I have a 79 F250 4x4 C6 NP205 and factory dana 60's front and rear. When I hit 50mph I get a serious vibration throughout the whole truck. I have checked the u-joints and there is no slop in them. I know the front drive shaft has a little play in it at the slip joint. I have been running 33's for about 8 years on this truck and never had a problem. I just swapped on a friends set of stock tires off his 95 F350 and still the same problems so i know its not the tires. When going over 50mph and letting off the gas you can hear a loud noise and it still vibrates. That noise and vibration is at its worse when you are going over 50mph and just slightly on the gas. I checked for play in the rear driveshaft and didn't find any. I looked to see if any weights fell off and they all seem to be on there. I am totally stumped. Anyone have any ideas what this could be? Any help would be great.

Thanks

Jeff

 

Check the differentials, sounds like a diff about to go.

Also check your shocks by having a friend follow you around to see if you have some wheelhop.

 

What do i look for when checking the diff? I am thinking it would be the rear diff. Could this be the carrier bearing?

Thanks

Jeff

 

[updated:LAST EDITED ON 27-Jul-02 AT 11:43 PM (EST)]carrier bearing is a good poss. also check the trans. transfer case mounts and bolts but i have the same truck and there is no carrier bearing in the driveshaft

 

Do you think it could be the pinion bearing? Or is that something that rarely goes bad? It has 157,000 miles on the rear end and never messed with as far as i know and its stock open diff.

Thanks
Jeff

 

is it a 2-piece shaft fro the rear??

 

No its a one piece shaft. Besides the u-joints getting sloppy when worn out, can they get real tight and cause this vibration?

Jeff

 

With that many miles on your truck , I believe that I would replace ALL ujoints on the truck....My 77 had way better than a 100k and I just decided to go ahead and do'em all at the same time----they were really in bad shape as they hadn't been greased in who knows how long!!! I just had these visions of a ujoint breaking and seeing the truck doing a "pole vault" at 60 mph---end over end----I would change'um if it was my truck-----fd :-X11

 

 

I'd have to agree with fatdaddy.. Chcnge them U-joints.. I have experienced exactly what he imaged and luckily it was late at night.. Other wise the person behind me would have been in bad shape.. I check my U-joint regualrly just as often as I do an oil change. Just because of the fear of that happening again.. Ended up having to replace my tranny because of it.. Anyway, I have a similar problem on my 73 Ford F-250 4 wheel drive. I only get the vibration when going downhill.. And it could be on just a slight grade.. Doesn't have to be a huge hill.. I never have been able to figure out the problem.. I have replaced just about everything in the drive train.. Not to steal from ford429s post, but you guys have any clue what could be causing this ?

 

50 YB-----Check your transfercase mounts very carefully , when I pulled my np205 down for a rehab the origional mounts were very decomposed------and check the nuts that hold the yoke housing for each drive shaft on the xfer case.....fd

 

When you get that wierd grumble/growl on deceleration and the U-joints aren't the cause check the diff pinion bearings for play. The growl is sometimes caused by the contact patch between the ring and pinion changing due to direction of loading. The pinion uses crush sleeves and shims to maintain the position of the pinion and the preload on the bearings. You may want to check with the boys in the; Transmission, Differential, Axle and Transfer Case forum for info.

Use the diagnostic chart from the Ford OEM manual to track down a problem. It is the best way to find those elusive problems. If you don't have a paper manual you can get a CD from the FTE store. It is WELL worth the money.

You can also find a bad U-Joint by "hand" if you crawl under your truck just after it has been driven and "feel" the U-joints. They will be warm from normal operation, but if they are HOT...

You are lucky not to have that 2 piece driveshaft. I gave up on doing U-joints on those. Now I just take them to the driveshaft shop and have them replace the joints and balance the shaft. Of course I live in a big city with two local truck driveline shops that do the balancing. I found that it was only a few bucks more for the shop to replace the joints and balance the shaft, than to balance only with my U-joints. The difference wasn't worth my time and effort.

 

This may sound stupid, but I found this out the hard way. What you are describing sounds exactly like what happened to me when I was driving my '74 Highboy about 18 years ago. I simply forgot to take it out of 4 wheel high. Make sure your transfer case is in 2H. When this happened to me, the truck shook very violently. Enough to the point that I thought the truck was going to rip itself apart. It scared the daylights out of me. The truck has never felt any ill-effects from the incident and that's just a testament to how well built Fords are.

Graffe

 

Looks like I need to give more details. But I will be checking what you guys have suggessted. Yes, I have made sure the truck isn't in 4 wheel drive gears and the hubs are not locked. I have had the U-joints replaced and the drive-lines balanced. I have also replaced the transfer case mounts and bolts and even lowered it because I was told by a shop that it may be because of the angle of the driveshafts. Now to the nitty gritty. My truck has the NP205-divorced transfer case with NP435 tranny. All the driveshafts are 2 piece slip shafts. ( or whatever they call them )the problem occurs at any speed going down hill.. Thanks for the tips so far..As for the differential I haven't changed anything other than the gear oil every 30k miles.