Last weekend, I drove home a really cheap 2004 F150 4.6L STX RWD with extended cab and long bed with 150k miles. It had a cylinder 2 misfire and running lean codes. I replaced the coil, which fixed all the codes. When pulling it out of the drive way for a test drive, while accelerating, the truck started shaking and suddenly the rear wheels locked up and the truck came to a screeching halt. It did this a couple more times right after another while accelerating from a stop at 5-10mph. After letting it sit for about a minute, it never locked up the rear again.

I replaced the differential fluid today, there were a couple minor metal shavings and the fluid was definitely old. I drove it again with some minor rumbling/shaking during acceleration from a stop, but no major issues. I even took it up to 70mph on the freeway and it runs really smoothly.

I'm thinking it might be the drive shaft universal joints causing the shaking? But could they make the rear lock up like that? The transmission seems to be fine, but i'm going to replace the filter this week.

 

I would look at the park brake mechanisms inside the rear rotors make sure they aren't sticking or dragging

 

That would be awesome if that's the case. I'll crawl under there in a little bit.

 

Seems like there was another member a year or so ago that had his rear axle lock up and it was the friction lining came off one of the brake shoes inside the rotor and jammed up locking the wheel... I had the same thing happen, but it was just rubbing in there making a racket it didn't lock up on me. It may be worth taking apart and applying anti seize to the little scissor mechanism that the cable attaches to on each side where it pivots inside the drum

 

So, everything looks fine from the exterior, the scissor mechanisms are attached to the cables and in the correct position. These trucks have drum and disc in the rear? Is the drum solely for the parking brake? I have never worked on drums before, so i have no idea what to look for.

 

that’s a great engine. Does it have a LSD rear? If so, make sure you put in the ford modifier, then go to gravel/dirt lot and do a bunch of really slow figure 8s.

You may want to do plugs, boots/springs, and TB clean. Suggest waiting though for plugs/boots/springs until you get some miles on it and make sure you have no coolant leaks. Any coolant in wells will compromise boots and then later/eventually cause misifires (so best to deal with any leaks first).

 

I did put the modifier in, I didn't find any signs of coolant in the well, just some corrosion and rust on the boot. I bought all new plugs, coils and fuel injectors, so I'll be changing them all out eventually. I really just wanted to get the codes cleared so it could pass smog. Just waiting for the evap system to complete its checks.

 

wonder what the stains are from ?


take an exact measurement of coolant bottle when stone cold. The monitor it (only when totally cold) over a few thousand miles.

maybe you dont have any leaks. Just saying that if you do, and you change your boots first, you’ll be doing it again soon (and chasing misfires).

 

Had a GM 12 bolt lock up once. Ended up a ring gear tooth broke off and jammed the gears. Odd but that happened.

 

I had a previous gen 2wd that also suddenly locked up from, as another poster here describes as a possibility, the e brake linings delaminating and jamming.