Can Redline MT-90 make a transmission worse (long)?
 

First, some background. I just bought a low mileage '88 GTU (28,000 miles) from its second owner. The car came with pretty much zero records. Despite the low miles, and generally excellent condition, it seems some maintenance was not done. I've been changing all fluids, filters, plugs, wires, rear brake pads, etc. The diff fluid was black and a little foamy and I think it was never changed before; the plugs were the really old style NGK SD10A/SD11As that were probably original, etc.

Based on numerous posts I've read here, I decided to try Redline MT-90 in the tranny and Redline 75W90 in the diff. When I loosened the fill/check plug on the tranny I could see the corners were a bit rounded off so at least that was probably changed once before. Maybe about 12 ounces of fluid came out of the fill plug when I loosened it, so the tranny was pretty significantly overfilled. The fluid looked clean and the drain plug magnet didn't have too much metal on it, so I figured we were in good shape.

Before the fluid change, the transmission shifted great at lower RPMs at any temperature, but had a slight grind upshifting into second or third if shifted at high RPMs. Now, 500+ miles after adding the Redline MT-90, when it's cold it grinds at any RPM during the 1-2 upshift unless I double clutch or really, really granny shift into second (like at 10 MPH). When cold, there is also an occasional gear clash feeling shifting up into third or down into second. If I drive for 10 minutes to warm up the tranny, there is no more grinding, but the 1-2 upshift remains kinda notchy. I should add that the PO told me he had the shifter bushings replaced by a Mazda dealer in the last year and everything about the shift lever feels smooth and precise.

My questions (sorry for the rambling) are:

1. Should I ditch the Redline MT-90 and try something from AMSoil, NEO, or Royal Purple or should I go back to dino oil;

2. Am I just delaying the inevitable? Should I just have the tranny rebuilt?

3. Can the second and third gear synchros really be shot after just 28,000 miles?

4. Is this the result of overheating because the tranny was overfilled by one of the previous owners?

Thanks,
David

only 12 ounces ... that sounds way low ... how much mt-90 went in?

The 12 ounces was how much it was overfilled... that's what came out of the fill/check plug. The normal 2.6 quarts or whatever it was came out of the drain plug when I later removed that.

MT-90 will not damage the tranny... perhaps the tranny was in bad shape already, and the wrong weight oil had been previously used.

Or there is an issue with the clutch slave or master and the clutch is not being fully disengaged.

doh misread! Seen some success w/ a mix of mt-90 and redline 80-140 ... not sure about "recommendeds" but worked for me w/ 100,000+ mile trannys.

sorta defeats the purpose of using MT-90 if you use a 140 weight oil with it.

If you are getting syncro crash (which I suppose if possible with MT-90, but pretty rare) then you could mix the MT-90 with a 85W90 or similar weight,(what people sometimes due when getting syncro crash when using Redline Super lightweight Shockproof gear oil)) but I wouldn't recommend using anything as thick as a 80W140.

I guess I'd describe this as more of a synchro clash than actual grinding. I feel friction through the shift lever but I don't hear any actual grinding, and the lever still goes fairly easily into gear.

If there is an issue with the clutch slave or master, would this problem go away or lessen as the car warms up? What makes me suspect the gear oil is that right after the oil change, there was a significant change in symptoms, namely instead of occasional gear clash/grind in second and third only at high RPMs and even when fully warmed up, there is now gear clash mainly between 1-2 and only when not fully warmed up.

Is it unheard of for this kind of problem to develop after just 28,000 miles?

Also, I didn't mean to suggest that the MT-90 had damaged the tranny, but rather that maybe it is not appropriate for my application (i.e., an NA daily driver-type car, not being raced).

Also... I found numerous threads in the Third Gen forum in which Redline users reported a similar tendency for crunching/grinding from first to second only in cold weather or when the car is cold. Now I know my transmission is totally different, but is it possible that Redline is less effective when temperatures are cold?

You sure it wasn't "MTL" that you used?
Please don't reference to the FD guys, since they tend to misshift and kill their gears all the time.

Could you tell if the fluid you took out was significantly thicker than the Redline MT-90 you put in?
Icemark may be right - thicker fluid can sometimes mask a dying transmission.


-Ted

Definitely MT-90. I couldn't really tell if the oil that came out was thicker than the MT-90 that I put in. I would say it was pretty similar in viscosity; definitely lots thicker than 10W30. I guess given how clean it was in comparison with the rear diff fluid, ancient spark plugs, and other neglected stuff, maybe they did put in thick fluid to mask failing synchros.

On the other hand, if the relative thinness of the MT-90 is what is causing the cold shift issue, wouldn't it actually thin further as the tranny heats up? The shifting is definitely much better, good in fact, when the tranny is warm.

85W90 should be about the same viscosity as warm 20W50.

The T-II gearbox in the RXX-7 had the same 2 - 3 sychro clash that you described starting 12,000 miles after a re-build. MT-90 cured that problem, so I've been very happy with it. I did not experience the 1 - 2 shifting problem exactly as you described, though I have to shift very slowly when first driving on very cold winter days (defined as below 25 degrees).

If the transmission work that was done on your car was carried out at a dealer, I would suspect incompetence before I would blame Redline.

I'm one of those fd guys that can't shift but i changed my trans fluid to Royal Purple 75w-90 last week and i've noticed the difference. I had that 1 > 2 Shifting issue before i put it in, it's a *bit* smoother now but that's probably psychosomatic. It's really noticeable on the highway & during WOT pulls not as loud or shaky as it used to be.

does the Redline contain friction modifiers?

usually u can prolong a dying tranny with something like GM synchromesh... really helps with worn synchro's and improves shifting alot

the honda guys love the stuff since they always lose their 2nd gear synchro damn quick

NissanConvert, are you saying you switched to Royal Purple from Redline?

Ottoman, I'm not sure if MT-90 contains friction modifiers. It supposedly does not contain LSD additive, and from the bottle I still have, claims "perfect synchronizer coefficient of friction." Of course, the bottle also claims "eliminates notchy shifting even when cold."

George (Attila), since you are somewhat local to me and seem to have had a tranny rebuild, is there a place you can recommend or warn against? I was thinking I might get an opinion from RP Performance (former Rotary Performance) in Manassas. So far I haven't attempted to drive this car on any really cold days since I haven't had it that long; 35 degrees was probably the coldest. Though the problem goes away more quickly on a warmer day than a colder one.

Thanks everyone for the input.

NM ....

I switched to royal purple from ??? yellow brown liquid. But not in the diff (yet?).

I still have notchiness and the second gear synchro still hates me when it's cold. (I granny shift until it warms up)

yw

My gearbox was re-built by PFS as part of the overall conversion to the 3-rotor. (It didn't seem smart to put a used gearbox of unknown quality behind that much torque. Besides, the whole drivetrain was already out.) Bret at RP should be able to do a good job for you. PFS is now located a little south of Frederick, Ray at PFS can certainly do the job, but he may be backlogged. You can get his number from the website www.pfsupercars.com

George