Rear Driveshaft Replacement

[pokismoki]

the vibes might be coming from the stock torque converter and NOT the shaft..

[lucas287]

1 hour ago, pokismoki said:

the vibes might be coming from the stock torque converter and NOT the shaft..

 

Very doubtful. I've experienced TC chatter/shudder/vibes - whatever you want to call it - and this is not it. My TC was replaced at 34,000 miles and since was flushed at 72,000 with the new fluid. I can actually force my TC to shudder by manipulating the apply rate in HP Tuners and it's indeed different altogether. 

[pokismoki]

i would take the stock shaft to a driveshaft specialist, they have special machines to balance them to a tighter tolerance than GM mass production balance work.

 

using the HPT software, have you tried isolating the vibe theory by completely disabling the TCC function in all gears and in V4 mode first?

 

could also be getting lugging from a zeroed slip table, or too early of a gear shift..

Edited May 4, 2021 by pokismoki

[Jjblur2003]

These are known to pop at 110 or more mph. My vibration went away after I went aftermarket. Definite mod if critical speed is over 100

[pokismoki]

just did a trans filter change on the truck today and discovered GM never installed the mounting nut that holds down the rear trans mount bushing, damn thing has been floating on the cross member for 50K miles, check your mount for the nut guys, cost $12 from the dealer

 

this alone would cause a vibration and shake on the chassis, allowing the transmission to lift up and down against the rear crossmember, rattling away

Edited June 27, 2021 by pokismoki

[Grumpy Bear]

13 hours ago, pokismoki said:

just did a trans filter change on the truck today and discovered GM never installed the mounting nut that holds down the rear trans mount bushing, damn thing has been floating on the cross member for 50K miles, check your mount for the nut guys, cost $12 from the dealer

 

this alone would cause a vibration and shake on the chassis, allowing the transmission to lift up and down against the rear crossmember, rattling away

 

What a way to increase profits.

Remove critical parts.

 

[lucas287]

Here are a couple posts I made on a different forum. Maybe someone here will find it helpful:

 

I've been stewing this over and running some calcs and I can't see justifying spending money on a new larger driveshaft. In my scenario, that is. I have a '16 CCSB so it's the 143" wheelbase. It helps that I'm 4wd too because the driveshaft is shorter. My DS is 67" from u-joint to u-joint and diameter is 4.5". Using Spicer's calculator, I played around with these results: https://spicerparts.com/calculators/...rpm-calculator

I don't know the wall thickness, but based on carnage pics, it can't be that thick. Still, though, I ran the traps for a few scenarios:

Style D
OD x Wall Thickness = 4.54 x .083
1410 u joint
Critical Speed = 4550 RPM

Style D
OD x Wall Thickness = 4.5 x .154
1410 u joint
Critical Speed = 4459 RPM

Style D
OD x Wall Thickness = 4.54 x .259
1410 u joint
Critical Speed = 4337 RPM

Then, I used an Engine RPM calculator and GPS verified RPM @ any given speed.

All in all, near as I can tell, the critical 'ground' speed would be anywhere between 123-130 MPH.

Maybe I just got lucky and got the best factory combination?

[lucas287]

Went on vacation last week so I dropped my truck off at Driveshaft Specialists in San Antonio for the week. Told them they had carte blanche! Do what they think it needs to both driveshafts - even if they need to make a new one. Got a call from their tech with my truck on the lift and he said there's absolutely nothing to even do. The stock AAM rear shaft was perfectly balanced and the stock UJs still look fine. He said "I can start running up the bill and replacing parts, but I don't see a reason to". He speculated that if the rear was that good there was no reason to even pull the front shaft.

Based on that clean bill of health and the stats I posted earlier - I'm still confident that my stock DS is safe for 115 MPH. Until I'm trappin' higher than that - I won't even think about my DS. 2wd guys that's a different story though.

Also - hats off to the guys at Driveshaft Specialist! That's how business should be done!

[Grumpy Bear]

3 hours ago, lucas287 said:

Went on vacation last week so I dropped my truck off at Driveshaft Specialists in San Antonio for the week. Told them they had carte blanche! Do what they think it needs to both driveshafts - even if they need to make a new one. Got a call from their tech with my truck on the lift and he said there's absolutely nothing to even do. The stock AAM rear shaft was perfectly balanced and the stock UJs still look fine. He said "I can start running up the bill and replacing parts, but I don't see a reason to". He speculated that if the rear was that good there was no reason to even pull the front shaft.

Based on that clean bill of health and the stats I posted earlier - I'm still confident that my stock DS is safe for 115 MPH. Until I'm trappin' higher than that - I won't even think about my DS. 2wd guys that's a different story though.

Also - hats off to the guys at Driveshaft Specialist! That's how business should be done!

 

Run the calc's on my 2015 RCSB V6 6L80E 10 bolt 3.23 30.5" tall tire. Pleeeeaaaassssseeee.