Added MT90 Fluid, Now 3rd Gear Grinds

Hello Everyone,

I inherited a 2006 Tacoma (4L, MT, 4X4, Access Cab) 10 days ago after my father-in-law passed away. It has 112,000 miles on it and seems to run great. As I wasn't sure what maintenance had been done on it, I replaced the MT fluid with Redline MT90 over the weekend. Since then, I've had an issue with third gear grinding a little bit when the transmission is cold. Prior to the change, I never once had any grinding.

Is it possible my transmission doesn't like MT90? Should I try it out for a couple more weeks to see if it gets better? The fluid I drained out looked pretty clean, and it was red, which seemed odd to me. I wish I knew what it was.

According to Toyota's website, the truck had the clutch replaced at 75k miles at a Toyota dealership, so I assume they replaced the fluid at that time.

Any suggestions you guys might have would be greatly appreciated!

Thanks!
Joel

 

I put MT90 in mine a while ago, wasn't too impressed with it either. The guys who tuned my car (nissan) said MT90 isn't good, and that Porsche MT fluid is the best. But it's $70 a quart. So they said Nissan MTF is also pretty good, and far cheaper. That's what I put in my Tacoma now.

 

I put mt90 in my 08 5 spd and hated it. It made the shifts feel very notchy. No grinding issues though.

 

I used MT90 on my 6 speed 2nd gen and it was notchy. Then I switched to Royal Purple and all was fine.

 

Just their regular ol

$30 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 or is there some MT specific stuff?

 

Just their regular 75W/90 stuff. Only reason I tried RP is I used their synchromesh oil in my civic and shifted smooth.

 

I'll have to give it a shot, thanks.

 

It was the clutch pedal squeak that bothered me after then after the clutch release bearing noise... then I went auto.

 

OP, neither of my Tacos very much liked the MT90, either in the 5-speed or the 6-speed.

I just looked up the viscosity of MT90. It shows to be 15.5 cST @ 100 degreesC which is near the upper limit for those in its class. Translation: its a bit on the thick side. I suspect that may be why the 3rd grind suddenly showed up when cold; if it was not previously there as you noted and if it had never been changed the gear oil that was in there might have sheared to way less than 15.5 cST so that you were effectively running a much thinner gear oil when it was changed than the thicker MT90 you put in.

Manual transmissions like to shift very well with thin gear oils. Problem is the bearings and gears have greater wear. So you may want to look around for for a

$30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 GL-4 with a viscosity less than 15.5 cST and see if that helps.

My all time favorite is the manual transmission gear oil part number GM12346190 or ACDelco 10-4059, same stuff. It may be very difficult to find because about a month ago it was suddenly discontinued without explanation. I have been actively buying all the old stock I can find.

 

I find it odd the mt90 caused a harder shift.
Ran it in my 240sx and have it in the t56 in my gto. Seemed to improve shifts but I was never clear on exactly why.

 

I’ve had best results mixing equal parts of Redline MTL (75W80) and MT90 (75W90).

Like others have said, you could try a lighter oil like MTL or similar. Whichever the case you’re not doing any damage with a top of the line synthetic.

 

Thanks for all of the feedback guys. I think I might try draining some of the MT90 and adding some redline MTL. I have some leftover from my Mazda 3.

I have actually been able to keep it from grinding if I just shift nice and slow into third. But I don't like having to be so cautious.

 

One thing to realize is that this is not a sports car transmission. It requires a steady deliberate shift. Part of it is the throttle lag which prevents the RPM from falling at the shift. It was a big adjustment for me, coming from decades of spirited shifting. No matter what you put in it, it will never shift fast and slick. I feel like I'm driving an 18 wheeler. If you insist on ramming the gears, you will pay the price. The advice to blend MT90 and MTL to meet your temperature needs is a good idea for cold climates. Many race cars run very light oil in the transmission, but they are not trying to get 300,000 miles out of their transmission either. Discretion is advised.

 

I've had zero issues with Redline MT90... of course I live in California where 50 degrees is considered " Freezing Cold." Above is correct about shifting - its a truck, not a sports car - I wouldn't mind a short shifter but then again, the 10" shift rod extension doesn't help either... I get in and just pretend my truck is something from FedEx or UPS... no point of going fast or shift quick either....

 

Yeah, I hear you guys on it not being a sports car. But there is a noticeable difference between how it shifted before the MT90 and now. I never once had a grind with the old fluid, and it started immediately after switching, so I believe I can safely correlate the issue to the fluid and not my driving.

 

12346190 has a new number of 19369226 but it is 75W-85 mt gear oil now instead of 75W90. The new ac delco number is 10-4119.

 

I have not been able to find out any specifics on the new part. So I deciding to play it safe for what I have found to work so well and have been hoarding all I can find. I have been able to source some more if someone is seriously interested you can PM me.

 

Never had any issues since I've switched to MT90.. Shifts better then it did before..

 

I did mt90 as well. Didn't really feel a difference in my second gen except my wallet felt a lot lighter. Will probably go with conventional stuff next change. Same for front and rear diff.

 

Damn I didn't find any negative posts about MT90 at all when researching it and now this thread, lol

I've been using it in my truck for maybe 40k miles now, TBH I didn't really notice much difference with it but it certainly didn't make it worse.