yep it also works to compare high carbon to low carbon steels. cast iron will give big sparks steel gives smaller sparks. the harder the metal the finer the sparks.

restore49 wrote:

Stay away from trying fiberglass - do not flame dry Brake Clean toxic Gas - I know some folks are not keen on JB weld - have done multiple repairs years ago with no issue (not the quick) - if you grind away at the weld bead you can weaken.
 

DO NOT HEAT BRAKE CLEANER AT ALL DONT EVEN SPRAY IT ON A HEATED SURFACE. forms toxic gas.

use caustic soda based degreaser instead which is fine to be warmed you can also use oven cleaner most them are caustic based too.
for general degreasing of parts a solution of high flash point kerosene and phenol warmed to 50deg celcius works very well especially with gear boxes fill with the solution and heat with a immersion heater all the oil residue will come out then its only the kero to remove.

as for grinding the weld back be careful not to remove all the weld. although excessive build up is why many welds crack right beside the weld. the reason is welding affects the stress lines in the metal. normally the stress lines run straight along the length of the material welding causes them to have a peak this forms across the weld forming points of increased stress either side of the weld the more over build up the worse it is good welds have proper penetration, low build up(almost flat), and a clear travel pattern. post grinding and heating helps with this so does preheating which helps with penetration and by having the metal at a more even temp slower cooling also allows the metal to normalise better.

Thank you for your warning, trainzkid88. I take your point about toxic gas. And you have provided some interesting alternatives. Particularly intrigued by the kerosene and phenol approach.

Also appreciate your careful thoughts about grinding. As it turns out, I have been able to source the Permatex Spray Leak Sealant and it is on its way here. Using the Permatex, I do not need to consider grinding and can leave well enough alone. If it doesn't work, we may be having this conversation again down the road, of course.

not trying to stir the pot but "DO NOT HEAT BRAKE CLEANER AT ALL DONT EVEN SPRAY IT ON A HEATED SURFACE. forms toxic gas." That is not right that's very generalized. that's like saying if you don't put a seat belt on every time you get into a moving machine or truck you will die. what you have to look out for with brake clean is the Chlorinated brake clean which most is not nowadays. in order to create the "toxic gas" you need to have the chlorinated brake clean Hi heat over 500F if I remember right and ARGON. most welding gases have varying amounts of argon. most times it happens when a welder has cleaned part with it before he goes to weld and starts right in on it. what is it making is phosgene gas they used a lot of it in WW1 very nasty stuff. so use a point of care with it but you can still use it.

A bit of progress. I was able today to thoroughly clean the interior of the differential crack and then apply several coats of Glyptol 1201 enamel (designed for, among other things, painting and sealing the insides of oil tanks). As you can see from the photo, I used a heat lamp to help 'cure' the paint. My hope is that it will have penetrated the (very fine!) crack, while retaining some flexibility as a coating. Such, in any event, was the advice of the Glyptol company's chemist. Tomorrow I will replace the diff cover. As soon as the Permatex spray seal arrives, I will use it to, fingers crossed, seal the exterior side of the crack. (I should add that the 'red' interior is the effect of the heat lamp--though Glyptol 1201 enamel is also red...)

 

If there is a Ford dealer in your area they use a Anaerobic sealer for differential covers on F450.

not all products clearly mark whether they are chlorinated or not hence the generalisation. and yes it would depend a lot on temp for the reaction to happen.

In the way of an update: differential is once again filled with gear oil. It's been a couple of days and just a bit of movement (no work). So far no sign of any leaks. On the inside of the diff the crack was painted with several coats of Glyptol 1201 enamel (www.glyptal.com/glyptal_products.html) and allowed to cure with a heat lamp. The exterior of the diff along the welded crack, after being thoroughly cleaned, was coated with several coats of Permatex Ultra Black silicone (www.permatex.com/products/gasketing/ultr...cone-gasket-maker-4/) and allowed to cure. My hope is that the Glyptol will have penetrated and sealed the crack on the inside and that the Ultra Black silicone will have sealed it on the outside--as well as remaining slightly flexible so as to not crack itself.

Today I changed oil and fuel filters (and crankcase oil, of course. Am working my way checking the various gear boxes, making sure that they have adequate lubrication. Need to swap out tthe front tires for a mounted pair that came with Hanna. Almost ready to put her to work.

Hi, Onfoot.
Good stuff and fingers crossed.

Just my 0.02.