Which ZF transaxle to use?

Real ineresting thread this.

I decided to do a bit more research so googled for 'bmw M1 ZF gearbox', and unearthed this old post on the pantera forum:

Pantera East has signed an exclusive contract to provide Pantera owners =
with Transaxle Ring Gears ("cruise" ratio of 3.77 prox) in 9310 material =
(better than even the original). Gearset will be pre-lapped (run-in) =
and engraved with setup information for correct installation. As you =
may know current Retail price for ZF Ring Gears is close to $3,000. Our =
price will be $1950. However if we can get deposits for 20 pieces we =
could do $1600 ($350 savings from an already drastically reduced =
price). Hurry, once the order is completed we will not be able to =
increase production to get a better price.

Also available will be an overdirve 5th gear (.655). Made from 9310 =
material and guaranteed perfect (some factory gears have been showing up =
out of round, making for some hellatious racket. Current retail price =
is $1,300-1,500. Our price will be $995. However, if we can get =
deposits for 20 pieces we could do $890 (an additional $105 savings).=20

Feed back is appreciated. Remember time is limited to finished =
production. Order yours today. Only $500 holds one or both.

One more thing! A very limited quantity of NOS BMW M1 gearboxes have =
been located and purchased ready for sale. As you know this transaxle =
is the latest version of the ZF type "-2" updated by ZF to BMW =
specifications. Improved syncros (smoother shifting), stronger bullet =
proof case (gusseted for added strength in critical locations), CV =
output flanges (makes an especially simple and low cost conversion to CV =
drive axles, etc. are a few of the benefits. Perfect for ultra high =
performance GT40 conversions and can be used in a Pantera by "flipping" =
the Ring & Pinion. Cost "less than half of what you'd expect". =


[/ QUOTE ]

Note that Marino states this late -2 box is "Perfect for ultra high performance GT40 conversions"

Heres another from http://realbig.com/detomaso/1999-04/500.html :


> I've also heard the M-1 case is stronger, although we
already know from Jr Wilson the early case will take 900 horsepower, so whats
the use?

>>>Dash-1 gearbox cases as well as some Dash-2 cases suffer a chronic
weakness in cars that subject them to high horsepower and high load factors.
Eventually the case fatigues and right at the junction where the flat top of
the case angles up to meet the bellhousing, a crack develops, which then
heaves all the oil overboard and quickly toasts the internals.

This is NOT a factor for street-driven Panteras, just all-out race cars with
mega-power and beaten hard. Junior was relatively gentle with his gearboxes
because all he ever did was accellerate to speed and then keep it there.
Road course use, banging up and down gears again and again is what does 'em
in. In fact, didn't John Parsons blow up his ZF case that way?

The M-1 case is substantially stronger due to massive webbing being cast into
this weak spot. Essentially bulletproof, and somewhat essential for any
600+horsepower dedicated track car.

[/ QUOTE ]

Maybe it is worth looking for on of these boxes that have the extra strengthening ??

Oh, and the search also pulled up a post from Ross about his ZF ratio swapping I'd missed /ubbthreads/images/graemlins/wink.gif
And another post, this time after a search for "pantera zf gearbox"

>Can a ZF really take the power of a 427?

I dont think it can at least not without alot of work.

>>>Piece of cake. Other than the cheesy synchro design (common problem with
ALL ZF gearboxes, and bound to fail eventually regardless of horsepower), the
Pantera gearbox is REALLY strong. Pikes Peak hillclimbers routinely put 700
hp or more through their Pantera ZF's (their gearbox of choice.) Now, THOSE
guys manage to break ZF parts by banging gears at 7000 rpm with no clutch, but
in a Pantera application, once the ring and pinion has been safety wired and
the synchros are good, you can pretty much FORGET about your gearbox, no
matter WHAT kind of motor you've got.

[/ QUOTE ]

my head is spinning. Totally confused now :|

One thought though. The thinner input shaft. Could this possibly be in order
to try to absorb some of the torque, so that it twists like a torsion bar rather
than simply snapping ??

