Hello Ncdiesel. As I agree with Jerry about bad drive line angles producing a vibration, there is a couple of thoughts that come to mind as I read through your description of how the problem comes about. I am not saying that these are the problems, just things to check out. First is rotational twist on the drive line as you build boost (10lbs) at 2000-2200 rpms you are applying more rotational torque to the drive line than (8lbs) at 2000-2200 rpms. Look for anything loose or ill fitting that might shift and touch in the drive line, skid plates, sheet metal, speedo cable, brake cables, exhaust system,fuel and brake lines, pinion nut, ect. The next thought is harmonics. This is the sound wave produced by the combustion action in the cylinder. This sound wave is produced in all engines (about 18-22MHz in a gas engine...not sure on a diesel). Next think of the entire truck as a tuning fork. Any loose metal or to close fitting metals any where can setup the vibration. Other places that are possible are the "drum effect", a loose baffle in the muffler , something loose in the fuel tank and the hollow of the driveshaft itself. Just food for thought....I hope this helps

Interesting that you mention this, as I just went through this with another rattle. After the rebuild, I would get a low, but vehicle wide "hum", for lack of a better word, on deacceleration only. There was no origin to this hum and I couldn't figure it out. No vibration, just a hum - like the truck was humming a single note song. Fortunately, while nursing a bad ankle, I was driving with my foot pulled back against the seat because it felt better in that position and felt a very small vibration under my foot. Looked under the truck, under the location my foot was at and an exhaust hanger was resting against a cross member. Loosened it and moved it up a few inches on the pipe and problem solved.

At any rate, back to my problem at hand. This previous experience has helped me narrow the current vibration down to something most definitely mechanically amiss. It isn't harmonics or sympathetic vibration. I know what a vibration hitting the right "Trooper" note sounds like now (-;

What is the consensus for solving this problem? Shims? Double jointed carden driveshaft? Get suspension back to like new condition?

Thanks again for all your help,

NCDiesel

HEY SPEMCER GLAD YOU GOT ZEROED IN ON IT , FIRST IF YOU HAVEN,T CHECKED ON THEM , CHECK THE REAR SPRING HANGERS FOR THE BUSHINGS FRONT AND REAR, I HAVE SEEN MORE OF THESE THINGS WORN OUT IN THE LAST FEW MONTHS THAN I HAVE IN YEARS AND YES THERE WAS A SHIM KIT AVAILABLE MANY YEARS AGO BUT ARE NO LONGER AVILABLE, BUT MOST ANY SPRING SHOP SHOULD HAVE THEM I WOULD TRY A 2 DEGREE SHIM FIRST AND TILT THE PINION UP IN FRONT SO THAT UNDER ACCELERATION IT WILL BE TURNING UP INTO A NORMAL DRIVING POSITION,DON,T GO TO FAR OR WHEN YOU TRY TO PUT A BIG LOAD IN BACK IT WILL BE TILTED UP TO FAR , BUT I DOUBT ANYTHING UP TO 4 DEGREES WILL GET TOO EXTREME JERRY

It looks like Matt at Independent4x has a complete set of busings. I'll start with bushings since they are easy. I'll do shims next if that doesn't help or help all the way.

Now, when it comes to shims, I want to make sure I have this right in my mind: The added torque makes the pinion crawl up higher on the ring gear. This is turn makes the front of the pinion shaft go down. That increases the angle and that increase is what is making the vibration. That means the thicker part of the wedge goes forward, or towards the front, if I get shims.

Sound like I got this??

NCDiesel

NCDiesel

NC--

Thanks for posting the link to a great driveline tutorial and thanks to Pirate4x4 for his expertise. Here is the link again for those who want to go there:

http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html

Paul

Wow, every time I run into a problem, NCdiesel is two steps ahead of me

You may all recall, I'm swapping in a c223 from an '81 pup into my '79 postal jeep. Well, things were humming right along until I called my local driveline shop for some help with the rear driveline. They seemed to think that anything besides a stock rear single cardan u-joint for the slip yoke at the back of the axle was unavailable. Now, I admit that the angle down to the rear differential is a little severe, and that a normal u-joint is not going to cut it, but I would think there has to be *something* available. JERRY, I noticed you mentioned a double-cardan joint. Do you (or anybody) know a supplier for such a joint that will work with the 4 speed tranny/transfer case combo out of the '81 diesel pups? (I believe it's a MSG-4T???)

Rough measurements are 21 inches from rear of output shaft in tranny to center of u-joint on the rear diff. Roughly 9 inches of drop from shaft to shaft. That works out to about a 25 degree angle.

