OBX diff problem...need input quick.

[lbhsbZ]

I searched and didn't find much on this.

 

I was planning on taking the car out for its first track day tomorrow, and giving it quick once-over today. I took it for a spin and noticed a little clunk in the driveline somewhere. With the rear wheels on the ground, I can get about 30° of driveshaft rotation....WITHOUT THE REAR WHEELS TURNING!!. I must be missing something. It did the same thing (clunk) with my old gears, now with the new ones aswell. Its not pinion/ring backlash. I set that at about .005-.010 on both gear sets, and when I disassembled the last one, the backlash was good. The only thing I can think of is that the OBX diff is either coming apart or that this is Standard operating procedure for the OBX...like the helicals moving around in the center section. I don't have time to tear the diff out and apart before tomorrow morning, so I'd figured the wiser choice would be to ask for advice before I say screw it and load it up on the trailer.

 

I have another (4.64) gearset that should be arriving next week, and I have plenty of cases. So, if the OBX is already cooked, I might as well finish cooking it and have some fun at the track, then get a powerbrute or proper quaife for next time.

 

What does HybridZ think I should do?

[lbhsbZ]

Well, I opted to not chance blowing it up. I'll tear it down tomorrow and see what the problem is.

[JustinOlson]

I'm very intersted to see what you find to be the problem.

 

Justin

[lbhsbZ]

me too.

 

What other diff out there can reliably handle 500ft/lbs in a road race car?.....I really dont' want to cough up 1500 cocos for a quaife. Can the powerbrute handle it without constant rebuilds?

[lbhsbZ]

Ok, I got it all tore apart and here's what I found. The washers are toast...one of them is gone, the others are paper thin with pieces broken off. I had them organized (())(()). I have less than 20 miles on the diff, all of which have been in our parking lot at work. Since the washers were gone, there was nothing keeping the two center gears (is that the right term for them?) preloaded against the outside of the case, so every time I'd transition the throttle, the gears would either slam together or slam apart against the case. Now, I'm wondering if I'll have the same problems with new washers.

 

My understanding of the Quaife type diff is as follows:

 

When power is applied, The ring gear spins the case, and consequently the scroll gears,which drive the center gears apart from each other against the case...The scroll gears on the left side of the diff are forced towards the right side and the scroll gears on the right side are forced towards the left side of the diff. Under deceleration, everything is the opposite, and the two center gears are pushed towards each other, compressing the bellville washers. If there is any differential in center gear speed under decel, the loaded bellville washers are acting as clutches, and unless they're made out of kryptonite, will wear pretty fast.

 

Additionally, if you install the bellville washers in a manner as to preload the sun gears against the case, ANY wheel speed differential, even under accel, will make the washer rotate against each other. Since the washers aren't designed to act as bearing surfaces, this means that if ANY differential rotation occurs within the washer stack, the washers will wear considerably.

 

Here are the options as I see them:

 

1: reduce the bellville washer stack from 8 washers to 6 or 4, and install a torrington bearing assembly between them to assume the differential rotation load and relieve the washers from rotating against each other. This should allow the diff to function properly under accel, even if I should happen to lift a rear wheel (which I can't see happening, and if it does, diff function will undoubtedly be the least of my problems), as the sun gears will still be preloaded against the case, The downside to this is that I will probably loose all function of an LSD under braking or off throttle conditions....which I'm not really sure if I need anyway, or what good it does.

 

2: Replace the bellville washer stack with a stack of precision ground flat washers and shim stock, allowing only oil clearance between them. There will be no preload, but if the surface finish is good enough on the washers and oil clearance is adequate, it should still function properly, and be much more wear resistant than the bellville setup. Since the washer stack will generate friction when compressed, I will still maintain off throttle LSD function. The downside to this is that I will lose ALL LSD function if I lift a wheel, because there is no preload.

 

What should I do?

 

I think that a stack of bellville washers, without any proper bearing surfaces, makes no sense and is failure prone, and I don't understand how the hell quaife gets away with it.

[JustinOlson]

Aren't these OBX diffs know to have very poor quality bellville washers? Increashing the preload likely accelerated the wear of these poor quality washers. Thats all that I can think of. Hope your able to figure something out that is reliable.