Going for a lie down to recover... /ubbthreads/images/graemlins/wink.gif

p.s. Gary, thanks for posting those pics /ubbthreads/images/graemlins/wink.gif

Ross Nicol

GT40s Supporter
John I have read those articles before.On the Pantera forum there was a post of how Jr Wilson broke his ZF.Apparently the car got air after a full power launch and broke the input shaft when it came back down.900hp and antics like that surely prove the strength of the box.
Lynn I didn't intend to offend you if this is what happened I too only intend to supply factual info to the guys on this forum, to aid them with their choices.
900hp !! Blimey. no wonder it popped ! /ubbthreads/images/graemlins/blush.gif

I'm still confused though.
If the later -2 M1 boxes had their casings strengthened along with better synchos, why would they then fit a weaker input shaft ?

There also seem to be a whole host of different gear ratios, according to the RBT site.
Which are the best set ? (based on 100% road, 1005 track, 50/50 ).

I have all but given up on a T44 to mate to my 427, mainly due to the cost.
If I were to use a ZF -2, am I looking for trouble ?

Lynn Larsen

Lynn Larsen

I am sorry if my comments added to your confusion. But in light of the fact that you are planning to use a 427, I am glad that you will now look very closely at the gearboxes you are considering. A 427 is going to produce torque that is at or beyond the theoretical limits of the transaxles commonly considered for use in a GT40 replica. (But, these limits are commonly exceeded in GT40 replicas, just not to the extent a 427 can:) On that note, thinner does not always equate to weaker (metallurgy, unsupported spans, strength of supports and a lot of additional factors beyond cross section determine strength) and while the published torque capabilities of the M1 were slightly lower than the standard -2 (I am working from memory here and don't have the exact numbers) there was not and, typically, is not an explanation of the limiting factors prompting the published number. Although, I suspect the final number has more to do with covering the manufacturer's butt in light of MTBF and similar statistics than anything else.

Indeed, I came VERY close to buying an M1 from an individual in Europe when I was in the planning stages of building my car. What prevented me was not concern over the units capabilities, but were the financial arrangements the individual was insisting on without the opportunity to physically inspect the gearbox. I was concerned because I had heard stories of people buying transaxles (type doesn't matter) that had been in storage for many years, as was the case here, only to find that the portions of the internals that were not oil covered were rusted beyond use.

Ross, no offense taken because, like you, I am only trying to relay the facts as I know them or as they have been told to me. And as I said at the outset, I am not a ZF expert by any stretch of the imagination and my statements are based on research I did, at least, 4 years ago. The bottom line is that John will do his research with a few more questions in mind as a result of the conversation. And, that is a good thing, since he will, hopefully, have a more satisfying car as a result.

Thanks guys, and you are spot on Lynn, I now have a whole host of questions whereas before I didn't realise there were so many differences to consider.

I have a -2 available locally to me that is from a Pantera. Since it is local I should have the opportunity to examine it prior to buying. What should I look for ?
The downsides are that it needs to be flipped, it has pantera drive couplings (I'd prefer CV joints as I think they would be stronger), and it will need a new bellhousing to fit the 427.
Is it worth considering, or should I skip it and hold out for an M1 box ?

If someone could mail me the details for whats involved in inverting the pantera box I'd appreciate it so I can see what I could be getting into. As I understand it this requires flipping the diff over. How about moving the gear linkage ?
I'm sure someone posted a link to the ZF manual a while back too, but can't find a link to it now.
Are any specialist tools required ?

I'm mechanically minded and not daunted by the prospect, just like to know how nuch swearing would be involved /ubbthreads/images/graemlins/wink.gif
Sending the box over to the US to be sorted by RBT would probably make it an expensive proposition, so I'm keen to either do it myself or get a local gearbox specialist to do it for me.

