Not sure what this means, but sometimes if I shift straight from 3rd to 5th/6th at high RPM, the blocker rings on the synchros will unlock before their job is done, and the splines on the target gear will buzz against the lockring for a split-second before engaging.

I changed trans oil a few months ago, from the stock stuff to a Group 5 synthetic made by AMSOil. I did not include anti-slip additive in the new oil. Before the change, I regularly had trouble with rough engagement in lower gears. Now I'm occasionally having trouble with rough engagement in higher gears. What gives? Is the new oil too slippery? Are the friction surfaces glazing? I don't get it.

A mechanic at my shop (who was wrenching on a Porsche 911 at the time) suggested using Redline ShockProof gear oil. Never heard of it before, but he swears by it, says it's worked wonders in every car he's put it in, no matter how it's driven. Sounds too good to be true, but what do I know?

Thoughts? Advice?

 

$20 says someone is going to say something about GL5 vs GL4 oils. Wish I could be of some help but just giving you the headsup incase you want to pre-warn people not to comment on that aspect.

 

Just a thought. You are probably under warranty on a 09. Take it to the dealer. I would not mention I changed the tranny fluid.

 

The GL5/GL4 comparison is valid. AMSOil says on the packaging that some limited slip differentials will require the addition of an anti-slip additive so the lockup mechanism will work properly. I haven't had any issues with it in the diff thus far, even without the AS additive, but I suppose it's possible the same considerations apply to the friction surfaces in the synchros too.

Still, I wanted to see if anyone's got any theories NOT related to oil chemistry, because oil chemistry I can change any time I want.

 

The indie mechanic who works on my 8 drives a heavily-modded RX-7 to work every day. I'd prefer to take my chances with him. The warranty will be done in another two years anyway.

 

it does that cuz the shafts are spinning way too different speeds. you can get into 4th without letting clutch out then 5th. your syncros are trying to match the shafts but 3 to 5 at 9000 is not gonna happen.
usually when theres more than 4000rpm difference the gear is gonna lock out.
the only gear oil I would put in my tranny is MT-90
GL-5 is just not suited for our tranny.

 

I'm not doing it at 9000rpm. Maybe 7000rpm, if I had to guess. But either way, unless I misunderstand the way synchronizers work, the blocker ring should just rub and rub and rub against the side of the gear until everything's going the same speed, regardless of how different the speeds used to be. Shouldn't it?

I'll take your gear oil recommendation into consideration. Any suggestion on which brands I should consider?

 

the block ring will block until the syncros have matched the shaft speeds. but if you doing 7000rpm in 3rd the transmission is spinning at 7000rpm when you going into 5th thats a big rpm difference.

a very popular oil is Redline MT-90

 

I know it's a big RPM difference, and in some cases it does work as I expect it to, but in other cases it simply unblocks the synchro lockring before the gear is fully synchronized. It's like the friction surfaces are losing their grip on each other 95% of the way through the sync process.

Can I go with Redline 75-90? The straight-weight stuff gets way too thick in cold weather. EDIT: Nevermind, stupid question, that's exactly what the MT-90 is.

 

I heard GL-5 fluid might cause syncros to wear down, replace the right fluid see if it helps
your car is so new why you replace it?

 

lol get your hater blockers put back on and that should solve the problem

 

Short answer? Because I know better than the car company. :whistle:

The straight 90-weight stuff was way too thick in cold weather, and the lower gears shifted rough. It's gotten a lot better since I switched.

But yeah, I think I'll go back to GL4 synthetic instead of the dino **** it came with.

 

you know better yet you got problems? lmao

 

Someone's sarcasm detector needs a tuneup.

 

maybe new plugs and coils

 

Hehe, yeah, it's been a whole year already.

 

I was wondering whats the light flashing in my head its misfiring.