All,

I'm having a serious problem(s), and any help you can provide will be helpful before a mechanic takes all my money "searching" for a problem.

1986 F-150 4x4, 302 EFI, Auto Trans w/OD

I was driving cross-country and had been on the road for about 3 hours when my truck started seeming to slip. I was traveling at highway speeds, and if I tried to accelerate, the truck would actually slow down. The engine wouldn't even rev, even if I pushed the gas to the floor, the truck would just slow down. If I backed off on the gas, the truck would re-engage and i could slowly pick up speed, but if I pressed the gas too hard it would immediately slow way down (faster than if I took my foot off the gas). I pulled over onto a side street and came to a stop and then tried to take off quickly. The engine didn't rev, and the car just started slowly moving, and then after holding the gas down for maybe 5 seconds, it corrected itself and took off. It drove fine for the next 4 hours or so, but then I took an exit, and as I started coasting to slow down, I heard a horrible grinding noise.

It sounded like I was dragging my muffler behind me or something. If I would apply the gas, the truck would slam into gear and the sound would go away, but as soon as I took my foot off the gas the grinding sound would come back. I pulled over and placed the car in park. When I tried to put it back in gear (any gear) it made the worst grinding sound I've ever heard, the whole truck started shaking, and of course it wouldn't engage the gear. It sounded like I was throwing a handfull of wrenches into a wood chipper. Seriously the worst grinding sound I've ever heard. Way louder and more aggressive than grinding a gear in a manual transmission when shifting. Nothing I could do seemed to make a difference other than putting the transfer case in neutral. I got a tow to a local auto shop, and when it came off the tow truck I started it up to show the mechanic what it was doing and nothing happened at all. It dropped right into gear smooth as silk with no sound at all.

The mechanic checked it out and said the transfer case was dry and destroyed, so he put a salvaged transfer case on it, test drove it and I picked it up. 85 miles later I'm on the side of the road with the same exact symptoms. It started losing power under acceleration and 10 minutes later grinding like crazy and refusing to go into gear. Towed it 85 miles back to the shop, and no symptoms. The mechanic hopped in and drove it around the block several times with no issues.

He's tearing the T-case apart again to investigate, but something tells me this isn't the issue. It only seems to manifest once everything is good and hot, and then it seems to go away once the car has rested for awhile. Any ideas on what this could be would be appreciated. My mechanic is stumped.

 

Did anyone drop the transmission pan to see if there is any metal in it?
Hows the transmission fluid? Did you check the fluid level?

 

Remove the trans dipstick, sniff the fluid. It's probably burnt. My guess is, your AOD has fried its guts (a common occurrence with this trans), will need an overhaul.

Excepting the POS A4LD, the AOD was the worst A/T foisted on mankind by FoMoCo. Owners manuals and sales peeps told people to drive in Overdrive, but...

People drove in O/D in heavy stop and go traffic. The constant shifting up/down .. in/out of O/D fried the AOD's guts and it didn't take very long for this to occur.

People also towed in O/D, another big no no.

 

I know this sounds far fetched, but it sounds like you are driving down the road in 4x4. That would explain all the noise, and the burnt up transfer case. It explains everything really, even not wanting to go. If the tires are just a smidge different front to rear, and it's in 4x4 on dry pavement, after a few miles it will start binding the drivetrain. Pulling off to the side of the road in the gravel would let it relieve the binding.

 

transmission fluid level was good and the color and smell was good, but the mechanic is dropping the pan today to look for signs of failure.