Just want to give my review of the relatively new Redline MT-LV synchromesh fluid. I currently drive a 2004 rx8 with an early S2 transmission, that was showing signs of wear. I could "beat the sychro" (not a grind, just hitting the synchro teeth) in 3rd 4th and 5th gears occasionally, depending on rpm, trans temp, etc.

I went through a bunch of gear oils to try to improve it, and shift action in general, as this has worked for me before with other cars.

I used:

Redline MT90
Motorcraft XT-M5-QS
Motul Gear 300v
Redline MTL
Redline MT-LV

The MT-LV is by far the best I have tried, both hot and cold. I have about 2000 miles on the fluid change so far and continue to be impressed. The shifts are easier to make quicker, and I don't feel the sychro teeth hitting the sleeve with a quick gear change like I used to.
Also, the clunk I used to get from viscous coupling within the transmission when going from neutral to first is cut in half when cold, and almost 100% gone when hot. Which leads me to believe the better shifting is a combination of low viscosity as well as friction coefficient. I don't notice additional noise.

Be advised: it is a very thin fluid, but is GL4 rated.

Worth a shot. I don't know how well it will work for racers, but as a street fluid, so far it's great.

 

It may be GL4 rated, but it’s still only a 70W75 weight oil.

 

Yes it's light. Long term, not sure how it will work out, but since these (street) transmissions seem to show synchro issues first as a wear point, it might actually help long term.
The synchros seem to "like" it as far as I can tell. The gear teeth and bearings might as well, or not. I will keep running it though, as it is worth it to me to try it. The "recommended" mt-90 was dreadful. I have has similar experience with "recommended" lubes in quite a few BMW, Mazda, and Toyota manuals as well, with long term (250k plus miles in one case) good results, using non-recommended lubricants, based on how I perceived shifting action, noise, etc. I have probably tried over 20 different lubes in multiple transmissions over the years. Every trans is different, YMMV.

 

Well the only time I had what I would call synchro issues (since 2005) were it being notchy when cold using MT90 and then having a 3rd gear synchro break (different oil, lost a 1/2” long piece). The trans itself always either broke or had bearing drag issues first.

otherwise I wouldn’t recommend running a thinner fluid. The trans gets very hot just from the exhaust even if you’re not beating on it. Some of those trans you listed are rated for a lighter fluid, but it’s your choice. The people who know & rebuild this trans for extreme use tell me to stay with the Ford Motorcraft oil. I’m reluctant to try lighter fluid based on my experience and issues.

.

 

Over the years I've found just about every used rx8 gearbox I've inherited or bought has syncro issues . I've also been in lots of 8's driven by others and noticed some really bad gearchange habits that many people get into so I'm not surprised by this.
The car I just bought graunches into 4th quite badly at high rpm and is also hard to change down into 2nd from high rpm, without graunching.
I think I'll give this stuff a try (if I can get it) and see if it improves it at all as that sure beats rebuilding the trans.

 

Bret,

Every CAR I've inherited or bought has synchro issues. I tend to buy them cheap and thus abused.

I have always had good results experimenting with different fluids. Not perfect, not "like new", but much better usually, and improved enough so that the transmission is no longer the focus, and I can move onto other things on the car.

Team RX8, all but the BMWs called for a gl4 80w-90weight, or 75w-90 oil, and I ran all kinds of stuff, depending on what was available at the time, that I thought might work. Most were lighter in viscosity, but some were not. Some synthetic, some mineral.

The BMW transmissions took a special fluid or ATF in a couple of cases. I tried all kinds of fluids for those as well. Mostly lighter there also is what worked, but again, some just have different properties that don't show up on a data sheet even though viscosity is the same on paper.

I did have a 1969 f100 with 3 "on the tree" that I left alone. It had the same stuff in it when I bought it and when I sold it. Interestingly, the synchros in that trans, (I think only 2nd and 3rd were synchromesh, 1st and reverse were sliding gear.) were trouble free!

 

Just bought some (it just arrived into NZ this week ) and went for a before and after test drive ! Cost was $103.00 for 2quarts so it def. aint cheap!
Before : This was on new synthetic oil of recommended viscosity . Initially it was still graunching when downshifting into 2nd but while the oil was relatively cool ............. it wasn't graunching into 4th . Was surprised by this so kept trying and and sure enough ....as the oil heated up it started graunching and got worse and worse.

After : After fully warmed up ..................No more graunching into either gear . The only thing I notice is that it's harder to change up into 4th and downshift into 2nd than it is for the other gears ...but ..................No Graunch !!!!!

True test will be after a few thousand kms to see if the improvement is permanent or not but so far .... I'm very pleased!

