is great!

For the install, I poured 1 quart of trans fluid into the new converter then slipped it on pump/input shaft while the transs was on the jack. It engaged fine. Took a little bit of a shove to get it through the seal, but nothing unusual. The trans went in textbook perfect - easiest I have ever done. Of course, this is the first time I have used a real transmission jack (the first one I did years ago as a teenager was a bottle neck jack on top of a skate board!)
I lined up the torque converter bolts and with a little push on the jack it all slipped right together. There was no binding and no fighting. I installed all the bell housing bolts as usual.

I air tested the low/reverse set, it engaged fine. Is easy to test through a hole in the housing. I didn't test the rest. I did not use a feeler guage to check the clearance on the clutches - not sure how to change anything there if I did. There were no shims or anything inside the clutches. I did check the thickness on the disks and they were all to spec.
If I check the clearance on the forward clutch how is it adjusted if out of spec?

Of course, I am really hoping it is something that can be fixed without pulling it back out - but am concerned it isn't

I put a new modulator on- a green strip adjustable - and installed the pin. Vaccum lines are connected. Don't know yet if it needs adjusted as I can't drive it, but thought that was more of a shift concern and not with the clutches engaging. I adjusted the band 1-1/2 turns out from 10 lbs torque, but again, I thought that only affected the shift.

Would there be anything with the valve body? Or is it most likely a problem with the forward clutch?

Thanks again.

 

I had the same issue with mine...I pulled it from a running vehicle, drained the fluid out of it, removed it (along with the engine, all in one piece), then installed in my '78 F100...Filled it back up, checked all my lines, etc...started the truck, put it into gear, and it would "jump" forward, but nothing more...come to find out it was air in the lines...eventually it cleaned itself out, and runs like a top now...probably not the best way to do it, but I would start it, and just continue to shift it through the gears, and give it a little gas, and eventually it started moving....and hasn't slowed down since.

 

Was wondering (hoping) if it was an air bubble or something. Thought I might take off one of the cooler lines and pump some oil into a bucket and see if the helps.

Thanks

 

I disconnected the line to the radiator (not the return) at the radiator and put the truck in gear - same as when I flush fluid for a change (except for a flush I do the return line). I only get a trickle of fluild. It is pumping, not just a drip, but it is very weak. Sort of falls out the end of the tube rather than pumping out like it should.

I have not put a guage on the trans, but it is obviously weak. Any ideas? it is a new pump.
Why does it work in reverse? For reverse I have to rev it a little and it sort of jumps in gear, but then it works as usual. Push the break it stops, let off the brake it sort of rolls, push the gas it moves. No jump after the initial jump.
Anybody else have issues with air bubbles like the reply from CalebJns above?

 

How long did you bleed it? did you give it any gas while disconnected? Also double check where your lines attach to the transmission...just ensure they are secure and not allowing any air in....and I think it was mentioned already, but check your vacuum line all the way up for leaks...if you haven't, it may be worth while to run a new one...

 

I ran for about 3 minutes. I did give it gas. I will run longer and see what I get.

I tightened the lines good, but have not double checked - will do that.

Vacuum line is new. It has a metal line most of the way - about 6" of rubber at both ends. New rubber lines at both ends fit nice and snug.

Thanks again for the responses - I will keep playing with it.

Bullit390 - Great truck! Bet is hard to keep tires on the back!

 

if you disconnect a cooler line & start the motor the fluid should come flying out of there with 15 to 20 pounds of pressure,it sounds like you have pump trouble,sorry,Gerry

 

was afraid of that. I will keep playing with it in hopes it is an air bubble.

I think I will put a pressure guage on it - the pressure test port is on the opposite side of the trans from the lines, that may let me know if there is something else going on inside.

Will check back on progress.

Was also thinking of going ahead and rebuilding the valve body. I have not had one of those apart before. When I take it apart, will there be springs and BB's going everywhere, or are all the small parts contained enough they don't just fall out?

 

Good Luck...makes me sad to not have one on the road...

 

First thing I would do if disconnect the shifter linkage and manually shift the trans into park.

Start the truck and let in idle for 15+ minutes to circulate the fluid.

The with help, have somebody with their foot on the brake manually shift the trans into 1,2 or Drive and see if you get movement.

Otherwise, pull the pan and have a look. It might be as simple as an improper VB gasket (there are more than one) missing check ball (which an air check would have caught) or for one reason or another maybe the filter pick-up is fubar.

Never know until the pan is pulled, could also be a snap ring or pressure spring just laying in there as well.

BTW the modulator is needed for the trans to operate in Drive. 1 and 2 and reverse are full manual. So without the modulator vacuum hooked up the trans "should" freewheel in Drive.

Josh

 

Redandwhiteford could you post a link to the Bronco post with about 100 pictures of a C6 rebuild?
Thanks

Jim
77 F150