Hello, all. New to the board, and new to my latest addition to my vehicular addiction...

I have just purchased an '85 F-150 4x4 with a 351W and a 3 speed automatic, with 71k original miles. It's quite ugly (rust in the bed, cracked windshield, faded desert-tan paint) but runs quite well for a $900 truck.

My problem for now is, when I'm driving above about 45MPH, and slow down (as if to come to a stop) the truck starts shuddering violently. I know it isn't (or at least it isn't *just*) the brakes, since it will do it even when I don't touch the brake pedal. It smooths out around 25mph, sometimes a little higher, but it feels like I'm driving over a washboard, even on the smoothest of pavement.

Is this possibly a transmission problem, or does it sound more like an axle? The rear axle does make an interesting *ping* noise from time to time if I put it in reverse (after driving forward then parking) or if I put it in drive (after reversing, then putting in park). Does it every now and again when I shift from R to D, but not always. I'm worried that it may be a bearing failure in the input to the rear axle, as I had a '72 K-5 Blazer that completely demolished it's own rear axle due to bearing faliure.

The shuddering (vibration) really seems to be coming from the FRONT of the truck when it does it, but I'm still getting used to how this beast feels, so I'm not 100% sure about that. I figure I'll ask you folk here that have had more experience with your Fords than I have.

Thanks in advance!

 

Your ping noise may be a loose rear end or bad u joint. Does it howl at all? I would get the rear checked out. First the noise, then the howl, than the loud violent clank of metal when it goes out!

 

Check to see if the front hubs are not locked in and ensure the transfer case is in 2 wheel drive.

I believe that driving around in 4 wheel drive on pavement isn't the best thing for the system, parts will end up braking.
If you feel the "shuddering" is coming from the front,
take a few mins to check and see if the front axle is locked in to 4 wheel drive,
if it is, there maybe be part of your problem,
if it isn't, then check your driveshafts (slip yoke worn, bad U-joints, etc).

 

Lift the truck up to check that your hubs are unlocking properly spin the driveshaft and axles to make sure everything is unlocked

 

Thanks for the replies, guys.

I tracked the shuddering down, and it was the front rotors. They are slightly warped. When I posted this question, I hadn't driven it too terribly much, and had not noticed it doesn't do it when I don't apply the brakes. Now that I'm driving it more, it has reduced significantly. It is, in fact, barely noticeable now.

The *ping* noise I heard, upon more in-depth troubleshooting, doesn't seem to be coming from the rear after all. I'm fairly certain I have a bad trans mount. I'm still going to have it all checked out by a certified mechanic (rather than my shade-tree methods) before I trust it 100%, since it's just a good idea to.

Still, all in all, it's a nice truck for $900. I'm actually looking forward to the snow this year, since it's the first time in about a decade I've had a 4x4. Sure beats trying to drive a '63 Chevy C-10 around...