So I have had my car for 2 years now, bought it with 33k on it and i'm at about 44k now. I never had a problem with getting it into reverse until last week. I went to get it inspected at aamco and later that day it started grinding when going into reverse and did it 4 times within 4 days. So I brought it back to aamco to try to find out whats going on, they thought it was pretty normal and a common thing. So i looked it up on here and found out that it happens a lot. I though it was weird that it hasn't done it once in 2 years but then started doing it all of the sudden.

They suggested that it might be because the fluid is starting the thin out causing the input shaft to stay spinning longer than it used to causing it to happen frequently. They explained it grinds do to the lack of synchos for the reverse gear and that made perfect sense to me. They said new fluid might help it run more smoothly and I want to keep up on my car so i decided to have them change the fluid.

When the guy tried to look up in the computer what fluid it takes the only thing that was coming up was saying it took regular automatic tranny fluid which doesn't make sense so we looked in the manual and it said the same thing. So I went home and did some research on this site and found out that its a common issue for the wrong fluid to come up in the computer and its really supposed to take 75w90 synthetic fluid, and more exactly only the specific on gm recommends.

So i called the guy at aamco back and told him what i found. And he looked into it, it took an hour of him calling up dealerships and doing some research to find the same info i found out. So i went ahead today and had them put in the correct kind of fluid. They used 75w90 mobil 1 stuff, which i don't think is the exact one gm recommends but close enough.

When i was waiting for it to get done, i overheard the mechanics talking and said that the fluid that was in there was a lot different than the new stuff they put in. So i was thinking could maybe the dealership i bought it from changed the tranny fluid and put in the wrong stuff, just going by what the incorrect info in the manual says to use? And would that do any real long term damage to the tranny if it wasn't right. The guy at aamco said it wouldn't really hurt it if they did use the wrong stuff it just wouldn't drive very smooth. I wouldn't think the dealership would change it at 30k though, especially when GM says the F35 never needs to be changed. So could that have been the factory stuff and GM changed what should be going in there afterwards?

But anyways, now that they changed it i couldn't believe how much smoother it shifts. I didn't think it would have made that big of a difference, especially cause it supposedly never has to be changed for the F35 according to GM. I'm hoping this will make reverse not grind anymore. Thanks for reading that rant, any input would be nice.

 

LULZ.

Reverse gear is synchronized.

The reason the fluid coming out looked way different than the Mobil75w90 they put in is because Mobil75w90 is a true hypoid style gear oil.....the stuff in the F35 is a GL4 fluid, but its much more like a thicker ATF than gear oil. ANd if you put Mobil 1 LS in there you need to get it out ASAP, because it may be nice and smooth now, but its gona be unhappy in a while, Mobil1 LS is designed for positraction rears like in a Camaro etc.....the friction modifiers in there for the posi are the opposite of what you want in your transmission.

 

So clarification, i for the life of me couldn't find where to fill my tranny with the fluid, and whats the exact fluid im suppose to use?

 

Here's a shot of the fill /check plug on the side in this thread. I have no top plug. Had to use a funnel & hose to fill it.

https://www.cobaltss.net/forums/2-0l-lnf-performance-tech-153/filling-transmisssion-fluid-211047/

Here's a post about the fluids...

https://www.cobaltss.net/forums/show...96&postcount=2