Factory LSD installation into 915 - stub axle issue
 

I have a '74 915 which was rebuilt, all stock, now looking to install factory ZF LSD from '86 Carrera. What's the issue with fine-spline vs coarse-spline stub axles?

i.e. what parts are needed and are they readily available? Do the entire axles and CVs need to be changed? Anyone who's done, please share your experience.

This can be a bit of a bugger, depending on how deep you want to go. If your current CVs are still stock, then your '74 has the 108mm flanges w/2 pins & 4 bolts. Also, as you noticed, the output flanges are coarse splined. The path of least resistance, if you can find them, is to use 108mm fine splined flanges w/the LSD. This is basically the same flange you have now, but with fine splines instead of coarse. They are not easy to track down though. I ended up using a set of G50 output flanges that I machined to fit (the axle stub is too long to fit in a 915 diff.) because I was not able to locate a set of the later, 108mm fine splined flanges (which I think came on the turbos??). I did this all in an effort to retain the bigger 108mm flanges w/the bigger CV bolts.

A second alternative would be to swap all your CVs, axles, output flanges and stub axles over to the 100mm 6-bolt variety. These are pretty common and I bet it'd be similar in $$'s to the 108mm fine splined flanges... believe it or not.

A third alternative would be to frankinstein it and use 100mm, fine splined output flanges & CVs on the inboard side (next to the transmission) and keep your 108mm CVs & stub axles out at the wheels. This would require a mix-matched axle CV combo...

Clear as mud?

There is a thread that I started or participated in with Grady Clay where we discussed some of the pros & cons... I'll see if I can find a link...

Tom

Here's the thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/591069-cv-joint-axle-half-shaft-compatibility.html

Yikes! This is opening a can of worms! Thanks for the link.
If I swap the entire axles/CVs etc, does it impact the hub?

It's possible that there is a simpler solution. I tend to do things the hard, complicated way at least once! I don't know for certain about the hub and if it's compatible with all the various stub axle and CV options. I looked in PET and there seem to be similar part numbers between years/series for the rear hub, but I don't know from personal experience. Maybe someone else will chime in...

Tom

I just went through this exact process where Jones Autowerks rebuilt and installed an lsd my 1984 915 for installation in my 1974. Bob knows someone who makes the 108mm fine splined and we used them so the tranny bolted right up to my existing axles. I suggest you give him a call.

Mark,
Thanks for the tip. Got a number? How much was it for rebuild and install?
I have to make a decision to buy the LSD once I know it can be done without selling a kidney.

Actually if it is the LSD I am thinking of, Bob called me up and had me retrofit course spline side gears into what was originally a fine spline LSD.

Regards,

Matt Monson
Guard Transmission llc

Matt, that may be exactly the solution. Bob and I discussed several solutions and I thought he landed on a fabricated output flange. I'll ask him when I see him on Monday.

Very interested in the answer to this as it seems easiest way to solve.

I used to have a PDF showing the actual parts but the link is no longer active. This company offers their own fine spline, 108mm drive flanges.

http://www.albinsgear.com.au/

Jäger,
Just be aware that if I'm correct its not an option I can offer to you. The LSD in question was one of mine and not an original ZF unit. My gears won't mesh with a factory unit.

The 100mm fine spline output flange is the simple way to go IMO. The later SC and 84-85 Carrera used these flanges. MUCH easier to track down a pair of these than it is to find those fine spline 108mm flanges used on the 930 and '86 Carrera. As Tom said, you can use a later set of G50 flanges from 87-98 and have them machined. I know Rothsport does this modification.

If one wants to go the G50 flange route, just be careful with the 964 output flanges! The G50 964 (2WD Carrera 2 = G50.03, .04, .05) flanges are same part number as 87-89 (G50.00/01/02/50) flange 950.332.209.01 But the G64 trans (4WD Carrera 4 G64.00/01/02) are a different number and differ from left to right on the trans as well. Stay away from the Tiptronic too because those are a completely different p/n that starts with 943! However, the 993 C2 (G50.20/21) and C4 (G64.20/21) both use the desired flange 950.332.209.01

Anyhow........... I think the 100mm CV axle is not as bad as it's been made out to be. Yes the M8 mounting screws are a problem if they come loose. It does happen and when it does it can cause a lot of damage. But as long as they're checked occasionally (especially if car is tracked, it should be part of your pre-event tech inspection w/out question) or locked with some Schnoor, Nord-Lock or Stage 8 lock washer setup atop the CV torque distribution washer "moon plates," VW P/N 87-5081-0, they are good for a long time. I've had the 100mm CV on my '79 racecar for a number of years (many more years than i've owned it) and also a 1970 GT class 911 (cstreit's former car) for a long time with no problems in terms of losing axle shafts to faulty tightening.

