6MT Slipping Out of 5th Gear

[takethecake]

Hey guys, wanted to get some advice on this issue I've been having - did a quick search but most of the existing posts are about grinding only or warranty replacement, not slippage or self-repair. Car is a 2013 BRZ w/ ~80,000mi, and within the last year/10-15,000 miles the transmission has started to have trouble staying in 5th gear - it will just slip out into neutral, sometimes with a horrific grinding noise if I don't clutch in quickly. It seems to occur most often when I'm giving it steady gas in 5th gear and suddenly take my foot off the accelerator, or if I hit a bump in the road while in 5th. Never happens in any gear other than 5th.

I replaced the tranny fluid at ~30k miles and again at ~75k, the second time was shortly after I noticed the problem. I also installed the mtec shifter springs/perrin & whiteline bushings around 75k to see if that would help at all, but they didn't (altho the shifting overall did improve).

I'm wondering if this is a progression of the 5th gear grind issue a lot of people have noted in the early run of cars (I did notice that before but it never really seemed that bad), and since I'm out of warranty, what I might be able to do about it. If I take it to a mechanic/dealer, I imagine I'm looking at a >$1k repair? I've never worked on a transmission before but I am mechanically inclined and have plenty of time on my hands - what equipment would I need to, for instance, swap out a synchro if that's what the issue is? Any recommendations for sourcing a replacement synchro or entire tranny?

Thanks everyone!

[twag4]

Gears kicking out of a gear is normally an excessively worn or bent shift fork.

[ermax]

I know on Honda's the syncro sleeve would slide over a ring/spring which would catch on a detent in the sleeve which held it in gear. These rings would flatten out with time and no longer hold it in gear. I've never been in this tranny so I'm not sure if they have a similar setup.



That is a picture of a syncro set, sleeve and rings for a B16A. Sleeve being the part at the top center of the image. If you look closely at the inside of the sleeve you will see a grove which catches on those rings that are also in that picture. On a Honda you can buy those rings cheap. But if you can't do the work on your own it's probably not a cheap job. I've done a lot of work on Honda tranny's and it's really not rocket science. I've bashed up the faces of the sleeves so bad they wouldn't slide into gear anymore. I would tear it down and literally file the faces one by one so they had a diamond shape again and the problem was solved. Those were in my idiot days of daily flat shifting. Hahaha.

[humfrz]

I'll ring up ol @Ultramaroon for you ..... he is pretty good at tearing up ...... errr, I mean tearing into transmissions.....


humfrz

[takethecake]

Thanks guys, appreciate the input!

I would think that if it was an issue with the selector fork, that it would affect all gears and not just 5th? But I'm still fairly new to how transmissions work so forgive me if I'm mistaken.

This is my daily but I have other cars available, so I could afford the time to drain the transmission, remove it, and open it up and at least see what everything looks like inside. Just thinking it might be a good idea to have a plan of action before doing that (and not exactly relishing it since it took me a good hour to get my stupid front pipe back on after I installed the bushings earlier)

[ermax]

Originally Posted by takethecake

Thanks guys, appreciate the input!

I would think that if it was an issue with the selector fork, that it would affect all gears and not just 5th? But I'm still fairly new to how transmissions work so forgive me if I'm mistaken.

This is my daily but I have other cars available, so I could afford the time to drain the transmission, remove it, and open it up and at least see what everything looks like inside. Just thinking it might be a good idea to have a plan of action before doing that (and not exactly relishing it since it took me a good hour to get my stupid front pipe back on after I installed the bushings earlier)

It's possible to bend the selector for 5/6 without bending the others. But yeah if you bent something that impacts 5th it would probably impact 6th in some way too.

[Ultramaroon]

Originally Posted by takethecake

Thanks guys, appreciate the input!

I would think that if it was an issue with the selector fork, that it would affect all gears and not just 5th? But I'm still fairly new to how transmissions work so forgive me if I'm mistaken.

This is my daily but I have other cars available, so I could afford the time to drain the transmission, remove it, and open it up and at least see what everything looks like inside. Just thinking it might be a good idea to have a plan of action before doing that (and not exactly relishing it since it took me a good hour to get my stupid front pipe back on after I installed the bushings earlier)

It's the shift fork. Look in my sig line for a link to the manuals and you can study up on the transmission. I'm at work now but will check back later tonight.

[Ultramaroon]

Originally Posted by ermax

It's possible to bend the selector for 5/6 without bending the others. But yeah if you bent something that impacts 5th it would probably impact 6th in some way too.

Ah, I got distracted and sat on my reply too long. The shift fork in question actually selects between fifth and reverse.

[takethecake]

Ah, that would make sense - perhaps the much lower speed in reverse (compared to 5th) is why I haven't been seeing problems there.