 

Justin

[lbhsbZ]

Yeah, its been stated that the washers suck...but I don't see how they can be 2 or 3 times as shitty as the washers that Quaife uses. They're made of steel, which is not meant to be a bearing surface. Better steel will only prolong the agony...but not too much. Think about it, you have a sharp edge of the ID or OD of the washer contacting the same edge on the next washer...If I lift off the throttle at 130mph, there is an enormous load on that square nanometer of contact area between the two little washers. If I lift quick, I can get the tires to chirp. If I can overcome the available friction between 315/35/17 R compound tires, I cannot even imagine what those stupid little washers are going through.

 

Another option may be to replace most of the washer stack with clutches and steels, and retain only 1 or 2 bellville washers. The preload probably won't change the LSD function under acceleration, but it will work as a 1.5 way or 2 way and maintain considerable LSD function under off throttle or braking. The only downside would be wear. The 2 options in my previous post would cause almost no wear to the diff unit, while adding the clutches (especially as small as the would have to be) would introduce a wearable part to the diff, and require maintenance and occasional replacement....I'm a set-it-and-forget-it kind of guy.

[JMortensen]

I thought the Quaife was a 1 way LSD and didn't do anything on decel, that's why the FWD guys love them so much. I know the Quaife has adjustable preload, because John Coffey talked about having his adjusted previously in this thread: http://forums.hybridz.org/showthread.php?t=93879

 

I think the Torsen acts sort of like you describe, but my impression is that the Quaife is strictly a 1 way deal. Basically when you accelerate the helical gears "walk" up the side gears and in this case I guess they compress the springs, and it's the friction on the springs and the case that keeps the inside wheel from slipping. Seems to me like your solid spacer idea is a good one, although with it set up that way you won't be able to preload the gears so it might be more likely to spin one tire.

 

You might want to do a little research online and see if you can find an exploded view of a Quaife and see how they adjust preload. The Tru-trac that I referenced in that above thread had a wedge on a bolt, and you tightened the bolt to preload the gears, but I have no idea how Quaife does it. I know the Tru-trac didn't have Belleville springs in it, but it was also notoriously noisy and made kind of a crunching noise especially when doing a slalom like maneuver.

[lbhsbZ]

Basically when you accelerate the helical gears "walk" up the side gears and in this case I guess they compress the springs, and it's the friction on the springs and the case that keeps the inside wheel from slipping. Seems to me like your solid spacer idea is a good one, although with it set up that way you won't be able to preload the gears so it might be more likely to spin one tire.

 

 

I'm not sure I understand what you're saying here...it seems to contradict the theory of operation as I understand it. Can you edit it using the terms "center gears"( the 2 big ones) and "side gears"(the 12 little scroll looking ones) please?

 

And I don't think that any load is introduced to the springs under accel, only on decel....am I wrong?

[JMortensen]

Side gears are always the ones that the CV's or axles plug into, they're the big ones. That's the technically correct name. The helical gears are the little scroll ones. If you read that thread I linked to, me and Drax and blueovalz get into it about the different styles and there are some links (which are probably mostly dead now) that might help explain some of it.

 

Bottom line is that the side gears drive the helical gears, the helical gears ride up the side gears and hit the inside of the case, where they rub against it and create friction which is why the gears are kept from turning at different speeds. If your diff has belleville springs in there between the gears and the case, then the gears will be compressing the springs and probably spinning them pretty hard against each other and the inside of the diff itself, which would explain why you're having the problem you're having.

 

I'm pretty sure I'm right on this one, but we may have been disagreeing due to using different terminology...

[lbhsbZ]

just read the link you posted.....my brain assploded when I got through the part from the Gleason BSME. I don't understand all those numbers...I just make stuff work or blow it up trying.

[lbhsbZ]

Bottom line is that the side gears drive the helical gears

 

Umpossible.

 

The side gears (two big ones) have no positive mechanical connection to the case, which is driven by the ring gear. The side gear are the "driven" gears, which are driven by the scroll gears (12 little ones). The scroll gears move with the case. So the scroll gears, or helical gears, drive the side gears, not the other way around.

