Clunk when going into first gear?
 

Almost every time I shift into first gear, there's a loud clunk noise. Anyone else have this issue or know why it's doing this?


I have about 250 miles on my BRZ and the grinding/syncro crunch is now gone from second gear. I guess the triple cone syncro's had to be broken in?
I'm about 80 city/20 hwy and I'm getting 28 mpg on my first tank of gas. This is pretty amazing.


Can't wait to fully break in the vehicle and push my brz a little harder.

This is normal according to most people.
This is the same tranny from the lexus IS line .. which is loud.
I personally like it.

you might wanna try search/technical sub forums

It's normal. I think it's even mentioned in the owner's manual.

Same transmission as the IS250? I'm a little disappointed, I thought they would've built a better or modified one for our cars :(

The auto transmission otoh is amazing. I would've purchased an auto if I didn't love driving manual so much.

I've only heard good things about them, I'll have to dig around to find that post and how much hp/torq they can handle.
I remember it being higher than anything I plan on in the next few years though.

It's based on the Aisin unit from the IS250, but it's been heavily modified. I don't have my source on hand, but I remember reading somewhere that approximately 80% of the parts have been changed out. Someone feel free to correct me if i'm wrong though.

If you want to avoid that noise, you could press on the clutch in neutral for 3-5 secs before putting into 1st gear.

This is more or less accurate. Its based on the same unit but not the same tranny.

Also I think I remember reading somewhere that this tranny unit cannot handle all that much extra torque and hp above stock safely... Someone feel free to correct me if I'm wrong though.

I know this is an old thread... forgive me.

But does anyone know the exact cause of the clunk?

Stock trans (not sure about clutch) is rated for just above 200 ftlb torque (about 210). In practice it's been found that it can handle above 300 just fine if you're nice to it. The number at which your trans gears go ka-boom is supposed to be 400. Don't get close to 400.

You'll obviously need a different clutch for those much bigger numbers, but the trans will hold them reasonably well enough. Otherwise, start looking into stronger gears that will hold higher tq without an issue.

Yes, the intermediate shaft is still spinning after you clutch in and come to a stop, so when you put it into 1st, it brings the shaft to an abrupt stop. Sometimes, you can feel the car get bumped forward a little bit. It's normal and can be avoided:

Thank you!

Appreciate that.

Chas3wba0 is correct. You're hearing the effect of the 1st gear synchro doing its job. The transmission is stopped, so selecting first forces the input and intermediate shaft to suddenly stop as well.

It is also repeatable after you've stopped. If you reengage the clutch in neutral before selecting first each time, the engine (via clutch) will spin the input shaft. If you hold the clutch in for 5-6 sec the input shaft and intermediate shaft will have enough time to slow down on their own, so when you select 1st it's silent because nothing is spinning.

No problem, I was confused when I first noticed it too and read a similar explanation somewhere else on this forum. Did a bit of research and confirmed that it is most likely true :thumbsup:

Also corrected my post because my last statement was slightly inaccurate

I am having an issue similar to this, not on stand still but lets say slowing down and putting it in neutral to roll over a bump, once I shove it back into 1st, It feels like I am grinding the gears, Its like the gears are trying to mesh after slapping each other 1 or 2 times and it engages. Sometimes if I don't put it in 1st hard enough, it would push my shifter out. Anyone know whats the issue?

Clunk when going into first gear?
 

I'm no expert by any means, so correct me if I'm wrong, but I've been told the synchros for first aren't designed to engage when the car is rolling. If you're still rolling you can go straight to second without issue, at least that's what I've found. Personally I never use first unless I've come to a complete stop. The car will idle at 4-5 mph in second without stalling.


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Hmm..thats interesting, but in my case, I guess the only way for me to go over bumps is to do a complete stop before the bump and go onto 1st or try to roll over the bump, go to a stop and then go into 1st, because I am sure to stall trying to go over bumps at 2nd.

How low did you go?
I go over them at 30 on a 30 posted road. Suspension does what it's supposed to.
Why put it in neutral? Just put in the clutch if you need to. If you're moving, 2nd works fine.

Very much dislike the soccer moms that stop before each one to crawl over it in their SUVs.

Anything under 5mph, 1st goes in buttery smooth. Just wait a little bit after u clutch in to let things spin down a bit

You may just be feeling the synchros engage. If you're curious, do some googling about how synchros work to help illustrate what's happening.

When you push to select a gear, you're moving a fork between two gears on a shaft. The fork slides toward one of them, but before it engages, there are two matching cone-shaped rings that rub together with a film of oil until they are moving the same speed. Once they're matched, a ring slides into place with wedge-shaped teeth to engage the chosen gear and lock it to the shaft and you can drive away.

