What are your thoughts on this rust? Can I repair or do I need to replace?

[Boots97]

My $0.02 coming from MN

Your leaf springs are shot. Replace them both, can go new or used, although I'd recommend going down to a state like KS or MO if you're getting used springs and make sure to get them in pairs.

Push on the backing plate. Not with your whole weight, but strong enough for you to feel it. Is it crumbling apart? If not, clean it up with a wire brush and paint it to prevent new rust. If it's falling apart, replace the backing plate.

Don't worry about the axle. It's a 10 bolt axle. clean up the mating surface where the plates meet and drive it till the axle blows apart. 10 bolts aren't known for their strength and Suburbans being more a** heavy makes these axles moan and groan. Once your axle blows up, get a 6 lug 14 bolt K1500/Light Duty K2500 axle from a junkyard (again, further south) or get an 8 lug 14 bolt K2500/K3500 and convert it to 6 lugs with new axle shafts and JB6 brakes. A lot more work to do a conversion, but same result.

You need new U bolts. U bolts are torque to yield and yours are trashed anyways.

EDIT: Also, would recommend replacing all hard line with NiCopp brake line and hoses with Stainless Steel Braided hoses. Buy the NiCopp at your local Auto Parts Store or on the AGS website. Don't buy it off Amazon, the stuff isn't legit NiCopp.

Also, when your 10 bolt dies, I'd recommend keeping all your brake parts. Being a Suburban, you already have JB6 brakes, so you could buy a 8 lug 14 bolt and just buy new 6 lug axle shafts and reuse the JB6 parts that you already have.

Here's a link for the SS braided hoses that I used recommended by @df2x4 and @Schurkey

Classic Tube SBH6055 Classic Tube StopFlex Brake Hose Kits | Summit Racing

Free Shipping - Classic Tube StopFlex Brake Hose Kits with qualifying orders of $109. Shop Brake Hoses, Sets at Summit Racing.

www.summitracing.com

 

[Schurkey]

My $0.02 coming from MN...

God bless you. You've saved me a heap of typing.

 

[SDgunner]

Always begin with safety and functionality components. Also, components that need replaced, "while you are in there". Your initial question was about backing plates and that you had plans for rear brakes and spring work. Nothing else was shared about what else you were considering.

Having lived in a salt on the road rust state and worked in shops where I dealt with rust daily, I was prone to draw the line pretty quick on putting money in a "rust bucket". Out here in the PNW, we don't deal with rust too much, if at all. My girl's 1990 K2500 with 129k miles, is worth it to keep putting money in it, especially since the body is straight.

The problem I have is that I really like this vehicle. I don't see many suburbans of this era (or any for that matter) with the tailgate. It's my ice fishing/winter rig and while I don't want to stick 10k into it I'd like to keep it going as much as reasonably possible. I should maybe look for one from down south and use this one for parts.

 

[SDgunner]

My $0.02 coming from MN

Your leaf springs are shot. Replace them both, can go new or used, although I'd recommend going down to a state like KS or MO if you're getting used springs and make sure to get them in pairs.

Push on the backing plate. Not with your whole weight, but strong enough for you to feel it. Is it crumbling apart? If not, clean it up with a wire brush and paint it to prevent new rust. If it's falling apart, replace the backing plate.

Don't worry about the axle. It's a 10 bolt axle. clean up the mating surface where the plates meet and drive it till the axle blows apart. 10 bolts aren't known for their strength and Suburbans being more a** heavy makes these axles moan and groan. Once your axle blows up, get a 6 lug 14 bolt K1500/Light Duty K2500 axle from a junkyard (again, further south) or get an 8 lug 14 bolt K2500/K3500 and convert it to 6 lugs with new axle shafts and JB6 brakes. A lot more work to do a conversion, but same result.

You need new U bolts. U bolts are torque to yield and yours are trashed anyways.

That was the initial reason I was under here! I want to pull a llittle bigger ice shack and was looking at adding air bags. When I saw the state of the leaf springs I decided to just go with heavier leafs and new shocks. Then I decided to take a gander in the brakes and here we are!

 

[fancyTBI]

My '92 has looked like that underneath for 15 years or better. Clean it up, replace the brakes and springs (which you already stated you were doing), paint it if it makes you feel better and move on. If/when it gets worse, go grab a 14 bolt from a light duty 2500 and swap it in. I've seen much much worse. I've seen a few vehicles where the axle tubes get weak from the U-bolts holding in junk. Yours still seems fine.

