Transfer case flush?

[73Chevy]

I'm about to change the gear oil in my transfer case (NP205) on my 1973 chevy truck. When I change gear oil in diffs, I always spray out the diff with brake cleaner and get out the last bit of oil and gunk at the bottom. There's usually quite a bit.

Can I/should I try the same thing with my transfer case? Obviously I can't open up the TC as easy as a diff, so I only have the drain and fill plugs to work with. Can I empty a can of break cleaner into the fill hole and let it drip out? Maybe fill it with something less harsh like mineral spirits? Would that be a bad idea?

The idea is to get the last little bit of old gear oil out since I'm replacing it with synthetic and what's in there could be 40 years old...

 

[tommygunn]

I'd argue for brake cleaner over mineral spirits if you're looking into doing this. Brake cleaner is a really volatile chemical...it'll break down crud and evaporate away once its done and not leave anything else in there to end up mixed up with the new oil. Mineral spirits well, tend to be really bad viscosity modifiers to say the least.

But aside from that I have no advice its a hard call to what kinda playing about I'd say would be safe and smart.

 

[73Chevy]

That's kinda what I thought, brake cleaner is meant to evaporate quick and leave nothing behind. I was thinking I could blow some air from my air compressor into the fill hole to help dry the brake cleaner out before refilling.

 

[hounddog]

Transfer case is vented also.

 

[demarpaint]

Why not just a simple flush with some additional gear oil, and leave the break cleaner or mineral spirits out all together?

 

[73Chevy]

Originally Posted By: demarpaint
Why not just a simple flush with some additional gear oil, and leave the break cleaner or mineral spirits out all together?


I plan on using $20/quart royal purple...don't want to waste any of that.

 

[demarpaint]

Originally Posted By: 73Chevy
Originally Posted By: demarpaint
Why not just a simple flush with some additional gear oil, and leave the break cleaner or mineral spirits out all together?


I plan on using $20/quart royal purple...don't want to waste any of that.

Then use something cheaper for the flush or leave it alone, and drain and refill. There is always going to be residual fluid and junk in the transfer case. JMO

 

[73Chevy]

Originally Posted By: demarpaint
Then use something cheaper for the flush or leave it alone, and drain and refill. There is always going to be residual fluid and junk in the transfer case. JMO


That's why I was thinking about using brake cleaner, it should clean out the residual oil and not leave anything behind. Is it going to hurt anything?

I'm especially concerned because I'm switching from old, old, and dirty, to fancy, expensive synthetic.

 

[demarpaint]

Here's my thinking. In order to really flush the transfer case you'll need a lot of brake fluid. Small amounts of it might not flash off quickly and when mixed with fresh gear oil will break it down. There are gears and maybe a chain in there that can easily collect brake fluid. If it were me I'd shorten the interval, or just change the fluid refill and enjoy. That's just my opinion.

If you are 100 % positive can get every bit of brake fluid out leaving nothing behind, go for it. Or better yet contact the maker of the brake fluid and ask if they recommend it for a transfer case flush. JMO

 

[73Chevy]

Originally Posted By: demarpaint
Or better yet contact the maker of the brake fluid and ask if they recommend it for a transfer case flush. JMO


Funny you say that, I was noticing on the can of brake cleaner it said nothing about cleaning differentials on the can. Am I the only one who uses brake cleaner for this? I thought it was normal practice....

I would assume the MFG of brake cleaner would probably say no to using it in the transfer case juse for liability reasons.

After filling it with Royal purple I expect to never service the TC again the way I drive, so I want to make sure I get it right....

 

[demarpaint]

I don't think brake cleaner was ever marketed as a flush for transfer cases, and probably why they don't mention it on the label. I guess........

I've seen guys spray it into carbs and throttle bodies too, something it wasn't intended to be used for either.

I understand where you're coming from, I'd just double check to be sure, a whole can is a lot of brake cleaner. Maybe they can tell you how long it will take to totally flash off and if it would be harmful to the new gear oil. At least then you can be certain.

 

[73Chevy]

FWIW, I just used a whole can of brake cleaner to clean my rear end, but it's a huge chevy 14 bolt. I let the brake cleaner set in a drain pan for a few days, and it almost completely evaporated, leaving a few ounces of gear oil behind. Seems like it seperated completely from the gear oil after it had time to evaporate...

 

[demarpaint]

A transfer case has two plugs and a vent IIRC, so it might take a while longer for the brake cleaner to evaporate.

 

[Trav]

I cant see much good coming out of this. The small amount left after draining is not going to significantly contaminate the new fluid.
Spaying brake cleaner in the fill hole wont get at the components in the rear of the case anyway and may not be very beneficial to the seals, the risk in this case far out weight the benefits IMO.

Get the unit up to temp and drain it, thats really good enough and all it needs.

 

[demarpaint]

Originally Posted By: Trav
I cant see much good coming out of this. The small amount left after draining is not going to significantly contaminate the new fluid.
Spaying brake cleaner in the fill hole wont get at the components in the rear of the case anyway and may not be very beneficial to the seals, the risk in this case far out weight the benefits IMO.

Get the unit up to temp and drain it, thats really good enough and all it needs.


Exactly, sometimes you can kill something with kindness.

 

[Rob_Roy]

I think you are making this more complicated than it needs to be. I understand that you want to get all of the old fluid out, but you don't need a solvent rinse to accomplish that. Take the truck for a nice ride to get everything warmed up, then drain the current fluid out of the t-case. Refill with some el-cheapo 80w90 and drive the truck normally for a week or so, then drain and refill with your preferred gear lube.

 

[Astro14]

I guess I've never even worried about this aspect of changing transfer case/gear oil...whenever I've drained them, the fluid comes out looking reasonable...a bit darker than when new...or a bit cloudy sometimes (deep water)...

Do yours really have a lot of gunk in the bottom when you go to change the fluid?

Mine don't, at least, I think they don't, even when I get a bit of moisture in the diffs, it seems to come out OK with the gear oil...with a 30K interval (unless I've dunked the axles, then, it's next opportunity) the fluid always comes out clean. With the design of the Toyota, for example, I can't see into the bottom of the diffs...you remove a drain plug, not pull a cover...so I've never seen any gunk that would need to be flushed...

Are you obsessing over this? Or is it a real problem?

 

[CharBaby]

Originally Posted By: Rob_Roy
I think you are making this more complicated than it needs to be. I understand that you want to get all of the old fluid out, but you don't need a solvent rinse to accomplish that. Take the truck for a nice ride to get everything warmed up, then drain the current fluid out of the t-case. Refill with some el-cheapo 80w90 and drive the truck normally for a week or so, then drain and refill with your preferred gear lube.


+1

I have done similar. Use the el'cheapo fluid and then drain & refill with your prefered fluid

 

[Kuato]

Originally Posted By: Char Baby


I have done similar. Use the el'cheapo fluid and then drain & refill with your prefered fluid


That would be my call also. Normal drain and fill with the cheap fluid, drive it for 500-1000 miles (or more), then put in the RP.

I'd stay away from brake cleaner -- wonder how the chemistry of the brake cleaner would affect the fresh fluid you are putting in.

 

[cancov]

Originally Posted By: Rob_Roy
I think you are making this more complicated than it needs to be. I understand that you want to get all of the old fluid out, but you don't need a solvent rinse to accomplish that. Take the truck for a nice ride to get everything warmed up, then drain the current fluid out of the t-case. Refill with some el-cheapo 80w90 and drive the truck normally for a week or so, then drain and refill with your preferred gear lube.

+2, I completly agree