Bang for the buck Functional Renewal of rust belt '99 C2500

[Road Trip]

Missing parking brake cable > heat-cracked brake shoes > crusty diff cover = old truck rabbit hole!

So as you all know, you can start working on one specific problem requiring
a fix, and then it just morphs into a semi-related 2nd area, and before you
know it you're working on a functionally unrelated yet geographically adjacent
3rd area.

****

It all started innocently enough. Time to get the annual NY state safety inspection
sticker. The CEL is still out thanks to sorting out the ignition system, so that's a big
hurdle out of the way. Slid underneath just to give a quick visual & make sure that
I'm not going to fail for something stupid/obvious.

And there it was, conspicuous in it's absence -- the parking brake cable to the RR
brake assembly is completely MIA? Hmmm...there's no fresh witness marks showing
recent removal? it's all crusty like it's been like this for many moons? How did the PO
get this thing past inspection for x number of years?

So that's problem #1. When I removed the axle & RR drum, I was surprised to see
that the friction material on the shoes were badly heat cracked between the rivets.
(10.5" 14 bolt FF, 13" drums)

Surprised only because the brakes were so smooth & quiet that I didn't think there
was any latent issues with the brake system? That's problem #2.

Alright, while I'm back there it looks like the rear diff cover has zero signs of being
disturbed? You know, no excess goo ringing the cover, the bolts all match & look like
they were undisturbed, etc.

That's no showstopper, I'll just service the diff with fresh fluid while I'm under here.
But the amount of scaly rust made me lose confidence in the integrity of the cover.
It had never leaked, so the amount of rust was impressive. (Here in the rust belt we
actually see engine oil pans start to weep oil from pinholes in the sheet metal from the
rust. (!) So sourcing a new cover was problem #3.

****

So I've got a few photos that cover the deep hole I ended up digging for myself in the
brake system, but tonight's show & tell is only about the rear diff cover.

Purely out of curiosity I took a brief look at the aftermarket diff covers. Even though
some of them are pretty spendy.

Then I found the Gale Banks diff cover videos on YouTube, and via a custom clear plexi
see-through cover he gave me some interesting insight on gear lube dynamics under the
cover at highway speeds. (LINK)

Especially what happens when the $$$ flat-faced aftermarket covers don't guide the gear
oil back up to where the ring/pinion intersect?

After it was all said & done, it reminded me that when you make changes to a part of the
truck that's contrary to what the factory part delivers by design...you better have a really
good reason why. (!)

Given the above, I decided that I'd like to replace the too rusty cover with a new one (made
to OEM specs) ...or maybe a NOS part, or even a clean, rust-free used one I could swap in?

Some sellers threw a coat of black paint on covers that were as rusty as the one I had, and
then had the cajones to ask $50+ for it? I seriously considered new & be done with it, but I
couldn't tell if they were made with as thick a gauge of steel as the one the truck originally had?

Good news -- I found a used rust-free 14 bolt diff cover from a ebay seller in Cali for $14?
Sure, it was a bargain because it had a cosmetic dent in it, but it looked like it was finesseable?
Of course, with shipping & NY sales tax it was closer to $30 to the door...but I consoled myself
that it was a fraction of the price of admission for the big ticket aftermarket covers. :0)

OK, without further ado, here are the photos that you have been waiting for:

Dented diff cover. It looks exactly the same in person that it did on the ebay auction. Here in the rust belt this is a rust-free gem!

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A couple of minutes with the ball end of a ball-peen hammer, working the dent out backwards from how it was made. (outside in, not the center 1st)

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Note: The trick that I read about that works best for me is to visualize how the dent was made, and then try to hammer it back out as if you were watching the dent creation video being played in reverse. (All those times that I used to go right for the highest point in the dent first was exactly wrong!) In English, I circled the periphery of the dent with the ball peen hammer until it was all but gone. Then I switched from ever tighter circles to long, sliding hammer blows in order to honor the curvature.

