Let's Talk GMT900 DriveShafts !

[swathdiver]

Those Z56-PPV Tahoes definitely have superior driveshafts ...

Nope, same ones. Their 3.08 gear keeps the driveshaft speed within limits.

Thanks for the extra info swathdiver
The UJoints I purchased and am going to use on my rear driveshaft
are a 1350 series U Joint. IDK if the 1355 you mentioned is the same or not.
I don't think I've ever used a 1355 series

1355 is the OE from AAM.

Where do you guys purchase your u-joints from?

I buy my AAM parts from dealers on Ebay or directly from their websites.

 

[Marky Dissod]

Those Z56-PPV Tahoes definitely have superior driveshafts ...

Nope, same ones. 3.08 keeps the driveshaft speed within limits.

This is mildly irritating news. Just what is the PPV's top speed limited to, that makes 3.42 3.73 or 4.10 so dangerous?
Makes no sense for a pursuit vehicle to be given the weakest / slowest gears.
Anything with a 6.0L & a 3.73 or 4.10 will give a 5.3L PPV with 3.08 a 'run' for its money.

 

[mikez71]

Just to add another data point....
my 2012 Z71 has a steel (rusty) driveshaft.

 

[Foggy]

This is mildly irritating news. Just what is the PPV's top speed limited to, that makes 3.42 3.73 or 4.10 so dangerous?
Makes no sense for a pursuit vehicle to be given the weakest / slowest gears.
Anything with a 6.0L & a 3.73 or 4.10 will give a 5.3L PPV with 3.08 a 'run' for its money.

The numerically low gear ratio is way more efficient at the hwy speeds they would travel frequently..
And of course in a high speed chase they would need to be flying triple digits.. A 4.10 would suck for all that

And at a 80 mph "punch" I would the 4.10 would flat out run out of gear (as you wouldn't want to use
the overdriven gears for 100% throttle for any amount of distance)

 

[Marky Dissod]

... in a high speed chase they would need to be flying triple digits. 4.10 would suck for all that.

Crunched some numbers with this calculator

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs velocity at shift points with tracer

www.blocklayer.com

You crunch those numbers yourself, bet you'll wonder why GM chose 3.08 over 3.73 for a PPV,
especially when the SSV gets 3.42.

 

[Doubeleive]

This is mildly irritating news. Just what is the PPV's top speed limited to, that makes 3.42 3.73 or 4.10 so dangerous?
Makes no sense for a pursuit vehicle to be given the weakest / slowest gears.
Anything with a 6.0L & a 3.73 or 4.10 will give a 5.3L PPV with 3.08 a 'run' for its money.

depends, the 6.2 caprice can probably hit 160 or more given enough runway and no limiter
on the suv's there is more drag so not going to hit 160 in stock formation anyway
I have had mine up to 145 and it might have had a little more, who knows... if I hadn't passed a cop while doing it I might have found out.
I would speculate that a stock ppv tahoe 5.3 could hit 145 I doubt it would go much more than that, the ppv speedo's go up to 140
no idea what the challengers do I imagine around 140-160 though
the sheriffs around here get ditched routinely on high speed chases there just not trained for it (they have the fords and chevys), highway patrol will take over if they have the opportunity.\
sometimes if the chopper is up they will get a few but even then I have seen them fail incredibly enough the choppers do 160 I don't think they can much more.
a trick they will do is get the chopper up and then drop out from a car chase (the suspect then slows down) and they let the chopper follow them home

 

[Marky Dissod]

I would speculate that a stock ppv tahoe 5.3L could hit 145MpH
I doubt it would go much more than that, the ppv speedo's go up to 140MpH

With 6L80, 3.08, & 265/60R17, it'd hit 140MpH on top of 4th.
With 6L80, 4.10, & 265/60R17, it'd more quickly hit 140MpH in 5th.
Top speed is not nearly as important as ability to accelerate, though,
and that's where 3.73 or 4.10 would shine, even with taller tires (not saying that's a good idea for a pursuit vehicle).

 

[swathdiver]

This is mildly irritating news. Just what is the PPV's top speed limited to, that makes 3.42 3.73 or 4.10 so dangerous?
Makes no sense for a pursuit vehicle to be given the weakest / slowest gears.
Anything with a 6.0L & a 3.73 or 4.10 will give a 5.3L PPV with 3.08 a 'run' for its money.

