M5A1 coming along...

[Douglas Greville]

Originally Posted by jdmcm

For the more delicate pieces I did not want to blast but had years of corrosion, I used the old molasses and water bath...both final drives were placed in a 50/50 molasses and water bath, took about three months total. They went in frozen solid and covered in scaly rust...they came out like they just left the factory...we were able to spin the them apart by hand...everything was pressure washed, disassembled, new seals and re-assembled

I am rather worried that what you have done is a cosmetic repair rather than a mechanical one. To the best of my knowledge, rust on gears is much more of a problem than it first appears. Yes it can be removed, but the issue is that the gears have a surface hardening and a softer "inner". If the surface has been sufficiently removed or damaged by pitting, the "inner" will not stand the wear loads.
Final drives are a highly loaded item and any failure will be spectacular - worse at speed.
A friend of mine in the UK had a final drive (epicylic) lock up on him in a CVRT Striker, fortunately it was just as he had slowed to enter a round about (no idea what you call them in Canada - traffic circle?). It slewed him and left him blocking the entrance to the round about. He called on a friend, they broke the track and pulled it onto a nature strip then towed it home with his Saladin. Total time was 2 to 3 hours.

Now granted a CVRT is a much more complicated final drive than a US WW2 design, so the failure mode is probably more spectacular, I suspect the failure mode for a Stuart one would be stripping of the teeth. This would then mean no drive on that side, which sounds tame. Bear in mind that US tracked (eg M113) vehicle training states that if a track is lost (which is the equivalent to this failure), the driver is forbidden to brake the good side as the result will be a slew and rollover. The only time braking is considered is if a collision of greater threat to life is about to happen.
Pretty dire stuff.

If you don't believe me, give it a try on any brake steer (US WW2 or FV432) style vehicle. Even fairly slow, any attempt to stop with just one tiller results in a sharp response on that side. I tried it last weekend on dirt as a check before writing this email and it is indeed a sharp response.

I suggest you be careful about speed and do continual oil checking for metal. If your final drive plugs are the same as the ones on my M3A1 Stuart, they should have magnetic inserts in them. If not, I suggest you obtain some (they do exist in the civilian world), quite likely some of the US specialist hardware companies stock them.

Regards
Doug
www.owningtanks.com

[jdmcm]

Doug

precisely why I used the molasses and water to remove the rust, the process of chelation will not remove the hardness from the gears as would acid, sand blasting or chemical stripping. The sugars in the molasses do not have the ability to penetrate the surface of the metal just the rust on top...after the gears and bearings were washed and oiled thoroughly they were inspected for damage and pitting. I am keenly aware that if the hardness of gears is effected you end up with a mess, I owned my own trucking company and have plenty of experience in the replacement of heavy truck differentials. We found that after a truck had sat for a year or more, the top of the ring gear inside the differential was often rusty as it had sat out of the oil for the extended period. On good quality gear sets this never proved a problem if the oil was changed regularly after the truck was put back in service...but if they were cheap import gears...a slight brown tinge of rust signaled immediate replacement lest they "grenade" and take out more parts or cause an accident...