Redline lightweight Shockproof gear oil

Loaded 50/50 LWSP and MT-90 when I installed a stage 1 Happy Meal in my NB1 5-speed. Much smoother shifting, no noise or vibration on deceleration, and sublime rev-matching downshifts.

I had been running the Ford stuff before switching and I really can't complain. Its great...I had issues with long distance at hwy speeds in 6th gear...and this with the mtl has helped alleviate that problem. Plus I had paid more to get the Ford stuff locally.

Better than stock fluid, but this and Redline's MTL don't compare to Motorcraft Manual Transmission fluid. That's the best fluid I've used in my Miata so far and has reduced the grinding/notchiness of my transmission more than any other fluid.

Redline MTF the synchronizer crunch when shifting from 2nd to 3rd gears in my 1997 Miata. I' very please with the MTF despite despite the higher cost

Yesterday, I changed to half Lightweight Shockproof (LWSP) and half MT90, on my 1,600cc Miata and drove the car for a few hours over the Angeles Crest and into the lightly traveled, winding roads with hairpin turns, which descend from the San Gabriel Mountains into western Mohave Desert. In still air deserts are quiet places, and you can really hear what is going on with the car. My experience is that with LWSP the gear box is a lot quieter, and this comes at the cost of slightly increased shifting effort.

The NA6 (1,600cc) engine has a lighter fly wheel than the NA8 (1,800cc), which makes the gearbox more subject to gear roll-over clatter. Both versions of the car have this noise which is pronounced when on engine braking. On the NA6 it is worst. Flywheels mitigate the firing pulses of the engine, averaging them out before those pulses reach the gear box The lighter the fly wheel, the more the pulses come through. Our Miata gear boxes started life as Asian market light pickup truck engines. Bob Hall, one of the originators of the Miata concept, worked on the B series pickups, and would have known that gearbox well. These 5 speeds were also used on the RX7s.

In the US this transmission was imported in the B2000 half-ton pickup. These are quite sturdy gear boxes, with very loose tolerances, in the gear to gear spacing. Therefore, for lubrication they will accept just about anything. The engine firing pulses, with a light flywheel, coming into the input shaft can and do cause the un-driven gears on the counter shaft to go into resonance with their mating pairs on the output shaft. And this creates a lot of clatter, which is an unpleasant noise in a car with as little sound proofing as the NA Miata. Generally 'better' gear boxes in passenger cars do not have this clatter. So it sounds like a 'cheap' gear box, which it is not. It is, however, basically a truck transmission, and with trucks designers are little concerned about noise. Lastly, the repeated impact of this roll-over clatter has to have some effect in work hardening the gear faces. For those of use who drive in the mountains we are engine braking about half the time, and that is when the roll-over clatter is worst. So there are a number of reasons to want that noise gone.

Heavier oils limit gear roll-over noise, however they also increase shifting effort. With their greater film thickness, they dampen impact between the gear teeth. I had been using half Redline MT90 and half Redline 75W140, which helps with this gear clatter, but does not eliminate it. The LWSP proof has an unusually high film thickness, and so it goes still further in damping impact in during the resonance of gear roll-over. With half and half LWSP and MT90 some of the clatter is still there, but overall, gear box noise has been reduced below the level of the MT90/75W140 mixture.

At this point I have LWSP in the differential, and 50/50 in the transmission, and all the running gear is quieter.

I like this LWSP stuff.