S6-37 6mt swap info (broken off from junk yard thread)

[Gt4]

I kind of lost interest once I realized I own a S6-37 already. I don’t think it shifts any better, even compared to the completely stock 420g in my e39 M5.

From what I remember, I think my low mileage Z4M Coupe feel worse than pretty much any E46 M3 I drove while shifting 1-2 on the street. More notchy.

[Obioban]

I had a Z4M Coupe and 1-2 was notchy. And peoples on Zpost were also complaning about it over the years. Not sure it will be a night and day difference if someone do the swap.

I kind of lost interest once I realized I own a S6-37 already (in my 128i). I don’t think it shifts any better, even compared to the completely stock 420g in my e39 M5… much less compared to the auto solutions kit in my e46.

[Gt4]

I had a Z4M Coupe and 1-2 was notchy. And peoples on Zpost were also complaning about it over the years. Not sure it will be a night and day difference if someone do the swap.

[Obioban]

Saw this thread the other day and meant chime in. I have an S54 touring in the shop running a full ZHP trans. It's all a direct swap with a modded driveshaft.

What flywheel?

[Anri]

That's not the only difference. The input shaft on the V8 420G is longer than the I6 spec 420G.

Kaiv,

I was pointing the G420 was specifically designed to go in M5
and M3. E34M5 G420 6spd also have different input shaft but
the design is the same.

I have had rebuild 20+transmissions and with mixed match
bell housing some went to NASA E30 M20 spec and other model
Getrag's for street driving.

I can't see the bell hosing having affect on the shifting characteristics.
I have also converted SMG to manual and I have never seen anything
different in shifting characteristics. If the needle bearings are worn out
and etc that is different.

Changing the shifter fork, new synchronizer, new springs, the gear box
will shift just like it came from the factory.

Unfortunately those parts are not available for G420 and nothing can
be done.

Regards,
Anri

[kaiv]

This is very true. The Autosolutions kit made my 420g a lot more fun. Kaiv told me every 420g feels different and some are way smoother than others so maybe one day I'll get a low mileage trans from an SMG swapped in and see how much better it is.

To clarify my statement for everyone, my observations are after doing well over 100 SMG to manual conversions, all with the same bellhousing work, same shifter etc. There is a range within which most transmissions fall and they feel mostly the same. But every once in a blue moon you have one that a bit harsher than average or one that's exceptionnally smooth. I'm guessing it's part manufacturing tolerances, part wear and tear over the the life.

[kaiv]

Terra,

Remember BMW engineers will never do anything without
a concept they have in mind, otherwise they would have had
the G420 on std 330i as well...make 1 gear box for all, just like
Mercedes loves to do this trick. they use the same box from
1.8 S/C up to 2.0 up to 3.2 V6 S/C.

The G420 is also covering E39M5 only the bell is different.

(...)

That's not the only difference. The input shaft on the V8 420G is longer than the I6 spec 420G.

[kaiv]

Saw this thread the other day and meant chime in. I have an S54 touring in the shop running a full ZHP trans. It's all a direct swap with a modded driveshaft.

[Anri]

Anri, do replacement parts exist for the 420G and is there a shop that can reliably rebuild (replace syncros) for the 420G? A few years ago, some shops were saying that this gearbox was very difficult to rebuild.

Hi,

The G420 box used to have a Patent on the Synchro and
pretty much on all the parts but several years back I think
the patent dropped...and the company started to sell
Synchronizers only. No other parts are available what so ever.

If the shifting fork wears out which is responsible to keep
the gear in, then you get pop-out of a gear scenario and
then the tranny become part out....or find good unit with
synch issue and swap the shifting fork/s.

I have a tranny guy who I use for rebuilding one of those,
have done 3-4 so far.

Regards,
Anri

[Slideways]

Anri, do replacement parts exist for the 420G and is there a shop that can reliably rebuild (replace syncros) for the 420G? A few years ago, some shops were saying that this gearbox was very difficult to rebuild.

[Anri]

Hi,

Kaiv told me every 420g feels different and some are way smoother than others

Let me lay down the Schematics what is involved in the
"shifting feel characteristics" on any transmission.

I want start with shifter deign. BMW has been using the
same design since 1983. Installing short shifter kits they
indeed change the leverage and also eliminate the OEM
bushings which are there to eliminate noise, and smoother
shifter feel. Ones short shifter kit is installed the transmissions
noises are all transmitted to the shifter.


In the pic the Selector shifter long rod has arc/seat, ball, spring.
If the shape of those machined arc is deep the shifting feel will
be notchy with addition to the spring rate. At installed height
they are pretty hi....18lb...So if I reduce the spring pressure and
the depth of the arc/seat those parts the shifting characteristics
will become softer and less mechanical feel.

