Hello, I have a 1986 F-250 truck with 460 V8 2wd which I bought with a bad transmission. I pulled the trans and sent it to get rebuilt by a local shop. After getting it reinstalled and put back together and filled with fluid, it seemed fine and shifted though all the gears, but it always had a slight problem when shifting into reverse, it would shift but it would take 4-5 seconds before it would actually engage after selecting reverse on the shifter. Shifting from park to drive for example, it would start moving right away, but when shifting from park to reverse, it would take a few seconds before it would actually start moving.

Anyways long story short, the truck only has maybe 100 miles max since the "rebuild" and now I don't have reverse at all. When I shift to reverse, it's as if it's in neutral, it will roll but no power. All of the forward gears work fine, first gear, second, and third all work as supposed to. I have no clue what the "rebuild" actually consisted of, except that it was supposed to be a full rebuild by a supposedly good shop. The original problem the trans had when I bought it was that it did not have 1st gear at all. With the shifter in drive, it would start in 2nd gear. When selecting 1st gear on the shifter, the wheels would lock up completely (no movement at all).

I did some reading and saw that no reverse on a c6 might be caused by a piston seal? Obviously I'm not a transmission expert, but is it possible to change this seal by just dropping the valve body, or is it more involved?

 

I had the same thing happen when I used the old torque converter off another transmission that went bad. All the junk from the other transmission ended up in the "new" transmission, and it would make a buzzing noise and didn't want to go in reverse.

I just went to a trans shop several years ago, wanting to know how much they would charge to rebuild a trans if I brought it to them. They gave me a number and said it would not have a guarantee. I said why, and they said they need to properly clean out the oil cooler system at their shop or they won't guarantee it. And they would only give me a $100 break for taking it out myself.

 

The piston seal for the reverse drum is unfortunately in the reverse drum. You would need to disassemble a large portion (most of it IIRC) of the rotating assembly. So much more involved than the just the valve body.

Franklin2 does bring up a salient point tho. Did you re-use the converter? Flush the transmission cooler?

If it is the rear drum's piston seal I would suspect either the rebuild was just putting in new clutches or that they damaged the new seal during installation. Note: Getting to that seal and installing it can be a real pain or at least it was for me

 

Paging @Mark Kovalsky

 

I have nothing to add to what skaeke wrote. He covered it very well.

 

Thank you all for your replies. I did not reuse the old converter, the rebuild came with a reman torque converter. I installed new trans lines on the truck before putting in the new transmission and I flushed the cooler the best I could by spraying brake clean through the lines and blowing them out with compressed air. I did that several times until clean brake cleaner came out. I'm thinking you guys are right about the rebuild just being new clutches.