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

[99xcss4]

I do not know about 8 lug 2500s because they could be semi float or full float rears but but I think all the 3500s with 350 had 4l80e as the automatic option

 

[99xcss4]

11.5 inch full float axles as options.

I think the aam 11.5 did not come out until 2001 so no gmt400s got it only gmt800s I do not know if it could be had on the last few years of the c3500hd or not

 

[SDgunner]

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 --

Nice restoration! those projects can be a pain but it's nice to have it done right!

 

[Hipster]

??? What am I missing?

Looks like every vehicle I've ever seen. Nothin' special about that. Brake tubing looks better than most.

Probably want to replace the leaf-spring on the right side, and inspect the left-side spring thoroughly.

Maybge common in the frozen wastelands not so much here. Looks like big chunky scaley flaky layered rust in the video.

 

[454cid]

I think the aam 11.5 did not come out until 2001 so no gmt400s got it only gmt800s I do not know if it could be had on the last few years of the c3500hd or not

Yes, it's an 800 and up axle. Anything earlier than an 800 with an AAM 11.5 is a swap, or a Workhorse chassis. 3500HDs were Rockwell (early HDs) and Dana 80.

 

[454cid]

Maybe pull the backing plates and hit them with a needle scaler again, and slop some phosphoric acid, primer, and paint on them followed up by some Cosmoline or Fluidfilm? If GM doesn't have new plates, I think Dorman does....as much as I hate recommending Dorman parts. I think I'd spray the whole axle with something.

 

[JJF20]

New here, have experience with restorations and mtce. And running trucks/vehicles in the salt for a long time.

For a winter vehicle, carry on with what you are doing, and oil spray the whole thing when you are done. Inside and out. It’ll help slow that rust down. There’s various products, or just take it into a place that does it. It’ll probably be good to do it once now, let it soak in and then have it done once again, and again every year. Itll make a big difference. It makes a mess to work on it, but better than rusting out. I wouldn’t recommend Woolwax types right now, you’ll want something thinner that’ll creep. You can use something thicker later.

From the video, those backing plates look ok to use. While you have it up on the lift and accessible, I’d also consider cutting adjuster slots in them.

Good luck with it, that’s a good winter truck.

 

[Boots97]

Maybe pull the backing plates and hit them with a needle scaler again, and slop some phosphoric acid, primer, and paint on them followed up by some Cosmoline or Fluidfilm? If GM doesn't have new plates, I think Dorman does....as much as I hate recommending Dorman parts. I think I'd spray the whole axle with something.

X2 forgot that as well. You can pull the backing plates and dunk them in Coca Cola, Pepsi, Dr. Pepper or any soda with phosphoric acid. I’ve done this in the past with rusty AK parts and it works wonders.

Also, Dormans website cross references all its parts. Use their website to find said cross referenced part and find that. Don’t settle for Dorman if at all possible. Every Dorman part I’ve used except lug nuts have been absolute junk and a huge waste of money.

 

[454cid]

X2 forgot that as well. You can pull the backing plates and dunk them in Coca Cola, Pepsi, Dr. Pepper or any soda with phosphoric acid. I’ve done this in the past with rusty AK parts and it works wonders.

Using pop would be an extremely weak phosphoric acid solution. You can get Ospho or another product like it, at the parts store. I often use a deck cleaner that is phosphoric acid, from Home Depot.

 

[Road Trip]

Nice restoration! those projects can be a pain but it's nice to have it done right!

Sir, sounds like we're on the same page. Years ago, when I moved to New England
I started the summer car + winter beater thing. Working on the summer toy was
always fun, but fixing the winter DD was always a rusted solid horror show.

It took awhile, but I eventually figured out that restoring only the functional bits
on the winter/backup vehicle gave me 2 vehicles that I didn't mind working on.
Sure, the winter vehicle might remain homely, but it was a reliable ride without
the constant dread of "what if system foo fails & requires a fix?"

So that's why I named my thread 'Functional Restoration', because that was my
original plan, as-new mechanicals, but no effort/$$$$ spent on the curb appeal.

But now that old chore truck with the rumbly big block has worked it's way into
my heart & convinced me that I need to follow the lead of some of the other folks
in here and do a little more than I originally planned. In classic project creep fashion,
my new plan is to eventually turn it into a clean(er), confidence-inspiring, long-term
working member of the family.

And if it outlasts me & reminds my grandsons of their grandfather when they see/use it,
then so much the better. :0)

****

BTW, the takeaway of my original reply was the discovery that the backing
plates on this truck were much heavier gauge steel than I anticipated. (I've
had plenty of scaly parts go into the blast cabinet whole, only to come out
looking like shiny swiss cheese after. :-( Taking the long-term view, I'd rather
have the part fail the blast cabinet inspection with both feet on the ground instead
of failing in flight when I need it most. :0)

I've actually replaced backing plates on other cars due to excessive rust = weakness,
but thanks to the extra beef on these that ugly scale was just cosmetic. Who'da thunk?

Nice to make your acquaintance. Best of luck with your ice shack towing machine!