Maybe not good enough for the center of the hood, but not too shabby under the 8' bed of a chore truck. :0)
Of course I proceeded to toss the cover into the blast cabinet, where all surfaces were cleaned up:

The interior surface post blast cabinet. The gasket/sealer should adhere plenty alright. Who knows -- maybe surface micro-dimpling = better gear oil toss? ;0)

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The outside looked good enough to paint. And I did, which would explain the paint seen on either side of the ring gear relief. But there was a tiny shadow of the original
dent still visible...not from a normal person's perspective, but of course the camera made it look like the Grand Canyon -- so I decided that a little more free practice cosmetic diff cover bodywork was in order. (What can I say? @johnckhall has really raised the underbody bar with his extremely tasty frame resto, so I have no choice but to bring this cover repair up a notch. :0)

Straight Bondo has no strength. JB Weld is overkill. But as Goldilocks would say, aluminum filler is just right. Here it has dried, and ready for sanding.

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De-dented Cast Blast painted Cali cover on left. Original cover after 24 winters in upstate NY on right. NOTE: Oil residue is from the removal process, not a leak.

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I also have a fresh Fel-Pro gasket, plus 14 new factory-style flange bolts. (The old bolts were pretty crispy.)

Anyway, I don't know if in the long run I actually saved any money by buying a dented
original cover...but I just look at working the dent out as a free practice session where
I could bust some rust off of that skill in an out of the way area. And if it doesn't hold up?
I'll take pics & rework it with the really good stuff: JB Weld, the time-honored 2-part epoxy
New Truck in a Tube! :0)

Besides, being an original part the Cali cover is robust and is confidence-inspiring. I'll get
that cover installed...and then know that I can now place this area into the 'no worries' pile.

More on the brake stuff in a following post. Got some good info & photos on setting
the rear wheel bearings up for success.

For what it's worth. Cheers --

 

[fancyTBI]

The “new” cover looks great. Your original looks identical to the one on my 10 bolt that I replaced years ago. Getting ready to do the same on my C2500 but it doesn’t look nearly as bad. Keep it up!

 

[DirtBag]

When you put it back together using the FelPro gasket....do you use RTV or something as well or just the gasket? Getting ready to do mine and am new to the process.

 

[Road Trip]

When you put it back together using the FelPro gasket....do you use RTV or something as well or just the gasket? Getting ready to do mine and am new to the process.

Greetings DB! I'm happy to share with you the process that I have finally settled on
after trying different methods over the years. (Disclaimer: If you ask 5 mechanics
about how to seal up a diff cover you will no doubt get at least 5 different answers.
My method may seem a bit overcautious to some, but it will work in the real world
where the parts may or may not be exactly assembly line straight.)

OK, big picture time. My '99 C/K service manual was at it's most accurate back
in '99, and they had no way to know that sealers were going to evolve over the
next couple of decades. Even so, we'll start with what the factory manual says,
and then I'll discuss how I build on top of this guidance with today's sealants.

First, let's check out what the factory manual tells us to do:

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Note: There is only a single "Drive Axle Final Assembly" section in my manual. So instead of just specifying 35 ft/lbs for the
torque spec, they should have referred the mechanic back to p. 4-103 in order to pick the correct torque for whatever axle
they are working on. FWIW I've included the specs here in orange.

As for guidance on what to use on the cover, they specify 'a thin layer of sealant'. And that's all you really need IF your cover
is perfectly straight. (As in, the PO didn't reef down on the bolts & distorted the diff cover's mating surface?)

So here's where I depart from the service manual on purpose. Since I live in the real world, if at all possible, I *always* use a
diff cover gasket. This gasket will allow a less than perfectly flat cover to still seal 100%.

And to answer your question, yes I do use a thin coating of sealant between the Fel-Pro gasket and the differential cover only.
This gives me 2 benefits. The first is that the gasket now becomes one with the cover, and also gives me that last little bit
of insurance against seeps/weeps/leaks. The second benefit is that installing the gasket dry against the machined flat
mounting surface on the rear end allows me to remove the diff cover down the road, clean the surfaces, reinstall the cover,
and have it still be leak free.

