Flush a transmission

Shu47

Shu47

Senior Member
I am changing the transmission gear oil in a 1947 1 ton truck that has not been driven in years. What is the best method to flush the transmission before putting in the new gear oil? Or should I just drain and refill with new. Will flushing just stir up stuff better left alone? Thanks for whatever advise I can get.
 
If you aren't planing on doing an overhaul any time soon and the ****** in question is otherwise functioning normally, I'd just drain out what will come out after a warm up run (if that is possible) then refill with recommended lubricant and run it for a short period say a few days or so (depending on how much it is driven) then do another change. Transmissions don't have the same build up of carbon from combustion like an engine does but they do make a little metal from normal wear and tear. The idea would be to get that stuff mixed up into the existing lubricant so it can be quickly drained out before it has a chance to settle. If you don't like the looks of what is in there now, go ahead and dump that and refill for a quick change later.

If there is some sludge in the bottom it's sometimes better to let the sleeping dogs lie until you do an overhaul.

Kerby
 
Thanks for the reply. I will just go with pouring in fresh and then do another change after putting a few miles on it and see how it looks.
 
You can unbolt and remove the tower. Easier to flush it and this way you can look at the gears for missing teeth. Someone can suggest a good type of fluid to use. I just use a little wd or mmo. I haven't had one that was gunked up bad yet.
 
Thanks Tinker for the suggestion. Right now I am having trouble getting the floor panel covering the transmission off due to rusty screws so I can't take the top off easily at this point. If I get that panel off in the future then I might use your recommendation.
 
Get some PM Blaster or WD40 and spray ever bolt you can see for about 2 weeks. They'll come out eventually. My 38' looked a little like your truck. First thing I did was wash the whole truck in engine oil :D
 
To remove the screws from the floorboards use a hand held impact screwdriver that you hit with a hammer. I have removed impossible screws from door hinges screws to carburetor screws.The Kit which Sears and I'm sure others offer, comes with a variety of bit sizes, I ground one bit down to use on small screws like carburetor size.
 
After setting for several years, I got my flatheads back on the road. After draining the rear ends and transmissions, I simply sprayed WD40 into the drain and fill holes to rinse them out. If I did anything wrong, it hasn't shown up yet.
MIKE :)
 
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