The reason why G420 2nd hooks on a cold weather is because
it's the gear that sees the most abuse from all the rest.
G420 has 3 piece Synchronizer design for smoother shifting.
When the 3 piece synch start wearing out and the clearances between
the synchros do get larger more oil gets stuck in and the reason why
it's getting harder to upshift till the oil sees heat and then is back to normal.

3 Pics Synchronizer does not like many errors from the driver, what
I mean is some time during the life span the driver will randomly
grind the gear either one but 2nd as I mentioned is the most abused
of all the rest. When the shifter rod arc also starts to wear out the
ball with the tired spring will also affect the shifting feel and the reason
why there are many variation in the G420 primary the synchro and
then its the rest.

This is why the SMG is better to convert because it almost never
made an error grinding the 2nd gear and the synch condition is
much better.

1 piece synchro is much more rigid and can take a lot of driving
errors/grinding vs 3 piece.

On my M5 the G280 with MT90 on cold weather (45F) shifts the
same way if outside is 90F. This is because the Synchronizer is 1 piece.
The G280 requires ATF oil, thin viscosity. On a customer of mine
with E39M5 2nd gear started getting hard in mornings and I changed
the oil with ATF and it improved by a lot in those cold mornings.

Regards,
Anri

[Anri]

Yep, fair enough. The jump from 1st to 2nd is likely going to be noticeable compared to the 420G. Can't say how much without actually feeling it though. I need to drive a Z4M before fully committing to this swap, but the math has me pretty convinced.

And good point on the graphs. I posted pictures because I figured it was the easiest way to share. In the spreadsheet I made, I calculated speeds at 10 rpm increments so that you can mouse over the graphs and look at the numbers that correspond to each. Here's a link to a read only version (make a copy if you want to mess with it) of the spreadsheet in case anyone wants it: https://docs.google.com/spreadsheets...it?usp=sharing

heinzboehmer,

The gap between 1st and 2nd will be barely noticeable.

I spotted something more interesting 2nd to 3rd the RPM
drops down to 5300rpm instead of 5250rpm for the G420.

SG6 2nd gear at 2.50 is taller vs 2.53. At 2.50 the gear is closer
to 1.66 means less RPM drop. This is right were the HP starts
to climb and make larger increments. If you note those say +/-60rpms
will add around +/-8rwhp which is good thing.

So basically the SG6 is better than the G420 from 2nd to 3rd
which is more important than 1st to 2nd.


Believe me little shorter 1st is not going hurt the performance
at all. It has been years now I have not seen single I mean single
E46M3 with stock wheels...any aftermarket setup will add drag
to the M3 and little shorter will help to lift the additional drag/weight
added over stock wheels.

Thanks for making the chart it's similar to mine.

Regards,
Anri

[terra]

Keep in mind the diesel engine/transmissions are 20* so if you bolt that trans to our engine it will be 10* of horizontal.

Thats true at the bellhousing end. But if you’re using the N5x variant of the transmission, the bellhousing has the correct tilt and the rear case will line up as it is supposed to with the 330d parts.

But without a solution for the flywheel and clutch, it’s a bit of a moot point regardless

There is someone making any adapter to do just that but I'm not sure what the benefit is when a stock clutch is likely just as capable at holding stockish power.

Well the non-M input shaft is physically shorter so it won’t reach the pilot bearing in the crankshaft. So if you want to use the much easier to find non-M variant of the transmission, you either have to use the 330i flywheel (with integrated pilot bearing) and clutch, or devise some means to space out the pilot bearing if you want to use the Z4M/M3 flywheel with the Z4M clutch (or any other 22-spline clutch/pressure plate combo that might fit).

I can’t say for certain if the M3/Z4M flywheel is better suited for this engine, but I imagine it is.

[Bry5on]

For what it’s worth (similar internals) I bought a Getrag 560 brand new from Getrag (not a reman) for my personal car and it suffered from the same symptoms as worn ones - notchy 1-2 shifts when colder, generally two-stage shift motion (1-N-2) that the 420 also suffers from, particularly when cold. The ZF internals seem to be less sensitive to this, although I can’t say why without disassembling both. The shift carrier in the ZF does seem to make a big impact, and that cannot be replicated with the Getrag. It’s a small difference, not everyone will care or notice, and everyone is free to not change their factory M3 parts of course

At least from my experience, there is an improvement with the ZF box, but it’s not as big of a change as I’ve felt from ZF -37 to ZF -53. Tradeoffs!

[EthanolTurbo]

This will be my last post on this topic but I am truly baffled why anyone would do this swap if their current gearbox is in good shape. For a SMG conversion, it almost makes sense if yo.

The improved "shift feel" between the two gearboxes will largely be determined by the replacement transmission's treatment with a prior owner and there are so many variables that effect feel that its impossible to compare the ZF and 420g back to back.

This is very true. The Autosolutions kit made my 420g a lot more fun. Kaiv told me every 420g feels different and some are way smoother than others so maybe one day I'll get a low mileage trans from an SMG swapped in and see how much better it is.