C-6 trans question

junkyardjeff · January 11, 2009, 12:57:56 PM

I have a C-6 that came out of a 77 f350 that wont up and down shift correctly when left in drive,it will work fine when manually shifted but it wont automaticly. The only things I have done to it since taking it from the donor truck is to add a Lokar shifter and change the fluid,when cold it wants to start out in second and when hot wants to start out in third but will manually shift just fine. Jeff

junkyardjeff · January 11, 2009, 12:59:37 PM

I forgot that it had been rebuilt and sat for a couple years before installing in my 66 F250. Jeff

phat46 · January 11, 2009, 08:56:04 PM

Is the vacuum line connected to the modulator? Is the modulator the correct one for the trans? Is it adjusted correctly? I'm no trans guru, but those were the things I was asked when my C-6 was acting up.

wayne petty · January 11, 2009, 09:22:45 PM

i usually find that when it happens... the governor slugs have been dropped and a tiny dent on one corner.. just enough to hang up...

it is unlikely. but... did they go through the valve body and check or replace the springs..... rust on the pistons.. rusted springs... as they were not soaking in the transmission fluid... rusted other parts.. ...

there are people who know tons more than i ... but this is where i check when the act up...

junkyardjeff · January 11, 2009, 09:33:03 PM

When I installed the shifter I had to force it togather and since it bolts to one of the governor? plate bolts I looked at the instructions and realized I had it on wrong so I installed it correctly thinking it could have put stresss on the case but its still acting up. The modulator valve is hooked up and its getting vacumn,I think it worked fine when the motor and trans were still in the donor truck but it sat through a couple winters before I reinstalled the motor. Jeff

Crosley.In.AZ · January 11, 2009, 09:50:41 PM

the governor is internal on the output shaft... you did not bolt anything to the governor , I would say.

Check the vacuum the modulator as mentioned.

If you remove the tail housing , the governor is held on with 4 bolts... you can remove and clean this if desired. You'll need a tail housing gasket.

junkyardjeff · January 11, 2009, 10:54:12 PM

If that plate with the 4 bolts that I bolted the shifter to is not the governor what is it,while the trans was stored I kept a yoke in the trans to keep anything from getting inside. Jeff

junkyardjeff · January 11, 2009, 11:18:17 PM

The more I think about it is I think most of the fluid drained out when I pulled it so during the 2 years it sat there was not enough fluid to cover the valve body and other parts low in the case so I guess something is sticking,is there anything I can put in the trans to free up whatever is sticking and I will try replacing the modulator and see what happens. Jeff

enjenjo · January 11, 2009, 11:23:34 PM

Quote from: "junkyardjeff"The more I think about it is I think most of the fluid drained out when I pulled it so during the 2 years it sat there was not enough fluid to cover the valve body and other parts low in the case so I guess something is sticking,is there anything I can put in the trans to free up whatever is sticking and I will try replacing the modulator and see what happens. Jeff

If it's rusted, no. But you can get a rebuilt valve body at a reasonable price. I believe the last C6 valve body I got from D&E cost me like $40.

wayne petty · January 12, 2009, 01:16:32 AM

i am wondering... my brain tired right now... but is it possible... jeff that the kick down lever is being held in the applied position..

the shift shaft has an outer tube... that the shift lever is attached to ...

the kick down lever goes through the middle of the shift shaft...

the kick down lever only moves against a spring loaded piston a few degrees... can you rotate the kick down lever and feel it spring back to its stop... remember is only moves a little bit.. but it should spring back... if you do not feel it spring back.. it might be wedged...

oh.... can you also pull the vacuum hose off the modulator... see if it has quite a bit of suction... i have had several of the threaded hose adaptors on the back of the intake carbon up.. including the holes drilled past the threads..

Crosley.In.AZ · January 12, 2009, 07:04:24 AM

Quote from: "junkyardjeff"If that plate with the 4 bolts that I bolted the shifter to is not the governor what is it,while the trans was stored I kept a yoke in the trans to keep anything from getting inside. Jeff

That is the 2nd gear servo. it is not just a plate, about 2.5 inches deep. If you unbolt that too far the internal band struts fall off , then you have more fun.

junkyardjeff · January 12, 2009, 09:29:47 AM

I took the vacumn line loose at the trans and motor and blew air through and nothing came out but when I disconnected it at the modulator with the motor running it did not effect the idle too much so I will check the connection at the motor that has one of those threaded hose adapters and I will pick up a new modulator too. Jeff

Okiedokie · January 13, 2009, 12:54:45 PM

The C4 in my 46 does the same thing. It was rebuilt and worked fine for a while. Then it begin to shift odd. It works fine if shifted manualy or if you light foot it. From a standing start at slow speeds it seems to shift normaly. I replaced vac mod, and vacum hose from motor, no change. An old time mechanic suggested the 20 mph in reverse and drop into drive treatment. Did it as much as my mind would let me with no results. I have been told that the govenor may be hanging up [same thing that the rev to drive deal is supposed to address. I read in a tranny manual that it might have a cracked gasket between valve body it seems. For now [couple of years?

] I am manualy shifting. Joe

junkyardjeff · January 13, 2009, 05:35:57 PM

The owner of the local trans shop said it sounds like the governor sticking and it did sit with the tailshaft exposed for about 2 years so thats where I am going to look first,I am going to drive it awhile and see if it frees up. Jeff