fastimes

I'm planning on changing my gearbox oil in a few days. I've decided to go with conventional GL-4 (Driven 80w90 Gear Oil).
I have a receipt from the previous owner for a transmission oil change using synthetic, done a few hundred miles ago.
I will drain the best I can, and use a suction gun to try and remove the old oil. What are the ramifications of not getting every last drop of synthetic out of there?
Will remnants of syntheic contaminate the fresh conventional oil?
Has anyone done this switch back to conventional?

Thanks!

bashcraft

What's the reason for changing back to conventional?

Mine has had synthetic for the last 12 years.

ignatz

I doubt any remnant of synthetic will matter much, but I've never used synthetic. What I can say is my shop guy (Dave Herlinger - Corvette Repair) warned me not to use synthetic, as, in his experience, the synchros quickly "disappeared". Not sure what he meant exactly but he rebuilt many many transmissions and differentials. I figured, why go against that much experience for an unknown "improvement" with synthetic. So, as fastTimes is doing, I stuck with conventional gear oil.

fastimes

Call me a purist. I do use synthetic in my "modern" daily driver, but I believe in sticking with what was used originally (somewhat).
I know the advances in technology have been great, but with the limited mileage I put on my C3, I can't see how staying with conventional would be a detriment.

Rescue Rogers

I dont think you'll have a problem..you're not leaving enough to do much in the way contamination. I think most say not to use certain synthetics due to it corroding some metals.

Paul Cangialosi does a test comparison in this video for synthetic vs conventional. I use the GL 4 myself


This is the video summary

Published on May 25, 2017
I discuss some of the new oils today for manual transmissions and take apart a Muncie 4 speed that welded up. There has been a great deal of misinformation about GL-5 based oils corroding synchronizer rings. I've never seen this happen in 1000's of tranmissions I've serviced. We have seen more GL-4 based oils come to the market within the past 3 years, but prior to that everyone was OK using GL-5 oil for the past 20 to 30 years. The new GL-4 oils are a plus because we now have better formulated oils for our muscle car transmissions.
Get my Muncie Book here: http://amzn.to/2qZU6lL
My website: http://www.5speeds.com
GL4 Oil - http://www.gl4oil.com

L-46man

Tried them ALL, Amsoil, Redline, Royal Purple, all synthetic in one way or the other etc. DOES NOT WORK PROPERLY...let me explain. (M-21 Close-ratio)

Inside a Tranny are Synchros....these have a device called a BALK RING on each gear...these slow down the sychros so they can match from speed-to-speed. They are little circlip-looking brakes.

The lubricity and slippery-ness of the Synthetics do not allow the gears to slow down enough between fast shifts....

I went back to conventional...and change it at 30k.

I love synthetic IN EVERYTHING ELSE...not in my transmission.

My two cents.

Unkahal

I DO HAVE synthetic AMSOIL ATF in the CE...different animal