Hey guys, same 89 f150 4x4 w/ 302.

Don't have this problem often, but when I do it's disconcerting. At stops or stoplights, I'll roll to a stop and wait with my foot on the brake. Occasionally, I can feel the truck lurch or adjust slightly and the idle increases as if I've shifted into neutral or park. After a few seconds, the truck will lurch again and the idle drops as if I've just shifted back into OD or D.

A few times on hills, I'll roll backwards a few feet after letting off the brake and stepping on the gas, then the truck decides to shift back into OD and I'll continue on my way. This happens on flat ground as well, but isn't near as nerve-wracking.

I'm wondering if this is connected to the transmission feeling like it's shifting hard or too early and killing my power output. No codes appear and my speedometer (speed sensor?) doesn't seem like it's acting up. I don't know when the ATF has been changed last, and it's a damn good possibility that the fluid is 140k mi old. I found a diagram with the trans bolt patterns so I'll get the trans model before the day is out.

Anyone have ideas or have a similar problem?

 

I have a similar problem in my truck, 1990 F150 351W 4x4 E4OD (out of a 91 FSB that I use to have). I know for a fact the tranny is good because it was my Bronco that it came out of before she was scrapped, so I've been trying to track down my problem... As for what my truck is doing: Sometimes, mostly on the highway or at higher speeds, my truck willl "kick" or "buck" as I'm going down the road. Feel like I'm trying to ride a damned bull to work. Only happens on occasion and only if I've been driving a while and the trans is heated up. I installed a tranny cooler and it helped a lot, but I still get the kicking and bucking on occasion. Another issue I seem to be having is that my tranny will slip gears into neutral whenever I'm in Drive or O/D. Usually the neutral slip doesn't happen until right after the "kicking," so I can only assume they are related. I can usually hault this slip by dropping into 2nd or 1st (depending on speed) and punch it. The F150 loves full throttle and the only issue I've ever had punching it would be the immediate drop in RPM's like she's gonna die, but then they shoot right back up, like a delay of sorts, and I go flying.

These three problems concern me: The bucking, slipping into neutral, and RPM drop. As I said though, it doesn't happen all the time. Sometimes I can "solve" the issue temporarily by dropping the gear into neutral and then back into drive. It works for a little bit but the problem still insists. She has her good days and her bad days. The only thing is, her bad days are really, really bad. There are days when I have to shift manually (it is an automatic after all) from 1st to 2nd and then into Drive for her not to act up at all.

I still haven't figured it out yet, but I figure I'll toss my problem up in here and see if someone can't help us both out.

If it matters any, my speedo, with the engine turned off, sits about an inch below 0mph and when I put her in reverse the speedo moves backwards about another inch or so. Never had this problem in any other vehicle I've owned.

 

The torque converter could be low on fluid.