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Old 07-10-2009, 10:33 PM   #1
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1982 28' Airstream 280
Port Angeles , Washington
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Vibrations

This is a description of my vibration problems on a 82 280 Excella diesel and the fix.

When we picked up the AS in Sacramento and headed out on the 1000 mile trip home we encountered several problems one of which was a vibration starting at about 55 mph and getting worse as we went faster. I knew that diesels can vibrate more than a gas but this just wasn't right.

At about 500 miles I got quite a racket coming from the transmission and we were free-wheeling. Engine was running but it was like being in neutral. We followed the tow truck and AS into the shop and enjoyed a week of unscheduled vacation.

Turned out the flex-plate broke and after some discussion with the shop and serious checking some of the alignment pins on the transmission adapter ring were missing. Further checking proved that the transmission was about .045" to one side. There had been a recent engine overhaul and the reassembly was not what it should have been.

I was not happy however I felt that by correcting this problem the vibration would be gone and we could begin a happy association with the AS. Unfortunately that was not the case. The vibration was still there with very little improvement if any.

After getting home and taking care of other issues and the arrival of winter the AS kind of got put on the back burner. I really don't like crawling around in the cold and mud.

With the arrival of spring my ambition got a fresh start. The u-joints were tight and appeared in good shape and the carrier bearing looked good also. As I lie there scratching my head I started looking at the driveline angle and something didn't look right. I got out my protractor and took some measurements and hit my reference material. After checking my numbers and rechecking my measurements I put 3 degree wedges under the spring mounts to tilt the pinion up so the u-joint angle offset the center u-joint angle. After a test drive there was still a vibration but it now started at about 65 mph. This was an improvement but it still wasn't right.

Next I took a really close look at the drive shafts. Both shafts had balance weights and I could find no evidence of lost or removed weights. I decided to bite the bullet and pulled the shafts and took them in to be balanced. It turned out not only were they out of balance but they both needed to be straightened. After some magic massaging by the driveline guru I remounted the shafts and took the test drive only to find a new more severe vibration. I was a good deal less than happy.

Back under the AS I removed the rear shaft to try to isolate the problem to the front or rear shaft. With the rear shaft out I had wife crank up the engine, put it in gear and run it up to speed while I watched underneath. The front shaft was bouncing all over the place. After a close look it turned out the new strap kit for the front u-joint that the balance shop had supplied was the wrong one. The front u-joint was not tight. After digging the old straps out of the scrap box and remounting the shaft things looked better. The test drive proved the vibration was gone and the AS actually has a very smooth and comfortable ride.

I realize this post is pretty long but I learned several things and still have several unanswered questions.
The AS even after 27 years once again has a very smooth and comfortable ride.
Even the best shops make mistakes.
Don't assume anything, check, check and recheck everything.
I don't know how the pinion angle could be so far off, how it got that way and how long it has been that way.
How the driveshafts got bent, no sign of impact on them or the bottom of the coach.

I hope nobody has any problems similar the mine but if you do these are some things to check.

Cheers, Dan
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Old 07-11-2009, 07:22 AM   #2
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1974 20' Argosy 20
Richmond , Kentucky
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Dan,

Great write up! We have a harmonic vibration on our 310 that probably starts at 35 or 40 mph. It doesn't really get worse and you can't really hear it much, its more a seat of your pants type of vibration.

I'll have to get underneath it this summer and start checking things out. We had planned on pulling the drive shafts to get them balanced and your post just reinforces that need.

Thanks!

Brad
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Old 07-11-2009, 10:18 AM   #3
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Brad<<<<.>>>>>If you are going to pull the driveshafts ,just replace the U joints and amid-ships carrier bearings(It think thats a 2 peice driveshaft) while you have it apart. It will cost a few bucks but will be money well spent. Any good driveline shop will do that for ya and they will check the balance on the shafts also. Seat of your pants vibrations are most likely driveline or a bad tire. Im about to do the same thing to the wifes F150 .
Dan
Driveshafts get bent from torque and will show now signs of being hit.In my 45 yrs over the road I have seen shafts tied up in knots and actually twisted in two. Mostly from being stuck in the mud or snow and ice with heavy loads.
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Old 07-11-2009, 11:52 AM   #4
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1982 28' Airstream 280
Port Angeles , Washington
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Mike you are correct that u-joints and carrier bearings are the first and cheapest things to check. I also agree that drive shafts get wrapped up especially when stuck. A big part of the scenario is a manual trans. Dump the clutch and something has to give. However on the AS the Isuzu is not a big power engine and the torque converter on the turbo 400 trans allows for lot of slip and a soft make up.

I guess the bottom line is these units are 25 to 30 years old and things do happen. Right now my AS is vibration free and I'm a happy camper.

Cheers, Dan
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Old 07-11-2009, 10:16 PM   #5
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1989 34.5' Airstream 345
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Dan,
Thanks for the concise walk-thru...I hope to never have to use your experience, but knowing it's there is the best insurance, and the price is GREAT!!!
mike
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Old 07-12-2009, 07:46 AM   #6
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A worn transmission mount or carrier bearing (center support bearing) can also cause vibration. If you feel a vibration from the drive line, another important thing to check is if all the u-joints are aligned with each other. If you turn the driveshaft until the front yoke is pointing straight up-and-down, all others should be that way too. A u-joint that has a grease fitting can vibrate if it has no grease in it. And, if everything looks okay, you can still have a bad u-joint. It can "stick" or seize internally.
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