6th gear grinding

[Razz]

Originally Posted by D-VO

I guess the problem now is since I'd like to race, the 6th gear grind will soon turn into a transmission rebuild. Thanks guys.

I like this part. I like to race. But he shifts from 3rd to 6th!!!!

[Yruyur]

Originally Posted by Gen

4th grinds every single time over 5k RPM unless I take a good 2 seconds between clutch in and shift.

Link in my signature about my second transmission I have now.

Sent from my flux capacitor using Taptalk

[Sigh-on-Rice]

I agree with enigmaaron. If you accelerate to 35 mph in 1st, 55 mph in 2nd, and cruising speed of 65 mph in 3rd, I would skip from 3rd to 6th. Why would I shift to 4th, 5th, and then to 6th when I keep the speed at 65 mph? I just make sure to wait until the RPM comes down before shifting into 6th gear. But I personally wouldn't do 1-3-6. That I'd agree with others saying you're being lazy.

[empower-auto]

who needs synchros anyways.

[JohnS_Rosamond]

I know this belabours the point, but there are rsponses here that are talking about Road Speed (...goin' 50 mph). It's not about Road Speed, it's about transmission gear RPM. Why do you have to shift into 4th or 5th? because not all the gears are spinning at the same rpm at the same time.

[D-VO]

Originally Posted by SkAsphalt

I can shift into 6th well above 5000 RPM without any problems..but that is because I shifted from 5th...If I skip a gear (typically go from 4th to 6th) I let the engine wind down and I move it into 6th then when the engine speeds would match the gearing for going X km/h. You are just shifting bad.

Also, D-VO, "I skip gears because the engine has enough torque to accelerate well in the rpm range at which it falls when I skip gears." You do know this car has minimal torque right?

Have you seen what the powerband looks like? The dyno shows nice cruise acceleration to 3500rpm then it drops off and you do know the car only weighs 2700lbs right? Its really easy to find this sweet spot while driving the car as well, so Im sure everyone who's driven the car can feel it. There is no need to go through all the gears while cruising because you still get good acceleration as if you were running through all the gears. Added I found that my fuel economy is better using this method. This is dependant on how quick you'd like to accelerate as well. So if you wanted the best acceleration you' d do 123456, but I dont care about that because Im cruising. So I skip.

[Jayde]

The only time I skip gears is going from 4th to 6th or 6th to 4th. I found that the tranny likes it better when I don't skip gears, as others have stated. Oh and I occasionally skip 2nd on the first shift if the tranny is cold and doesn't want to go into gear. Though after that, it goes in fine.

[Sigh-on-Rice]

Last night, I tried 1-2-6 on a freeway on ramp WOT to 55 mph and then to 6th. I usually wouldn't shift into 6th until RPM drops to 3k in this situation, but I purposely shifted into 6th at 4500 RPM. No grind.

I then tried 6-4-6 and 6-3-6 both at 55 mph, but no grind either.

Now, I don't know how you're grinding it.

[flippy]

FAIR, NEXT.

[ItsOnlyNoe]

I haven't looked at the internal diagrams of the transmission but as with most transmissions most of the first couple or 3 synchros are usually double synchros and/or stronger material. The overdrive are usually made of softer material to reduce noise during engagement. Like someone up a few replies said its not about speed of the vehicle it is more related to input and output transmission speeds. That could be related to why 6th gear may have worn out quicker. 6th gear is an overdrive and cannot withstand constant fast engagement. Learning to properly rev match can lengthen transmission life. Some driving school focus a lot on proper shift engagement. Wish ya the best and if in fact the transmission is just bad, I hope the dealership works with you.

[CamryDS]

Originally Posted by Jayde

The only time I skip gears is going from 4th to 6th or 6th to 4th. I found that the tranny likes it better when I don't skip gears, as others have stated. Oh and I occasionally skip 2nd on the first shift if the tranny is cold and doesn't want to go into gear. Though after that, it goes in fine.

I do this as well 1 --> 3, it does a small hump because I somehow cannot ever get it to go in smooth from 1 -->3 in the morning, all other times I go 1,2,3,4,5,6.

[Porsche]

This is a revived older thread, but I thought I'd add my thoughts for what they're worth. I'll address your points D-VO for the sake of convenience.

