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

[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.

[discoelk]

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 makes sense if you find a cheap ZF.

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. Because of this, the shift comparisons from Z4/zhp/e46m are a little meaningless imo. Having owned both transmissions, neither is going to be Honda levels of great but they're both nice with all new parts and some delrin carrier bushings.

The gear ratios are basically identical. No way you're going to notice 50 or 100rpm when driving.

[heinzboehmer]

Hi,

I actually love pedantic people because that is the only one way
to go further ahead and improve and mostly understand.

I did not wanted to go into deeper details but I have to now.

Note: I mentioned in my previous post that I can calculate
so called effective final drive ratio.

But in more simple language for those who does not know
how to calculate.

In order to calculate the effective final drive ratio one
needs to take the gear ratio and multiply by the differential.

SG6 4.35x3.62=15.747 effective final drive.
G420 4.23x3.62=15.312 effective final drive

The chart you post is fine but because the curves are not
very clear vs speed vs rpm and it makes it little bit confusing
not as clear as the chart bellow. I made very nice excel charts
so I can see things in close details when I calculate tires size,
vs HP vs TQ vs RPM vs Speed etc.
It's like dyno-chart if you print the chart to show the HP vs RPM
in say 20rpms increment vs a curve.

In the chart I made for us here pay attention on the speed
vs rpm vs RPM drop vs TQ vs speed.

So now if you look at the HP chart vs the SG6 rpm drop then
you will see loss of HP not by much but S54 needs every single
hp and tq in the world.

Something to suggest when you compare setup it does not
matter what it is you need to be fair and measure the rest to be
the same, in this case will be use the same tires size for both
gear box comparison. Because if you tweak one you can tweak
the other as well.


The rpm drop from from 1st to 2nd will affect the HP with around +/5-RWHP
and that is +/-9hp at the crank I can make the chart even closer to each other
but its a lot of work..the point I am making I think its understood.


I agree whit you, this is very small detail which will not be noticed day to day
driving but 0-60mph selling nonsense it does make a visual difference
if its 5sec vs 4.8sec its a window sticker mind game...back in the year of 2000.

(If anybody wants help with the differential gear ratio for the track, or tire size
let me know I will apply the data and reply)


Regards,
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

[Anri]

Hill,

E34M5 3.8 is rated at 340hp DiN
E46M3 CSL is rated 360DiN
20hp at peak revs is not that much
off.

Now, take a look how BMW Engineers
re-design the S65 6 speed gear box.

This is because the power grew and
also the Torque curve is more in the
lower revs compared to E46M3 (stock
for stock)

Boy that gear box is as heavy as the
S54 alone...

Ratios are also changed vs G420.

Regards
Anri

[George Hill]

I have an 8spd with a 4.44 diff soooo why would I want to drive that diesel 3.23 ratio, lol.

My point was it seems silly to think that an engineer in 2002 (ish) would be like "you know what, I want to use this clunky transmission that was designed in the early 90s but BMW is making me use this superior shifting quality transmission that was just developed."

Everything is a trade off, time marches on and technology progresses.

[Anri]

Hill,

G420, G260, G560, G280, SG6, list goes on and on.

Gear box ratios are design for the given package and need.

- 0-60mph (nonsense) but sells the car.
-Curb weight
-Engine power hp v tq
-Engine RPM
-Fuel economy (little bit)
-6spd gives the opportunity to play with rear end much more than 5spd
for example E34M5 6spd uses 3.23 final drive. E34 540i uses the same
G420 but paired with 2.81 all based on all of the above.
- E31 850CSi used G560 with 2.93 final drive.
- E34 M30 535i used G260 pair with 3.46
- Overall package


Gear ratios, what's the purpose and the need ?

On my daily E28M5 I replaced the G280 with G260 paired with 2.56 rear end
from E36 325td Euro. On the freeway I am at 75mph with around 2100rpm..
just like Diesel Tractor

Go drive Euro E36M3 3.2 6spd Evo, soooooooo much better than E46M3
same gear box but the diff is 3.23 and paired with much stronger engine velocity in the
lower revs. Its also lighter by a bit.

Do you think that is the case or was it the 420g was designed in the 90s and they kept using it because it was a known concept but then time marched on and a better option was had (S6-37) and they started implementing it (E46 330i) before mass adoption and the 420g was phased out?

Also the input shaft is different on the V8 420g as well (just in case someone was thinking about trying to change the BH between the two).

Hill, never forget when BMW Engineers design a part for specific model they do it
so called Factor1-2-3-4...that meant that the part will withstand 1, 2, 3 times more than
the intended purpose is all based on "we want to make sure the part will not break at all
cost" BMW 188mm diff can hold waaaaaay more power than the gutless S54 can ever make..
but BMW put 210mm. E34M5 on boost the 210mm can hold min 700rwhp/TQ+. (Not on
drag strips with glue on the ground..)

I forgot but is the SG6 input smaller than the G420 ?



Regards,
Anri