I'm of the opinion that the 100mm CV is plagued by its screw size and the CV itself has good torque and angularity capacity. The six M8 screws are torqued to only 30 ft-lbs = 180 ft-lbs of total clamping torque. 30 ft-lbs isn't all that tight. Whereas the 108mm CV has 6 M10 screws torqued to 60 ft-lbs ea. = 360 ft-lbs of total clamping. So the 108mm CV certainly is secured much better than the 100mm CV. And Porsche had to have good reason for providing the 108mm CV on the 930 (not to mention the early cars w/out a lot of power) and on the 86-up cars. So maybe the 100mm CV was a VW-based cost cutting approach? Either way, its proven to be sufficient in my limited experience.

I have a personal interest in this because i've researched the coarse 100mm output flange (what i've currently got, unfortunately) vs. 108mm coarse conversion on my racecar. I found a coarse set of 108mm output flanges which appear to have the same shoulder, shaft, spline & end recess dimensions as my 100mm coarse flanges. It's just that they have four M10 bolts and two roll pins. I suspect they may be from a Sportomatic trans?

Since mine's a dedicated racecar I like the idea upgrading to the stronger M10 bolts (i've yet to see a M10 screw be loose during a nut & bolt check) and larger CV having more angularity. Plus one can improve on the factory axles by getting floating axle shafts. One of the downsides to factory axles is their positive stop/shoulder that puts a lot of stress on the inner race.

Floating axles & a bulletproof 930 CV would be ideal for a racecar IMO. Offroad VWs are big fans of the 930 CV. But they're also heavier, which is counterproductive on a racecar. Of course there are finned/lightened 930 CVs available. All it takes is moar money? :rolleyes:

Sorry for the rant. Just adding more info to the can of worms Jager is opening! :D

Thanks Matt, if I can't figure this out, I will raid the kids college fund and buy one of your nice GT LSDs which I assume is more plug and play with the correct coarse splines for my '74.

Thanks Kevin. Wow, all these years of tinkering with 911s and I thought the axles and LSDs were just interchangeable at least in the '74-'86 range. I helped with the rebuild of my 915 but haven't seen the guts of a LSD. Of course, I have the 4 M10 bolts with the 2 locating pins.
Now to pick your brain since you've let the worms out of the can.
1. I have a lead on SC axles with the 6 Allen bolts (M8?) and it includes the outside stub axles to the hubs. Are there any issues with the outside splines mating to the hub?

>The 100mm fine spline output flange is the simple way to go IMO. The >later SC and 84-85 Carrera used these flanges. MUCH easier to track down a >pair of these than it is to find those fine spline 108mm flanges used on the 930 >and '86 Carrera. As Tom said, you can use a later set of G50 flanges from >87-98 and have them machined. I know Rothsport does this modification.

2. I'm still not sure there is a fine spline stub axle readily available w/o mods which fits my '74 915 7:31 R&P and mates up with the '86 LSD I'm looking to install. Are you saying the stock stub axles from an SC (100mm fine spline) will work? If so, and if these are more readily available, I will take the plunge and buy the axles and LSD and then search for these, rather than the machining option.

blackbird here have the axles you want

Yes, that's my source, I still need to ensure the SC outside stub axles will fit the splines in the wheel hub for a '74. I'm learning not to trust that everything is interchangeable.

Tom,
I'm desperate to try anything to make this work but I'd rather not go down the machining path. A buddy of mine located a pair of 6 bolt fine-spline stub axles in his parts bin so I hope they're the right ones. I located a set of SC axles end-to-end to the outside wheel stubs. What I don't know is if the wheel stub splines fit the hubs on a '74 so I'm entertaining your hybrid frankenstein option 3 as an alternative. I would have 6 bolt flange on inside and 4 bolt flange on the outside. So the only parts needed in this scenario are the inner CVs (and the fine spline stub axles for the LSD)? My car has a Carrera engine and 993TT brakes and even a Mazda cooler so what's some more Frankenstein bits.

Steve, the hubs appear to be the same 74-89:

Pelican Parts - Product Information: 911-331-065-33-M260

I'm in VA right now at my brothers 50th birthday party, but I'll let you know what Bob says on Monday.

Hi Steve. I'm looking forward to your feedback after you get the LSD sorted. I found an alarming amount of noise and vibration at first. I also have wevo blue mounts which adds to it. I've gotten used to it and think its obvious in my car as I have no sound deadening anywhere. Also I am interested to hear your thoughts on the performance of the LSD. For me (I have a US 915 from an 83 with factory LSD). I'm not completely sure my track times are better but I do feel way more stability and safety in braking and trail braking turn in. And on the autox course ,where I have been known to go, an incredible improvement in off throttle stability and high speed decreasing radius entry. So overall I love it but not convinced my track times are a lot better. Maybe see you at pocono and we can compare notes.
Rick

Mark,
Thanks for the info. Checked part# also and it appears the hubs are the same so hopefully I can swap axles without worrying about machining.