Originally Posted by D-VO

I normally skip gears as [I] drive and typically shift 1, 3, 6. A couple of days ago I revved 3rd gear out to about 5k rpm, shifted into 6th and had a really bad grind.

Your synchromesh mechanism is worn, worn more than it should be at this time. It is worn BECAUSE you have skip shifted repeatedly, which puts UNDUE WEAR on the synchro ring as it attempts to synchronize the speeds of the two shafts and their spinning gears so that they may mesh smoothly.

When one shifts from 3rd @ 5000 rpm straight into 6th (skip shifting TWO gears), the disparity in shaft speeds is far GREATER than it is when shifting 3-4-5-6, sequentially. Matching these "wildly" disparate speeds is what is causing extraordinary wear on the poor, long-suffering 6th gear synchro ring … and it's wearing out and dying an early death in consequence.

Also, shift slowly enough to allow the synchro ring to match the shaft speeds so the gears mesh when possible. Forcing a shift, speed shifting, also exerts undue wear on the machinery. It's quicker, yes, but it comes at a cost. Some gearboxes are sturdier than others.

If you have not had your gearbox repaired, you might want to try this "trick":

Take it up to 5000 in 3rd (as you described). On standard tires that is 56.3 mph.

Now, your 6th gear will be spinning at 2489 rpm at 56.3 mph.

We want to match those two speeds.

De-clutch. Shift to NEUTRAL.

ENGAGE clutch in NEUTRAL.

Bring rpms to ~2489 rpm (less as road speed drops). Use the throttle as needed.

Now shift into 6th gear.

There should be NO GRIND.

In fact, if you've matched the revs exactly, the gear lever should drop effortlessly into 6th WITHOUT even using the clutch.
But, one should always use the clutch anyway, because it's virtually impossible to match the gears EXACTLY and with the engine driving the input shaft, we're back to suffering excess wear on the synchros if we do not use the clutch.

You've just performed a double-clutch UP-shift.

I guess the problem now is since I'd like to race, the 6th gear grind will soon turn into a transmission rebuild.

Perhaps, but that depends on the track. You'll see 128 mph at 7400 in 5th gear. That may suffice for most tracks. If not, learn to double-clutch and match revs on the upshifts. Here are the speeds at redline:

5th @ 7400 rpm = 128.3 mph

6th @ 5676 rpm = 128.3 mph

In other words, engage 6th gear when the revs are at 5676 rpm @ 128.3 mph (in neutral, clutch engaged) … and the lever should slide right in with no grinding whatsoever.

YouTube has many useful videos to help one understand how a gearbox works. Watch, study, and think about it and you'll come to understand why this "trick" is working. Accompanying this will come the understanding of WHY one should not skip shift without using the double-clutching technique to match those shaft speeds, and thus minimizing the wear on the synchro rings. All of that is far more than I can explain in words, here.

Oh, and you may wish to find the thread on s2ki.com about a Honda engineer discussing why it's really bad to skip shift on their gearbox. That's what first opened my eyes, and you may find it equally useful.

I hope this has been helpful. (And I hope I got this right, but if not, somebody please help us!)

[FT86RGV]

Lately this problem has been happening to me as well. Under hard acceleration if I'm in the upper rpm range when I try to shift into 6th gear from 4th or 5th, I also sometimes get a grind. Even if I let the rpms drop a good chunk it still happens. The only way I've been able to avoid it is if i really wait on it for a good 2-3 seconds with the clutch engaged. Happens most often under full throttle on the highway when I've shifted into 4th or 5th gear to pass and then back to 6th to continue cruising.

[enigmaaron]

Originally Posted by FT86RGV

Lately this problem has been happening to me as well. Under hard acceleration if I'm in the upper rpm range when I try to shift into 6th gear from 4th or 5th, I also sometimes get a grind. Even if I let the rpms drop a good chunk it still happens. The only way I've been able to avoid it is if i really wait on it for a good 2-3 seconds with the clutch engaged. Happens most often under full throttle on the highway when I've shifted into 4th or 5th gear to pass and then back to 6th to continue cruising.

I get that too, you really have to be at a steady speed and let the rpm settle in to where they should be for 6th before shifting into it to avoid it, at least in my experience.