4.10 vs 4.56

SpareParts said:

Wonder if a 08 Suburban has the same rear end as my Yukon. Guy about 2 miles away from me is parting out a Suburban and will sell the front diff and rear end together for $350.
It is G80, GT5, 6lug.
Here is the RPO tag
View attachment 480452

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That Suburban is rare! It's got almost the same L76 6.0 V8 as a Pontiac G8, the rear axle is a 9.5" ring gear, and is still a 6 lug. $350 is one heck of a deal - as long as nothing is broken

Yeah. I will get them if he still has them in a couple of weeks. They have been for sale for close to a year so not going anyplace fast.

mikeyss said:

That Suburban is rare! It's got almost the same L76 6.0 V8 as a Pontiac G8 ...

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Almost ...

Compared to the cars' L76, the trucks' L76 has
*0.7 lower scr - Holden cars' L76 has flat top pistons, trucks' L76 ihas a small dish & valve reliefs
91 octane is recommended (not 'required') for the Holden car's L76; the trucks' L76 can use 87 without issue
*the Holden cars' L76 might not have Engine Half@$$ if it came with a stick-shift (definitely disabled for T56), every trucks' L76 has Engine Half@$$
*obviously the cams and the intake manifolds are each different (although the similarities are interesting)
*the Holden cars' L76 has different injectors that flow quite a bit more than the trucks' L76; definitely worth noticing

Either makes the LQ9 look a bit dated, although the trucks' L76 might have slightly lazier throttle response.
Any L76(t) / LY6 / L96 / LC8 would make a fine upgrade to any truck that came with a 5.3L.
(I'll even suggest that most people would rarely if ever notice going from an L92 / L9H / L94 to an L76(t) / LY6 / L96 / LC8.)

mikeyss said:

... the rear axle is a 9.5" ring gear, and is still a 6 lug.
$350 is one heck of a deal - as long as nothing is broken.

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So long as the ring&pinion don't need repair or replacement, it's a helluva deal alright.
Even if the ring&pinion do need repair or replacement, think you might still come out ahead.

If the 08 Suburban has the 14 bolt rear axle, the universal holders on the rear axle may not be directly compatible with your 07 Yukon drive shaft. A change was made around that year to use larger universal holders with the 14 bolt rear axle. The good news is if this is the case, you can use a conversion universal joint to mate up the two.

@swathdiver may have more information on this issue.

Well, l am going to have to take my truck back to the shop that did the re-gear and u-joints.
I looked underneath and there is fluid leaking from the transfer case output shaft where the main drive shaft connects. It was not leaking before this work. I am guessing driveshaft vibration can cause seal problems? I had no work done on the transfer case.

Do you have the steel driveshaft or aluminum.
You need to make sure you’re drive shaft is balanced well. This is even more important with a steel shaft as there is more weight.

It comes down to critical speed.
The faster the shaft is spinning the more unstable it becomes and any kind of imbalance will drastically increase this effect.

This is a big reason a lot of manufacturers went to aluminum shafts because you can get away with more shaft speed because there is less weight.

With you’re change in gear ratios you’re shaft speed has drastically increased and you have now uncovered a problem that was not really a problem before because of the stock gears.

I will say that shop should have known about this potential issue and warned you but most likely is not something they did.
Well technically it was but at you’re request.

I would replace the seal and have the shaft balanced

my vote is cut your losses and buy the new drive shaft. it's out of balance because it was damaged while changing u joints. you can't balance for damage to ears, since that's where it bolts into the balancer.

I think Dorman is the only one making new shafts for these or I'd say oem gm only, replace the seal and put the new shaft in yourself.

As far as new shafts go I just had new driveshafts made for my other diesel pickup that I manual swapped. It had an aluminum rear shaft from the factory.

I had a brand new steel shaft made with heavy wall tubing and spicer 1450 ends it was a stout shaft and balanced perfectly it had zero vibrations and my local driveline shop charged me 520 for it that was with new joints as well.

I don’t know what prices driveline shops around you would charge but I can’t imagine an aluminum shaft would be too far off from what I paid.

As far as the shaft being damaged bent or distorted from changing u joints idk but it would be very easy to find out just chucking it up in a lathe, which a driveline shop should be able to do in 5 mins.

Either way though with the substantial increase in shaft speed the driveshaft needs to be throughly checked or replaced as it will end up causing problems with the transfer case if not

I have personally had horrible luck with drive shafts being made up. for me they all library at least a little bit.

but others never feel it. it's become a pet peveve of mine

Thanks for the tips on the drive shaft. The shop said they balanced the shaft when they replaced the u-joints. The driveshaft is steel. Anyway, taking it back to them since I paid them to work on it. The shop mentioned that if the old u-joints were loose and worn, I would get vibration because the gear change would make it spin faster, so I told them to replace them if they looked worn. But if they can't fix it, then I'll look at replacing the shaft.

IF, I do need to get a new driveshaft, which ones should I be looking at that can handle the shaft speeds needed for the 4:56?

Most likely will need an aluminum but I’m sure a good driveline shop would be able to tell you it depends on length and gears let them know what you have and they should be able to set you up.

The truck is sitting at the shop but I did get a call from the shop owner yesterday. He told me that the pitch angle on the driveshaft is off 15 degrees due to the lift and also the driveshaft is too short. The owner said the tech he had do the u-joints and driveshaft install did not know driveshafts that well and did not catch this problem. I had the driveshaft pitch angle adjusted a by a different shop a couple of years ago, but maybe they did not do it right. I told the owner I was not having any vibration or leak issues before I brought the truck to him for regearing and u joints. But he said the loose u-joints I had were probably absorbing a lot of the issues, plus the new gears are now spinning the driveshaft much faster now, and with the tighter u-joints, other problems are unmasking. The driveshaft he will have to farm out to a driveline shop. So, now I am waiting to hear how much this is going to cost me. Fortunately, I have the Spohn adjustable rear control arms, so changing the pitch on the diff should not be too big of a job.

Got the truck back and took it for a spin on the highway. The drive shaft got lengthened and balanced, and sits in the transfer case rear output seal much better than before. The shop where I took it had sent the drive shaft to a shop specializing in drive shafts. After I got it back home, I looked underneath, and I did not see any more leaking. Yay on that! However, I am still hearing a bit of rumbling on the 6th gear when I take my foot off the gas at highway speeds, albeit better than before. So I am guessing something in the transfer case or 6th gear may be getting a bit worn, and I am hearing it more now because things are tighter. It could still be the driveshaft, but I don't want to throw more money at it, and it doesn't solve the problem. I might just take it to a transmission shop and have them listen. The transmission works fine, but does have a 160k. Problem for another day.

Anyway, the 4:56 gears seem to be a good decision at this point. Definitely better get up and go on the streets, and the engine runs fine at highway speeds with 6th gear putting it about 2400 rmps. Still have not towed on a hill with it, but I am sure it will do way better than the 3:42s I had in it.