Ernie's diff....iculties

Okay suckers how about Friday? We'll do our usual breakfast deal in the morning.

 

The 348 diff looks identical to the 308 diff . .. can anyone confirm this?

Anyone got a 348 diff out right now? I have a 308 diff out and I wanted to compare the internal differences to the 348.

Seems weird to have such a small amount of static breakaway.

Also of note one of my 308 diff's chattered after rebuild with "regular" LSD gear oil and I added a tube of LSD additive and it went away . .. I change the oil regularly and no chattering without additional additive.

Sean

 

See post 105. I did remember it the way we spoke. It is the ramp and cup angles that make the difference. There is an interplay between static preload, cup and ramp angle that results in lock-up which is what you want. extra preload just makes for more drag in the system when you don't want it. So my vette has a higher preload than the 348 but the 348 can spin both wheels when I want it to lock up but has no preload. So the 348 system is what i'd rather have vs the vette system. i,e, on when I want if off when I don't

 

My 308 has a ton of static lock up . .. it seems like going from hardly any to a lot under cornering will create some interesting dynamics.

What about the 40-45# static breakaway number? Is this from some manual? It's interesting 'cause the internals look the same as the 308, but the ramp angles might be way different too.

 

The 348 ramp angles look shallower than the 308 meaning more load during accel and decel.

Now I've got to pull a 308 diff apart to compare . .. from memory they were 45/45 . . . I'm trying to get FBB's old 348 back on the road next week too and put the half shaft back in my track 308 . .. anyone in the neighborhood wanna come play with F cars ?

 

NEXT WEEK! You are insane. I owe an appology to you wife for selling you my car. Or perhaps she should thank me...A husband around only when she needs one.

 

lucky,

If I don't go racing next week and you are working on the 348 I could come by. I may be able to gather some stooges too like Ernie and Bruce maybe even Lou. Lou is drooling over your new 348 project and wishes he could play. I think really he is envious because even with the super charger he is under gunned vs the 348 on the track. But be warned if we all come down there will be lots of BS and very little work and then there's lunch! Escondido is too far away so if you got a bar be que we could save some time and bring down some meat. Over a beer you can tell us how you got the name "lucky" and I hope it involves a girl...

 

her boyfriend's stoked . .. especially with the boxster I bought her

 

Hopefully no paying customers are reading this . .. "all paying work officially on hold"


sounds good . . .you met lucky but I got plenty of stories so no worries there . .. um . .. college in Long Beach

 

Yeah...Long Beach.......hot girls,..married one ;-).

OK,.. lets do it.

Sean, you call the date. Rev up the BBQ.

FBB, organize the pv/south bay Fcar boys, ...bring MEAT !!

I've got the wine and beer covered..........

(or, we could actually focus on the task at hand, soft drinks and fast food.)

I'm in, either way.

-L

 

Hey all,

I just went thru this whole thread and no one noticed there was no spring in the 348 diff's . . am I missing something . . that is where the static preload comes from isn't it?

I also found it interesting the 355's seem to have static preload . . I have seen lots of wear on the 308 diffs . . maybe they wanted to try and extend life since the 348 has more power.

Cheers

 

exploded views of both for comparison . .. so will someone confirm there are no springs in the 348?
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I guess that's called "missing the trees 'cause the forest is in the way"

 

Nope no springs inside the diff.

 

so "next time" you have 'er apart maybe take some measurements and see if there's room for a 308 spring if you want more static breakaway .. . I'm thinking about taking the spring out of one of my 308 diffs . . . when I've got one apart I'll see if the ramp angles look similar.

thanks,

cheers,

Sean

 

I don't see how a spring would fit in there. The cross plates and friction plates are already touching once you have it all slapped together. I guess "maybe" you could replace the washer with the spring, MAYBE. But I would have to see what this spring actually looks like you are talking about. Besides, I'm not planning on taking this thing apart again.

 

don't worry about it if you're not planning on taking it apart . . . just wanted to make sure it was clear why there was such a diff (no pun intended) between the two diff's . . .thought guys were looking at this thread originally did it for a living but that doesn't mean they take this stuff apart and analyze it I guess.

cheers.

 

You can replace a washer with a belleville washer which is in essence a spring. But I don't think that is the answer. I'd try making another clutch plate and add it in if you want more lock...or you could get another diff and I could weld it for you and make a spool.

 

which is what is in the 308 diff's.
edit: meaning that is the answer if you want more static lockup . .. there were guys pulling 308 diffs apart during this I thought . .. maybe they didn't realize that other washer was in fact a spring and not just a spacer . .. you can't create consistent preload without some kind of spring . .. the preload that you guys saw from the stack (barely any) would instantly start decreasing when there's any wear 'cause there's no spring rate to keep pushing on the clutches.

 

totally wrong direction I think

 

No it's not really the wrong direction.

I would think that if you wanted it to lock up more you would have put in another cross plate and friction plate. Sure the spring would keep the plates pushed together, but it's the friction plates that do all the work. Once the torque induced force starts the spider gears pushing the posts up the ramps, in the cups, that is where the grip comes from, it doesn't come from the spring/washer. If you wanted better lock up what you would actually need to do is change the ramp angles in the cups, because then that would changed the rate at which the friction plates start to contact the cross plates. So adding more plates would be the way to go because you would have more surface area. I'm sure the spring would help a tiny bit from a dead stop, but its really the sun gear/spider gears that do all the work pressing the plates together.

 

Just to add to the confusion. I believe some may not understand what is being discussed. The 308 has a washer behind the clutch pack that is not really a washer, but is actually a cone shaped spring called a belville spring. Once the two sides of the carrier are clamped together, the belville places a load against the clutches. In both the 308 as well as the 348, two clutch plates are to either side of two clutch discs, with the 308 having the belville on the backside of the pack to provide initial force we call "preload".

In the discussion above as well as the parts drawing, the 348 appears not to have a belville spring, and so the clutch runs loose until torque is applied and has no such preload. I do not believe one would want to simply remove a clutch plate and replace it with a belville washer. Doing so would put all grip and wear at the extreme inner or outer edges of the clutch disc. I believe you would want to keep the two outer clutch plates with the lined clutch discs between them, and the belville to the outside of the clutch pack in all cases.

Someone said the 355 went back to a belville spring clutch. Anyone know why?

 

So what it the diameter of the belleville washer? If it's the same size as the washer then I guess you could swap the two. But I wouldn't tear apart the gear box just to change a washer. Though if you already have it apart......then I guess you could. That is if it will fit.

You guys can see a picture of the washer we are talking about on the first page. It's the one with a little indexing notch in it.

 

I'm not confused . .. the 308 has a ton of static breakaway with the same number of clutches because of the belleville spring which is about the same diameter as the clutches.

If you want to increase static breakaway you need a spring . .

I think the washer you're talking about is like 2" in diameter with a tang on it . . the 308's have these and the tangs break off in certain scenarios . . . doesn't seem to kill anything just starts wearing a surface in the diff that shouldn't be.

cheers

 

I used the wrong wording . . .I said "inscrease static breakaway" . .. I meant "if you want any static breakaway" . .. this was the first thing I noticed on FBB's car which worried me that the diff was broken . . . the explanation is there is no spring like the 308 diff's have to correctly preload the assembly . .. shimming something to create preload without a spring is called "binding" and it goes away as soon as the clutches wear by the shim thickness . .. the spring creates a calculated load on the clutches and the correct spring rate makes wear almost insignificant.