Have a great weekend all,

Ross Nicol

GT40s Supporter
John download the assembly and service manual from www.erareplicas.com there are no pics but you can still get the info.I emailed them and they gave me the site to download pics as well.Maybe try that the pics are handy.Also get a ZF manual (hardcopy)from the Pantera club in US (orange county if I remember correctly.If you're mech minded you'll be ok but does help to have a gearbox person's ear, especially for shimming backlash etc but the manual is detailed enough for the uninitiated.You will no doubt have the odd swearing session but the result is worth it.You could use the uni joints at the box and C/V's at the upright.The good thing if you go that Pantera box is you don't have to move the gear linkage, it will be on the RHS when you flip.When you flip the box obviously the crown wheel has to change sides and there are oil drain holes to be drilled between cases.All this is covered in detail in the ERA manual along with a lot of clutch/starter info.ERA should be applauded for making this detail available it certainly helped me a lot.Tools yes the most difficult thing is to get the bearings off the sides of the crownwheel.You can't extract the crownwheel unless you remove the bearings first.I cut the cage off the bearings and had a puller made to use with my porta power and I'll take pics later when your at that stage to help if you want.
The rest normal tools will do like a Press etc.

Dave Wharran

The ERA manual has a section on flipping the ZF. You can get it at http://erareplicas.com/download.htm#manual by clicking on the ERA GT selection.
A factory manual on the ZF is also very helpful. I got mine off of ebay. Pantera specialist like Hall and others sell them too.

Working on the ZF, if you do it as outlined in the manual, does take some specialized tools. A puller for the carrier bearings is one. In order to get the diff out of the case, you either have to pull the inner races of the carrier bearings off the diff (not much room hence a special puller), or take the limited slip part of the diff apart while still in the case.
I spent a week or so of evenings making a handfull of pullers and mandrels to make the job easier. If you get the factory book, it shows some pictures of the various tools so you have an idea what to make or use.

Adding a few holes in the inner case for gravity oil flow, drilling a new oil level hole and a drain hole, milling the inside webbing of the case for ring gear clearance, moving the vent, etc need to be done. There are oil holes in the side plates that collect and route oil to the carrier bearings. Since the sideplates will be "upside down", I added those same type holes opposite the existing ones. While it's apart, install safety wire on the ring gear bolts
You can purchase these with the holes already drilled in the heads.

The shift linkage didn't need to be changed for the ERA. It ends up on the right side of the transaxle.

If you can successfully work on other types of transaxles, you should be able to work on the ZF.

As an observation, I purchased gaskets from a third party seller as opposed to using RBT. All of the gaskets were marginally too small, like they were cut wet and shrank up. I've purchased all part from RBT since then. Lloyd is very helpful when answering questions and ships parts quickly.

I have just a few pictures on the net HERE

Ron McCall

Wouldn't the shift pattern be backwards if you flipped the trans.
btw:the LS unit comes apart very easily inside the case.and you do not have to press off the bearings to remove it ! I have personally had 5 ZFs apart for resealing or ring gear safety wiring..

Ross Nicol

GT40s Supporter
Looks like Dave and I responded to your post at almost the same time there John how's that for service? Ron the shift pattern will remain the same although I believe you are correct with being able to disassemble the LSD to remove the Crown wheel/LSD unit and boy you would be an expert after 5 of them.I have safety wired my crown wheel bolts as any ZF owner should.Note that one too John.I still reckon John should replace the carrier bearings when he flips the crown wheel, as they are cheap which can't be said for that one behind the pinion.I've only stripped 2 of them so far.

Ross Nicol

GT40s Supporter
Should have read my post it was a bit disjointed, the problem of posting while working.What I meant was I have stripped 2 ZF's so far and rebuilt only the M1.If you do get the opportunity to inspect the Pantera box before purchase John you would want to inspect the crown wheel and pinion condition(easy remove cover plate)and also inspect condition of gears,dog teeth and synchros.To access the gears you have to split the box by removing about a thousand nuts from the rear cover (ok not a thousand but it feels like it).You don't have to remove the nuts which hold the rear cover but it's hard to tell which ones are which.Check the drain plug magnet for iron particles.Large pieces would not be good.
In summary Pantera ZF 1/No modification required to shifter
2/Crown wheel flip required
3/oil drain holes to be drilled
4/New oil level & drain hole
5/mill webbing for crown wheel
6/add oil holes to carrier plates
7/ move vent
8/ lock wire crown wheel bolts
9/ Replace carrier bearings
10/ Fit new oil seals and gaskets
11/ Check if ERA bell housing will fit 427
Of course I probably have left things out but most of it is there and relatively easy to do.
Thanks guys, most helpful.