NOTE: Some folks who figure that they will never remove the cover again will elect to use the sealer on both sides of the
cover gasket. It's a judgement call. My preference is to make the diff servicing as easy as possible down the road, and
so far this approach has worked for me over the years.

So what sealer am I using? Currently, I'm using Permatex Ultra Black Gasket Maker, part #82180. IF the directions are
followed, it's never failed to meet/exceed my expectations. (And I'm an old Aviation Form-a-Gasket guy, loved how it
worked, hated it if I ever had to go back in after the fact. :0)

Here is are the instructions on the back of the cover. I've taken the liberty to
underline the steps that some folks skip, not allowing them to get their full
money's worth out of this stuff:

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IMPORTANT NOTE: The Ultra Black that I'm using (#82180) requires that you allow it time to set before torquing & also before placing it into service.
If this is a backup vehicle and you can wait, then you get to pay $7.48 at Amazon. (LINK)

On the other hand, if this is your DD and you don't have the luxury of time, then there's the 1-minute version
of this sealer (#25229) where you don't have to wait. This quick-turn requirement will cost you $17.07 for
roughly the same amount of sealer at Amazon. (LINK)

Of course, by following the directions either will work for you 100%. The choice of which version to use is whichever one best
fits your timetable and/or your budget.

SUMMARY:

1) The '99 C/K Service Manual is written so that you will simply use a 'gasket maker' sealer.

2) Some mechanics will instead opt to use a cover gasket to ensure success while fixing in the field.
A few will install the gasket dry. A few will seal the gasket to the diff cover only in order to facilitate
future maintenance down the road. And the rest will seal both sides of the gasket to really seal
the deal. (The 'once bitten, twice shy' crowd. :0)

3) There is a torque spec, and it's dependent upon which rear end your truck has. May seem
like overkill, but following the torque spec will give you proper retention AND at the same
time help you avoid distorting your cover (ie: future leaks down the road) w/excess torque.

One last thing. Some people prefer to suck out the old 90-weight via a tube through the
fill port (instead of pulling the cover) ...but at least in my 14-bolt full floater there is a large
circular magnet on the bottom near the ring gear that captures all the (ferrous) metallic
foreign worn-off particles floating in the lube.

Fortunately for me there were no big chunks, but there *was* a lot of superfine metallic 'mud'
piled all over this magnet. If replacing hard parts in the rear end was a <$50 deal, then I wouldn't
worry about all of the above that much.

BUT things like new bearings, ring & pinion, etc., are quite expensive in both parts
& labor...and oil in good condition is the key to maximizing the life of your components. (!)
Given this, I don't have a problem changing the oil periodically & giving that magnet a
good cleaning and a hard look at what it has collected for my viewing pleasure.

****

Apologies for the length, but your question was a good one, and I just wanted
to be clear in what works best for me.

Best of luck. Enjoy that good looking truck --

 

[DirtBag]

Wow! Thank You for taking the time to put that together! I'm going to do mine this weekend and I already have that particular sealant and a gasket on hand! THANKS!

 

[fancyTBI]

@Road Trip, you are so right about asking 5 different mechanics and receiving 5 different answers. I picked up a gasket for my cover and my dad (a former GM mechanic who worked on these trucks when they were new/a few years old) asked “why? Just use gasket maker.”

I am going to use a gasket and sealer when I do mine. You make a strong argument for using just gasket maker, though. I typically apply Permatex High-Tac to the surface, apply the gasket, cover it, then install the cover.

Appreciate all the well thought out responses you share. They are really informative and helpful.

 

[Road Trip]

I am going to use a gasket and sealer when I do mine. You make a strong argument for using just gasket maker, though. I typically apply Permatex High-Tac to the surface, apply the gasket, cover it, then install the cover.

Appreciate all the well thought out responses you share. They are really informative and helpful.

