What did you do to your NNBS GMT900 Tahoe/Yukon Today?

[kbuskill]

Critical Speed is a term used to describe the speed at which a driveshaft would whip or bend or self-destruct. Exceeding this speed can also damage the transmission or transfer case and differential due to the whipping and vibrations.

CS is determined by calculating the tube length of the propeller shaft or the length between centers of the u-joints, the diameter of the shaft, thickness of the material and material used and the u-joint sizes.

Brent, aluminum shafts are not solid, they are tubes as well. They must use larger diameter tubes and usually thicker wall diameters to equal or exceed a steel driveshaft. In my racing days, aluminum driveshafts were all the rage for a time, until every single one of them twisted off, no match for the horsepower and torque of our motors back then.

https://spicerparts.com/calculators/driveshaft-safe-operating-rpm-calculator

My rear propeller is 53-1/2 inches long, 3-1/2 inches in diameter and has a metal thickness of .083 inches and uses 1350 u-joints. CS = 4,556 RPMs

My front propeller is 28-1/4 inches long, 2-3/4 inches in diameter and has a metal thickness of .083 inches and uses 1344 u-joints. CS = 5,000 RPMs

I have as yet to actually put a tape measure to mine to verify, this information is internet derived.

Ok... riddle me this...

My 4L60E with I am assuming similar driveshaft dimensions and a 3:73 rear end.

What would be the critical speed of my driveshaft and how does that translate to safe top speed for my truck???

 

[swathdiver]

Ok... riddle me this...

My 4L60E with I am assuming similar driveshaft dimensions and a 3:73 rear end.

What would be the critical speed of my driveshaft and how does that translate to safe top speed for my truck???

I'm coming up with about 112 MPH. Which is what Dorman says for their stock replacement. It's an aluminum shaft, 4" in diameter and 75 inches and change long.

 

[kbuskill]

I'm coming up with about 112 MPH. Which is what Dorman says for their stock replacement. It's an aluminum shaft, 4" in diameter and 75 inches and change long.

That's right... I forgot your truck is 4wd which means my shaft is quite a bit longer than yours...... Thanks for the info.

 

[Doubeleive]

doesn't seem quit right, my rpm's will hit about 5500 +/- stock, so why would they allow it to exceed cs?

 

[kbuskill]

doesn't seem quit right, my rpm's will hit about 5500 +/- stock, so why would they allow it to exceed cs?

Are you talking engine rpms or driveshaft rpms???

 

[Doubeleive]

Are you talking engine rpms or driveshaft rpms???

engine, I was thinking driveshaft was spinning the same speed, derrrr... lol

 

[Rocket Man]

Got my new tails installed in The Machine.

 

[gooffeyguy]

Installed that "Deslugger" thing onto the AC compressor.

I ordered it from RockAuto last week along with some other stuff and it was delivered Monday. Figured what the hell, it can't hurt!

I pulled the front up on ramps and removed the 4 bolts that hold the front splash shield on. Once that was off I could pretty much sit underneath with my head between the radiator and accessory pulleys. With that cover removed it makes it real easy to access the AC compressor plug. I zip tied the box to the hard brake line that runs along the to[ of the frame rail next to the compressor.

On a side note, related to driveshafts...

My Mustang has a FMS (Ford Motorsports) aluminum driveshaft. It is larger diameter than a stock steel one, 4" vs 2.5" or something like that. It's held up behind a 600hp motor doing 5000rpm clutch dumps on slicks and 130mph trap speeds

 

[Doubeleive]

View attachment 227931 View attachment 227932 Got my new tails installed in The Machine.

I was hoping for laser beams

 

[Tonyrodz]

I was hoping for laser beams

They are--invisible!! Shhh....

 

[R3cord303]

Someone said yesterday that you’d need resistors for the hybrid tails to avoid hyperflash- no you won’t because only the brake lights are LED. The turn signals are still incadesent.

 

[Rocket Man]

Installed that "Deslugger" thing onto the AC compressor.

I ordered it from RockAuto last week along with some other stuff and it was delivered Monday. Figured what the hell, it can't hurt!

I pulled the front up on ramps and removed the 4 bolts that hold the front splash shield on. Once that was off I could pretty much sit underneath with my head between the radiator and accessory pulleys. With that cover removed it makes it real easy to access the AC compressor plug. I zip tied the box to the hard brake line that runs along the to[ of the frame rail next to the compressor.

On a side note, related to driveshafts...

My Mustang has a FMS (Ford Motorsports) aluminum driveshaft. It is larger diameter than a stock steel one, 4" vs 2.5" or something like that. It's held up behind a 600hp motor doing 5000rpm clutch dumps on slicks and 130mph trap speeds

Deslugger thing? WTH?

 

[wjburken]

Deslugger thing? WTH?

Had to look that one up as it was new to me as well. Never heard of a clutch timer to clear out fluid in the a/c compressor or that it was even needed.

How do you know you need one or that it’s doing any good?

 

[the_tool_man]

Someone said yesterday that you’d need resistors for the hybrid tails to avoid hyperflash- no you won’t because only the brake lights are LED. The turn signals are still incadesent.

Thanks for clarifying. I didn't know one way or the other. I was just speculating that it might be a risk.

 

[R3cord303]

Thanks for clarifying. I didn't know one way or the other. I was just speculating that it might be a risk.

For sure. Friday I’m going to the junk yard. They said they have a hybrid 2008 sitting in the yard so i’m gonna try and swipe the d pillar trim but the said they only have one tail light. Minimum I’ll look at the harness.

 

[the_tool_man]

For sure. Friday I’m going to the junk yard. They said they have a hybrid 2008 sitting in the yard so i’m gonna try and swipe the d pillar trim but the said they only have one tail light. Minimum I’ll look at the harness.

Cool. It will be informative to know if the Hybrid D-pillar appliques are different from Escalade ones. If they're the same, I'd guess Escalade ones are far more commonly available than Hybrid, and would be an acceptable substitute. I have a pair, and can take measurements if necessary, for the good of the community.

 

[R3cord303]

Cool. It will be informative to know if the Hybrid D-pillar appliques are different from Escalade ones. If they're the same, I'd guess Escalade ones are far more commonly available than Hybrid, and would be an acceptable substitute. I have a pair, and can take measurements if necessary, for the good of the community.

Coolieo. I’ll ****** em and bust out the calipers.

Gotta get dat areo

 

[Sam Harris]

View attachment 227931 View attachment 227932 Got my new tails installed in The Machine.

Nice!!

 

[Derick]

Did an oil change on the burb. First time with the fumoto oil change valve. Handy, clean (for the oil drain - filter change is still messy AF), but very very slow even on hot oil. I'm trying to get a sub-$30 full synth oil change. I've been using supertech oil for a minute now, which is 16 bucks, and the supertech oil filters are 4 bucks, plus an extra quart at like 5 bucks is right at 25 plus tax. However, I could only cross reference the supertech 10060 which is the pf43 clone. The pf63 extended filter like I wanted, well I couldnt find its supertech match....so I went AC delco on the filter at 8 bucks. Plus 4 bucks for a bottle of MMO. So it was 35 bucks. Oh well, maybe next time in 5k.

 

[the_tool_man]

Did an oil change on the burb. First time with the fumoto oil change valve. Handy, clean (for the oil drain - filter change is still messy AF), but very very slow even on hot oil...

I was wondering how long it would take. Put my Fumoto on last change. +1 on filter mess. There's nothing like balancing a full-to-the-brim cup of hot motor oil while laying on your back.