Finally have a question that a search didn't help. If I want to change over to syn. in the 5 speed trans. and the two differentials should I flush first or just dump the old and add the new?

Thanks

 

I would do a full flush to make sure all the old stuff is out before I put the synth in.

 

Drain it. Let it sit. Fill r up.

 

unless its full of water i wouldn't bother flushing it. i've got 3 quarts of redline MT90 that i'm itching to dump into my tranny. local parts jobber sells it for $7.99 a quart, not a bad price for synthetic gear oil.

 

I did a really lazy, sorta worthless flush when i switched all my cases over. Drain, pump a few ounces of new through, watch the draining fluid turn clean, insert drain plug & re-fill. I wasted a little synthetic, but it eased my mind that there wasn't much left after draining the old.

 

With a 5spd there is no need to flush, or no real way to flush it. I do just what tulsa_97SR5 does, pour a tiny bit in and wait till is comes out. That doesnt so much flush as is does push the last of the sediment out the bottom.

If you are still looking to buy your sythetic I am an AmsOil dealer and can have it shipped direct to you, cheaper than in the store.

 

Seems like I should see what the oil looks like when I drain it out, if it's black and/or gummy or looks like it has never been changed then I could see trying to do some sort of flush. I have heard that flushing can do more harm then good by actually causing particals to float into the bearings and synronizers.

4x4, when the time comes I'll look ya up. Thanks

 

My 91 5 speed has Amsoil 75w-90 in it. I changed it about 2 yrs ago. All I did was drain and fill. Still shifts like new @ 152k.

 

I have heard that rumor with autos, again cant do on a manual since there are no in/out lines.

The way a flush works is it hooks up to your cooler lines and the new fluid is put in the line returning to the tranny, and the line to the cooler is put to the waste bucket. They then fire up the truck and us the tranny pump to flush it. Since that is how it works I dont beleive that a flush could harm a tranny, the tranny is pumping the fluid like its running everyday down the road.

 

Drain, fill w/ cheap fluid, drive around, drain, fill w/ synthetic.

 

Never thought of that, I like it.....

 

Well, except that some (probably dirty) remnant of your cheap fluid is in the tranny with your good synthetic.

I like the pour/drain a little idea.

 

Yeah, just have to face that either way you are going to have some old remnants in your tranny. But neither way will leave enough remnant to harm anything. Most synthetics are compatible with any oil, unlike DOT 3 and 4 brake fluid.

 

I was thinking along the lines of using a solvent based solution like mineral spirits, fill and drive a very short while then drain. I have heard for years of guys doing this but have never tried it myself. I just wonder what mineral spirits would do to the seals...hmm.

 

Bad idea - as noted above, a small amount of whatever you put in will be there with your nice new fluid.

A solvent will work on breaking that new fluid down.

Use a small amount of your synthetic to wash the old fluid out.

 

I HAVE THE BEST IDEA EVER!!!!!!!!!!!!!!

Remove the tranny, tear it apart, start wiping all the old fluid out. Then get Q-tips and start working all the cracks, then start blowing compressed air through everything. Take a bif wiff, if u can still smell oil keep cleaning. Man I should have thought of this sooner!! I know what I'm doing this weekend!

 

And next weekend, and the weekend after that.

 

I suppose you could use kerosene if you wanted to flush it out, but I wouldn't really bother with it. I would just run it for while so it was nice and warm and drain.

 

I've had Redline MT90 in mine for about a year and 8k miles so far. I just drained and filled when I did it. I think in another year I will drain and fill w/ MT90 again, and then it will be mostly synthetic.

 

When I changed all mine over to synthetic, I just let it drain until it didn't drip any longer. The old gear oil was fairly clean though so I didn't worry about it. I'm using lucas oils heavy duty synthetic, and the tranny shifts quite a bit smoother.