They say there is no "liquid mechanic" but I have been hearing great things about Redline Shockproof and its ability to fix gear grinds. Has anyone used it? My gears are grinding from 3-4 majorly but also occasionally 2-3 and 4-5 and it only does it once it gets hot like 15 minutes of driving. Is there any other good transmission oils for problem gearboxes?

 

I take it you have a manual tranny?
Use redline mt90. Works great! However, I'm not sure if changing the oil would solve your issue.

 

My tranny started grinding horribly from 3-4 (or from any gear to 4th) at high RPMs. The point at which it was grinding got lower and lower in the RPM range as time went on. This was due to using the wrong tranny fluid.
After putting in Redline MT90 the grinding was significantly reduced. I can still grind 4th if I shift at 7000 rpm or higher, but it's a LOT better than it was before. I just try to let the RPMs drop below that before throwing it in 4th and I don't have any problems. I guess the damage has been done.

 

MT90. It's the best. It's not going fix your problem if you have done permanent damage (hope not) but it's going to help.

 

Where can you get it? Do you have to buy it online? The red line website says Shockproof heavy is good for problem gearboxes but I think that may be too much for a daily driver??

 

I get mine on-line. Not sure you can even get it in an auto parts store. I know I can't around here. So buy an extra for just in case. Stick with the MT90.

 

I'm happy with this. Works very well but I had no grinding or other issue when replaced the fluid. You can get it easily if you have a dealer nearby - that's how I buy my oil and tranny / diff lube.
Redline MT-90 is also good but it won't fix an already existing problem.

 

Sorry to bring the thread back to life but I wanted to let the club know that redline Shockproof does fix gear grinds. My tranny is butter smooth now. I was very impressed.

 

It didn't fix anything it was just time for a fluid change. I have used nothing but factory Mazda fill for 127,000 miles and have had no transmission issues (knocks on wood).

 

it will not fix a bad transmission, plus Shockproof is a racing only fluid unless you want to change it out every 100 miles or so


.

 

My car grinds 2nd at high rpm's, 5th, and sometimes reverse. My previous fluid was motorcraft 75 90 gl5 (dealer flush) and I read a bunch of great reviews about redline mt90 so I decided to make the switch. I expected a significant difference, and its honestly not even noticeable. I'm not bashing redline by any means; I just advise that you go into it open minded. If you expect it to solve all your problems (as I did) you'll be disappointed. It's only transmission fluid, after all.

 

They have 3 grades of that oil, which one did you use?

 

I used the heavy Shockproof which is much different than mt90. And it lasts for about 15k miles. I'm sure if your gears are already destroyed the oil can't help but for me it worked great.

 

It actually took a long time for my grinds to go away. The grind in 4th at high rpms lingered for almost a year, but now it won't grind no matter how high the rpms are so something definitely worked. But as you said, it won't fix an already busted tranny.

 

Hmmm maybe there's still hope for me then; I made the switch about a month ago. Mines an 04 and the most prominent grind is when upshifting or downshifting into 1st or 2nd gear. That being said it's likely being caused by the faulty shift fork design. I'm not sure if that makes a difference, but I guess ill just wait it out.

 

If the Redline isn't working for you try the Eneos - it works a treat in the RX-8 Tranny.

http://www.eneos.us/product/8

 

I thought GL-5 was bad for the rx8 tranny :.

 

depends on the oil, but originally the service manual stated GL4 or GL5

 

No it doesn't. The shearing action of the gears meshing breaks it down. Originally Redline stated it was not for street use, but I don't see that listed any more. As a longtime user of it I can tell you that I need to change it twice per year for my car, which mostly only is used for autox competition, several hundred miles per year.

 

How often are you suppose to Change mt90? So about how many miles should I go of street driving before changing it? At 100 bucks per change I can't change it too often. I heard of people going several thousand miles on it

 

You can follow our owner's manual service schedule for it, changing it more often won't hurt though.