C6 problem

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Dec 2, 2002 | 04:09 PM

johnfl

Thread Starter

Tuned

Joined: Apr 2001

Posts: 307

Likes: 1

From: Phoenix since 4/05

C6 problem

My son has a C6 behind a 390 in a '73 3/4 Camper Special. 3rd gear seems to have gone by-by. He says it works OK in 1st and 2nd if you shift manually but 3rd seems to be running in something between 1st and 2nd. I asked him if it felt like it was slipping but he was hung-over and beat from the weekend so I didn't get a legible answer. It won't shift out of 1st if you run it in drive either. Fluid level is good but we had to go get him halfway home from the desert yesterday. We towed the trailer with a different truck and he drove his truck and camper home (about 30 miles) in 2nd.

Replacement time or fixable?

JohnF

Dec 2, 2002 | 04:21 PM

wrangler76

Senior User

Joined: Dec 2000

Posts: 296

Likes: 0

From: Carson USA

C6 problem

The problem I've always had with my C6 tranies is the vaccume hose. The hose usually gets hung up on something and pulls off the transmission case. Then it won't shift into higher gears. I like easy fixes like that... cheap too!

Dec 3, 2002 | 02:52 PM

dfisher1

Posting Guru

Joined: Jul 2001

Posts: 1,613

Likes: 2

From: Gainesville, FL

C6 problem

John,
From what your telling me is he was towing a trailer/camper and lost 3rd gear.
This sounds like a clutch. Its most likely to show in third gear.
If the vehicle is shifting manually from park to low and back successfully then the bands are OK.
A vacuum modulator could cause a late shift but not a slip.
If it is a clutch, then your going to have to pull it and take it in.
Sorry,
KingFisher

Dec 3, 2002 | 08:13 PM

fordmaniac21

Elder User

Joined: Sep 2000

Posts: 718

Likes: 0

From: Golden ,CO USA

C6 problem

i had the same problem with the c6 in my truck a few months back. somehow the vacume line going to the tranny came off so it wasnt getting any vacume. hooked it back up and had all my gears again. you might want to check the vacume lines.
'75 F-100 4x4, 4" lift
35x15.5x15 super swamper TSL/SX
mini-spooled 9" rear end
390 w/ cam,headers,
and 4 barrell edelbrock

TRIED TRUE and FORD BLUE

Dec 3, 2002 | 09:29 PM

Art

Senior User

Joined: Jul 1999

Posts: 472

Likes: 1

From: USA

C6 problem

[updated:LAST EDITED ON 03-Dec-02 AT 10:31 PM (EST)]Some C-6 transmission facts:
Due to its geartrain, two clutches are used to obtain 1st , 3rd, and Reverse gears. 2nd gear uses only one clutch and the only band in the transmission.

One of the clutches (the "forward clutch") is common for all forward ranges. The other clutch used to obtain 3rd gear ("front clutch") is also used for Reverse!

Therefore - if the trans does not slip in 1st, 2nd, and Reverse, all clutches as well as the band are OK. Then the problem is either with the vacuum modulator (perhaps the vacuum line is blocked or off) or inside the valvebody. Transmission removal would then NOT be required.

My opinion of C-6 transmissions is that the valve bodies can be finicky with contaminants in the oil, and the "filter" mesh on earlier models is way too coarse.

Good luck

Art
https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=3467&.jpg

Dec 3, 2002 | 10:59 PM

LxMan1

Moderator

Joined: Dec 2001

Posts: 22,436

Likes: 17

From: Louisville,Ky.

C6 problem

Definately a modulator valve problem. Pull the vac line off at the tranny. If it has fluid in it, replace the valve. If not, check for a broken or unhooked vacuum line.
Jimmy

Dec 4, 2002 | 07:36 AM

johnfl

Thread Starter

Tuned

Joined: Apr 2001

Posts: 307

Likes: 1

From: Phoenix since 4/05

C6 problem

SOLVED!! You guys are the greatest! I used to know all this stuff but have forgotten most of it anymore. It's nice to have a resource like everybody here. The vacuum line had come off behind the motor, how we can't figure but it did. The info on the power flow through the clutches and band is a bonus.

JohnF