 

[SDgunner]

My '92 has looked like that underneath for 15 years or better. Clean it up, replace the brakes and springs (which you already stated you were doing), paint it if it makes you feel better and move on. If/when it gets worse, go grab a 14 bolt from a light duty 2500 and swap it in. I've seen much much worse. I've seen a few vehicles where the axle tubes get weak from the U-bolts holding in junk. Yours still seems fine.

My tubes are certainly rusted a bit in that area but still seem structurally sound. That area held a lot of dirt and moisture in there.

 

[Boots97]

Having lived in a salt on the road rust state and worked in shops where I dealt with rust daily, I was prone to draw the line pretty quick on putting money in a "rust bucket".

Not to be mean, but you have no idea how bad rust is in the Upper Midwest, Northeast, Great Lakes Area, and Southern Ontario/Quebec compared to Lower Midwest states like MO. My truck is from central MO with some rust and it's better than 60-70% of local GMT400s from around here. Despite my rust, I get heads turned and compliments from people when I go out shopping or getting work done at a shop when I can't do the work myself. It's super weird and creeped me out at first, but I've gotten used to it.

I got my 14 bolt from a northern Kansas junkyard and the Tech working on my truck at the GMC dealer I go to told me that this axle was WAY nicer than any used axle they would've ever ordered.

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Here's the 14 bolt from KS

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[Boots97]

God bless you. You've saved me a heap of typing.

No Problem! Learning from what I know and passing it on to the next GMT400 owner!

 

[Road Trip]

Youtube Link

How do you think I should handle this rust? I can replace the parts but $ is adding up and then I have to pull the axles when everything is working well in that department.

Greetings SDgunner,

Thanks to purchasing a '99 C2500 with a missing e-brake cable vs. an impending
NY safety inspection, I was forced to open up the quiet & smoothly operating rear
brakes, and discovered a still functional yet sketchy mess traceable to the PO's
benign neglect. (See 1st attachment.)

Given the sheer amount of rust/scale on the exterior surfaces that face the
pumpkin, I was concerned about a possible loss of structural integrity. I
decided to remove the backing plates & ran them through my blast cabinet
in order to be able to prove/disprove to myself that they were still fully
functional. (See 2nd attachment.)

After blasting every square inch of both backing plates, I was impressed
by just how robust GM had made them. Actually confidence-inspiring
enough to reuse them, as opposed to sourcing a minty used set from down
south or possibly lucking into a set of NOS ones.

Once they were strictly clean, I did put the POR-15 to them in order to
help them last as long as possible here deep in the rust belt. (See
the 3rd attachment.)

And finally, the photo right after I pushed this functional resto over the Finish Line.
(See 4th attachment.)

****

That's the thumbnail sketch. If you are interested in the actual blow by blow,
follow the link to the section in my functional restoration thread where
I (unwillingly) dove into a set of perfectly-behaving rear brakes and
found plenty of stuff to make better. (LINK)

The bottom line is that those backing plates on my JD7-equipped C2500
were still strong like new, so in my case the rust turned out to be
cosmetic. But if you can gain access to a blast cabinet, it's worth the
piece of mind to go looking for trouble, not finding any, and putting it
all back together so that it functions like the day it rolled off of the
assembly line.

Safe travels --

 

[movietvet]

Not to be mean, but you have no idea how bad rust is in the Upper Midwest, Northeast, Great Lakes Area, and Southern Ontario/Quebec compared to Lower Midwest states like MO. My truck is from central MO with some rust and it's better than 60-70% of local GMT400s from around here. Despite my rust, I get heads turned and compliments from people when I go out shopping or getting work done at a shop when I can't do the work myself. It's super weird and creeped me out at first, but I've gotten used to it.

I got my 14 bolt from a northern Kansas junkyard and the Tech working on my truck at the GMC dealer I go to told me that this axle was WAY nicer than any used axle they would've ever ordered.

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Here's the 14 bolt from KS

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No doubt there are places in the states that have worse rust than I experienced in KC, Mo. I have seen real bad and some not so bad but it is all bad when you compare to PNW area. This is Nirvana out here compared to where I lived.