delco1946 Posted March 8, 2019 Share Posted March 8, 2019 I just bought a 1981 F250, trailer special. Its a beefy truck with 4x4. I'm just staring to play with it, but it wont go past 4HI (in the transfer case). It seems that the issue is likely the truck wont "let" me shift into N or 4Lo because it thinks the needed requirements have not been met. The requirements to shift into N and 4Lo are that the automatic transmission needs to be in neutral, and the truck needs to be stopped (foot on brake so i assume there must be some sort of brake activated switch). I think this must be some sort of electrical or vacuum issue - I'm guessing related to some sort of switch that tells the system I'm in neutral and stopped. I have twice been able to go into (transfer case) neutral and then 4Lo with the truck off, and the key in accessory position. The 4x4 lever moved smoothly (suggesting that the mechanical linkages are lubricated or a nonissue). Normally tho, i can't shift lower than 4Hi. anyone know what/where these switches might be and if they're an electrically activated switch or vacuum activated?? I will mention that in case its vacuum operated, my booster is going bad (leaks) altho i can brake fine for now. I can't find any references in my manual, repair guide or online. Im loading a picture showing some wires sticking out of my firewall near the brake pedal, hoping someone might know what they should be connected to (fingers crossed its as simple as someone disconnecting a wire harness but the wires could also be for a trailer hookup too). Any help/ideas is appreciated! Christopher Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 8, 2019 Share Posted March 8, 2019 Christopher - Good news and bad news. First the good news - the connector coming out of the firewall is almost for sure the connector to the brake controller. That is probably C1101 or C1106, as shown here: Electrical/EVTM/1985 EVTM/Trailer Option. In other words, your truck is wired for the trailer brake controller, but you apparently don't have one. And more good news - these trucks are fairly dumb/simple, and don't have any interlocks to prevent you from shifting into 4Hi or 4Lo. Further, there's no vacuum control that is going bad. It is all a mechanical linkage and you MUST be in Neutral and setting still to go into 4Lo. Now for the bad news - I think the "Insert (Shift Forks)" have worn out on your transfer case. You didn't give us much detail in your signature, like what engine you have, but most of the trucks had the NP208 transfer case. And I know for sure that worn inserts on the NP will cause problems like you are having as I've been there, had that done to me. My experience was that it would go into 2WD nicely. And it would go into Neutral ok, but it wasn't really in the detent on the shifter, so when you let go of the shifter it would slip out of Neutral sometimes. And it would frequently go into 4Hi. But never into 4Lo. I had the transfer case rebuilt and everything but those inserts was fine. They put new ones in and then it shifted perfectly. You can see the illustration, parts lists, and rebuild instructions on the transfer cases here: Driveline/Transfer Cases. Link to comment Share on other sites More sharing options...
delco1946 Posted March 8, 2019 Author Share Posted March 8, 2019 Christopher - Good news and bad news. First the good news - the connector coming out of the firewall is almost for sure the connector to the brake controller. That is probably C1101 or C1106, as shown here: Electrical/EVTM/1985 EVTM/Trailer Option. In other words, your truck is wired for the trailer brake controller, but you apparently don't have one. And more good news - these trucks are fairly dumb/simple, and don't have any interlocks to prevent you from shifting into 4Hi or 4Lo. Further, there's no vacuum control that is going bad. It is all a mechanical linkage and you MUST be in Neutral and setting still to go into 4Lo. Now for the bad news - I think the "Insert (Shift Forks)" have worn out on your transfer case. You didn't give us much detail in your signature, like what engine you have, but most of the trucks had the NP208 transfer case. And I know for sure that worn inserts on the NP will cause problems like you are having as I've been there, had that done to me. My experience was that it would go into 2WD nicely. And it would go into Neutral ok, but it wasn't really in the detent on the shifter, so when you let go of the shifter it would slip out of Neutral sometimes. And it would frequently go into 4Hi. But never into 4Lo. I had the transfer case rebuilt and everything but those inserts was fine. They put new ones in and then it shifted perfectly. You can see the illustration, parts lists, and rebuild instructions on the transfer cases here: Driveline/Transfer Cases. Hi Gary, thanks for the response. I don't know what type of transfer case i have but my engine is a 351M. Based on the chart you linked to, i think i might have the W1345?? My rear axle is 3.54 Link to comment Share on other sites More sharing options...
