Hanger bearing with suspension drop

[1970Tex]

Hey I'm looking for some feed back on my hanger bearing issue. 1970 GMC 1/2 ton, 350 engine, TH350 transmission, 4" rear drop springs, 2 piece drive shaft with solid rear (no slip yoke on rear shaft) and a clam shell style carrier bearing. I current have the transmission out at the moment (fresh rebuild) and noticed the bearing is shot. To be clear it separated from the shell. I've got a new one along with new u-joints on order. The old bearing was completely seized on, and i had to cut it off. After i got the old bearing off i noticed 2 things. 1- the front "horn flange" (i assume is to keep dirt out) had indentations consistent with internal cage/retainer of the bearing in it, and 2- the washer that keeps the rear yoke (front shaft) on was basically embossed to the pattern of the splines. Both telling me that there was extreme force pushing the carrier bearing forward, until the clam shell broke, finally relieving the stress on it by separating itself from the chassis. Now I've read many past posts on this issue, and the consensus is that the rear end moves forward approx 1/2" forward with a drop like mine. Other members have commented to switch to 1 piece drive shaft, made in China bearings, weld gussets to strengthen the housing and other say they blew the pinion bearing etc. My thoughts are to drill out the rivets that attach the bracket to the cross member, and re-attach it with about 1/2" spacers or washers to move the bracket forward to compensate for the forward movement of the rear end. The side effect of this would be the slip yoke in the transmission would go in and extra 1/2"? Has anybody done this? It sounds like a simple fix? The other alternative is take to a drive line shop and get the rear shaft shortened 1/2". Thanks!

[Richard]

Your driveline is not correct. You cannot run a fixed shaft between the carrier bearing and third member. Even if you adjust the bearing to take stress of it while static. The rear axle moves forward and back as suspension cycles. This true on both leaf sprung and coil (trailing arm) suspensions. A fixed shaft can be run between the carrier bearing and transmission. There should be a slip yoke on the rear shaft.

[biketopia]

Originally Posted by Richard

Your driveline is not correct. You cannot run a fixed shaft between the carrier bearing and third member. Even if you adjust the bearing to take stress of it while static. The rear axle moves forward and back as suspension cycles. This true on both leaf sprung and coil (trailing arm) suspensions. A fixed shaft can be run between the carrier bearing and transmission. There should be a slip yoke on the rear shaft.

Exactly this, you need a slip yoke on the rear shaft. Contact a local driveshaft builder and they will provide you with a sheet of all the measurements they'll need to build you a new shaft. Or drop off the truck with them to have one fitted, either a one-piece or two-piece with slip yoke will work. With a one-piece, you will likely need to remove the carrier bearing support.

[Richard]

Originally Posted by 1970Tex

Hey I'm looking for some feed back on my hanger bearing issue. 1970 GMC 1/2 ton, 350 engine, TH350 transmission, 4" rear drop springs, 2 piece drive shaft with solid rear (no slip yoke on rear shaft) and a clam shell style carrier bearing. I current have the transmission out at the moment (fresh rebuild) and noticed the bearing is shot. To be clear it separated from the shell. I've got a new one along with new u-joints on order. The old bearing was completely seized on, and i had to cut it off. After i got the old bearing off i noticed 2 things. 1- the front "horn flange" (i assume is to keep dirt out) had indentations consistent with internal cage/retainer of the bearing in it, and 2- the washer that keeps the rear yoke (front shaft) on was basically embossed to the pattern of the splines. Both telling me that there was extreme force pushing the carrier bearing forward, until the clam shell broke, finally relieving the stress on it by separating itself from the chassis. Now I've read many past posts on this issue, and the consensus is that the rear end moves forward approx 1/2" forward with a drop like mine. Other members have commented to switch to 1 piece drive shaft, made in China bearings, weld gussets to strengthen the housing and other say they blew the pinion bearing etc. My thoughts are to drill out the rivets that attach the bracket to the cross member, and re-attach it with about 1/2" spacers or washers to move the bracket forward to compensate for the forward movement of the rear end. The side effect of this would be the slip yoke in the transmission would go in and extra 1/2"? Has anybody done this? It sounds like a simple fix? The other alternative is take to a drive line shop and get the rear shaft shortened 1/2". Thanks!

Can you post a picture of both shafts including a clear view of the ends? When I saw this pop up again I was just thinking that maybe the unit was reassembled incorrectly when joints were changed? IDK, just a thought.

[HO455]

Actually the OP is correct. My 67 had the exact same set up in it. (See the less than optimal photo) As far as I can tell the base 1/2 ton trucks came this way. The rubber mounting of the carrier bearing absorbed the back and forth motion of the drive line as the axle travels up and down. The only sliding joint in this set up is the yoke at the transmission.

The OP is on the right track with his idea to move the carrier bearing. When the truck left the factory the bearing was in a neutral position in the bearing mount with the rubber centered with the truck at ride height.

When the axle travels up and down the rubber flexes forward or aft though it's designed range of movement.
When the truck is lowered (Or raised ) this forces the bearing's rubber mount to move beyond its designed range of movement. This results in the rubber tearing off the bearing or the carrier bearing mount starts flexing until it fails.

When installing a carrier bearing the truck must be at ride height (No using the 2 post lift for this job)and the carrier mount must bolt to the crossmember without being pulled or drawn into place by the bolts. That allows the bearing's rubber to be centered or neutral and have sufficient range of movement.

The other issue I've heard of is that the replacement bearings available today don't have the same range of movement that the original GM ones did but I've never seen a side by side comparison of a NOS carrier bearing with a modern repop. It wouldn't surprise me if this were true.

To the OP I would do as your planning and when you've got things bolted up remove the springs and then do a range of motion test. Find some way to verify the carrier mount is not flexing and that the yoke isn't bottoming out.

When I needed to replace mine I converted to a billet bearing with a sliding joint in the rear shaft. The reason being that my Burban was on air bags and there is no way to find a reasonable neutral position for the factory carrier with the larger range of motion that a changing ride height that being bagged causes.

Good luck and let us know how it works out.