 

Until I understood this, I was all confused about how the thing worked.

 

Edit:, for those picking nits, the quoted statement is true, but only under decel

[frank280zx]

Yeah, its been stated that the washers suck...but I don't see how they can be 2 or 3 times as shitty as the washers that Quaife uses. They're made of steel, which is not meant to be a bearing surface. Better steel will only prolong the agony...but not too much. Think about it, you have a sharp edge of the ID or OD of the washer contacting the same edge on the next washer...If I lift off the throttle at 130mph, there is an enormous load on that square nanometer of contact area between the two little washers. If I lift quick, I can get the tires to chirp. If I can overcome the available friction between 315/35/17 R compound tires, I cannot even imagine what those stupid little washers are going through.

 

Well they are the poorest quality steel in the world.. actually xander ( a member here) had the same thing happening as he did not replace the washers either ..

if you buy this diff... witch otherwise works great like you stated in the OBX thread replace the washers! and youl be fine!

http://forums.hybridz.org/showthread.php?t=107997&highlight=OBX+lsd

 

 

GARDNER SPRING

1-800-331-3263

MB1250-062

Bellevelle Disc Spring

Package Qty: 12

1.250 x 0.0630 x 0.062

 

they sell em at mcmasters

 

Here is the specs of the original washers (I took the measurements in mm so I have converted to inches as this is what mcmaster had in stock)

 

Max Outside Diameter = 31.75mm (1.250")

Min Inside Diameter = 16.0mm (0.629")

Thickness = 1.6mm (0.062")

Height = 2.33mm (0.092")

 

the mcmaster online catalog the high carbon steel belleville washer that is the closest match is part number 9712K83 which as the following specs.

Max OD = 1.250"

Min ID = 0.63"

Thickness = 0.062"

Height = 0.092"

[lbhsbZ]

Well they are the poorest quality steel in the world..

 

I highly doubt that, no testing has been done to prove it or disprove it, but I still call bullshit.

 

 

actually xander ( a member here) had the same thing happening as he did not replace the washers either ..

if you buy this diff... witch otherwise works great like you stated in the OBX thread replace the washers! and youl be fine!

http://forums.hybridz.org/showthread.php?t=107997&highlight=OBX+lsd

 

 

 

And he has never re-disassembled it to check the condition of his new washers, which were also not designed to be dynamically thrust and rotationally loaded, both at the same time.

 

 

 

Regardless, I think that bellville washers are not the correct piece to use under these conditions. Bellville washers are a progressive spring, not a friction surface....and under no circumstances should they be used as a friction surface IMHO. There are plenty of better ways to do it.

[JMortensen]

OK I know you have it wrong about how the LSD functions. Here's how it works. I've actually put quite a bit of effort into understanding these suckers and I'm convinced you're wrong...

 

The ring gear is trying to spin the carrier and move the whole car forward, you're right.

 

BUT!!!!

 

The weight of the car resists moving forward, so everything that can move before that side gear starts to move will. So what happens is the car is resisting movement and as it is "taking up the slack" in the drivetrain, imagine all the U-joints are slightly moving and the ball bearings in the CV joints are rocking to one side to remove all the slack.

 

At this same time the wheels are not moving, but the carrier does rotate forward. You can think of this as the case moving or as the side gears moving. Same difference. The side gears movement in relation to the LSD (they're basically rotating backwards relative to the motion of the LSD) drives the spiral gears outwards against the side of the case. They hit the side of the case and that is what finally forces the side gears to finally move along with the carrier. This is why you were turning the driveshaft and getting 30 degrees rotation before the wheels turned. The side gears turned backwards 30 degrees relative to the outside of the case during that movement of the driveshaft. All of the slack in the drivetrain has been taken up at this point and now the wheels start to move.

 

Now in your case you have these springs on the side. The springs are trying to prevent the spiral gears from wedging against the edge of the case as hard as they might without the springs. I would imagine this is done either to prevent noise or to make the LSD work more smoothly.