 

Brett,

I noticed the best gain in shift feel when the oil was full temperature as well. I got better and better results for the first 100 miles or so, and then the shifting has been consistent since then. It has really made the gearbox a pleasure to use, where before I was unconsciously or consciously changing my shift speed around the synchro action. You may notice better action with more miles as well.

On a side note, by accident last week I re-read some articles I had read years ago about John Britten. It gave me a chance to tell my wife and kids about him, and about his interesting take on engineering. He was really a genius, hopefully he gets thoroughly remembered in his native country!

 

Absolutely .... I must admit that I haven't read that much about his engineering methods, but I do know that he made pretty much EVERYTHING himself !

 

Brett,

I find him to be one of the most inspiring people I have ever heard about.


He designed decorative glassware prior to building a racebike. I am not stating this accurately, but: He believed that the fine arts, architecture, and mechanical engineering all had common first principles.

It took him 6 months to go from drawings to prototype racebike. Look at the design of the entire bike. New thinking in evidence everywhere.

He was severely dyslexic. He could barely read or write without help.

He died at only 45. Just a fascinating character. Worth reading about, especially for the rotor head that marches to the beat of his own drummer!

 

Kevin, Thanks for the info on the MT-LV. I've used MTL on various cars with modest success. You just gave me my next move. I will try the MT-LV hopefully it will cure a slight 2nd gear crunch.

 

Kevin, thanks for the info, but what I really need to know is how the various transmission fluid options smell when vaporized, since whenever I get my RX-8 <S1> really moving, the whole cabin gets an aromatherapy infusement of transmission fluid!

Relevant info: currently running MT90, no grinding yet on street or track, trans at 122k miles.

 

That ...aint right ! Do you have the oem boot etc in place ?

 

i have MT-90 but other than some notchiness when cold, my 115k mile S1 trans still shifts well. no grinds when warm. however, for short hillclimbs and autocross, i wonder if the MT-LV (being thinner) would reduce losses within the trans? regardless, because the MT90 has treated me so well, i'll probably stick with it since my trans is currently functioning properly.

 

I know for a while that some people were mixing MT-90 and MTL. I wonder if anybody is going to experiment with putting MT-LV in with MT-90.

 

I’m wondering why you would wonder that ...

 

Boredom, mostly.
Idle hands are the Devil's something something.

 

An update for those following this. I have about 5k miles on the fluid change and still have the same results. Faster sychro engagement with less lever force. I find the trans more of a pleasure to use as a result. I notice the difference at all rpm. Again this is a street car, it may not be the best in comp. use, but I definitely like it a lot for the street.

As far as odor, my other 2007 RX8 has the gear smell permanently in the interior, and when it was running, the cat would cook the trans, and the lovely odor of sulphur EP compounds came wafting into the cabin. My 2004 does not, and never did, even when MT90 was in the trans. Interestingly all the boots on the 2007 are fine, and it doesnt look like or smell like anyone tried to fill the trans through the top, nd the are no leaks. The smell is just "there". When I get that one running again I will let the forum know about the smell issue. I know others have this but I haven't seen anyone post a cause or a solution.

The MT-LV definitely smells better, for what its worth. It has more of a "futuristic" synthetic smell than a standard gear oil smell. Yes, I said futuristic. It's what comes to mind. Sorry.

 

Good to hear Kevin . Haven't put many miles on mine yet but it's still good. I did notice that if I redline third then try to quickly shift into 4th there is just a hint of a graunch .... nowhere near as bad as it was though.

 

You shouldn’t be getting any oil smells in the cabin with a good rubber boot that slips over the shifter top and seals around the chassis opening.

 

I have royal purple 75-90 in my trans. And its been in there for about 3500 km. Smoothest gear change and never had a complaint. It takes no effort to move the shifter into or out of any gear. Even reverse seems easier to grab whereas before it wouldnt fully engage until I started to release clutch. I had to keep a bit of pressure on shifter and start releasing and it would drop into gear.

 

Royal Purple will eat your synchros with time, it's GL5.
It's smooth for a while, sure. Then you lose a gear or two.

Use GL4 fluid only.

 

Ok thank you Loki I did look around and saw some were using it and it was easier to get. I will change that in the spring when I get the car out and set for summer.

 

The chassis shift boot was OK and sealed well, and the boot on top of the shifter tower was also Ok. What I did find later was that the fuel tank access covers were both ill-fitting. Once I get the car running again I will sniff around some more and report.

 

You probably have oil smeared around somewhere. While the trans is vented, it shouldn’t be producing any strong external smells unless leaking. Same for the differential.