Thanks for the positive feedback, it's appreciated! FWIW, one of my all-time favorite truisms is this:

"Experience is the Knowledge you've gained after you needed it."

Personally, the more I understand something, the more comfortable I am with it.

Therefore, my goal with my writing is simply to help others feel as comfortable as I
do in an area where (based on my penchant for learning stuff the most difficult
way possible) I've attempted to fix something every possible wrong way...and
whatever I'm describing is the only remaining way I found to do it such that I
don't regret it afterwards. :0)

****

Back to the diff cover subject. In the 1st attached photo is what I ended up with after
securing the gasket to the cleaned up diff cover. To me the inner beauty of this
solution is the promise that this cover will seal up nice, yet still come off easily down the
road for preventive maintenance w/no prying/scraping...and it will go back up as-is,
repeating the sealing cycle for no additional outlay. (!)

Note also that I was able to purchase (14) new metric 10.9-quality flange bolts for a
grand total of $9.07 from a local business that specializes in fasteners.

If you compare this to the 2 other screen snapshots I attached you can see that some
are trying to charge outrageous boutique/a la carte prices for diff cover bolts. There's a
lot of nonsense out there...all I'm trying to do here is show anyone with a '99 C2500
(or similar) 14-bolt a tested-good solution to something that we all need to do
periodically for best results.

Happy wrenching --

 

[termite]

Kudos on your top notch write ups including necessary steps, rationale for each, and anecdotal deviations that circle back to your point. Finally had time to catch up on the full thread and you’ve made that truck look great while keeping it functional as intended. Keep up the good work.

 

[Road Trip]

Perfectly smooth rear brakes opened up for a missing parking brake cable...discovered Can't Defer fixes needed

Steering & brakes are 2 areas where you simply can't cut corners.

Anyway, the brakes in this truck always felt so smooth & solid that I didn't
want to disturb whatever pixie dust was making this happen.

Or so I thought. Back in reply #71 I mentioned the need to get a fresh
NY inspection sticker...and thanks to a missing RR parking brake cable I
had no choice but to reluctantly open up the rear drum brakes. (JD7-spec)

I'll let the pics do most of the story-telling here. More common sense
than abstract theory is needed in the land of drum brakes:

At first glance no surprises -- Benign Neglect is typical of vehicles sourced from the used truck mfg plant. (But shoes are still meaty.)

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Failed inner seal on LR drum is allowing 90-wt to migrate to friction surfaces = grabby brakes down the road? Will renew seals on both sides.

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Attention brake drum balancing devos. Up 'til now, nearly all drums I've ever seen were balanced by small weights added/welded on during manufacturing.
These 64-lb suckers were balanced by weight being machined away. These must be at/near the min/max limits of what the factory balancing station could process?
Even so, they ran dead smooth as found at all speeds prior to these photos being taken. (!)

Showstopper in the form of heat cracked friction material found on shoes on both left & right rear brake assemblies. No choice but to start 100% rear brake rebuild.

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100% new brakes in the back, all the way through the backing plates. Good news -- scaly rust removed to find underlying backing plate still stout!

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After cleanup, brake backing plates were given the POR-15 treatment & then reinstalled on axle. (110 ft/lb on the 4 mounting bolts per the C/K Service Manual.)

Good news - original drums had never been turned! Last remaining shop in area capable of turning drums took bare minimum material needed to true drums per my request. (Yes!) Also, bearings & races passed visual & still ran smooth. New seals complete the near quarter-million mile refresh.

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[Orpedcrow]

Beautiful thread and a beautiful truck!
Thanks for sharing! Am I correct to assume there’s some photography going on here? These don’t seem to be typical cell phone pictures.

I like the idea of having two “old” vehicles too. Makes me want to find another old Honda. Maybe an awd wagon? Or first gen cr-v. I don’t hate my 2012 Tahoe, it just doesn’t have much soul and I’m not excited about it. I did love all the old Hondas I had though.