C6

Reply Subscribe

Thread Tools

Search this Thread

Nov 1, 2000 | 01:07 PM

priley

Thread Starter

Senior User

Joined: Jan 2000

Posts: 107

Likes: 0

My '88 F-250 460/C-6 started shifting funny the other night. Was OK until I got on it hard from a stoplight, then it started to downshift into second at 35, or when I barely got on it, and will hold in second for a long time before upshifting to 3rd. Checked the fluid level, it's OK. Any ideas? could it be the modulator? Would that show any codes?

Thanks, Paul

Nov 1, 2000 | 09:46 PM

Steve_Uzi

Laughing Gas

Joined: Mar 2000

Posts: 1,191

Likes: 0

From: USA

Sounds like a modulator valve to me... Take the vacuum line off of it and if fluid comes out.. its junk...

Also the modulator valve has a slotted screw inside the vacuum port to adjust the shift point, so take a look at that..

Could also be that your Dinosaur arm down to the tranny came off or the return spring up on the carb fell off...

Uzi... Yamaha Sleds, Honda Bikes, and Ford Trucks....

Nov 2, 2000 | 07:41 PM

deleontow

Laughing Gas

Joined: Jun 1999

Posts: 903

Likes: 0

From: Banning CA

One other thought, you may have a plugged or restricted vacuum line going to the modulator. though it more than likely is a bad modulator.

Dave

http://a2ztowing.homestead.com/a2ztowing.html

Nov 13, 2000 | 04:12 PM

priley

Thread Starter

Senior User

Joined: Jan 2000

Posts: 107

Likes: 0

1st, thanks for the suggestions.

2nd, I pulled the vacuum line off the modulator, sure enough, it was leaking. Went to the local auto parts store, bought a new modulator, transmission filter and a dozen quarts of ATF. Changed the modulator, drained the torque converter when changing ATF and it still upshifts and downshifts funny. 1st to 2nd upshift sometimes waits until 35 or so (light throttle), 2nd to 3rd until 40-45 (light throttle). Then instead of downshifting at low speeds, drops into 2nd at about 30-35 when slowing, and 1st before stopping. Prior to this problem, I didn't even notice the downshifts.

Also has started slipping in 1st and 2nd under load. During the 1st to 2nd upshift under load, the engine rpm picks up between shifts then settles down, don't notice any slipping in 3rd. Any ideas???

Thanks, Paul

Nov 13, 2000 | 05:02 PM

deleontow

Laughing Gas

Joined: Jun 1999

Posts: 903

Likes: 0

From: Banning CA

Sorry Paul, sounds like time for a new trans. The slippage shows signs that you are loosing hydraulic presure inside the trans. which could also fool the valve body into shifting at the wrong times. If slippage was only in 2nd gear I would say adjust the intermediate band, but since it is slipping in 1st and 2nd, I believe that the trans is about to take a dump.

Dave

http://a2ztowing.homestead.com/a2ztowing.html

Nov 13, 2000 | 10:48 PM

priley

Thread Starter

Senior User

Joined: Jan 2000

Posts: 107

Likes: 0

Thanks again for the reply. I kinda figured it was about time, with 165,000 on it.

Can you tell me what is a reasonable price for a rebuilt installed? I've heard everything from $750 to $2000+. Looks like B&M and Jet offer rebuilts for $1200-$1400 just for the trans. Obviously there must be some big differences.

Since I use the truck to haul a camper and a small motorcycle trailer (1000#), I'm thinking of an RV type rebuild with a heavy duty torque converter. Is it worth the extra $$$?

Thanks again, Paul