Getrag 245 4th Gear Synchro Issue??

[andyleonard]

A new-to-me 125K 81 245 OD box has a nasty grind from 5th to 4th. The rest of the gears/synchros are excellent and there's no bearing noise. It's not the "one little bolt in the wrong place on the seal retainer" issue as I am aware of that and gear engagement into 5th is fine, just coming back down to 4th has no synchro. Other than this issue it feels like a tight, low miles box from a little-old-lady car, which it is.

 

I did change all the seals and there's a strong possibility I have over-torqued the output flange on reassembly (been working on newer cars). Given that the usual suspect for a bad synchro is 2nd, I did a search on "bad 4th" and found some writing that indicated maybe - or maybe not - an over-torqued flange will produce my problem. 

 

Is it worth pulling the flange, re-torquing it and trying again or should I pull the box and go through it? Could I have snugged the synchro onto the gear? 

 

 

[Mike Self]

Before delving into the gearbox itself, check these two things...

 

1.  make sure the clutch hydraulics are allowing the clutch to disengage fully--I know this problem usually manifests itself in lower (or all) gears, but it's easier to check than pulling the gearbox.

 

2.  check your tranny mount, its bracket and the metalastic joints that hold the shifter bracket to the gearbox.  Make sure the bolts are tight, and the mount and joints haven't turned into black goo.  A loose shifter bracket can cause all kinds of funky shift problems, depending on what's loose.

 

If that all checks out, then at least you've satisfied yourself you've done the easy stuff first...

 

cheers

mike

[andyleonard]

This is a new install/new parts in a 2002. Everything's right.

 

I'm trying to see if anyone has had over-torquing issues.

[Preyupy]

I am sure it is not an over torque issue.  If you understand the internal workings of the gearbox you know that there actually is no 4th gear per se.  4th gear is the 1:1 ratio and all it does is lock the input shaft to the main shaft, all of the other gears are still spinning inside the box but all of the power goes directly through the main shaft and not through any of the gears.  The fact that you don't have a problem with the synchronizer  when upshifting from 3rd to 4th is very interesting, usually when there is a problem with a synchronizer it is the same on upshift as well as downshift. 

 

There is the possibility that you have a front input shaft bearing that is not shimmed correctly and the primary gear is too far forward but that usually causes problems on upshifts too. 

 

The other possibility is the rear main shaft bearing may not be shimmed properly and is floating in the case.  This should be easy enough to diagnose, with the car in gear (2nd  should be fine) lightly put your hand on the shift lever and accelerate hard then suddenly lift off the throttle, does the shift lever move forward and back?  If so the entire main shaft is moving in the case. 

 

I am sure there are other possibilities but I don't remember ever having a 4th gear synchronizer problem with a 245 box. 

[TobyB]

Yeah, that's a 265 issue- with the aluminum shift forks...

 

Shimming could do it, but I agree 100% with Byron- you'd think it'd do it either up or down.

 

What happens if you blip hard when you double- clutch from 5th to 4th?

 

That would set the gearbox rotating the same way a 3-4th shift would.

 

I wonder if it's something gone wrong with the synchro itself?

 

t

 

[andyleonard]

It feels like the 4th synchro is either split or stuck. There's no synchro at all coming back from 5 to 4. Feels like a racing dog box. There's a tiny scratch going up from 4 to 5 if you hurry.

 

Beats me.

[andyleonard]

For the record, releasing and re-torquing the flange did nothing ... as expected.

 

So in we go.

[andyleonard]

On 11/19/2018 at 10:01 AM, TobyB said:

 

I wonder if it's something gone wrong with the synchro itself?

 

t

 

 

I thought about this and agreed with Toby. So much for thinking outside the box. The new 100 mile MTF oil looked like the California Gold Rush. Unfortunately I never saw the original oil as my son dumped it under orders and didn't comment. Pulled the front cover and found the shims present and appropriate sizes front and rear, no janky bearings, everything looked stock and unopened at 125K miles and NO TEETH WHATSOEVER left on 4th gear synchro. Synchro pushed smack up against the gear doing nothing, slider looks OK, not perfect but not damaged, so it wasn't my imagination; it was like driving a non-syncho box for that shift.

 

I wonder what did it?

[stephers]

Just a question, was the output shaft seal ever replaced while trans still in the car?

[andyleonard]

19 minutes ago, stephers said:

Just a question, was the output shaft seal ever replaced while trans still in the car?

 

Yes. I did it - trans out - and changed the oil before installing it in a different car. My original post was to ask if I might have over-torqued the flange but I'm sure I never got over 100#s. Can't see how that would matter anyway but internet. Shims were/are in place.

 

Got a theory?