 

That's how it works. I may or may not be back tonight, getting tired and actually trying to finish some work, but I'm sure this will continue on into tomorrow. Looking forward to it! I love this stuff

[lbhsbZ]

The side gears are the ones that the axles are stuck in, they are the last things in line, which means that they are the DRIVEN gears, and cannot be the DRIVE gears.

 

OK I know you have it wrong about how the LSD functions. Here's how it works. I've actually put quite a bit of effort into understanding these suckers and I'm convinced you're wrong...

 

The ring gear is trying to spin the carrier and move the whole car forward,

 

Correct

 

 

you're right.

 

 

I know I am

 

 

BUT!!!!

 

The weight of the car resists moving forward, so everything that can move before that carrier starts to move will. So what happens is the car is resisting movement and as it is "taking up the slack" in the drivetrain, imagine all the U-joints are slightly moving and the ball bearings in the CV joints are rocking to one side to remove all the slack.

 

I concur

 

 

At this same time the wheels are not moving, but the carrier does rotate forward.

 

 

once again, I agree

 

 

You can think of this as the case moving or as the side gears moving. Same difference.

 

 

no, different difference. The side gears are connected to the axles, the scroll gears or helicals move with the case.

 

 

The side gears movement in relation to the LSD (they're basically rotating backwards relative to the motion of the LSD) drives the spiral gears outwards against the side of the case. They hit the side of the case and that is what finally forces the side gears to finally move along with the carrier.

 

my understanding is this: before the axles BEGIN to turn, the case has to load itself against the scroll gears...at which point the scroll gears begin to move with the case until the gear tooth clearance is removed between the scroll gears and the side gears, at which point the side gears are resisting being driven by the scroll gears, and that forces the scroll gears inward into the case and the side gears outward into the case, at which point the axles begin turning.

 

This is why you were turning the driveshaft and getting 30 degrees rotation before the wheels turned. The side gears turned backwards 30 degrees relative to the outside of the case during that movement of the driveshaft. All of the slack in the drivetrain has been taken up at this point and now the wheels start to move.

 

 

correct, my thoughts exactly.

 

 

Now in your case you have these springs on the side. The springs are trying to prevent the spiral gears from wedging against the edge of the case as hard as they might without the springs.

 

The spring washers are between the two side gears, and have nothing to do with the scroll gears (helical gears)

 

 

That's how it works. I may or may not be back tonight, getting tired and actually trying to finish some work, but I'm sure this will continue on into tomorrow. Looking forward to it! I love this stuff

 

I'm tired too....sleep well.

[frank280zx]

I highly doubt that, no testing has been done to prove it or disprove it, but I still call bullshit.

 

 

 

And he has never re-disassembled it to check the condition of his new washers, which were also not designed to be dynamically thrust and rotationally loaded, both at the same time.

 

 

 

Regardless, I think that bellville washers are not the correct piece to use under these conditions. Bellville washers are a progressive spring, not a friction surface....and under no circumstances should they be used as a friction surface IMHO. There are plenty of better ways to do it.

 

You don't need any testing to see that they are of very poor quality, next to that if you google search on OBX you see that on other forums they also change out the washers. with success. however good luck with it.

Share on what you find and not call bullshit on! the qaife part uses a similar set up untill than ill be happy motoring with belville washers

[bjhines]

IBHSZ is going through exactly the same thing I went through with regard to the differences between good and poor designs.

 

I could not believe the crappy design of the 300ZX CLSD unit. JM and I argued about the movement of the side gears in the CLSD units until I finally tore down a NISMO CLSD unit and proved that it worked the way I had described. It turned out that JM was ALSO RIGHT... because the shitty 300ZX CLSD worked the way HE described.

 

This is a great opportunity to IMPROVE on the crappy OBX design. Lets see what we can do to improve it.

[johnc]

What should I do?

 

Put new washers in the OBX and sell it on eBay. Take the money and buy a PowerBrute or Nissan Motorsports CLSD. Last Saturday I saw an OBX equipped WRX break and lock up the rear wheels. We had to put a floor jack under the diff and roll it off course.

[lbhsbZ]

I already ordered a Quaife unit, so my immediate problem is solved.

 

I'd still like to make the OBX work though...just because it doesn't look like too bad of a unit, it just needs some design modifications and I'm sure it will work great.