weird vibration at speed 60 plus

[y5mgisi]

I have known of semi float axles, (12 bolt in particular), to have bent axle shafts which would do something similar.

[Keith Seymore]

Originally Posted by y5mgisi

I have a vibration above 55 with mine. ITs desperately annoying. For me, it appears to be a faulty drum. In the driveway, i put the rear end on jack stands and brought the truck up to 60mph. Vibration. Unbolted the tires, still vibration. un bolted the axle shafts, so that only the driveline would spin, and the vibration was gone. THen i noticed how wobbly the one drum is. I made several videos of it as i tend to over document my driveway shenanigans.

https://www.youtube.com/watch?v=MTpCtPVOcrk


https://www.youtube.com/watch?v=1Dgeq4pcTP8

Nicely done -

In particular the way you separated out the various potential root causes -

K

[75chev4x4]

Originally Posted by y5mgisi

I have a vibration above 55 with mine. ITs desperately annoying. For me, it appears to be a faulty drum. In the driveway, i put the rear end on jack stands and brought the truck up to 60mph. Vibration. Unbolted the tires, still vibration. un bolted the axle shafts, so that only the driveline would spin, and the vibration was gone. THen i noticed how wobbly the one drum is. I made several videos of it as i tend to over document my driveway shenanigans.

https://www.youtube.com/watch?v=MTpCtPVOcrk


https://www.youtube.com/watch?v=1Dgeq4pcTP8

Nice job, ur a brave man I dunno if I could do that at 60 mph on jack stands. I watched your videos and I notice the slip part of your driveshaft it near the tcase. Mine is at the rear diff , does anyone know if that is right? I cant remember if it was that way when I took it out or not. I really messed this thing up when I changed the u joints. Took everything apart over a few days then put it back together, I know now I should have marked the shaft with a grease pen and tooks some pics. Maybe the darn thing is in backwards. Smaller slip end is at the rear diff?

[geezer#99]

I've searched and found some like yours but they could be wrong too. Easy to swap yours around.

[75chev4x4]

Ok, funny thing on my shaft is there is a line scribed where the two joints come together. I might put it back that way and just flip the u joint around and see if that helps.

[75chev4x4]

Originally Posted by Oldriginal86

Don't know how the shaft is presently installed in your truck with a lot of talk about flipping this and that but the shaft appears to be install backwards. The slip yoke end should be at the transfercase and solid end should be at the rear.
Posted via Mobile Device

Sorry I didnt see your post before, u might be right. I could have this thing in backwards. Thank you

[y5mgisi]

I really believe that factory was with the slip at the t-case. But i too have seen it both ways. And as far as the bravery, i was extremely careful to never put myself in real harm while i was doing it. I had it about an inch away from my other truck with it in park and the ebrake set. This way, if the 78 left off the jack stands at 60mph, it would only make it an inch before it slammed into my other truck. No momentum to build up. The other thing is it takes an extraordinarily light throttle to get to 60 with the tires off the ground. Like very light. Then, to top it off, all the time that it was doing 60 sitting still, i was in the cab. Realistically, very little to go wrong when its all done "right".

[y5mgisi]

Here is a pic from a 76 suburban brochure.

[75chev4x4]

Ok, glad to hear you were safe about it. Thanks for the driveshaft shot. Im gonna switch it around tomorrow and see if that fixes this problem finally haha. Thanks

[y5mgisi]

Found another pic showing it at the tcase.

[75chev4x4]

Ok guys hopefully I can explain this so it makes sense. I pulled my driveshaft today and I realize why I put the driveshaft on the way I did(backwards). My rear u joint was a 1350 rear diff yoke and driveshaft side also at that end. On the other end that was at the transfer case it was a 1310 joint I believe on shaft and yoke side. So with the joints I had this was the only way I could put it back together. Now to put the driveshaft on the correct way with the slip joint at the tcase I believe I will need a conversion joint of 1310/1350 at the t case and at the rear diff. This seems odd 2 me, but I know the trans was swapped from a th350 to a th400 so this might be why the joints are conversion joints. Anyone have any thoughts or advice before I go buy thses?

[Oldriginal86]

Sounds like more than just the trans was replaced. Rear or T-case? Has the driveshaft been pieced together from different trucks?

[75chev4x4]

The rear end is original 14 bolt ff. I was asking myself about the driveshaft too. I dunno if thats what was put in when the turbo 400 was added or how they did it. But a 1310 1350 conversion joint is the only way I could figure 2 make it work. Not taking pictures before I took this thing apart is really biting me in the butt right now.

[Oldriginal86]

Was the truck an automatic from the factory? What T-case do you have now?

[75chev4x4]

Yea turbo 350 from factory with 203, now has turbo 400 with 203.

[lilspike]

You need a 1350 slip yoke and a 1350 replacement yoke for the 14 bolt. End of conversion joints. What you have now is a conversion drive shaft.
Matthew
or vise versa..

[y5mgisi]

You know whats funny, i seem to remember mine being just the other way around. I wanted to try flipping mine around but couldn't for some reason and i think thats why. Now i really wonder! I'll have to climb under there and measure but im almost certain i cant flip mine to the way yours is cause the ujoints are different.

[mrolds88]

One thing I have noticed on this thread is that you have a 203 case and you say you can feel some of the vibration in the steering wheel. You may want to check out the front driveline also. Loose u joints both in the shaft and the front axle and weights on the shaft.

[lilspike]

That is a very good point to check the front as well! Would pay to make sure the T/C mounts are in good condition too. Most are deteriorated and squashed after all these years.

[75chev4x4]

I have the part time kit so my front shaft doesnt spin in 2wd. Its gotta be in this rear driveshaft im sure.

[motornut]

[QUOTE=y5mgisi;6278510]I really believe that factory was with the slip at the t-case. But i too have seen it both ways. QUOTE]

I believe factory is front,both of mine are front,my rear most u joint went last year.had some vibration,did both

[75chev4x4]

Ok guys made some progress today I think. Ran the truck on jackstands up to 60mph and still had the vibration with drums on. Pulled both axleshafts and ran it up to 60 mph. Still had the vibration but it wasnt a rough as when the drums were spinning. The vibration is still apparent without axleshafts in though. Still with axleshafts out, I ran the truck at idle in drive so prob 15mph and climbed under to the driveshaft. Marked it with a sharpie while it was moving. While it was moving the sharpie mark seemed to go all the way around the ds but after I shut the truck off and rotated by hand I could see it had not. The sharpie only contacted on about half of the ds. I did several different lines to be sure and all marked the same half spot on the ds. Also noticed that on my pass side brake drum that I replaced prob 5 years ago(junkyard orginal gm drum) that it has a weight on the face and the driver side drum(original to the truck as far as I know) does not. I looked for a place were the weight might have fallen off but could find no evidence of that. I will post pics of drums. So what have I got here? Anyone have any thoughts? I have a few but wanna see what everyone else thinks before I do anything else. Thanks for reading!

[75chev4x4]

Driver side

[75chev4x4]

While putting it back together I realized the pass drum that I got from the junkyard years back was not a factory gm drum. Has the part number 5117 on it and does not say gm anywhere on it.

[y5mgisi]

That is interesting. Its further interesting to do those runup tests tho isnt it? I had a good time doing that "investigating". Im going to venture to bet you and i both have two issues. Out of balance drums and drivelines. I am contemplating just going to disc brakes in the rear since its so cheap. And then then getting the drive line rebuilt and balanced up at sixstates here in Portland.