Manual trans cleaning additives?

[SecondMonkey]

I'm changing the 80w90 oil in my big old SM465 '79 truck transmission. For all I know this could be the first time it's ever been changed, it has less than 50k on it. I'm using fancy Amsoil oil, and it's going to cost a lot to fill the entire thing up. I expect it to last forever, more or less.

Anyway, I have a gallon of cheap 80w90 GL5 gear oil from a brand I've never heard of and can't remember. I'll never use it for anything. I want to "flush" the trans with that for a few hundred miles before I pour in the Amsoil. Is there anything useful I can add for cleaning the trans? Would something like MMO work in there? I have no reason to think it's extra dirty, but it is 30 years old.

 

[AdRock]

Just throw the cheap stuff in there for a few hundred miles and then change it again and put the good stuff in. It'll be fine.

 

[Zaedock]

You really don't need a flush, unless there's water contamination. If you want to check out the insides, pull the PTO cover.

Post up on how you like the Amsoil. I run a '53 SM420 in my '92 Jeep Wrangler. I'm currently running a mix of Coastal (GL3/GL4/GL5 rated) 75W90 and 85W140 to get a 80W110. It's been shifting well in the cold and doesn't make as much noise when I'm on the trail all day being a little thicker. The Coastal is the only parts store oil I've found that provides smooth shifting. It doesn't have as much sulfer smell and is probably easier on the synchros.

 

[Petrou]

for what its worth, your idea is good, nothing wrong with it at all, dont worry about adding anything, fill it, take it on a nice drive say 50 miles one way and 50 miles back. interstate if you can, then dump the oil when its hot, this will allow any sludge build up to fall out with the oil

on big rigs what we used to do when a truck came in with say 500,000 miles on it and never had trans oil changed, yes it happens alot. 100k is recommended for 80-90 and 150k for 75-90 synthetic. Anyway we would will the trans with atf and run it for approx 3hrs at 1800 rpm then drain it when hot. This was a method used and told by us to use from the manufacturer, eaton made most of them. well all except mack and few odd balls. this works for yours, fill it with atf and run it for about and hour or so with the high idle set, then drain hot. or the dive idea works too. any other questions just I.M. me

 

[tomcat27]

+1

 

[MolaKule]

Just use the cheap gear lube, run for a hundred miles and add the new MT fluid. The cheap(er) lube will clean it out.

I recommend against using anything that will reduce the viscosity of the fluid, even for short mileage.

 

[Audi Junkie]

If you really just want to flush and don't have enough of gear fluid, you can fill it up to the top with some ATF.

 

[mechtech2]

Trannys don't get sludge like engines do.
No water and contaminants from blowby, and much less heat.
When you dump the old oil, it is enough.
Save your flush money for your next fluid change.

 

[SecondMonkey]

Originally Posted By: mechtech2
Save your flush money for your next fluid change.

Well, it won't really cost me anything to flush with the cheap fluid...since I already have it. It's not something I would ever use for service. Otherwise it's just going to sit on the shelf next to the jugs of used oil for the next 10 years...

 

[mechtech2]

In that case, then go ahead and flush it.
Drive it a day or two before putting in the good stuff.