Hi Rick,
I find my car wiggles the rear end under hard braking from 140 at Pocono and I can't get on the gas early in tight turns so hoping the LSD helps with both of those issues. Did you need to rebuild your LSD before installation? Gary Fairbanks is telling me they are pretty hardy. Definitely looking forward to chasing you again as our old cars are in the minority among the herd of GT3s. I may even make it out to an autox this year to give you some competition but I'm rusty having been away from it since 1999.

I did not rebuild the LSD. It was tested and deemed not necessary during the Trans rebuild. Yes the braking stability and slow speed wheel spin much improved. Places like entering the octopus at Thunderbolt you can really feel the diff locking up and keeping everything quiet. Who is setting it up for you?

I spoke to Gary Fairbanks on Friday, I'm planning to have him do it as he's the tranny guru on the East Coast. BTW, having a problem with finding 2nd gear in tight left hand turns (Pocono CCW, Devils' Elbow), are the Wevo mounts semi-solid? Alex also recommended them. I have no sound deadening either, but who cares when you're on track.

Steve,

Can you measure your axle length? I can measure my 915 axles to get you in the same ballpark. Tom's great thread link (I have that saved in my list of links about axles/CVs) did a nice job of getting Tom Butler to put together those part numbers and dimensions!



The outer stub axles are indeed the same from 74-85. The 6 bolt stub axles are P/N 923.332.232.01 and this same stub part number shows up in the '85 diagram. The complete CV axle is also the same from 74-85, if the CV is the small 100mm joint with six M8 bolts. Part number 923.332.033.02

Note that the outer hub (the female splined hub containing the lug studs) is the same from 74-89 for the narrowbody/non-turbo body cars. So your hubs are splined just fine and of a proper "depth" to receive whatever axle stubs you acquire.

As far as the trans output flanges, that's a challenge to figure out. I would see if someone can compare a set of their fine spline flanges with the dimensions of yours. You need to measure the shoulder, the shaft length, spline length and if there is a recess at the end of the shaft. There's a good topic on the 914world forum that talks about the output flanges and what to look out for.

914World.com - The fastest growing online 914 community!

I know their issue on the 914 forum is the fitment in the 901 trans. But its still a good comparison to see how the flanges can seem the same but really are not.

KTL,
Just be aware that the 914 differential is not a 901 differential. It is a 911/914 differential which happens to be the same as the '72-74 915 differential for 7:31 cars.

Haven't clicked over there so don't know if they are trying to go earlier or later on their installs but each has its own challenges. This is why we make 5 different LSDs for '64-86.

I hear what you're saying Matt. Was just using the 914world topic as a reference point to demonstrate the importance of correct output flanges.

When going simply by part numbers, the CV axles and outboard trailing arm stub axles are very easy to define. But the trans output flanges varied over the years depending on the diff, so I didn't want to state any sort of definitive choice from a certain year to seek out. Seems best approach is to measure what Steve's got in hand with his fine spline '74 108mm flanges and then see what later 100mm flanges match up with that?

I only have coarse spline flanges on hand, one set of '79 SC 100mm CV size, one set of 108mm CV size (four M10 holes, two roll pin holes) of unknown origin that matches the dimensions of my '79 set. My trans setup is iffy for comparison purposes since my FrankenPorsche racecar chassis is a '79 SC but the trans is an '84 915. A 915 with an unknown make of performance diff that uses the coarse splines.

http://forums.pelicanparts.com/porsche-911-technical-forum/750448-guard-diff-omg.html#post7455472

Steve, just picked up my 915 with the new Guard LSD and Matt was exactly right. He switched the gears in the LSD to match the flanges in my 74 (early type with 4 bolts and 2 studs). Good luck!

Thanks Kevin and Mark for the follow up. I can't really measure anything right now, car is put away in winter storage. Just gathering parts for spring project.
A buddy with '78 SC had the opposite issue installing a Quaife with coarse splines so he has his fine spline stub axles available. I figure I'll pick up 6-bolt SC axles and in theory, this should work.
Thanks all for the input, I will report back with my findings.

After speaking with Gary Fairbanks, he put me in touch with Tom Conway at CarQuip. After a long chat with Tom who seems like a really nice guy as he patiently explained ramp-up % to me, I'm now leaning to a new KAAZ LSD with 60% ramp. It has more clutch plates than the factory ZF (i.e. less prone to wear), would be brand-new, bolt-in to my coarse-spline stub axles without monkeying around with changing stub axles, CVs, and hub axles.
I have not heard much about this option. At $1500, it's a better deal than rebuilding an unknown used LSD. There is a nice LSD parts explosion here showing 6 clutch plates per side, for a total of 12 plates:
KAAZ USA | Technical Intro
I assume the people on this thread have looked at all the options, what's your opinion of KAAZ? Any anecdotal or personal experience welcomed!

