C-6 Question

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Jun 24, 2021 | 07:57 AM

jwrrogers

Thread Starter

7th Gear

Joined: Mar 2021

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C-6 Question

I'm having a little trouble with the transmission in my '71 F-250. Transmission was rebuilt about 10 years ago but then it sat in a garage (with fluid in it) for most of that time. Less than 2,000 miles driven in 10 years. But now I'm getting it restored. There are no leaks whatsoever but when truck is first started up and I put it in gear, I have to rev the engine up before it will engage and move. Initially there was a very long lag before it would engage but after using Seafoam TransTune it seems to be getting better. The lag is much shorter and I don't have to rev engine near as much. And it only seems to do it when truck is cool. Once it gets going, then it is good rest of the day. Any thoughts?

Jun 24, 2021 | 08:15 AM

Mark Kovalsky

Frmr Ford Trans Engr

Joined: Aug 1999

Posts: 24,730

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From: SE Florida

There is a check valve that prevents the torque converter from draining into the pan, I will bet yours is leaking. After the trans sits for several hours it will take a minute or so to refill the torque converter.

The way to test this theory is to check the ATF level BEFORE starting the engine after it has sit at least 8 hours. If the ATF level is WAY overfilled before starting the engine, that's your problem.

I do not know the C6 well enough to know where that check valve is located. In the E4OD/4R100 (which were developed from the C6) the check valve is in the pump body. You need to remove the trans to get to it.