2000+ Rear Axle ?'s

[NorCalAnthony]

Hey Everyone,
I have access to a 2000 Yukon XL parts truck and had a couple of questions about the rear end that I haven't been able to answer searching around. I have an '89 K5 that I'm slowly fixing up and eventually want to put rear discs on it. Would it be possible to pull off whatever necessary parts and brackets from the donor and just stick them on the K5's 10 bolt? Or would it be better to just pull the entire rear axle from the donor and relocate the spring perches and shock mounts and throw it under the K5? From what I've found online the newer axle (8.6" 10 bolt) should be about 1.5" wider and basically make the rear as wide as the stock front already is but I haven't seen anyone do this on a '73-'87 ('91) to confirm that. I know that it would be more or less a stock replacement (besides the discs) since they're both 10 bolts but I'm only planning on using 33" or maybe 35" tires and don't plan on wheeling it that much or that hard. Also, the newer axle has a G80 in it (according to the RPO in the glove box) and I was curious if GM started making them any better than the older ones that were known to have a high failure rate. What do you guys think?
Thanks,
Anthony

 

[cyclic]

My future plans are to do exactly that, swap in a complete disk brake late model rear end. Should also allow you to keep the parking brakes. Biggest thing to look for is getting the correct gear ratio, once that is right, the rest is pretty easy.

 

[paratrooper307]

Converting the axle to work on the K5 is likely going to be easier than trying to make the modern parts fit your old axle. Rear axles on 73-91 GM trucks are actually 3 inches narrower than the fronts. You'll likely need an adjustable proportioning valve and some other brake tweaks to make the rear discs work properly.

 

[Greg Ducato]

Personally, I don't think there is much to gain from factory style rear disc brakes in a truck like this, most of your stopping power is in the front anyway and I think the parking brake set up will be just as prone to mud or water contamination as factory drums would be. The newer G80 diff is just as bad as the early ones from what I have seen so no upgrade there, both rear ends have the 30 spline axle so no upgrade in that department. I would sell that rear and use the money towards a good differential for the rear end under the truck now. My two cents worth....

 

[NorCalAnthony]

Thanks for the replies guys. The main reason I'm looking at doing this swap is that I already have the parts truck so it would only be a matter of getting some new shock mounts and spring perches welded on and then sliding it under. My original plan was to do a bigger lift with some 37's and putting some 3/4 or 1 ton running gear under it at the same time but I wound up getting a killer deal on a complete parts truck instead of just the drivetrain like I was originally planning. Now with a baby in our future, I'm needing to scale down my plans/budget. If time and money weren't an issue I'd just wait a while longer and save up for some tons with discs all around.

I think I should be able to pull the proportioning valve off from the parts truck along with the master cylinder (if needed) and anything else that might be worth the time and effort to take off. I plan on stripping everything I can possibly use from the donor before I get rid of it but the rear will be one of the last things to be pulled since I still need it to be somewhat mobile.

Besides the initial cost I'm not sure why anyone wouldn't want to swap to rear discs. IMO they're easier to work on and they function better in harsher environments. I've never had any issues while wheeling my Frontier that has 4 wheel discs and even my dad's new Duramax is all discs and has a higher tow rating than any of GM's older trucks with drums...