I have located a place in the UK who were recommended by Lloyd in a thread on the pantera forum.
They are only 45 minutes from me, so I have a fall-back plan if I get stuck. I've also been told of another guy who rebuilds ZFs.
I have not called either of them yet, but will do so to see how much they would charge to rebuild the box, or just to flip the diff.

I mailed Lloyd to ask whether he thought the M1 CV joints are stronger than the pantera spiders.
I'm feeling less inclined to change the pantera ones for the sake of it now, especially if the Pantera guys are putting big bhps through theirs wit no problems.
I also found out via another thread that RBT sells rear covers with ports for connecting an external cooler, so have asked the price of these. So far no response though.

My biggest two concerns are (1) whether I can get a bellhousing to fit the 427 this way up (I'm sure someone must do one, else I'll get one re-drilled), and (2) how long it would last...
I'm wondering how they normally fail - total loss like casing split / shafts bent, just some dogs/teeth lost off a gear, or whether they get noisy(er) first to give some warning.
Anyone care to comment ??

You know, I must be thinking about these damn things too much. I was even dreaming about them last night /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/smile.gif


Ross Nicol

GT40s Supporter
John you sound like your at brain overload.Just go for it now as you have done about as much research as you can do without the reality of actually having a ZF.You'll still have little hurdles when you work on the transaxle but you can't take the theory much further.You've gone about this exactly the correct way in my opinion and concentrated on the most important part of the drivetrain.Good luck with the bellhousing.

Ron McCall

I spoke with Dennis Quella from Pantera Performance (he has personally built over 200 ZFs)He says that he had Kennedy Engeneered Products http://www.kennedyeng.com/ make him a FE bell for a ZF for a customer.He said that he thinks they still have the mold.I would give them a call.
You shouldn't have any problems with the power.The engine in my Pantera makes 660hp and 510 tq. I have Spicer replacement halfshafts and everything is great.My Pantera weighs about 800# more than a GT40 and I'm not exactly easy on it if you know what I mean /ubbthreads/images/graemlins/wink.gif.
RBT told me three quarts. My RBT flipped new ZF does not have provisions to know when the box is full (no site glass or hole at the right height). Is this normal?
I am thinking 2 1/2 quarts. The ERA manual explains where to locate the sight plug for a flipped box.
Thanks again guys.

Ross, I'll most likely go for it now. I'm terrible for spending ages planning & researching to make sure I do the right thing. I bl00dy hate wishimg I'd done things different in hindsight, especialyy when the wife says something like 'told ya so - waste of money that was' /ubbthreads/images/graemlins/tongue.gif

Ron, your post has put my mind at ease. I'm aiming for similar figures. I've mailed kennedy engineering about the bellhousing, thanks.

Incidentally, do you lot think it is worth crack-checking all the bits ?
The guy at the specialists said they do this as a matter of course on rebuilds.
Just wondered if it was really necessary.

Another interesting snippet - He also said these things generally only go wrong by destroying the crownwheel/pinion, which is partly due to a weak case design allowing it to spead a little and giving too much play in the gears when under load.


Lynn Larsen

Lynn Larsen

This sounds like a likely failure mode and this is true of any of the transaxles when you load them up with massive amounts of torque. I was reading recently where a guy in Canada, who builds lambos, is experimenting with beefing up the cast iron section wall in the Audi with an additional steel plate for this very reason. He machines off a little of the rear case to make up for the increased width in the intermediate bulk head. He had grown tired of pushing the pinion gear through the wall and everything else out the back of the transaxle!

In terms of fill level, I would assume that the critical bit in the ZF, as in the Porsches, is to have enough oil to get proper oiling of the diff. The crown and other gears will sling oil up onto everything else with much less than is required to get the diff wet (I have no clue how much is needed to do this.) I would also assume that a cooler alone will help with gear longevity, but that a sprayer onto the ring and pinion (at least) will add to the gear boxes reliability.

Hi Patrick. Do you (or anyone else) have a photo of the fill "site" hole location on the right side? The downloadable ERA manual does not have pictures and just talks about size, etc. I assume drilling and tapping this is not advisable without disassembly of the case.