C6 transmission questions

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Aug 12, 2001 | 06:38 PM

orangeford

Thread Starter

Laughing Gas

Joined: Aug 2000

Posts: 1,012

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From: Eastern, Idaho

C6 transmission questions

I have a 79 150 4x4 with a c6 When it is accelerating at half throttle or more. It revs about 100 to 300 rpm when shifting from 2nd to 3rd. Another thing is when you put it in revere it takes 1 second then has a clunk. What could be causing this? I dont know much about automatics so any help would be appreciated

Aug 12, 2001 | 07:59 PM

fordmaniac21

Elder User

Joined: Sep 2000

Posts: 718

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From: Golden ,CO USA

C6 transmission questions

mine does that too in my '75. when i put fluid in it it helps for easier shifts. try changing the fluid and filter. it might help. i havent done it yet. let me know.

Paul E Goodman III
'75 FORD F-100 4x4
390 4 barrel edlebrock, high-rise manifold, comp cam
35" mud terrains

Aug 12, 2001 | 08:02 PM

sparky

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Joined: Jun 1999

Posts: 2,415

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From: Comox Valley, Canada

C6 transmission questions

Quote:

How is the tranny fluid? Is it low, burnt smelling, dark color? When is the last time the fluid and filter were changed?
Low or burnt fluid and/or a plugged filter could cause the tranny to slip.
The clunking could be a u-joint as well as tranny slippage. I am not much of an automatic tanny expert, but I would change the fluid and filter first and see if that helps.

Sparky

Aug 13, 2001 | 01:28 PM

AaronW

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Joined: May 2001

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C6 transmission questions

My truck does it. I changed the fluid right after I bought it. The filter and fluid were in great shape, the inside of the tranny looked even better. New fluid and filter made no difference. I think I have a bad tranny mount though, I have been too busy to fix that lately, maybe that will help
Aaron

Aug 13, 2001 | 05:06 PM

6t6merc

Cargo Master

Joined: Apr 2001

Posts: 2,697

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From: Vancouver

C6 transmission questions

An intermediate band adjustment might help that runaway 2-3 shift.
Eric

Aug 13, 2001 | 06:04 PM

250two_by

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Joined: Jan 2000

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C6 transmission questions

Just a suggestion but you might want to check all your vacuum hoses, especially the one that leads to the tranny. If you have a leak either in the hose or where it connects to the manifold this will affect the shifting. It will make it hesitate when you first fire up in the morning or after long off periods. Take the hoses off and snip off about a half inch of the old connection and slide it back on. Worth a try.

Aug 13, 2001 | 07:53 PM

Like M. Fords

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From: LAT 46.55501° & LON -122

C6 transmission questions

Your Reverse-High clutch pack is wearing out and/or there is too much clearence in the pack. A rebuild is probably in order. a C6 is relatively easy to rebuild with a good book and a clean work space. If you do not think you are up to it, then give it to your local tranny shop or keep your eye out for a good used one. If you decide to fix your bad one, and you find out that there are only 3 friction plates in the clutch pack, ask them about adding one friction plate by using the pressure plate from another C6 Forward clutch. By macining the Reverse-High clutch drum for a second snap ring groove, I was able to add 2 friction plates for a total of 5 without needing to use the thinner Forward clutch pressure plate from a doner C6.

I had similar symstoms you are having on the 2-3 shift, but I didn't notice any problems with reverse. When I took the tranny apart, all three clutch discs in the Reverse-High drum were wore down to the metal core. I am lucky I tore it apart when I did. With any more friction material missing, I doubt that 3rd gear would have held any longer even after it had shifted.