Adding new fluid to really old transmission

[xjTrent]

Hey guys, I'm installing a transmission cooler on my Cherokee with 170k on the clock. This sucks but I bought the jeep with 165k on it and I'm pretty sure the trans fluid has never been changed so I'm not about to change it.
My question is will it hurt to add new fluid for the cooler? Should I add used fluid so that the detergent wont be as fresh and cause problems?

Btw the trans operates fine. I have alot of tools in the back so I wanted to add a cooler to extend my borrowed time before I need to rebuild.

Thanks,
Trent

 

[GrimmJeeper]

it won't hurt anything, I would drain the trans and put new fluid in it. the only time new fluid seems to cause problems is when the trans is machine flushed.

 

[xjTrent]

So this would leave a mix of new fluid and some old correct? Ive heard that the new fluid may screw up the syncros in the trans. Anyone wanna shed some light on this?

 

[old_man]

It appears by reading between the lines that this is an automatic....right?

If so just pull the plug in the pan and let it drain. Then refill wth fresh Dex fluid. I wouldn't personally go synthetic. IIRC, you will need somewhere around a gallon or a bit more. If you want, run that for a few days or weeks and repeat the process again, but if it is running fine, I probably wouldn't bother.

I like to strain the drained fluid through a coffee filter and look for sparkles or excessive black friction material. That will give you a good idea about the health of the tranny. AW4's are pretty much bullet proof if you don't run them dry. The filter in the tranny isn't much more than a screen and I wouldn't bother dropping the pan to change it other than it would give you a look at the bottom of the pan for signs of carnage and to clean off the crud from the magnet.

 

[DrMoab]

Since you are installing a new cooler there is a much easier way to flush the fluid out. Like Grimm said it won't hurt to add new to old but it really sounds like you need to anyway.

This is what I did and it worked flawlessly and didn't make a mess.

Take the pressure line going into the cooler and run it into a drain pan.

Have someone start the jeep, watch the fluid run out till it just starts to sputter. Then fill it with 4-5 quarts and do it again. Then again and maybe again. You'll see the fluid clear up and you'll know when it's totally flushed.

If you just pull the plug you won't get any of the old oil out that's in the lines or converter. This will give you pretty much all new fluid.

If you have any oil wholesalers in your area, take a 5 gal jug and have them sell it to you bulk. When I did mine I think I paid $30 for five gal. Pretty cheap and it was a good honest name brand. That should be more than enough to do a good cleaning full service.

 

[XJEEPER]

^ The Dr does it right.

 

[muddypunk]

So would this also work well on my 88 with about 190,XXX on it?fluid smells ok and looks ok its still pink not dark like my old Ford and Chevy.

 

[westvirginia24976]

Is the pressure line the metal line or the hydraulic hose line? I'm guessing the metal one?

 

[xjTrent]

The return line is the rubber one. follow it to the back of your transmission to make sure. I'm going to add enough for the cooler for now and flush everything including my torque converter when I replace my flex plate in the near future. I just wanted some insight on whether its a good idea to add new fluid to possibly really old fluid.

 

[DrMoab]

Pressure line is the one coming off the front of the trans. By the pump.