2000 F150 4.2L 4r70w knocking

Before you head out to the local junkyard looking for a compatible transmission, I would either performance and OBD diagnostic. The reason for my recommendation is that I don’t believe you have a transmission problem. It sounds to me as if it could be a sensor that has failed or is failing. I would start with the anti-knock filter since you say the transmission is knocking, it would seem to me to be best bet.

You can tell that this is a mechanical problem rather than a transmission issue because it is located in a specific gear, rather than affecting the tranny as a whole. Indeed, that is one of the strongest telltales that the issue is mechanical. If it were a transmission problem or a problem within the transmission (honestly two different ideas, for example, if it is a transmission problem, the tranny then it would be failing in more than one gear. Further, the transmission would likely be exhibiting problems such as slipping in all gears; there might be problems with transmission electronics such as the MAP sensor failing to do its job, turning your pickup’s performance into poor capability, and more.) If it is a problem within the transmission then it would be exhibiting other problems. For example, if it were a problem with the input shaft then you would likely have a pickup with very loud noises coming from that area as the input shaft complained that it had a problem very pointedly.

Believe me when I tell you it’s to your advantage if you take your pickup into a local full-service transmission shop with NIASE-certified technicians. They will quickly isolate the problem from which your pickup is suffering and report out on it. I would be willing to bet you a large cup of iced coffee you will find that the OBD report shows lots of 07XX errors which, by the way, are for various systems within the transmission. Let me know what happens, please.

Indeed, I was talking about the engine’s anti-knock sensor when I mentioned it — I was also thinking about different sensors that might also handle knocking, as well. It is the device that advances or retards the timing automatically as it senses the stresses on the engine. And, yes, it is the same report you get at AutoZone or another shop, though, their tests are nowhere near as detailed as the reports you will get from the dealer, for obvious reasons (they have the latest full diagnostic software from the factory that independents can’t usually get).

The transmission fluid filter is an internal filter that keeps debris and metal shards from running around the tranny, possibly harming delicate, small parts and openings. It is usually located on the output side of the transmission fluid pan so that the nasty stuff will stay in the sump where it belongs.