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Old 05-06-2008, 11:35 AM   #1
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Default Differentials.

I was looking at the diff picture loki posted in the oil pump thread and wondering if all pinion gears are supported only at one point.

Here's one like he posted:



It's got that extra bit of shaft sticking out the gear-end. is that supposed to go into a second bearing? The picture below suggests that may be the case. I can only imagine it makes the whole setup much less prone to flex and mis-meshing of the gears which is a pretty frequent reason gears fail.




sorry, that's huge.

Discuss!
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Old 05-06-2008, 11:46 AM   #2
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With the hp you are putting down any thought in getting one of the Diff set ups that the V8 guys use? Just have a custom Drive shaft made.
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Old 05-06-2008, 11:50 AM   #3
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where would the bearing go?

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Old 05-06-2008, 01:08 PM   #4
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ford 8" posi ftw!
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Old 05-06-2008, 02:43 PM   #5
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Quote:
Originally Posted by Braineack View Post
where would the bearing go?

i dunno, somewhere. it could be small?
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Old 05-07-2008, 08:14 AM   #6
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Quote:
Originally Posted by UrbanSoot View Post
ford 8" posi ftw!
If you want a boat anchor. I picked up the Caddy CTS-V diff for my conversion. Brand new they're $750 but then you need custom axles and the diff hanger and driveshaft. Y8's will see it when I get him over to weld some **** for me. 3.42 gearing, FTW.

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Old 05-07-2008, 10:07 AM   #7
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Why does the Ford 8" have to be a boat anchor? You can get them with aluminum casings, first off...secondly, presumably you're adding weight to the front-end of your car with a V8 conversion, are you not?...would you not want to help balance this by adding a little weight in the rear, where you'll already be starved for traction?
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Old 05-07-2008, 10:22 AM   #8
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Yeah i can't imagine that the all aluminum Ford adds any more weight to the back than a Turbo Kit adds to the front.
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Old 05-07-2008, 11:21 AM   #9
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so off topic. ford posi. not the point.


TWO BEARINGS = BETTER?


discuss.
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Old 05-07-2008, 11:27 AM   #10
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If a bearing up top will keep it from flexing i don't see any reason why it wouldn't be better. I don't see how we could to that to a miata differential though.

I haven't had a miata differential apart yet, the ones I have had apart have two bearings. One that is pressed onto the gear itself and another in the case. So the shaft is already supported by two bearings over the length of the main shaft.
Is this the case with the miata diff?
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Old 05-07-2008, 11:37 AM   #11
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Yes, two bearing are better. Does that mean we need to add a second one at each wheel? What about a turbo? How about one at each end, and another in the middle?

Sheesh, it's basic engineering.* If you can get away with one that will do the job, you use one. If you need two, you figure out how to put one in. Simply put, the design is adequate for the loads anticipated. You double or tripple the HP and torque, you get failures. It wasn't designed for that. Cost is the major driving factor in automotive design, and bearings (and the machining needed to support) them ain't cheap.


*Yes, I'm a mechanical design engineer.
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Old 05-07-2008, 12:00 PM   #12
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I am sure it would be better, but can it be done?
What would it take?
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Old 05-07-2008, 01:06 PM   #13
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Quote:
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Yes, two bearing are better. Does that mean we need to add a second one at each wheel? What about a turbo? How about one at each end, and another in the middle?

Sheesh, it's basic engineering.* If you can get away with one that will do the job, you use one. If you need two, you figure out how to put one in. Simply put, the design is adequate for the loads anticipated. You double or tripple the HP and torque, you get failures. It wasn't designed for that. Cost is the major driving factor in automotive design, and bearings (and the machining needed to support) them ain't cheap.


*Yes, I'm a mechanical design engineer.
who isn't a mechanical engineer. cal poly slo '98.

OK so my point was to analyze the potential failure modes of the tranny. if at triple the hp we flex the pinion away from the ring gear, it's going to fail. what can be done to mitigate it? is replacing it with a same-type setup going to also fail later?
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Old 05-07-2008, 01:10 PM   #14
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matt,

looks like it's called a pinion pilot bearing.





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Old 05-07-2008, 01:27 PM   #15
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That is an uber badass girdle, to bad mazda didn't design one in our case when they were designing a diff to handle a whole 110 rwhp.
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Old 05-07-2008, 01:29 PM   #16
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that's a 9" rear for a firebird. The diff used its crazy narrow to fit as you can see from the first pic.
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Old 05-07-2008, 02:49 PM   #17
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Would it even be possible to modify our carriers to include one of these? It may be very well worth it considering what Torsens go for these days.
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Old 05-07-2008, 02:55 PM   #18
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not with a standard meatball in place.
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Old 05-07-2008, 08:06 PM   #19
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Quote:
Originally Posted by y8s View Post
who isn't a mechanical engineer. cal poly slo '98.

OK so my point was to analyze the potential failure modes of the tranny. if at triple the hp we flex the pinion away from the ring gear, it's going to fail. what can be done to mitigate it? is replacing it with a same-type setup going to also fail later?
Okay, sorry for sounding so pissy. Yes, it would probably help, but at what cost? Where is the cutoff for failure mode in the torsen diff? 300HP? More? I'm really asking, not being rhetorical, as I don't have any idea. So, how many people have that level of power, and how many would really benefit from a fix?

Sounds like it might work, if you had the time and patience to work it all out. Fab up a stamped bracket, press in a bearing, and either grind a race on the end of a pinion (expensive), or drill the end and insert a pin to ride in the bearing. Then, of course, you have to drill and tap holes for mounting that bracket, all while avoiding clearance issues. Possible grinding/milling of the bearing caps for flats to provide a mounting surface.

I'm guessing the bracket would have to be 1/8" or thicker to be strong enough, and about 1" or more wide, depending on the bearing used. Is there room for that in a torsen diff?

All in all, considering the machining involved, it goes a little beyond the standard DIY project. Not many people have direct access to machine tools, so it would have to be done on a 1 to 1 basis. Possibly an exchange; send in a core, or pay a lot more. Not sure it's all worth it, when you can just get another diff.
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Old 05-08-2008, 12:02 AM   #20
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something like that would be awesome. but yeah, probably beyond the scope of DIY. great if you could find some shmuck to produce complete diffs with the ratio you want and the LSD you want. I dont want a torsen, I like my kaaz.
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