Do a search on the forums for Kaaz and form your own opinion. I gather the "made in Japan" quality they tout is still not entirely accurate today. This is based on comments from other forum participants that actually know the specifics around manfacturing a quality LSD.

KAAZ is manufactured in Japan. I have one installed in my G50 and it works fantastic. There's an overabundance of BS posted about LSD's on this BB. Call Ray at KAAZ USA. He is the president of KAAZ USA, and will explain the history of the company and his background in performance motorsport as both a race car driver and author.

KAAZ is a Japanese agricultural machinery manufacturer of large tractor-type bush hog mowers down to small engine grass trimmers. The disc clutch technology used in the wide variety of KAAZ LSD models is similar to that of the disc type clutch systems found in their agricultural mowing machinery. You would be a wise man to listen to what Ray has to say about KAAZ JAPAN and KAAZ USA before you make a decision. I believe he told me he moved to California from Japan to establish KAAZ USA in 1995. Very interesting fellow with no need to BS anyone.

Thanks for the feedback, I read conflicting reports about made in China vs made in Japan and after much research was all set to go with OS Giken but the KAAZ price is very attractive and Car-quip recommends them also. Right now, it's either OS Giken or KAAZ and happy to hear a positive report about KAAZ. How long have you had it installed and how is the car used? I need to know if it will stand up to severe track use. A local highly-regarded race shop runs Giken in their personal race cars, 3 race seasons so far without a rebuild needed.

Installed in January 2012 by a Porsche dealer with 3.2 liter engine and G50 removed. I drive HPDE's at mid Ohio and Putnam Park, but I've done dozens of days before and after the KAAZ install. I, like you, considered ZF, Guard and OS Giken, and many others. I was willing to pay up for the Guard or Giken. But I spoke to a well regarded "Porsche Transaxle Specialist" (BMC&G) who preferred the Porsche Motorsport factory LSD over Guard or Giken. So everyone has their own opinion and bias. You have to talk to everyone who really knows LSD's. Don't limit yourself to non-experts like myself or many others posting on these motorsport BB's.

I made up my mind after a number of long and informative conversations with Ray, KAAZ USA president. Other 911 drivers I've recommended the KAAZ brand to have also contacted Ray with questions and set-up advise, and are now satisfied with their KAAZ installation. I bought my SuperQ direct from KAAZ. He set it up so that lockup is limited to 80% on acceleration, and up to 100% on deceleration. This set-up configuration is "reversed" and unique to rear-engine 911's because of the 40/60 weight distribution.

As with any LSD out there, the amount of wear and failure rate depends primarily on how well it matches horsepower, torque and the demand put on it by driver style. Some guys overdrive their cars to a point where they tear up the best and most expensive machinery available. As far as I know Guard makes a very strong chrome moly cased LSD unit. But a 200 hp 1987 Carrera will never break the ring gear flange off the face of my KAAZ SuperQ.

As for performance; it's the most impactful handling modification I've made to date. Your 911 will not be nearly as prone to oversteering as before the installation. Hard braking induced rear axle shimmy is gone. You will enjoy learning a new corner entry and exit line with more understeer than before the install.

And don't listen to me, just call Ray.

Thanks for the detailed feedback, that is exactly the problem I'm trying to solve, the high speed 'tail wagging the dog' and inability to trail-brake late into corners then get back on gas. I have a stock '85 3.2l with just bolt-on stuff, making estimated 220ish HP so don't expect too much load on R&P. I do need to update my early mag case side-cover to later model 915 alum side cover.
Yes, I've talked to 4 different transmission specialists and I agree, each has his own bias based on his personal experience but want to get good value for my buck so KAAZ is still on my short-list based on your feedback. I will PM you as I prefer hearing about actual user experience more than the marketing pitch from anyone selling their product.

http://forums.pelicanparts.com/porsche-autocross-track-racing/583951-my-boxster-racing-car-project-7.html

The Gikens are doing the same thing. Search 6speed and RL and you will find examples on a number of makes and models. RL has a thread called "gotta get a Giken".

Thanks Matt, that's very nice of you, restraining from promoting Guard and even mentioning the competition.

In the interest of disclosure many people don't know that until about 90 days ago Brian was a PMNA employee/subcontractor. His opinion is almost as biased as mine. He was paid to promote their brand.

I'm sorry if I have offended you and you feel like I am trying to sell you something. Review my posts on this board and you will see that's not my intended approach to anything. I'll recuse myself from your thread and let you get the balance of your feedback from your peers.

I was giving you a compliment, no offense taken at all, I genuinely appreciate your input, not sure if my comment was taken the wrong way. I would prefer to hear all sides of the ongoing discussion about LSDs.