PPVs use P265-60-R17 tires and if they were wore down to 2/32nds of an inch, the top speed of the 6-speed Tahoe would be 135 mph. This has the driveshaft turning just under 5,000 rpms. In 5th the engine would be turning 4,250 rpms and in 6th, 3,325 rpms at 135 mph without including the torque converter slip speed.

Switch to 3.42 gears and now you are limited to 121 mph with a shaft speed of 4,964 rpms. 5th gear engine rpms would be 4,230 rpms and 6th, 3,309 engine rpms at 121 mph.

Switch to 3.73 gears and now you are limited to 111 mph with a shaft speed of 4,967 rpms. 5th gear engine rpms would be 4,232 rpms and 6th, 3,311 engine rpms at 111 mph.

Switch to 4.10 gears and now you are limited to 101 mph with a shaft speed of 4,972 rpms. 5th gear engine rpms would be 4,236 rpms and 6th, 3,315 engine rpms at 101 mph.

Without the 3.08 gears, the bad guys would smoke them in no time during a highway pursuit. Michigan State Police had the GMT900 PPV Tahoes up to 132-134 mph.

Myself and others on this forum have witnessed @badandyturbo's 2013 PPV run mid 15s in the quarter mile with Amazon long tube headers and no tune. Plenty fast for catching your average speeder.

 

[Foggy]

PPVs use P265-60-R17 tires and if they were wore down to 2/32nds of an inch, the top speed of the 6-speed Tahoe would be 135 mph. This has the driveshaft turning just under 5,000 rpms. In 5th the engine would be turning 4,250 rpms and in 6th, 3,325 rpms at 135 mph without including the torque converter slip speed.

Switch to 3.42 gears and now you are limited to 121 mph with a shaft speed of 4,964 rpms. 5th gear engine rpms would be 4,230 rpms and 6th, 3,309 engine rpms at 121 mph.

Switch to 3.73 gears and now you are limited to 111 mph with a shaft speed of 4,967 rpms. 5th gear engine rpms would be 4,232 rpms and 6th, 3,311 engine rpms at 111 mph.

Switch to 4.10 gears and now you are limited to 101 mph with a shaft speed of 4,972 rpms. 5th gear engine rpms would be 4,236 rpms and 6th, 3,315 engine rpms at 101 mph.

Without the 3.08 gears, the bad guys would smoke them in no time during a highway pursuit. Michigan State Police had the GMT900 PPV Tahoes up to 132-134 mph.

Myself and others on this forum have witnessed @badandyturbo's 2013 PPV run mid 15s in the quarter mile with Amazon long tube headers and no tune. Plenty fast for catching your average speeder.

Agree totally.. It's the DRIVESHAFT speed we are talking about here.
Really not much else matters pertinent to this conversation (as the OP, I'll say this)

 

[Charlie207]

Agree totally.. It's the DRIVESHAFT speed we are talking about here.
Really not much else matters pertinent to this conversation (as the OP, I'll say this)

The reality is that the radio always wins.

 

[swathdiver]

The reality is that the radio always wins.

When I was young and irresponsible, I beat the radio quite a number of times! 39 to be exact.

 

[Marky Dissod]

Those Z56-PPV Tahoes definitely have superior driveshafts ...

Nope, same ones. 3.08 keeps the driveshaft speed within limits.

PPVs use P265/60R17 ... wore down to 2/32", top speed of the 6-speed Tahoe would be 135MpH.
This has the driveshaft turning just under 5,000RpM.
In 5th the engine would be turning 4,250RpM and in 6th, 3,325RpM at 135MpH
without including the torque converter slip speed.

Switch to 3.42 ... limited to 121MpH with a shaft speed of 4,964RpM.
5th gear engine would be 4,230RpM, and 6th, 3,309RpM at 121MpH.

Switch to 3.73 ... limited to 111MpH with a shaft speed of 4,967RpM.
5th gear engine would be 4,232RpM and 6th, 3,311RpM at 111MpH.

Switch to 4.10 ... limited to 101MpH with a shaft speed of 4,972RpM.
5th gear engine would be 4,236RpM and 6th, 3,315RpM at 101MpH.

