OK, here we go. I have two 79's. the one with the problem is an f150 with a 460/c-6. it has a split drive shaft. I am getting a resonance in the cab starting at 55 mph. but, it is not constant but, is consistent. took it to a mech. we started out with new u-joints. that helped a little. took it to a tranny shop. was told that the pinion bearings are going out. but, when he checked for play in the rearend there wasn't much. still did not explain the resonating vibration. got underneath and checked the driveshafts for lineup. the rear u-joint is not quite lined up with the others. so, it may be an damaged driveshaft. another mechanic said that if it were a driveshaft then the noise would be constant. he thinks it is in the ring and pinion. so, my question is this. my other 79 is a 302 with a 3 spd and a solid drive shaft. can i swap out rearends and the drive shaft and just get rid of the 2 peice drive shaft?the 460 axle is a 3.50/3750 and the 302 axle is a 2.75/3750. one more thing my mechanic does high performance and he says that my stock 460 is unnaturally fast any insight into all of this would be appreciated.

 

Star,
They will not swap out. The 302 is a C4 driveshaft. The 460 is a C6 driveshaft. The pinion flange is different between the two. The C4 tranny is shorter than the C6 and driveshafts will not swap.
Option: Reuse 2 piece shaft. Buy C4 to C6 u-joint and swapped carriers. I bought a U-joiunt like this once at the dealership.
Good Luck,
KingFisher

 

thanx for thw info but, i still need to know the problem. do you have any idea what is causing this?

 

Impossible to diagnose w/out driving truck.I would check wheel balance & runout on tires or swap on known good. You could have one piece shaft built($$$$).Jack up rear,block it securely (support by rear housing,using rubber pad between jackstand & housing) bring up to speed.If not there,it is tires.If still there,the old chalk trick on the driveshaft will show out of balance.It could be anything from a bent fan blade to out of balance brake drums.With two similar trucks,parts can be swappped for testing.Ford bought back a 95 F150 while I worked there-vibration could not be found.Ford engineer came & we swapped rearends,trannys,you name it could not fix vibration/drone.Only one I ever saw bought back.Brian

 

Hi: I would consider taking the driveshaft out and having it balanced.

 

Has anyone checked the center support bearing?

 

that is one of my options. doe sanyone know what it costs to get asplit shaft balanced? also, both mech's have said that they have seen center bearings with alot more play in them than mine has they have lasted a long time.

 

I have a similiar problem, a drone type of vibration that on some occasions is really annoying like the truck's ready to shake apart and other occasions it drives like a dream...I found a new trick that seems to help, but hasn't helped my diagnosis either..and since it's so sporadic it's tough to blame wheel or driveline balance. If I let off the gas while cruising on the freeway and carefully shift into neutral then back into drive again the vibration seems to lessen in "amplitude." My C4 was rebuilt two years ago and the mounts were replaced last year. There's no play I can find...jowilker posted a while ago that the springs may be a culprit...meaning that the entire axle assembly is moving and somehow causing this symptom...I'm going to try and have my springs re arched and bushed next week..given all goes well with my ingition venture. Do you have a nine with an open differential?

 

that is interesting that you brought that up about the springs. Reason is, I was walking towards my truck the other day and noticed that one wheeel was sticking out further than the others. so, i got a flat board and a ruler. layed the board across the wheel and measured to the frame. the 2 measurements were off by 2 inches!!!. but, the trucks rides true. infact i recently had the front end aligned with no problem!!!!!!!1

 

also. I have a 3.50/3750 lb ford rearend. my local junkyard has a 3.50/3750 posi pumpkin but, suggests that i get a 3.00/3750 for better mileage and lower RPM.
can anyone give me some performance info here. because this truck right now is REALLY fast. it seems to be stock but, it will hit 100 mph on an Entrance Ramp!! is this normal?

 

Inspect your yokes. I'm having the same problem. After inspecting everything, changing the u-joints and ring and pinion. I noticed that the yokes had some wear were the u-joints connect at. Probably from and u-joint getting loose and wobbeling around. Don't know if this will fix it, I haven't bought new yokes yet. All I did was put in a larger u-joint to take up the new room and vibration went down a little.


Me_Bad_Dog(No Email Addresses In Posts!)
74 F-250 4X4
In process of rebuilding
460cid
np435
np205 devorced
looking for dana 60 open knockle front

 

 

My 1979 F100 had a similar problem, but it didn't turn out to be any one thing. Everything I did made it a little better until finally the sum total of everything cured the problem. One tip - when you put in new U-joints, press them in, don't let anyone beat them in. I took mine to a local shop because I just assumed they would press them in. I heard someone banging with a hammmer and went back in the shop and the mechanic was beating them in. I could have done that myself. They should be slightly tight with no perceptable play. If they're too tight they don't roll over right as the driveshaft turns, which puts rotational force on the transmission tailshaft bearing. Check your driveshafts to make sure none of the balancing weights have come off. Also check for play where the pinion shaft comes out of the differential (I guess you call it a pinion shaft, the shaft driven by the drive shaft). Also check for play at the transmission output shaft (tailshaft). There's a copper bushing in there that gets worn and could need replacing. Bill Jeffreys