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Wow...on another test drive. Loud noise, like something is dragging. I thought the new exhaust system had fallen off. I was on a rather dangerous section of highway, so I had my car towed off. In the parking lot - while waiting for a tow home I took a look underneath. It looks like main shaft running front to back is hanging where there should be some sort of bearing supporting it?

I guess you find a car that's been sitting for over 15 years, you also find some problems. I guess better here than far from home. I'm getting it towed home - and wondering how hard this new project is going to be. I've still got to get the rear caliper fixed!

Any tips on direction(ie website/video) on replacing this appreciated. Also - how hard would this be? I've never worked on any drive train stuff.

Thanks.
 

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Kevin,
Are you talking about the center support bearing?
The bearing and the rubber support housing are held in place by a cross support that bolts to the frame rails and the bearing is held up by a spring and cup on top of it.
Replacing the bearing requires separating the driveshaft sections and removing a large nut from the front half (IIRC), then installing the new bearing. Be sure to mark the driveshaft before separating the shaft, if you fail to get the splines realigned correctly you'll experiencing driveline vibration which will require having it rebalanced.
Kurt
 

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Discussion Starter #3
I'm not quite sure what I'm talking about! I was just driving, and then got the feeling I was dragging something on the ground. It was cold and dark. I think this has most likely gone beyond my abilities at this time.

When I looked under with a flashlight - I could see the main driveshaft sort of floating in the middle. Not sure exactly - but it didn't look right.
 

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I have never looked underneath an 1800; but, if its like the 140, the driveshaft has a front and back section connected by splines. There are three U joints. At the back of the transmission / OD, in front of the differential and sort of in the middle just in front of the splined section if I remember correctly.

If something is hanging down really low, as in dragging on the pavement, I am betting that your middle U joint failed. It is also possible that the rubber support for the mid bearing deteriorated and failed allowing the driveshaft to droop slightly which would likely lead to vibration. Because the rubber support for the mid bearing is held in place by the steel cross member that Kurt mentioned, it would not be possible for the driveshaft to drop really low below the car because it would hit that cross member - unless the cross member dropped off which would cause the center support bearing to droop leading to vibration and other bad stuff.

Assuming that the cross member has not gone AWOL, you probably need to plan for replacement of the center support bearing and its rubber suspension and the three U joints. All of this is doable if you have the tools; however, working under the car is a pain and getting the old U joints out and the new ones back in to the yolks is a pain. I disassembled my own driveshaft; but, took it to a shop to have the new U joints installed and get the shaft balanced (because, like a dummy, I painted over the registration marks that I put on the shaft when I took it apart!).

Edit

A little checking shows that the center bearing rubber support arrangement for the 1800 may be different than for the 140. Given your 1973 model year, it might be the same if it has the later type III driveshaft. The earlier type I and II driveshafts have a different center support arrangement; however, I think that failure of the rubber bushing on the type I and II arrangement would lead to the same problem. Whether it is type I, II or III, they are all two piece driveshafts with a center splined section and 3 U joints
 

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Aligning the driveshaft is not hard if you fail to mark it, and it can only go together correctly one way, so if you put it together wrong you just take the back half loose and put it together right. There will be no need for re-balancing. The vibration comes from the fact that universal joints are not constant velocity joints, so the driveshafts are slightly accelerating and decelerating on every turn. With the u-joints lined up, these little variations in speed are cancelled out.

The necessary alignment is to simply line up the universal joints correctly, like in this picture: There are also dozens of graphics on the internet if you simply google "2 piece drive shaft alignment" or something like that.



This is two halves of driveshaft from two different cars, but because the u-joints are lined up right, and both shafts were balanced on each car previously, I get zero vibration. Obviously if you bend a shaft or throw a weight you can get vibration, but vibration from putting it together wrong is easily corrected by putting it together right.

And a 73 will have the latest rubber support like a 140.
 

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My comments about the possibility of a mid U joint failure being the problem were out to lunch. I went out and took a look under my 140 this morning. The center support bearing is on the jackshaft side of the driveshaft, not the section connected to the differential as I was thinking last night. Complete failure of the mid U joint would result in the front end of the back half of the driveshaft dropping down on to the pavement and you would definitely know if that had happened.

Lloyd's point on the phasing of the driveshaft is correct. However, if you didn't put registration marks on the shaft and wanted to avoid the install, test and potentially remove and rotate to correct the phasing problem, then the shaft should be balanced and marked to show the correct phasing. Just $ versus time! It is interesting to note that the Volvo Service Manual says nothing about registration marks or insuring the correct phasing of the driveshaft during reassembly. I guess they assume that everybody knows that; however, they do go to lengths to tell you how to unscrew the two screws that hold on the taillight lens covers. Go figure!

As a related note, when my driveshaft was reassembled and the whole assembly was balanced as one piece with the center support bearing, they did alter the balance weights on the driveshaft from stock. I am not sure whether something changed or they just did that to make it seem like they provided value!
 

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However, if you didn't put registration marks on the shaft and wanted to avoid the install, test and potentially remove and rotate to correct the phasing problem, then the shaft should be balanced and marked to show the correct phasing. Just $ versus time!
No, you still miss the point. You line up the u-joints, they are just as accurate as a registration mark. The spline is odd numbered, there is only one way to put it together where they line up.

It's not some trial and error guessing game.
 

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No, you still miss the point. You line up the u-joints, they are just as accurate as a registration mark. The spline is odd numbered, there is only one way to put it together where they line up.

It's not some trial and error guessing game.
I have never counted the number of splines; but, based upon your comment, you are correct that for the case of simple separation of the front and back sections of the driveshaft it would not be possible to assemble the driveshaft incorrectly in terms of the alignment of the yokes, so phasing should never become a problem. If the center U joint is replaced, then it is entirely possible to displace the two sections of the driveshaft by 180 degrees relative to their original positions. The phasing of the yokes remains correct; however, if the two piece driveshaft was balanced as a single unit, then you have altered the dynamic balance of the shaft. If the balance of the driveshaft did not require much correction in the first place, the change in balance may not be material.

As an added note, when I took my yokes into the machine shop to have the U joints installed and have the balance of the shaft checked, I was assuming that the shafts would be balanced individually. The shop requested that I provide them with the center bearing and support so they could balance the shaft as a complete unit. I asked about balancing the shafts as individual units. They would not do that and advised that they would just charge me for the U joint replacement if I didn't want the shaft balanced as a complete unit. The shop dealt primarily with large industrial clients so I was operating on the premise that they were competent.

Just my experience, doesn't make it correct!
 

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Ah, I see a little more of what you are getting at. Sorry if I came off too obnoxious there.

In the end I do agree that marking them is the best plan, especially in the event of a u-joint rebuild.
 
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