Now, I could tilt the engine/tranny a bit to get a little bit better angle, but from what I understand, doing that would require some sort of cv (or near-cv) joint anyways, since the two shafts wouldn't be in the same plane anymore.

I read as much of the tutorial at http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html as would come up (I started getting connection refused errors), but it sounds like a double cardan joint would be the way to go. If anybody knows somebody who can make such a thing for my tranny, I'd really appreciate hearing about it.

Thanks all!

-----
ps. I'm working on getting some pics up on the web.

HI SPENCER , NO ON THE PINION ANGLE , WHEN YOU GET ON THE THROTTLE THE TORQUE OF THE ENG CAUSES THE PINION TO TURN UPWARD AND IF THE SPRING BUSHINGS ARE WORN OUT IT CAN LET THE DIFF TWIST TOO HIGH , AND IT MAY BE IN FACT GOING TO HIGH , PAST THE NORMALL ANGLE , WHAT HAPPENS WHEN YOU PUT THE WEIGHT IN THE BACK , THE BACK END SQUATE DOWN AND THE PINION TURNS UP AFTER REPALCING THE BUSHING , IF IT STILL VIBRATES , THEN GET A 2 DEGREE SHIM AND PUT IT IN THE BACK SIDE OF THE SPRING PAD AND THAT WILL TIP THE NOSE DOWN, TRY IT AND SEE IF IT DOESN,T HELP , THEN UNDER TORQUE IT WILL TEND TO TURN UP TO ANORMAL DRIVING ANGLE ,,ANYBODY EVER DONE ANY DRAG RACING WITH CHRYSLER CARS , THEY USED TO OFFER A BIG RUBBER SNUBBER TO BOLT ON TOP OF THE REAR AXLE RIGHT ABOUVE THE PINION SO WHEN IT TURNED UP ON ACCELERATIION IT WOULD BUMP THE FRAME AND STOP THE PINION FROM CHANGING ANGLES AND BREAKING U JOINTS , AS FOR THE DOUBLE CARDAN JOINTS I WOULD THINK ANY GOOD DRIVE LINE SHOP COULD MAKE ONE , FACT IS NISSAN DOES HAVE ONE IN THEIR PICKUP, FOR THOSE WHO ARE NO FAMILIER WITH THE TERM IT IS 2 U JOINTS AT ONE END OF THE DRIVE SHAFT IN A COMMON CARRIER BUT THE 2 JOINTS ARE CONNECTED BY A SMALL MOVABLE ARM IN THE MIDDLE OF THE JOINTS AS ONE JOINT TURNS ONE WAY THE OTHER CAN TURN THE OPPOSITE WAY THERE BY CANCELLING A DRIVLEINE VIB AND CAN TAKE EXTREM ANGLES, ROD GORRELL I BELIEVE HAS HAD ONE DONE ON HIS RODEO SOME PLACE AROUND WINSTON SALEM N.C., THEY MAY BE CALLED C.V. JOINTS NOW DON,T KNOW FOR A FACT THOUGH , BUT THEY HAVE BEEN USED IN LINCLON S CADDY AND IMPERIALS FOR YEARS .. JERRY

Thanks Jerry, I have it straight now. I thought we were talking about a torque flex in the diff housing, not a total torque rotation of the axle. Makes more sense and I will install any shims with the thick side towards the back. <img src="/forums/images/graemlins/smile.gif" alt="" />

Matts full bushing set was shipped yesterday, and should be here today. I'll install those over the next week or so and let everyone know how they do.

Thanks again to all!

Spencer

The Trooper was singing a happy song because it was on the road again, with a fresh rebuild, lovingly assembled by it's owner! <img src="/forums/images/graemlins/smile.gif" alt="" />

I believe earlier Jeep Cherokee's also used double-cardan joints in it's front driveshaft on some models.

I put those leaf spring bushings I got from Independent4x in today - Man the old ones were close to shot - not worn through, but very sloppy and the shoulders were gone on half of them. It made a handling improvement so pronounced I noticed it just pulling out the garage for the first time. <img src="/forums/images/graemlins/smile.gif" alt="" />

At any rate, it also very nearly completely eliminated my 2000rpm vibration too. I can still feel it, but I'll bet no one else can.

I've only driven 10 miles so it is still a bit early to call it a total sucess until I have a few more miles. So for now I'll cross my fingers and venture to say that I think I have this vibration licked with a $35 set of bushings and 3 hours of work.

Thanks again for everyone's help!

PS: The bushings for spring eyes are not exactly right on my 86 Trooper. The ID was a bit too large. I had to wrap the bolt with .007 shim stock to remove all play. The picture is after my signature.

NCDiesel