Are Ferrari differential internals common to anything else?

The end play is from gear wear, but like I initially posted, the diff that's in my car had the least wear of the 5 diffs I've seen, but still had .02" end float on the "looser" side.

The diff in these pics is not out of my car. It is from a spare gearbox I picked up but the excessive wear is what I've seen on most of the diff's I've tore down only on the driver's side though.

The wear on the shafts is what I've witnessed on every diff I've messed with . .. even my golf cart for which I designed and manufactured a limited slip diff instead of just welding the spiders gears . All of the driving load is translated thru these shafts.

From just basic machine design principles, allowing the output shaft to rock around on the spider gears has just got to be horrendous for wear. Gears are ground to some shape usually within .0005" and just seems crazy to let the contact patch move around like that. Might as well make the teeth with a friggin' grinder .

I don't want to try and put a 348 diff in a 308. If you think 308 parts are pricey you should call for some 348 parts. I also have a feeling the 348 diff is basically the same as the 308 diff . . . looks that way from the pic's Ernie posted and it has no static breakaway ... I'd like to hear why this is a good thing 'cause the 355 has static breakaway again (I'm told). I'd sooner buy an easily available diff from something else and modify it. On another forum someone mentioned an Audi diff might fit with pretty minimal mod's.


cheers

 

I'm not having problems with output shaft bearings. These shafts are not supported in anyway by any bearings. They are "captured" inside the carrier which is supported by the bearings.

 

Ask the factory for a spec? ... hmmmmm ... Verrel gave us that contact for ZF and I'm going to email the guy the info ... maybe he can come up with a value. If it is real similar to the G50 diff I'm pretty confident that the guys set up the race cars with these gearboxes will have a number that they look for. One guy told me .005" is "too tight".

 

Interesting . .. these race guys do not see gear wear like what I've seen. They think it's all about the crap gear lube I was running.

"Carbon" type discs can literally wear out in a single track session. Brass discs last somewhat longer."


Hee hee . .. that's what I call running hard .

 

yeah but in case you haven't noticed I don't do what everyone else does just because there was a friggin' poll on it mate.


I change the **** every 3 months so I didn't think it mattered . . I don't mind admitting that.


thanks for all the positive input about diff wear ... like I said... every diff I've pulled apart (3 from gearboxes I never owned) had massive wear in the diff . .. but you know all this already don't you 'cause you do it for a living?

can you tell me anything useful? . . I like how you piped in after someone else gave me the advice ... keep up the good work mate.

cheers

 

Once again I didn't realize all this was such common info in the Ferrari community about diff's and gearboxes ... have you actually taken one apart? This didn't start off as a thread about oil did it? Do you see no wear on these components that use whatever oil you reccomend? I'd really like to know what you have personally seen and how hard the gearboxes/diff's you've rebuilt get run.

 

Just for the record the G50 has different output shafts which could be made out of tougher material.

I guess now I would just like to hear from someone that has taken apart a 308 diff that has some miles on it and has seen minimal wear on these components. Even if there not track or hard miles I just want to hear that people have taken this piece apart and seen minimal wear. The end play everyone sees leads me to think that all the 308 diff's wear faster. They added the oil pump later which might keep the oil cooler. The diff could be getting really hot which I understand how the better oils will help.


Seemed like the problem people were discussing in the "oil" thread was shifting from 1st to 2nd when the engine's cold when going for ice cream ... I guess I need to read those 12 page threads where a bunch of people randomly chime in about "what they run" and take them more seriously if I really want to understand machinery eh?

 

Aaaaaaah . .. thank you Paul . . see you did exactly what I did the first "few" times in there. The fact I had a piece of gear tooth seperate on my latest assembly is why I'm getting serious about this 'cause it could've really hurt the box.

I thought about bushing the bore (the carrier bore I think you're referring to) but there's really not a ton of clearance in there to begin with. It's a pretty short area of support. The spider gears are what support the inboard side kind of like how the pilot bearing supports the input shaft for the clutch.

 

I got my new box of parts on Friday and will put one of the diff's together with 'em and see how much end float there is.

The guy that piped in on the other forum told me .005" is too tight for end play.

 

right on cheers!

All new inners I just measured .016" on driver's side and .012" on passenger. This diff is out of a spare gearbox I bought and had suffered the busted tab on the shim washer failure so might of eaten into the housing a few thou. The center "pack" of gears could almost float a few thou between the belleville spring load so could be some hysteresis (luv that word ).

Clutch wear doesn't effect the end float.

I was just looking at the oil level and it is WAY below the diff. I can see how oil can get flung around for the gear teeth but I think on the G50 gearbox the oil level is way higher relative to diff centerline. It is on the 915 gearbox which is in my 911.

 

Here's some pics of first gear after running the "soup" gearbox oil for 350 hrs of very very fun driving . Might of lost a bit of resolution in the upload but in high res the wear on the teeth and on ball bearings makes my palms sweat .... in a good way . Machinery just doesn't look any more beautiful than this. I haven't started drinking yet either .

cheers
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and final drive ... aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaah . I needed that.



Both pics are on the wear side of the teeth.
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Just made a very interesting observation. The oil level on my 915 gearbox is within 1" of diff centerline. The oil level on the 308 box is about 4" below. The inside of the diff is only lubricated by splash vs. being in a bath on the P cars. Based on this I'm not so sure the high end oil is the primary reason the P guys don't see any wear. Being in an oil bath is night and day for lubrication and cooling.

Looks like if I get serious about racing I'll be hooking up a pump to cool the diff . There's really not a ton of passages for the oil to just make it's way in there either.

Anyone know how the oil is circulated on the later gearboxes that have the integrated pump? I have a WSM but I don't think it's that clear in there.

Cheers,

Sean

 

Okay pulled the diff out of the car today.

Observed this as I was pulling her down and thought "ouch".
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Opened up the diff and saw these chunks on the driver's side pack. No sign of trauma to the passenger side. Also the massive end float dissappeared when I tq'd on the flange to remove it.

No sign of major trauma on the gears and I found one big chunk on the magnet . .. hmmmm
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So it looks like the tab on the thrust washer on the driver's side busted off, as I've seen on all the diff's I've pulled apart except for this one when I tore it down 350 hrs ago.

What I think happened is the chunk got stuck in the pack for a while and basically locked the diff up. The entire pack was shoved over to the passenger side when I was pulling the diff out of the car which is why it had so much end float on the one side. When I tq'd on the flange mouting bolt in unbound the pack and let it go back to the middle so there was no longer a bunch of end float.

This probably explains the excessive wear to me also. The tab acts like it's own little ramp shoving the teeth of the output shaft into the spider gears. Eventually it breaks off and just makes everything bind for a while.

The tab is about .07" tall and it seems like the center pack can float in the diff under load and make it quite easy for the tab to try and come out of it's hole and/or start binding up on the corner of it's own radius/ramp.
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Plenty of assembly lube still in there so I don't think it got real hot.
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Driver's side output shaft. Too bad I don't have pics when I put it together a few years ago. Didn't have this camera then.
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The thrust washer is steel which surprised me. Guess I can make my own out of steel and machine a thru hole for a dowel pin. There's a hole in the housing that the tab goes into that's pretty deep.

 

FYI this is 308 diff but pretty much the same I think minus the belleville spring. Also only took me 2 hrs to get it out of the case and another 1/2 hr to get it out of the car ... not a lot of room between the trunk and the rear head .