4th gear popout

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Nikita240
Posts: 10
Joined: Mon Jul 07, 2014 8:30 pm
Car: SR20DET S13 240sx Hatch

Post

Hi Nicoclub.

I have an SR20DET (1998 S13 Blacktop) and it developed a 4th gear popout.

It started after I completed my engine rebuild. As part of the rebuild, the things I did that affect the tranny are:
  • Installed Cusco motor mounts (no tranny mount)
  • Resurfaced flywheel
  • New SPEC Stage 2 segmented clutch and pressure plate
  • New throwout bearing
  • New Pilot bearing
  • New Clutch slave cylinder
  • New Circuit Sport V2 shifter with solid bushings
  • Redline MT90 fluid
Since then my car pops out of 4th when coasting. It doesn't happen under power, only after I lift (either immediately or after a few seconds).

It actually feels a bit different than other gears. It doesn't quite "pop" into place. As if the detent ball is not functioning. The shifter also slides around in 4th. I can feel it move back when I accelerate, and forwards when I lift. 3rd gear functions normally.

I've tried driving with the shift rubber boot off and it feels the same.

I did a bit of research and everybody blames it on synchros or the shaft bearings, but I don't see how that would be possible. I think that the detent on the shift fork might be gunked up or something, preventing the detent ball from holding the fork in place.

Does anybody have any experience with this?


CHAOSMOTORSPORTS
Posts: 3
Joined: Mon Jul 07, 2014 8:57 pm
Car: S13

Post

Might have to tear apart tranny and check your sincrows ..

Nikita240
Posts: 10
Joined: Mon Jul 07, 2014 8:30 pm
Car: SR20DET S13 240sx Hatch

Post

CHAOSMOTORSPORTS wrote:Might have to tear apart tranny and check your sincrows ..
Why would synchro's cause this? It doesn't grind or anything. Synchros aren't responsible for holding the gear in place. They only come into play when you are engaging the gear.

CHAOSMOTORSPORTS
Posts: 3
Joined: Mon Jul 07, 2014 8:57 pm
Car: S13

Post

They are responsible for holding the gear in place .. The synchro s are what puts the pressure on the gear to keep the shaft from poping out ..

Nikita240
Posts: 10
Joined: Mon Jul 07, 2014 8:30 pm
Car: SR20DET S13 240sx Hatch

Post

The synchromesh doesn't apply pressure on any gear. All it does is lock the helical gear's splines to the synchronizer hub splines by sliding over it. The synchro ring(s) just makes sure that the gear is at the same speed before the coupling sleeve slides over it's splines. I don't see how the synchomesh assembly is responsible for "holding" the gear. The gear is held by the nature of the coupling sleeve being held over the gears splines, which is held by the shift fork, which is held by the striking rods, which are held in place by detent balls.

240kc
Posts: 2
Joined: Fri May 11, 2018 2:30 am
Car: 1989 240sx fastback
1992 240sx convertible
1993 240sx fastback

Post

your 4th gear or input shaft is worn out. needs replacement. I rebuilt a few of these trays before.


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