nilknarf007 Posted January 15 Share Posted January 15 1985 F150 4x4 with 4.9 and NP 435 manual transmission. When I lock the hubs, I get a vibration that is proportional in speed with the rolling of the tires. No movement, no vibration. Even vibrates when still in 2wd with hubs locked. Checked the U-joints and all related mounts, and can't find a problem. It's so bad, I've only gone about 8-10 mph in 4wd. Anyone have any ideas? nilknarf007 1985 F150 4.9 IL6 NP435 4x4 Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 15 Share Posted January 15 I suspect you have a bad u-joint in that front axle. So I'd lock one hub at a time and see which one causes the vibration. If one does cause a vibration I'd lock the other one in, by itself, and engage the transfer case to prove that everything else is smooth. If that is smooth you'll know where your problem lies. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 15 Share Posted January 15 Don't lock the axle on dry pavement? There should be a sticker on top of the driver's sun visor explaining this and why it isn't a full-time 4wd system. Link to comment Share on other sites More sharing options...
Ifitaintbroke Posted January 15 Share Posted January 15 Totally off-topic for this thread, and sorry I can't help with your issue, but how do you like the Clifford setup? Link to comment Share on other sites More sharing options...
nilknarf007 Posted January 16 Author Share Posted January 16 I suspect you have a bad u-joint in that front axle. So I'd lock one hub at a time and see which one causes the vibration. If one does cause a vibration I'd lock the other one in, by itself, and engage the transfer case to prove that everything else is smooth. If that is smooth you'll know where your problem lies. Thanks Gary. I gave that a shot, and I got the vibration with both sides. Keep in mind though, I'm really going slow. The drive shaft to the front end is in really good shape. Not going fast enough for a u-joint problem to rear its head unless something was missing from it. I'm afraid if I go faster than idling in 1st gear (actually 2nd), something will fly apart. As far as switching the truck into 4wd, I'm familiar with how to do that. Plus, there isn't any dry pavement for miles. We're in the middle of a good snow. I did notice, however, that my 4wd shift lever doesn't have the positive "detents" that it used to. They're still there, but not as pronounced as it used to be. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 16 Share Posted January 16 Thanks Gary. I gave that a shot, and I got the vibration with both sides. Keep in mind though, I'm really going slow. The drive shaft to the front end is in really good shape. Not going fast enough for a u-joint problem to rear its head unless something was missing from it. I'm afraid if I go faster than idling in 1st gear (actually 2nd), something will fly apart. As far as switching the truck into 4wd, I'm familiar with how to do that. Plus, there isn't any dry pavement for miles. We're in the middle of a good snow. I did notice, however, that my 4wd shift lever doesn't have the positive "detents" that it used to. They're still there, but not as pronounced as it used to be. Most of this era TC levers use a block of rubber to push the stick against the detents. You might find the rubber has hardened with age. Edit: is the pivot pin rusted solid or packed with mud? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 16 Share Posted January 16 Thanks Gary. I gave that a shot, and I got the vibration with both sides. Keep in mind though, I'm really going slow. The drive shaft to the front end is in really good shape. Not going fast enough for a u-joint problem to rear its head unless something was missing from it. I'm afraid if I go faster than idling in 1st gear (actually 2nd), something will fly apart. As far as switching the truck into 4wd, I'm familiar with how to do that. Plus, there isn't any dry pavement for miles. We're in the middle of a good snow. I did notice, however, that my 4wd shift lever doesn't have the positive "detents" that it used to. They're still there, but not as pronounced as it used to be. How is the pinion slop and backlash in the front axle? Sometimes the lube in the front diff never gets changed and the gears and bearings eat themselves. Link to comment Share on other sites More sharing options...
nilknarf007 Posted January 16 Author Share Posted January 16 How is the pinion slop and backlash in the front axle? Sometimes the lube in the front diff never gets changed and the gears and bearings eat themselves. ArdWrknTrk, the rubber you mentioned has seen better days. I'll have to look into once I can spend some time underneath while dry. There is no slop that I can feel. There is no play front to back, side to side, or rotationally. Oh, and I can rotate the front drive shaft with my hand while in neutral and unlocked. It's not easy, but I can rotate it. I changed the front diff fluid when I bought the truck a little over 2 years ago. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted January 16 Share Posted January 16 ArdWrknTrk, the rubber you mentioned has seen better days. I'll have to look into once I can spend some time underneath while dry. There is no slop that I can feel. There is no play front to back, side to side, or rotationally. Oh, and I can rotate the front drive shaft with my hand while in neutral and unlocked. It's not easy, but I can rotate it. I changed the front diff fluid when I bought the truck a little over 2 years ago. Okay. We can eliminate bad mesh and the pinion getting sucked into the carrier as causes for your jerky front axle. And you say it doesn't change going straight ahead or turning? Link to comment Share on other sites More sharing options...
nilknarf007 Posted January 16 Author Share Posted January 16 Okay. We can eliminate bad mesh and the pinion getting sucked into the carrier as causes for your jerky front axle. And you say it doesn't change going straight ahead or turning? Nope. Stays the same. But I haven't driven it over about 10 MPH in 4wd due to the vibration. Don't know if it goes away at speed, but I doubt it based on what I'm feeling. Link to comment Share on other sites More sharing options...
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