Some tranny Q's

[99Super]

A question for you tranny gurus out there. I have a 900 5-speed in my 99 racer, a later model, from a 91 or 92.
When I first drove the car, the tranny worked fine. Then after switching to the Shock-proof, 2nd and 3rd sychros were largely inneffective. Switched back to Diesel engine oil and 2nd works good, but 3rd works fine sometimes, and other times not so much. Downshifts are better than upshifts.

Am I about to have the dreaded synchro spring failure?

john

[DrewP]

I don't think so, I ran MTL for a while in my fresh rebuilt 5-speed then switched to Shockproof (Heavy, now running Light) and it doesn't shift very well with the Shockproof period. It's too slippery.

I have always shifted it pretty slow to let the syncros do their thing, and I keep the Shockproof in it to protect the gearset as much as possible (my car was making something like 280lb-ft at the wheels for quite a while, and I don't like changing gearboxes).

Seems like a fair tradeoff for me, but the race car is going to get something that'll let me shift a little faster.

I bet if you drain and re-fill the box a few times and get all the remnants of the Shockproof out 3rd will improve some, sort of like how long it takes to get that Moly-Cote additive out of gearboxes, the suspended 'grease' particles take a while to wash completely out.

[Jordan]

I'm gonna have to jump on the bandwagon and do a +1 for Redline MT-90... shifts awesome. After just the first event and LSD install it got pretty nasty and sparkly, but with fresh fluid, it's great. I'm hoping it will degrade a little less quickly once the LSD breaks in a little bit.

[Luke]

I'm gonna have to jump on the bandwagon and do a +1 for Redline MT-90... shifts awesome. After just the first event and LSD install it got pretty nasty and sparkly, but with fresh fluid, it's great. I'm hoping it will degrade a little less quickly once the LSD breaks in a little bit.

I'm a believer

[DrewP]

John,

I am due for a fluid change, and will try a few rounds of MT-90 and see if my shifting improves and get back to you, I've been curious for a while, but have just been putting up with it and shifting real slow to let everything get happy before it engages.

[SwedeSport]

I have mt90 in my 91 box that's currently in my 86. It wont shift at all when cold , always hates 3-2 downshift at speed. Synchros are crap in it, but the mt90 made it tolerable when warm.

[99Super]

When I drained it, I ran the oil through a fine screen and got a couple of small flecks of brass, but that was it. I don't think I've done any damage.
I'll drive it a bit more, drain and fill again and hope it comes back. I'll just have to baby it a bit in the mean time...

john

[Edward]

I run a cocktail of 1qt of MTL, 1qt MT90, and 1qt of Shockproof in one of my 91 SPGs. It seems to shift well, a little better than my previous cocktail of 2qt MTL and 1qt MT90.

It has 223,000 somewhat hard miles and counting.