Cleaning Out A Tranny While Its Mounted In The Jeep?

In the continuing process of getting my "new to me" '56 CJ5 roadworthy, today I replaced the tranny and xfer mounts (did the engine mounts last weekend). While I had the skid plate and cross member off I drained the oil from both and it was a dark brown/nearly black color but with no discernible metal shavings in it of any kind (I was happy about this). I removed the pan on the x-fer and found about 1/16 inch of black sludge in the pan which I cleaned out. It was thick and caked on but was easily removed with a plastic scraper and brake cleaner. Took the top off the tranny because I suspect that it has the same sludge and confirmed it when I took a long screwdriver and scraped down deep for a sample.

My question is, with the tranny still mounted, what do you guys think is the best way to clean it out, or should I leave it as is fill it with the proper gear oil and move on? I don't have a true "shop" per se so I rely on hand tool, sweat and a lot of colorful vocabulary while I work. In the past (3A and M38) I've used brake cleaner, but it the sludge wasn't this thick. I've heard of using oven cleaner or kerosene but wanted to get some opinions before I go any further. I don't want to make more of a problem...

Any thoughts are appreciated - thanks in advance for the help!

 

In theory people may have filled a transmission with gas and gone through the gears with the transfer case in neutral for a minute. Then drained it out to find a shiny clean case left behind. In theory that kind of thing would also be best if done outside well away from any structure too.

 

I wouldn't use oven cleaner but I would feel safe using something derived from petroleum--gasoline, kerosene, even mineral spirits.

Oven cleaner is the best exterior degreaser/cleaner I have ever used though. It does what Gunk and other auto-specific aerosol degreasers fail routinely at. I do use a light touch with a brush to mechanically move and agitate heavy deposits, but the oven cleaner works a charm on cast iron and steel.

Is there a commercial manual transmission "flush" made just for the purpose?

 

I'd quickly looked at a couple "cleaning solutions" like Auto-Rx, and a couple SeaFoam and Lucas products, but if I understand them correctly, you add it to the transmission fluid and drive it for up to 1000 miles and then drain and refill per manufacturers specs. Other sources say petroleum based stuff like kerosene as already mentioned. I've used gas and oven cleaner on sludge covered sheetmetal and other parts, but never in an enclosed environment like a transmission.

I don't know if something like Simple Green will get the gunk out of the tranny without scrubbing, which is impossible with all the gears, etc inside.

I also assume that anything I put into the tranny is going to go into the transfer case since they are connected and share some fluid so I want to make sure I do this as close to right as leaving it in the vehicle will allow.

 

My preference would be to clean it by changing the oil a couple of times. GL-5 gear oil in a gallon jug from WalMart is not very expensive... GL-4 is preferred, but GL-5 is likely ok in this case. And vastly less damaging than gasoline, I'd imagine. You could possibly add some ATF to the gear oil ... or run straight 50W HD motor oil for a while. The detergent in ATF (lots of detergent in ATF) or HD motor oil will help to clean out the gunk.

 

Thanks for the ideas!

Hmmm.... add ATF (automatic transmission fluid, I presume) to the GL4. I hadn't considered that. I thought GL4 was really the only stuff to run in these because of the "yellow metal" synchros. Have heard about the 50W HD oil - are the detergents in there that potent to get the sludge out?

I've got mineral spirits handy from another project.

More research to come.

 

I have to agree with Tim. Don't use gasoline, kerosene, mineral spirits, simple green or anything else that could strip away the protective oil film from all of the wear surfaces in your transmission. Simply changing the oil a couple of times will do the job nicely. If your really set on getting it clean, add a little ATF as Tim suggested (1/2 pint?) when you refill.

You're correct that GL4 rated gear oil is compatible. Be are that some oils are GL4/GL5 dual rated. You don't want to use those.

 

As said above don't use anything to clean the inside because it will remove critical lubrication and residue may be left behind which could cause problems. Gear oil is non-detergent. The gunk inside will be fine. Just change the fluid. The reason it's important to use only GL4 gear oil is because of the brass synchros will become degraded by the additive in GL5. You have the potential to do yourself more harm than good.

 

I think it is worth remembering that millions and millions of transmissions have survived horrible abuse and no lube change ever. Don't overthink this.

That said, I like Timgr's approach.

 

Yes, ATF is automatic transmission fluid. If you go that way, realize that ATF is thin, and you don't want to add a whole lot. You could maybe mix ATF and 85W140 to address that to some degree.

I suspect that the difference between GL-4 and GL-5 isn't going to matter over the length of time you leave this mix in the transmission. I have no data, but lots of these transmissions have run plain GL-5 85W90 for a long time, without obvious damage.

Novak suggests 50W HD motor oil as a substitute for gear oil. Claims that shifting will be easier than with 85W90, and there's no problem other than perhaps the oil being too thin when operating in very hot climates. Valvoline racing oil is easy to obtain in 50W HD. HD stands for high detergent, as opposed to the old ND (non-detergent) oils. Motor oil contains detergents that will dissolve the gunk with a few changes.

Amazon.com: Valvoline SAE 50 VR1 Racing Motor Oil - 1qt (Case of 6) (822350-6PK): Automotive - ask your local parts store about getting a case for you. They should be able to beat the online price.

The current conventional wisdom about gunky engines is to run a few changes of motor oil through them, rather than any kind of motor flush. Modern engines using detergent oil that is changed frequently stay clean - detergent oil is very effective at keeping dirt and varnishes in suspension in the oil, rather than settling out on the engine surfaces. There is so much churning in a manual transmission, that it seems clear that detergent oil would be effective at scrubbing the case and gears.

 

Thanks guys - I think I'll just put in the GL4 that I've got and run it for a few months and then swap it out. I don't want to cause harm or more problems than "cleaning/dissolving" might be worth.

 

If you want to actually clean it out you have to use a solvent. Then refill with new oil.

 

I agree. If the trans was out of the Jeep and on the bench, you'd for darn sure be using solvents to wash and wipe everything clean and get it all nice and shiny, back to factory specs and all.

The only solvent that really robs all the oil deep in the pores of the steel is Acetone...and I wouldn't want to use that.

There's just the concern that the trans, in situ, would be left devoid of the thin film of oil on the surface of the parts if a solvent were introduced into the transmission oil and then driven as part of a method to remove gunk and sludge.

 

I wouldn't hesitate to use kerosene, gas or diesel. Fill it up, transfer case in neutral, first gear engine idling. Let it spin slow for a minute, then shut it off and let soak overnight before draining.
Your not going to hurt anything, there isn't any load on the trans and letting it free spin for a couple min won't get it warm. We aren't talking about driving without any oil.
Refill with oil. I would run the new oil for a few hundred miles; then while hot drain it and refill.

 

I'd do this, but not with gasoline...too volatile. Diesel fuel works well, and it has some lubricant properties to it.

 

I would agree with that. Gas is probably pretty hard on the seals too. Diesel would probably be best.

 

Please remember that exploding gasoline kills many people, quite often. Even the spark from a nearby electric motor can set it off.

 

I will pile on a little on this one. Never Ever clean parts or anything else with gasoline. VERY DANGEROUS.

 

Automatic transmission fluid works great. When I first got my jeep I ran it in the transmission, transfer case, front and rear axles. It cleaned them out really good. I changed the fluid in the spring and drained it in the fall. Then refilled it with more ATF.