anyone recognize these LSD internals from "other" car?
 

Hi all,

I'm new to this forum. I have a '73 911s for a track car and 2005 Boxster for the wife.

In my "spare time" I mod the heck out of Ferrari 308's. I have found the internals of the differential seem to wear pretty fast. I've posted a pic of what the insides look like. A guy that works on these for a living told me some of the internals are the same as some Porsche diff's. Didn't want to share which though .. sigh. I was able to buy all new internals from my typical parts guy at "not the end of the world" pricing which also led me to believe these are common parts to another manufacturer. Also FWIW this is a ZF diff with ZF part numbers on the gears. I spoke to a ZF rep who was willing to research it for me but I know how busy those guys can be.


Anyone recognize these parts?

Thanks all and Cheers,

Seanhttp://forums.pelicanparts.com/uploa...1223734047.jpg

couple pics . . one of the EFI conversion I do for the 2V injected cars . . another one of the independent throttle body conversion I'm working on. Thinking about building a thunder motor for my 911 and putting these on :).

cheershttp://forums.pelicanparts.com/uploa...1223734364.jpg
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Those appear to be the same as G50 ZF parts, but there's no way to know for certain without physically comparing them. (Taking the plates out of the bag so that we can see them would certainly help.) Our company carries all of these pieces, although we've updated/improved a number of them.

Paul

Thanks. I'll take some more pics. The output shafts/sun gears, spider gears & shafts seem to wear really fast.

Sean

Well then, it's almost certain that you've got a lubrication quality issue.

Yeah I'm going to change to Redline and the later gearboxes (1983) have an oil pump on them to boot.

This particular diff will be first one I've built with all new internals. I have a few spare gearboxes that I've been rotating parts out of over the last few years and I was always really concerned about the amount of end float on the output shafts. You know what kind of answer I get from Ferrari "tech" gurus when I ask how much end float should be in these shafts? ... "there's a lot in there" so I didn't worry about it until I just recently actually broke something in there.

No that I've reached failure I've decided asking for advice from the typical Ferrari guys is a waste of time ... that's why I'm here. :)

Every 308 diff I've played with had at least .015-.02 end float on the output shaft with used parts. I'm hoping when I put it together with new parts it should be down around .005". There's a thrust washer in there that could compensate for worn components if internals were unavailable or if the new components still seemed to show a lot of end float. This thrust washer was not available in various thickness from my parts guy but I can just make something if necessary. The bottom line is I think the excessive end float accelerated my failure 'cause I do run this car in the red ... the typical F car owners (u know 'em ;)) seem to be able to live with this part wobbling all over which is just horrible for the gear teeth in there.

How many hrs does a G50 diff last on the track? A season or more?

Thanks,

Sean

Hmm...an idea:

why not pull out a Torsen diff out the rear of Audi V8 <91' and mod it so it fits in your crown wheel? being purely mechanical device, you won't need to pull it out every now and then and rebuild. With little luck, it might fit straight in (being a ZF part and all).

I got myself complete Audi V8 rear differential for 100 bucks. It's going in the back on my Audi S4 daily driver (don't like the open one). Actually, Ill try to put one in the front as well (middle diff on S4 is already Torsen).

Well, your output shafts aren't Porsche style (although the gear form portion probably is, and the shafts could be pretty easily duplicated), but the spiders, cross shafts, thrust washers, and 90% likely the plates should all be interchangeable with one of the earlier Porsche ZFs.

While the end float shouldn't be ridiculously high, reducing it down to .005" isn't going to help the LSD "work" any better, and sounds to be entirely too small of a clearance. Those spiders and side gears are meant to be a bit sloppy.

You're going to "upgrade" to Redline? Let me give you a lubrication tip: Lubrication Engineers #9920

Interesting thought. Can you tell me more about this diff and the advantages of if over a typical LSD with ramps? Something Ferrari did on the 348's which is almost an identical diff to the 308 is they removed the belleville spring that preloads the clutch pack so there is no static breakaway. The loading of the clutch packs is facilitated thru the ramp angles that the spider shafts are sitting in. Does this make any sense from a tracking perspective? The then later model Ferrari (355) has static breakaway again as far as I know.