When selecting a gear, if the difference in speed between the two halves of the synchro are very close already, (like rolling in 1st and clutching-in to free-roll over bumps) the ring may just slide into place and the wedge-shaped teeth might bump their slots and jostle a bit to engage. It's the same effect as a grind, but it's not a grind, it's more a notchy feeling. If you can still shift smoothly at high rpm, it's not a grind. I've come to understand a notchy feeling is common among cars with triple cone synchros at low speeds. Also, you may want to try an aftermarket transmission fluid if you're still using OEM. Many people have found much improved shift feel with different fluid.

Some older cars may not have had synchronized 1st gears, but that's not the case with the 86. 1st, second, and 3rd gear use triple-cone synchros. They operate the same way as a "single" cone synchro, they're just designed to be more durable.

So, 1st gear can be engaged up to it's maximum RPM (I'm not sure what that speed is, 40mph?), although if you're traveling fast enough to be using 2nd gear, just stay in 2nd.

Say you're rolling at 20mph, and try to engage 1st, but you feel an abnormal amount of resistance. Some think this is a "lockout" of sorts, but it's in fact the synchro trying to make up a large speed difference inside the tranny. Once the speed of the input shaft is matched, the synchro engages to the gear. This resistance is smaller (only a bump) when you upshift, because the input shaft is naturally slowing down during a shift. Downshifting however, needs that shaft to speed up, so it requires the synchro to do a bit more work.

Stopping and starting again to roll over a sharp edge bump does provide you with a bit more control, but you can leave it in 1st, and feather the clutch if you need to be nearly stopped. There's no need to de-select 1st and go into transmission neutral.

You can also double clutch to engage first at speed (or any gear lower than what you're currently in), but that's a technique that takes a lot of practice. A lot of autocross guys will do this because there's typically a lot of tight turns that staying in 2nd would put you out of the powerband, but single clutch downshifting into 1st at 4000rpm is a strain.

My guess is that he is not in 1st when approaching the speed bump. He approaches in another gear, puts the car into neutral, slows down and attempts to put it into 1st.

My car use to have a very hard time going into 1st even at 5mph, after 30k miles, it's smooth as silk 5 and under. If you want you can also double clutch into first, although it's a bit tricky to rev match it since the gear is so short.

As others suggest, slow down more before going over the bump or just slip the clutch a little more in 2nd.

Edit: I see a couple of other people have basically already said what I'm repeating below, but I'll leave it here anyway.

Nah. What you're thinking of is the old sports cars that didn't have a synchronized first gear. My mom's MG Midget had to be completely stopped before you could put the car in first because first gear had no synchronizer. The transmission for the twins does have a synchronizer on first, so you don't have to be stopped to shift into first.

On the other hand...

First in this car is geared pretty low, and first gear synchronizers can be kind of temperamental in all sorts of cars. I rarely shift down into first while moving for that reason. You have to be going pretty slow before the synchronizer can handle it. Your issue might be that you're going too fast when you try to put it in first.

If you're talking about shifting from first to neutral and back to first fairly quickly, that can cause a synchronizer to goof up also. I haven't looked inside this transmission, but the way it usually works is that you have a shift sleeve that slides over the gear to engage it, with a synchronizer ring moving independently between them to help match the speed of the shift sleeve to the gear. The splines in the shift sleeve engage the teeth on the synchronizer, then push the synchronizer against a cone-shaped area on the end of the gear. Rubbing the inside of the synchronizer against that cone brings the shift sleeve and the gear to the same speed so that they can be engaged without grinding.

When you pull out of gear, it takes the synchronizer a moment to spin back down. If you try to shove the transmission back into that gear too soon, the synchronizer may still be moving faster than the shift sleeve, in which case it will grind. It'll do that in other gears besides first as well.

The same thing happens under normal shifting if the synchronizer is worn out. People think synchronizers wear out on the outside, where the teeth are. But in reality they wear on the inside, where the smooth inner surface rides against the gear cone. If it's grabbing against the gear cone, it will be turning at the speed of the gear and not the speed of the sleeve, so that it can't do its job.

Here's a rather dull but actually very thorough video showing how it all works in a generic manual transmission. It may not be exactly like ours, but it'll give you a pretty good mental picture of what's going on. You don't even need to watch the whole thing to get the gist of it.

[ame="https://www.youtube.com/watch?v=vOo3TLgL0kM"]Manual Transmission Operation - YouTube[/ame]