Question for those who run a double cardan rear

[Evan]

I am running a double cardan (front 1350) driveshaft in the rear. The shaft is brand new. On the highway it has a rumble/hum sound, under load. When I let off the gas there is a loud ratty sound. Pushing in the clutch and coasting makes the noise go away. I swapped in a spare and it does the same thing. Has anyone experienced this when running a double cardan in the rear?

 

[MAKG]

Check your driveline angles. Double cardan shafts are different from other types; the double cardan end should be on the transfer case/transmission end and should have ALL the angle. The single side should have no angle under normal load. Symmetrical shafts split the difference.

 

[Evan]

Check your driveline angles. Double cardan shafts are different from other types; the double cardan end should be on the transfer case/transmission end and should have ALL the angle. The single side should have no angle under normal load. Symmetrical shafts split the difference.

Hmmm. I do have the double cardan side coming out of the t-case, but the single side which is attached to the diff is operating at an angle.

 

[Hardwareman]

Pushing in the clutch and coasting makes the noise go away.

Are you sure it's not the throwout bearing?




Allen

 

[MAKG]

The release bearing wouldn't care about load. It would make noise all the time, perhaps changed (not necessarily gone) when the clutch is released.

 

[Evan]

The release bearing wouldn't care about load. It would make noise all the time, perhaps changed (not necessarily gone) when the clutch is released.

Yup. I'm 100% sure this is driveshaft noise. And the release bearing is brand spanking new.

I was thinking that as the front suspension of a stock truck cycles up and down the angle of the single joint is going to change, so the joint must not have to be EXACTLY at 0 degrees. Could I maybe get some shims to change my pinion angle closer to 0? Below is a pic of the angle it's at now.

 

[MAKG]

I didn't see the pic.

But yes, you can buy wedge shims, say, from 4 Wheel Parts. The good kind get held in by the leaf spring center bolt (it's not good when these pop out). You can remove the bolt with the springs installed by holding the leaves together with C-clamps. But if it has never been done before, you'll probably need to replace the bolts.

You want to center the joint at 0 deg. Of course it doesn't always stay there, or a joint would be unnecessary.

How important this is is a function of the driveshaft length. But if you're using a front driveshaft on the rear, it has to be very short.

Also, check that the driveshaft is not bottomed. Just removing the back end from the rear end is enough. If you need leverage to get it on or off, that indicates a problem. Otherwise, it's probably fine. Check at full-droop (frame on jackstands), as well as with the rear end resting on bumpstops (remove the shackles). Note that wedges will change this! If your shocks bottom before the rear end does, you need different shocks.

 

[Evan]

I didn't see the pic.

But yes, you can buy wedge shims, say, from 4 Wheel Parts. The good kind get held in by the leaf spring center bolt (it's not good when these pop out). You can remove the bolt with the springs installed by holding the leaves together with C-clamps. But if it has never been done before, you'll probably need to replace the bolts.

You want to center the joint at 0 deg. Of course it doesn't always stay there, or a joint would be unnecessary.

How important this is is a function of the driveshaft length. But if you're using a front driveshaft on the rear, it has to be very short.

Also, check that the driveshaft is not bottomed. Just removing the back end from the rear end is enough. If you need leverage to get it on or off, that indicates a problem. Otherwise, it's probably fine. Check at full-droop (frame on jackstands), as well as with the rear end resting on bumpstops (remove the shackles). Note that wedges will change this! If your shocks bottom before the rear end does, you need different shocks.

This is a stock length driveshaft that would normally go up front. Aside from the flange swapped onto one end, you could swap this shaft right onto the front of your Explorer. I am able to run it in the rear because of my doubler transfer case.

I have articulated the rear and determined that the slip yoke in not maxed out in either direction. The u-bolts and spring pack bolts are new so getting them off in order to install a shim should not be a problem. I agree that you'd want a shim that's held in by the spring pack bolt. It seems like they could work their way out otherwise.

 

[MAKG]

For a not-very-pleasant thought, is it possible the transfer case doubler isn't exactly square?

You would be hearing the splines on the back of the transmission eat themselves, more so under load.

 

[Shran]

Maybe I can chime in a thought here...something makes the same noise under the same conditions in my '88 Ranger. I have a double cardan shaft too. I replaced the carrier bearing and it helped a lot, for a while, but it's back. My truck is all stock, BTW. If it matters I have an automatic though and it rumbles when you accelerate, especially uphill, or let off the gas going downhill.

I've read that the driveshaft on these can be slightly out of balance if you take it off and don't get it back on EXACTLY like it was. According to my Chilton book anyway.

So I'm very interested in what comes of this, I'd like to get mine fixed too.

 

[Evan]

For a not-very-pleasant thought, is it possible the transfer case doubler isn't exactly square?

You would be hearing the splines on the back of the transmission eat themselves, more so under load.

That pic should be available above, now.

That is certainly possible, but when I ran my 2-joint shortened stock shaft I didn't have this noise. I also have a couple years and many miles on this doubler system. When a changed my clutch a few weeks ago I took everything apart and it looked good. I can't swear to you that everything is lined up perfectly, due to the limited tools I had available when I built it, but I can say it's very close.

Maybe I can chime in a thought here...something makes the same noise under the same conditions in my '88 Ranger. I have a double cardan shaft too. I replaced the carrier bearing and it helped a lot, for a while, but it's back. My truck is all stock, BTW. If it matters I have an automatic though and it rumbles when you accelerate, especially uphill, or let off the gas going downhill.

I've read that the driveshaft on these can be slightly out of balance if you take it off and don't get it back on EXACTLY like it was. According to my Chilton book anyway.

So I'm very interested in what comes of this, I'd like to get mine fixed too.

All the bearings, seals, and gears in the diff are brand new. I recently did the 500-mile new gear inspection and everything looked good back there. This is a rumble/hum when the driveline is under load, i.e positive gas or engine brake, and turns into a harsh ratty sound if I give it enough gas so there is no engine brake but also no power applied to the drive line. Push the clutch in and all the noises stop. I've put about 500 miles on it like this, and it's not getting any worse or any better.

 

[dumprat]

Yup it is your drive shaft angle. The pinion should point at the drive shaft. At most it should point 3 degrees down. You have way too much angle there. Cool idea! Spare parts should be easy to get.

 

[Evan]

Yup it is your drive shaft angle. The pinion should point at the drive shaft. At most it should point 3 degrees down. You have way too much angle there. Cool idea! Spare parts should be easy to get.

Looking at the pic, do you think it can be corrected with shims?

 

[dumprat]

Ya shims will do the trick. They are cheap. Try 3 dgrees anr go to 7s if you need them. More than that you might need to get some made at a machine shop.

 

[Evan]

Ya shims will do the trick. They are cheap. Try 3 dgrees anr go to 7s if you need them. More than that you might need to get some made at a machine shop.

I'm going to buy an angle finder today and determine the exact angle shim I need. Thanks for everyone's help on this.