Thank you for the link to the manuals - this is what I found there:



So are we thinking the actual shift fork shaft (in red) is bent? Or the "shift head" marked in green? I'm trying to visualize what's going on exactly - is it that the bent shift fork shaft can't keep the 5th gear sleeve where it needs to be and eventually it just backs off?

How would you go about addressing this then - would you order a replacement shift fork shaft and try to replace it yourself, or would you just look for an entire new transmission? I've got plenty of time on my hands so it'd be okay if this turned into a 2-4 week project, and I'm working with limited funds. Honestly this isn't a HUGE problem - a little annoying, but I've been dealing with it for about 6 months now, so I can put it off if it makes sense to (I can't imagine it would make anything worse).

And second question - any idea what idiotic thing I might have been doing to make this happen and keep from doing it in the future? I don't track/race/autocross or anything, just DD, and I don't feel like I'm really all that hard on the car (no launches lol).

[NoHaveMSG]

Bad syncro in my CRX behaved that way.

[Ultramaroon]

I think we're talking about the number three fork here.

https://demos.starbase7.net/t3Portal...02H8K00LX.html

[humfrz]

Originally Posted by takethecake

.........
So are we thinking the actual shift fork shaft (in red) is bent? Or the "shift head" marked in green? I'm trying to visualize what's going on exactly - is it that the bent shift fork shaft can't keep the 5th gear sleeve where it needs to be and eventually it just backs off?

How would you go about addressing this then - would you order a replacement shift fork shaft and try to replace it yourself, or would you just look for an entire new transmission? I've got plenty of time on my hands so it'd be okay if this turned into a 2-4 week project, and I'm working with limited funds. Honestly this isn't a HUGE problem - a little annoying, but I've been dealing with it for about 6 months now, so I can put it off if it makes sense to (I can't imagine it would make anything worse).

And second question - any idea what idiotic thing I might have been doing to make this happen and keep from doing it in the future? I don't track/race/autocross or anything, just DD, and I don't feel like I'm really all that hard on the car (no launches lol).

Oh, I reckon I'd check out the price for a shift fork shaft and head.

Then, I'd go up to my local auto shop and ask them how much they would charge to replace those parts (transmission in and transmission out).

Then I'd price a new transmission.

I would weigh the cost and time against whether or not I could live without 5th gear. See, 4th gear in my 2013 FR-S will take me up to 100 mph ....... and this old fool has not business going faster than that. 6th gear allows me to cruise comfortably.

What "caused it" ..... ?? ......

Did you buy the car new?

Well, I hope you get it sorted out and fixed.


humfrz

[takethecake]

Guys, thank you again so much for your help - definitely feel like I'm making some progress here. And yes, I did buy the car new so anything wrong is my own doing haha.

Seems like the parts would be pretty cheap - about $50 per gear shift fork, about $40 for a shift fork shaft. So I might just try to tackle this on my own - would be a great way for me to learn about working on transmissions, and worst case if I bungle something too bad it looks like I could probably get a used transmission for $500 or so.

So just need to figure out exactly what to order - I'd prefer to err on the side of ordering anything I might need, since I should be able to return anything unused. I'm looking at these diagrams and it's making my head hurt a little - I tried color-coding the same parts across each diagram but it'd be nice to get confirmation that I'm looking at everything the right way.

The first pic below is snapped from this pretty helpful youtube video I found:
[ame="https://www.youtube.com/watch?v=ujJqiApwIgk"]Text[/ame]





From this page, I think I want:
-PN# 32810C - Gear Shift Fork #3
-PN# 32809C*A - Shift Fork Rod #3
-PN# 32847A*C - Gear Shift Head (pretty sure this one is #3)

Any ideas on whether I should also get:
-PN# BRSN01 - Snap Ring
-PN# BRBL04 - Bolts (that appear to lock the shift fork to the shaft)
-PN# BRPI07 - "Pin" ?

(Are there any consumables required - gaskets, crush washers, etc - to remove and replace the transmission other than the fill & drain plug washers?)

What is the difference between the gear shift head and the gear shift fork - how do they interact with each other? It seems they both have the shaft passing entirely through them?

Also, any significance to the fact that the 5th gear is the same speed as the engine (input shaft gets locked to output shaft)?

And last, what does shift fork #4 control? The 6th gear hub sleeve? I'm confused why the "reverse & 5th" shift head I circled in green on my previous post is named that - I'm pretty sure it's mated with shift fork #4

Here's another good diagram taken from that youtube video:




Thanks and sorry for all the questions - hopefully this helps someone else out too!

[Ultramaroon]

Originally Posted by takethecake

Thanks and sorry for all the questions - hopefully this helps someone else out too!

If you daily the car, I suggest installing a spare transmission before digging into yours. Depending on your luck, you can find them between $500-$800.

I say that because, based on your questions, you have a long way to go. Just being direct.