Getrag 420G rebuild?

[Chanman1029]

The springy back forth has happened to me too. When there's a drop in the road at slower speeds. Or sometimes off a red light and turning. Pretty infrequently, but it happens. I'm 99% sure it's the diff. It almost feels like you're just stomping the has pedal and letting go right away.

At times on tight right turns where I'm almost to lock I'll get grinding coming from the diff. Or some weird sound. Also my right rear input seals have a little bit of fluid seeping out.

The only other thing is the axle is bad, which I think it is also causing some weird engagement. Anyways, I really think you should look into the diff.

I do have a very slight bit of diff whine that becomes noticeable around 70+ mph, but other than a very low whine it doesn’t make any other sort of noises. That is, assuming that my previous investigation of this noise coming from the gearbox is true

[sapote]

Not sure how much a used SMG trans goes for, but could you not get one, swap your bell housing over and see if the noise persists?

You don't want to swap out the original bell housing with other tranny. This will cause damage to the input shaft bearing as the dimension will change. The bearing was shimmed precisely at factory for zero axial plays, and the shim is only good for the matched tranny and bell-housing and the original bearing. When replace the bearing, one needs to adjust the shims again for zero plays and zero interference fit.

[sapote]

My synchros are very slow and have basically given up at this point..

Which gear? Cannot be all of them are worn synchros. especially the higher gears.

[sapote]

My synchros are bad in 3rd and terrible in 5th..

I have never heard of 5th synchro going bad. Most of the time the 1st or 2nd are going bad before the higher gears.What is the symptoms of the synchro problem?

[sapote]

this transmission does have a slight grind going into second sometimes, and very rarely will it be hesitant to go into a gear, where I will have to put it in a different gear and then go back to my desired gear. Not sure if that changes your opinion on things.

This is normal, except your 2nd synchro maybe a little worn - does it grind more with warm tranny and less when cold? What you said about the tranny does not justify for the problem listed in your first post. Look somewhere else.

[sapote]

Ive come to the conclusion that a diy rebuild is pretty much impossible. These transmissions were supposedly assembled in a manner that tolerances are so tight that special pulling tools are required to pull apart and press everything back together.

You need to know the trick of how to open the rear case, as the interlock pins (prevent more than one gear engaged) need to be removed and some pins have to be at certain location in order to separate the cases. Pressing out the gears from the shaft is nothing unusually.

[Chanman1029]

This is normal, except your 2nd synchro maybe a little worn - does it grind more with warm tranny and less when cold? What you said about the tranny does not justify for the problem listed in your first post. Look somewhere else.

I think it tends to grind a little bit more when the fluid is cold, but its only gets SLIGHTLY better when warmed up.

[sapote]

I think it tends to grind a little bit more when the fluid is cold, but its only gets SLIGHTLY better when warmed up.

your clutch maybe dragging and not released completely. check it out with rolling down hill / driveway method. Look for my post on this recently.

[Chanman1029]

your clutch maybe dragging and not released completely. check it out with rolling down hill / driveway method. Look for my post on this recently.

I just replaced my clutch and flywheel, hasnt changed.

[sina]

Has anyone put any other manual transmissions into these cars? Not like the 420G is anything special, if you're gonna shell out some serious coin it'd be nice to get something a bit slicker.

[heinzboehmer]

Has anyone put any other manual transmissions into these cars? Not like the 420G is anything special, if you're gonna shell out some serious coin it'd be nice to get something a bit slicker.

This piqued my interest lately: https://www.instagram.com/p/CPQanHap...dium=copy_link

Maybe George Hill can comment on alternatives for the 420G?

[cobra]

My driveline clunks so bad. It has for the past 50,000 miles and nothing has broken! It's just the M Clunk I was told. Get used to it?

What transmission oil are you using? I had 2nd grind a few times when running redline mtl and since switching to amsoil mtf it has been great ever since.

[tnord]

Which gear? Cannot be all of them are worn synchros. especially the higher gears.

3rd is the worst, and will grind if I shift too quickly even when warm. The transmission definitely shifts better after it's warmed up, and I double clutch 2nd/3rd/4th for the first 5-10min. I've rebuilt the entire shift linkage, changed trans fluid a couple times, replaced engine and trans mounts, replaced and bled the slave. There's nothing left that could be contributing to poor shift quality (well, besides the driver of course) besides the transmission itself.

[George Hill]

This piqued my interest lately: https://www.instagram.com/p/CPQanHap...dium=copy_link

Maybe George Hill can comment on alternatives for the 420G?

Hey thanks, yes I run a S6-53 trans from the N5x cars in my S54 swapped touring, I like it a lot compared to a 420g. This trans swap isn't for everyone, while I'd like to say it's the best solution out there, that's not quite the case. If you have a stockish powered 420g car now it probably doesn't make sense to do this conversion (financially) but I think it starts to make more sense if you a running elevated power as the S6-53 is stronger. BUT the S6-53 shifts so nice, it is night and day compared to most of the 420g's I come across, there are some rare exceptions of 420s that still are crisp but it seems like the majority coming through my shop are starting to have some kind of "issue."

So IMO if you want a nicer shifting transmission or are concerned about strength this is the way to go. The swap is pretty straightforward but does require a few "custom" pieces. The starter bolts to the block on the N5x cars and on our S54s the starter bolts to the transmission, so that has to be addressed (what I was talking about in the link Heinzboehmer posted above). Thats the "hard" part, from there a custom slave cylinder hose and shift lever bracket (both easy) and then a custom driveshaft, everything else is a bolt in affair.

[heinzboehmer]

Awesome. Next time my transmission is out, I'll be replacing it with one of those (or similar). I've always liked the feel of those ZFs MUCH more than the feel of the 420G. I would be doing it exclusively for feel. I do have some engine mods, but I don't run so much more power that I'm concerned about my trans.

For the driveshaft, did you have an M3 one lengthened/shortened or did you piece one together from multiple BMW driveshafts?

Your starter bracket solution seems super straightforward and I'm sure that Ronald (from AutoSolutions) would be able to easily make me a custom shifter carrier that still works with his short shift kit to swap in.

Thanks for the input!