delco1946 Posted March 8, 2019 Author Share Posted March 8, 2019 Hi Gary, thanks for the response. I don't know what type of transfer case i have but my engine is a 351M. Based on the chart you linked to, i think i might have the W1345?? My rear axle is 3.54 I took a look at the drawings, regardless of which transfer case i have, i'd have to pay someone to do that sort of work, taking apart my transfer case is wayyyyyy beyond my comfort level and probably tool level. Link to comment Share on other sites More sharing options...
grumpin Posted March 8, 2019 Share Posted March 8, 2019 I took a look at the drawings, regardless of which transfer case i have, i'd have to pay someone to do that sort of work, taking apart my transfer case is wayyyyyy beyond my comfort level and probably tool level. I think Gary nailed it, although I have had trouble getting these to shift if there is any "load" on the driveline. i.e. if you're in neutral and you let off the brake and the truck will roll, it may be difficult to shift past 4Hi. On inclines I have shifted as I let off the brake. Link to comment Share on other sites More sharing options...
Ford F834 Posted March 8, 2019 Share Posted March 8, 2019 I would expect a BW1345 in your truck based on the year and it being a F250. That’s not the only possibility, but that’s the common thing to see. I doubt they would put a NP208 in a trailer special. I’m sorry I don’t have much insight into how to fix your problem... but I will share this: My friend Jan bought a 1986 F250 that had the C6 and BW1345 transfer case. He experienced exactly what you describe. The transfer case would not shift. If he turned the truck completely off (and in Park) he could shift it easily, but not while running, even with the C6 in park or neutral. We swapped the transmission to a ZF5, and the problem went away. The transfer case could be shifted on the fly in neutral or with clutch depressed. I don’t know what changed, but that’s what happened. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 8, 2019 Share Posted March 8, 2019 You might start by going under the truck and making sure the shift linkage gate is free to move forward and back, and side to side against the rubber bumper. Maybe there's mud or rust packed up in there and the stick won't shift sideways to get into neutral or 4lo? Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 8, 2019 Share Posted March 8, 2019 You might start by going under the truck and making sure the shift linkage gate is free to move forward and back, and side to side against the rubber bumper. Maybe there's mud or rust packed up in there and the stick won't shift sideways to get into neutral or 4lo? I agree with Jim that you should slide under and check out the linkage. And, do as Jonathan suggested and try to shift with the engine off. And, you should consider upgrading your signature to tell us more about your truck. The fact that it is a 351M may come in really handy in the future. Link to comment Share on other sites More sharing options...
delco1946 Posted March 8, 2019 Author Share Posted March 8, 2019 I agree with Jim that you should slide under and check out the linkage. And, do as Jonathan suggested and try to shift with the engine off. And, you should consider upgrading your signature to tell us more about your truck. The fact that it is a 351M may come in really handy in the future. I have tried shifting with the engine off - in fact thats the only time it has ever shifted for me, with the key in accessory position (electrical on). Its only happened twice, but as i recall it was letting me shift in either park, neutral, or in gear. I'll try to take a look at the linkages. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted March 8, 2019 Share Posted March 8, 2019 I have tried shifting with the engine off - in fact thats the only time it has ever shifted for me, with the key in accessory position (electrical on). Its only happened twice, but as i recall it was letting me shift in either park, neutral, or in gear. I'll try to take a look at the linkages. In my truck there is a rubber block that acts as a spring to prevent the shifter from moving sideways and being able to drop into the neutral gate. If the rubber is petrified or the pivot rusted solid you won't be able to move the shifter sideways. Maybe it just needs some cleaning or lubricant. Link to comment Share on other sites More sharing options...
Recommended Posts