Tranny Oil as related to gear grinding...

[zeka]

...So I decided to give my x some tender loving care -- dealer cared for it prior to now; I have taken wrench in hand and am enjoying it.

1992 4 door 4.0L Manual 169,000 miles.

I decided to change all of the oils. When changing the tranny oil I did a boo boo; I drained it and filled it with hypiod gear oil -- because I had it. I think it was 90 wt. Well to my amazement the manual calls for dextron III ATF -- oooops! I ran it that way for about a week, but only on short trips, 20 minutes tops.

Prior to making the oil change, I was having some trouble shifting into first from a stop. The shifter was just hard to put into first -- unless I first did a little line up by first going into second (didn't actually have to go all the way into second, just had to move the stick a little in that direction) once I did this the shifter would go into first easily -- I have experienced this in many of my cars, the older volkswagen beetles behaved this way. I would also get some slight grinding if I didn't first nurse it into 1st via 2nd.

So once I made the oil change to gear oil then getting into 1st was about as hard but with less grinding, and the shifting seemed to work more smoothly.

Well I didn't want to go against what was recommended so I drained and refilled twice. The first time was intended to flush out the gear oil. I used Dextron III ATF and ran with that for a couple of days. The Dextron III ATF mixed with the residual gear oil seemed to work really well regarding shifting. I then drained and filled with amsoil synthetic universal ATF. Now the tranny does not seem to shift as well. It will grind in first if I don't do the 2nd gear line-up procedure from a dead stop -- not a problem if you are rolling though.

I am wondering if it would improve the shifting if I added a pint or two of amsoil gear oil.

Is it a bad idea to mix the ATF and the gear oil?

I have zero experience with ATF since all of my cars were manuals and all of them used hypoid gear oil.

 

[mrboyle]

It is not recomended to mix oils of any kind. The grinding you are experiencing is a common sign thet the tranny has a few miles on it and the syncros are wearing. The reason the hypoid oil helped was due to its ability to cling to the syncros where the ATF gets flung off. The reason the tranny uses ATF is for heat dissipation. The aluminum case heats and cools faster than the old cast iron ones did, there fore the manufacturers found that it was necessary to run a thinner lubercant that could transfer heat better than 90 weight. ATF worked and thats why .

 

[zeka]

Thanks Mike, makes sense...

Can you tell me why I don't have any synchro problem when I first line 1st up by partially goining into 2nd first. I have always had slight grinding when placing the vehicle in reverse (since day 1 and I am the original owner). I have always placed the car in 5th prior to shifting to reverse. Is this because reverse has no synchro?

 

[mrboyle]

Your are correct that reverse has no syncro, by putting the tranny in 5th. first you slow down the rotation of the counter shaft and this helps the tranny slide into reverse easier. The oppisite occurs when you engage 2nd before trying to go into 1st. You speed up the counter shaft which makes it so the syncro doesn't have to work as hard matching the input shaft speed with that of the 1st gear cluster.

 

[zeka]

...magic revealed -- thanks so much Mike!