Thanks for the input,

Sean

Thanks for the tips there. What would you consider acceptable end float? Reducing it was just to try and get more gear life out of it but I'm encouraged that this diff is used in Porsche's on the track. But do they need to be tore down pretty frequently under track conditions? This is pretty much the duty cycle that this one is seeing. I don't take this car out for ice cream :).

cheers

Another thought regarding the output shafts. Ferraris use the 930 CV joints. Maybe there's a chance I can use the Porsche output shaft and flange. The length and diameter where it goes thru the diff case would be concern though. Real bummer that parts not that same 'cause that's the one I see wear on every time a take even a street car setup apart. And the driver's side seems to wear way more than passenger which is why I've made it this long not needing new ones. I was just using up the passenger side pieces from my inventory.

Thanks for the input,

Sean

Well it's the usual Torsen/Quaife vs. clutch diff question. There are tons of info in the Interweb on pro/cons of each design and how they work.

Basically Torsen differential uses worm gears to send torque to wheel that has most grip, unlike open diff which sends the torque to wheel that has least grip.
It does this in continuous manner and varies torque split depending on the grip. It's also a purely mechanical device and doesn't wear as fast as ordinary clutch diff. Actually, Porsche used it on some water-pumper 4-bangers (968?)

It's usually used as a central diff for pricey 4WD cars and sometimes used on the rear as well. Drawback is that it acts as open diff when braking.

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Thanks for the info. Yep I've seen threads discussing the pros & cons of each.

Any thoughts on how long the typical LSD should last with new guts and good lube under track conditions? ... any hr estimates from anyone.

The gears should not be wearing out, period. Of literally thousands of LSDs our company has sold, I've never seen a side gear or spider gear "worn out" (surface hardness compromised). This is why I say your issues are likely lubrication and/or uncontrolled heat build-up.

Friction discs are another matter. "Carbon" type discs can literally wear out in a single track session. Brass discs last somewhat longer. But nothing beats a high quality Motorsports-style friction disc ... original ZF, Porsche Motorsports, or GT-brand. You could easily do a season of hard racing on these, although some teams opt to change them out twice a season. As for "how many hours", you really need to start with the good stuff, and derive your own baseline data.

Again, the oil brand can make all the difference.

Thank you for the input. New parts, new gear oil and we'll see how long she lasts.

I'm sure all the stocker gearboxes I've pulled down were just running "mud" for lubrication and it's common to see rust inside form them sitting forever.

Probably should start a new thread on this but maybe you can give me the quick answer on this. On my 911 track car and until I had this problem on the 308 the CV's were pretty loose but I got the impression don't worry about replacing them unless they click. The inner CV's were seriously trashed. A ton of brinneling in 'em. So I have 2 questions:

1. do you replace CV joints when you feel some slop?

2. if so, do you think this could be acclerating this wear issue? like I said these stocker boxes that I see the wear on I honestly don't think have had a rough life other than crappy lube and maybe loose CV's?

Thanks, I really appreciate the hands on experience you guys have.

Sean

"Something Ferrari did on the 348's which is almost an identical diff to the 308 is they removed the belleville spring that preloads the clutch pack so there is no static breakaway. The loading of the clutch packs is facilitated thru the ramp angles that the spider shafts are sitting in. Does this make any sense from a tracking perspective? The then later model Ferrari (355) has static breakaway again as far as I know."

Well, that's the beauty of an LSD ... any combination of plates, Bellevilles, ramp angles, etc is possible. Teams experiment all the time with 4,6, or 8 friction discs; thick, thin, or zero Belleville washers, and a multitude of ramp angles.

Are the internals available with different ramp angles for the G50 or is that something I'd have to cut myself. That piece is hard as a rock.

Thanks,

Sean

So far as I know, the early square-tabbed pressure rings only come with 30* symmetrical ramp angles. You wouldn't want to try regrinding the ramps. Grinding away the case hardening leaves too soft of a material, and the shafts would then imbed themselves.

Just wanted to post a pic of the clutch pack just to see if you do think it's the same as the G50.

As a side thought where's the oil level sit on the G50? It's nowhere near diff centerline on the 308 box and the other gears and bearings look fantastic. Curious because this diff slop seems common in all the 308's, even the ice cream & q-tip contingent :). From memory seems like the level on my 915 gearbox is way up near centerline.



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Just looked and on my 915 the oil level is near centerline. On the 308 it's easily 4 inches below. That's not good eh? Do you still think it's just an oil brand problem? Now I want to find out exactly what the later gearboxes with the pump are lubing.


cheers