1977 F250 Camper special ext cab 2x4
460/c6 3.73

I just noticed something and I am not sure how to describe it. I thought it was the differential starting to go bad and howl. It is intermitent....here is the whole story.

Two days ago I was heading into town to get some lumber ( silly me...there isn't any left...thanks Katrina. )....the trip to town (15 miles ) was fine.

Heading back I start having some fuel issues, which I do have from time to time ( I think the float needle is sticking or I have a bad fuel pump - also intermitent.....not the issue at hand )....so as the truck is starving for fuel I notice a hummmmmm starting at the rear of the truck. Strange, as it has never done that. I slowed down and sped up a few times...it was quite faint. A few more miles down the road the fuel issue repairs it self, the hum goes away and home I go with no problems.

I forgot about the hum this morning...heading back to town to see if I can get any lumber yet. Truck is running fine for 5 miles or so then I notice the front end starting to dance just a tad....the steering wheel had just a bit of wobble in it, like a tire out of balance or a tire with a small egg on it. I pull over and check the tires...couldn't feel anything...checked to see if any bearings were obviously loose...nothing. Started up again and drove another 3-4 miles and the hum came back. So now I am thinking the rear alxe is about to explode....and maybe resistance in the diff was causing the truck to bob about a bit...? Anyway, i turned around and headed home. The front end wasn't shaking at this point but the hum was still there....then it stopped and all seemed well again...then it started huming again.

I got home, jacked up the rear end ( and put on stands.... ) and started turning things to look for obvious slack or play. I didn't seen anything extreme.

I did notice, the diff housing was warmer than I expected it to be. How hot should this get? I could put my hand on it but it was quite warm.

I pulled the diff cover and drained the oil...it looked very clean. I was expecting to see metal shavings but it was very clean. The diff itself looks to be tight....?

What do you think???
HELP!

 

Did you have the proper amount of oil in the diff or you didn't check when you drained it? That could of cause some of your problems.
If you have a limited slip you would want to put a friction modifier to keep the oil from becoming to thin and heating up the rear end.

 

Oil was full in the rear.... It is a limited slip and there was friction modifier put in it ( went through it 3 months ago ) How warm should this be? What is the vibrations I was feeling?

 

It shouldn't be any hotter than a tranny, If you've been traveling for 30 mins or so like you did it would be warm, but not as warm as you said.
Check slop or any kind of slipage or loosness from the driveshaft.
Not sure exactally what's going on with your truck, but someone else might chim in and let you know.

 

U joints all seem ok. It is a 2 piece shaft...the splines between the two sections are a bit loose maybe.

How much play should there be? For instance, with the rear up off of the ground....how much should the rear tires turn before the drive shaft turns? There is a small amount of play here...

 

HOLD ON>>>SOMETHING IS FUBAR.

Trac Lock Diff....turn one wheel, the other should turn...it isn't. Are the clutch packs bad?

 

most of those limited slips work off of some resistance with the opposite wheel. this isn't a locker mechanism where there isn't any diff.

You can tell me I'm stupid if you want but try this. Jack up the frony of the truck and put you hands at three and nine on one of the tires. Try to shake it back and forth (Pull the tire towards you with one hand and away with the other. and if you can at all it's a tie rod end/drag link problem. Had this in the 77f100 a few months back, it was driving me nuts.

 

Amish77...I will check it out. I have had loose front ends before and I don't think it is the case but I will check it out....FYI, the front tires are wearing very even...no cutting or cupping.

This is what I did do though..i did do a tire rotate. Ran it....first several miles not an issue...then the vibration came back as well as the "bouncing"...i guess it isn't in the front end but the whole truck...which makes me think the drive shaft is out of balance and the carrier bearing is allowing the entire shaft assembly to "flop"....??? Once again though, this is not constant.

 

When you have the front jacked up, try moving the tire up/down. Get violent with it if needs be. My ball joints were bad when I got my latest truck, and the whole front wobbled like mad. Mine were pretty far shot though.

 

sorry guys but it ain't the front end.

I just swapped the carrier bearing...didn't do a thing.

How much play should be in the tail shaft in the transmission??? Is my tranny about to blow?

After swapping the carrier bearing, I took it for a spin...ran super smooth for about 2 miles....then the bouncing started...then the whine/howl. Shifting to neutral did nothing to change the noise. I stopped and turned around to head home. It quit. I drove all over town then back out on the highway again...i thought it started again but it seemed to stop before it got bad....then another several miles of highway and in town driving proved nothing.

 

Check the wheel bearings. Clean em up, check bearings and races. A re-pack never hurts.

Check ALL of your suspension bushings for wear and looseness.

Does the sound change with wheel speed? How about drive to coast, any "clunking" sound?

 

If your real careful-REAL CAREFUL, put the rear up on high quality jackstands and on a level surface(concrete only) you can lay under and observe while someone runs it and the problem might reveal itself. Check to make sure your driveline angles are correct. It should be 3 degrees for the front shaft and 6 degrees for the rear shaft with the truck on a level surface. Check all the rubber in the tranny support and engines mounts to make sure it is still intact and then check that the engine mount and tranny mount bolts are not loose and allowing the engine to "torque twist" the driveline. You said the u joints are OK but they can frequently look good but be bad inside. Lastly, have a real good friend hang underneath it while you drive down the road and..... (only kidding) Oh, another thing-make sure the harmonic balancer on the front of the crank is OK.

 

No clunks...from a stand still, shifting from park to D or R is a nice firm shift with no clunks ( like the old diff...which the pinion gears were shot...that one had one heck of a clunk )

You might be on to something with the engine mounts. I can say the drive shaft is not in a straight line, when under the truck and looking at it. Not sure that it should be though. It does feel like something "winding up"....More later tonight.

 

When you lay underneath and look at the driveshaft and how it runs from the tranny to the diff it is designed to be offset slightly. This is so the needle bearings in the u-joints will rotate and stay lubricated. A perfectly straight shaft wears the joints out quickly. Did you say there are holes in the driveshaft? If so then it would be out of balance and that might be your problem.

 

No holes in the drive shaft...

I am going to check motor mounts tonight...

What about the tail shaft in the tranny???