Sounds like GM is unwilling to spend any extra money on a driveshaft upgrade, then?
I mean, it does kinda make sense that the Challenger and Caprice were superior PPVs ...

 

[swathdiver]

Sounds like GM is unwilling to spend any extra money on a driveshaft upgrade, then?
I mean, it does kinda make sense that the Challenger and Caprice were superior PPVs ...

Well, what would a superior driveshaft entail? I'm not sure myself. The K2s went to 1415 universal joints which gives them slightly more flexibility, more strength and slightly more rpm limit. The GMT900 2500s used 1415s with the 6L90. All of my pickups use the same as the Yukon, 1355s.

Those are cars, not trucks. Of course they're going to be faster but obviously don't carry as much stuff. They also made more than 320 horsepower. I still think it's impressive what GM did with that platform.

 

[Marky Dissod]

Well, what would a superior driveshaft entail? I'm not sure myself.

Back when I was 'into' LT1 Caprices, the answer was a Denny's Driveshaft. With GM OE driveshafts,
Impalas (and Caprices) SS were driveshaft limited to 154MpH with 3.08 & 255/50R17 tires.
THE most (cost) effective performance mod was - still is - 3.73.
3.73 was the penultimate 7,000lb towing axle gear for Cadillac Fleetwoods.
Whenever a 9C1 or an SS upgraded to 3.73, the safe thing to do was upgrade to a Denny's Driveshaft.
Upgrading to 3.42 instead was a surefire way to not need a driveshaft upgrade.

Reasonably certain that the Aussie Chevy Caprice PPV (by GM's Holden) was similarly capable;
3.73 & 3.45 were almost as popular but not as effective without tuning due to the need to tune the 6L80 with greater finesse than required for the 4L60E.

 

[j91z28d1]

I read a paper on what Nascar went thru to balance drive shafts. it's quite a bit, something about 6th order harmonics, whatever that is. but shorter is better too. so the longer it is, the harder it is to balance for crazy high speeds steep gearing gets.

it's always been a good rule of thumb, when building a top end car, build it to top mph in the 1:1 tranny gear. makes everything happier

 

[PG01]

When I was young and irresponsible, I beat the radio quite a number of times! 39 to be exact.

Absolutely, myself as well. Just had to think faster than they could click the button….

 

[Marky Dissod]

I read a paper on what Nascar went thru to balance drive shafts. it's quite a bit, something about 6th order harmonics, whatever that is. but shorter is better too.
so the longer it is, the harder it is to balance for crazy high speeds steep gearing gets.

This is why the L05 Fleetwood-V4P could get 3.73 - the 200-horse L05 lacked enough power to threaten that driveshaft's critical velocity;
whereas the LT1 Fleetwood-V4P got 3.42 instead of 3.73, precisely because the LT1 had enough power to threaten that driveshaft's critical velocity.

it's always been a good rule of thumb, when building a top end car, build it to top mph in the 1:1 tranny gear. makes everything happier

Guessing that the rule 'of thumb' keeps driveshaft RpM under engine RpM?
In which case the 6L80 would avoid hitting its vMax in 5th & 6th, the 8L90 would avoid vMax in 7th & 8th, the 10L90 would avoid vMax in 8th 9th & 10th.

Forced to consider vMax, 3.23 would've been a better choice.
Taller tires would seem to permit 3.42, but the extra sidewall would NOT help high-speed handling without even larger wheels.

After 265/60R17, what was the next (larger-wheeled) Tahoe PPV tire size?

 

[j91z28d1]

the rule of thumb could be very old when it was just easier on the tranny to run 1:1 stright thru, especially manual tranny without external cooling. my tr6060 has a fluid cooler just like an auto. so not sure it matters as much. but in general any time you change a gear ratio you lose some power to it.

used to he a lot it top end racing back in the day I don't thinks it's done as much anymore. I don't remember the name, but car and driver used to cover one out in Nevada

 

[homesick]

Absolutely, myself as well. Just had to think faster than they could click the button….

Which one of you two was Dirty Mary?

joe

 

[swathdiver]

Back when I was 'into' LT1 Caprices, the answer was a Denny's Driveshaft.

Ok, but what makes it more better? Thicker tubing? Thicker cardboard tubing? Different material or type of steel or aluminum?