Downshift 4th to 3rd Issue

[SPD]

Hi,

I'm new to this forum and i have a question about a transmission issue. I own a Corolla SE 2001 and when I downshift from 4th to 3rd @ around 60-80km/h the gear slightly grind together (you know that nice noise), and I don't even force the gear in, it move in gear smoothly but grind on he's way in ;(

I try really smooth downshift, also a rev match or even double clutching and still do the noise.

Need your help!
Thank you

[Downhillzze110]

your 3rd gear synchro is going out. unless you know how to rebuild a transmission the only thing you can do is take it into a transmission shop

[fishexpo101]

If it is still making that noise even when you double clutch - might be looking at a pretty expensive bill to fix the transaxle.

Try changing the transaxle fluid out first. Fresh fluid can do wonders for various shifting woes. Might be a good idea to run whatever drains out through a filter (paper paint filter cone works perfectly - holes are big enough to let the oil through but small enough to catch interesting particles). Either than or less the drained oil sit for a while, then slowly pour off the oil - if you see lots of chunks on the bottom of the drain pan = potentially expensive problem.

Some have gotten relief using the so called "Scotty-Grey" mix. The DSM guys swear by it, helps others with a stick transaxle. At the very least, get you more time to diagnose what is going on.

[Flashmn]

If the manual says to use normal GL-4 gear oil in there, then use Redline MTL / MT-90, it might help. If its ATF it wants, then you're shit out of luck trying different oils. Cant remember if toyota swapped the transmissions to use ATF at some point.

[SPD]

Double clutch is actual working, I wasn't doing it properly

Now i'm much better at it but still need to practice. I will change the oil. Also a mechanic told me that Lucas Oil make good additive for Tranny.

I will let you know if the oil help.

Thank for the advices.

[Downhillzze110]

the oil may help but not permanently. if you're having to double clutch it is because your 3-4 gear synchronizer is going out and will be needing to be replaced.

[fishexpo101]

^^^ Exactly, by double clutching, you reduce the loading on the syncronizers to the point where they do not have to do all the work in bridging the speed difference between the layshaft and the transmission.

Since the noise goes away when you double clutch - you have just narrowed down the possible suspects to excessive syncronizer wear (very probably) and possibly bad gear oil.

Flashmn brings up a good point about GL fluid ratings. You can buy GL-4 and GL-5 gear oils. Though many are cross-compatible (according to the fluid manufacturer), there is quite a bit of controversy about how corrosive the GL-5 fluids are to certain metals (so called yellow metals) in the transaxle. You can guess where this is leading to - as almost all syncronizers are made from brass - there is some concern that running the wrong spec'd fluid will cause premature wear.

The same can be said with trying to shift aggressively or "rev" match the transaxle - done incorrectly over a period of time, will eat the syncronizerd pretty quickly.

Quick, easy fix - change the fluid with OEM spec'd fluid - should be marked in the owner's manual and Factory Service Manual. If it says use GL-4 oil, use only that. Don't be tempted to add any additives right from the start - you need to change the fluid first - then see if there is any change. If not, then try an additive. Stacking multiple additives will not fix the problem faster, if anything - they could potentially mask problems and you'll have a more expensive fix on your hands. Fluid exchanges will help, but will not fix any mechanical issues (wear and tear) inside the transaxle.

[Flashmn]

Additives are gonna make it worse. Yeah, I hear the lucas oil additive pop up every once in a while, you'd be tempted, but I'd stay away. Additives usually dont do anything good.