differential cover ink stamping = help needed

[Burdar]

Wondering how long they should be allowed to soak. I'd of course check them periodically during the process, but just curious if you recommend a certain time interval and if the stuff is used straight from the jug or diluted.

I'd start with 20 minutes.  No dilution.  If there are areas where there is some red rust, the galvanizing is already gone on those spots.  You'll be left with a bare area where that red rust was.  The rest of the galvanizing will shine right up and look new.  Soak the entire part.  Don't soak half of it and then turn it around to soak the other half.  You can end up with an etched line across the part where the water line was.

[Burdar]

thanks for the suggestion. It sounded like a really good way to do it, but alas it didn't work for me.

That's unfortunate.  It's probably going to be hard to find info on the marks you're looking for since it's an 8-1/4 rear.  Most information is going to revolve around the 8-3/4 and the Dana.

[RacerX]

Ordinary vinegar works just as good as the evaporust at a fraction of the cost...

More info on this please,  just ordinary white vinegar?
Completely immerse?
How long?

Ordinary white vinegar.    $2 a gallon at Dollar General.   I did find some 9% acidity at our
local grocery store which does work a little faster but you need to be careful about the soak
time or it will start to etch the parts.   

I use some plastic storage tubs from walmart.    Six gallons of vinegar in one tub.  Fully immerse
the parts.    Come back later.  I usually let them go overnight, but 4-5 hours seems to work for
light rust.   Scrub with a small wire brush.  The rust falls off like magic and leaves it looking new
underneath.   Like the rust was never there.   Some parts that were galvanized still show the
galvanizing.   For heavy deposits that don't come off with the first scrubbing I will sometimes
return the parts to the bath for a few more hours.   If you do not fully immerse the part any
areas that are not in the liquid will blacken.    For this reason it is important to use tubs large
enough to fully submerge the part or it just adds some extra work to the process.

I am usually de-rusting parts that will be refinished and did not have factory paint markings.
Also, the parts I am working on have usually been so rusty that any factory paint is already gone. 

I have a second tub with water and baking soda in it to neutralize the reaction of the vinegar.

Burdar is correct, the parts will flash rust quickly after cleaning.    Usually not a problem as it
comes off easily in the next step which for me is media blasting.   You could always hit it with
some phospho if you won't be blasting it.

It does take a long time to damage parts in vinegar.    I look at the crisp, clear part numbers
on parts that you couldn't even tell HAD part numbers as a gauge of how the soak times are
not adding any additional wear or damage to the metal.   I soaked a thin sheet metal splash
shield and it came out looking great...  much of the galvanizing was still present except where
the surface rust was so severe that it had eaten through it.   I don't have an "after" picture of
this part handy though...

For the price difference between this and evaporust for me it is a no-brainer.    Vinegar wins
hands down.

YMMV

[anlauto]

Wow that's impressive...I've used muriatic acid before, but that seems to do just as good of job buy way less toxic...

[7E-Bodies]

@RacerX beautifully written and illustrated reply. I'd LOVE to see the completion pics of that shield as I need to do my exhaust shields.

[Katfish]

 Thx RX!

I'm sold, vinegar for the next project

[RacerX]

@RacerX beautifully written and illustrated reply. I'd LOVE to see the completion pics of that shield as I need to do my exhaust shields.

Here it is...   The same rusty one in the picture above.   I haven't done anything with it since cleaning it
so there is a little bit of surface rust coming back.   But you can see the dramatic difference!

The black spots are not holes...  they are undercoating overspray or grease blobs (I didn't look that closely)
Just need to be scratched off.

[7E-Bodies]

Pretty drastic difference. Thanks for posting. How do you plan to keep it rust free going forward?

[RacerX]

Pretty drastic difference. Thanks for posting. How do you plan to keep it rust free going forward?

Looks like it was galvanized originally...    I was just going to media blast it (glass beads) for
the final surface clean up and then paint it since I can't reproduce the original coating.   

It is in a place that is not highly visible and it is not on a 1-of-1 show car so should not
be too much of a problem if it doesn't look 100% original.

For rusty parts I normally vinegar first then media blast.   I find this produces a better result
than blasting alone.   The vinegar is a chemical reaction and does a better job removing the
rust and leaving the original surface intact.   Blasting alone to remove rust tends to leave a
rougher, more pitted surface as well as being significantly more difficult.