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Straight cut housing for Quaife ATB Central LSD QDH9B

Would you be interested in a group order of straight cut housings for Quaife ATB QDH9B Central LSD?


  • Total voters
    15

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Mitsi_Itsi

Probationary Member
15
6
Mar 12, 2021
Amsterdam, Europe
Hey guys, the time has come for me to switch to PPG gears on my 2G Manual AWD DSM, but I am faced with kind of a dilemma: What to do with my central diff? (This is not a "Spool vs 4-Spider" thread, please keep reading!)

As we all know PPG offers a Solid Spool Type and a Spider Type housing. The Solid Spool is extremely strong and gives a fixed torque distribution of 50/50, which is great for drag launches, but terrible for cornering and street applications. The Spider Type housing combined with a 4-Spider is also a very strong option, but a 4-spider is an open diff, so it will be up to the Viscous coupling unit to try to minimize the rotation difference between the front and rear wheels. That is great for street use and maintaining grip in corners, but not optimal for launches as the viscous coupling uses friction to eliminate rotational difference, once such a difference has occurred. Meaning that on the start line if your car doesn't have enough grip, it will still spin the front wheels and then try to bring the rear ones up to speed after you have already lost traction on the front.

Now because I'm the type of guy that wants the best of both worlds, I'm looking into options for using my Automatic Torque Biasing central differential from Quaife together with the straight cut PPG gears. Getting a straight cut housing for the Quaife diff will bring all the benefits of using a LSD and combining that with the strength and the shifting speed of the PPG gears. And as an added bonus, those differentials are known to strip the drive gear, which should not occur any more with the straight cut teeth.

I have already contacted Quaife and asked them if they will agree to produce a certain amount of straight cut housings for the QDH9B Quaife ATB Central LSD and waiting for their response. I will be posting any updates in this thread.

I have identified a few potential issues, so I would love to hear your opinion on those and any other concerns that you might have:

1. Purely political - Quaife may see PPG as a competitor company and may not want to support compatibility with a product coming from their competition. However Quaife does not offer straight cut gears for this platform, so there is no direct competition in this case.
2. Diff internals strength - The ATB Central LSD contains helical gears inside which are responsible for the torque distribution. Platforms using PPG gears usually make a lot more power than platforms with helical gears, it is possible that the internal helical gears of that diff cannot handle the big power and fail.
However I know a lot of other platforms, making big power and using Quaife differentials with the same internal design.
3. Housing strength - The different teeth profile can change the strength properties of the housing. Considering this is a custom request to Quaife, they most likely will not be able to properly test the strength of the new housing, so a warranty from their side might be out of the question.
4. Teeth profile - Quaife will need to match the teeth profile used by PPG on the Intermediate shaft. Not sure how difficult that is, but some reverse engineering of the PPG teeth profile will be needed here, so it might be up to our community to do so and passing the findings to Quaife.
I think the tooth count expected on the diff housing is a good start. Please correct me if I'm wrong, but I believe the PPG Spider Type housing has 28 teeth!
5. Minimum number of units produced - It might be the case that they only agree to produce a minimum of X number of units. If that is indeed the case I can organize a group buy and try to meet the minimum units requirement and reduce the production price.
6. Price - It simply might be to expensive for them to design the straight cut housing, which may result in very high price per unit. In my opinion as long as the housing price is not more than the price of the actual diff, it should be fine.

Considering the points above, there is a big chance that Quaife refuses to support our community with such a housing. If that is the case, but enough people show interest, perhaps we can find someone else to make the part for us. Any suggestions are welcome.
Or maybe someone here has the knowledge and access to machinery to manufacture such a part? Let me know!

In the meanwhile I would like to know how many people will show interest in a group buy, so I can let Quaife know what number range we are looking at. You can vote in the poll, or leave a comment :)
 

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There is a good chance they will fail if made. The problem is the rim gets pretty thin where the planet gear pockets are. Grab the drawing from quaifes site, and you can see it.

On the other side, doing a 4 spider these days might be almost as hard to do.
 
There is a good chance they will fail if made. The problem is the rim gets pretty thin where the planet gear pockets are

Indeed, considering that the PPG teeth are bigger, they will need to cut deeper into the housing. However the more massive teeth would be perpendicular to the rotational forces which are of concern here, so in my opinion they should also increase the strength of the housing against those rotational forces.

On the other hand if there are two thin pockets around a tooth that is supposed to transfer huge amount of power, the teeth themselves may start getting ripped off.
 
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the teeth themselves may start getting ripped off.

Bingo. There is more to it than just the shape of the teeth. They have to have enough root material to support the forces being transferred from the tooth to the part. And that is Kurt's point about the Quaife design is that the wall is too thin so it doesn't break the tooth is deforms housing which deflects the tooth and it either cracks the housing or rips the tooth right off.

Also you have to keep in mind that straight cut does not equal stronger. To the contrary a helical gear of the same width actually has more gear face. Aftermarket dog boxes go to straight cut to remove the axial force component generated by helical gears which causes more deflection at the shaft bearings which they are stuck with for size.
 
Well, here's pictures of the PPG 4 spider housing, you will see how thin it gets.
 

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Also you have to keep in mind that straight cut does not equal stronger. To the contrary a helical gear of the same width actually has more gear face. Aftermarket dog boxes go to straight cut to remove the axial force component generated by helical gears which causes more deflection at the shaft bearings which they are stuck with for size.

Yes of course, the axial force is our biggest enemy with the helical gears. In the PPG case I believe the teeth are also be stronger simply because if their size, but I agree that a helical gear with the same tooth height and width as the PPG one, will be stronger than the straight cut one.
 
Well, here's pictures of the PPG 4 spider housing, you will see how thin it gets.

That's interesting Tim. You can definitely see where the cuts for the spider dogs actually went through into the hob runout on the outside. But What I'm having a hard time telling from the pictures is if the cavity for the spider gears extends under the full part of the gear teeth where they actually mesh? Doesn't look like it does. So the teeth are fully supported by material where it counts. Here is the Quaife ATB drawing:

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You can see where the bores for the helical gears for the torsen differential inside extend way under the teeth themselves not just the runout. And it's just way too thin. But I don't think they had a choice for packaging that type of diff in this space.
 
Well, here's pictures of the PPG 4 spider housing, you will see how thin it gets.

Those teeth does seem to cut deep into the housing indeed and also the canals where the gear shafts go, but the two don't seem to be overlapping much. Are there any cases of PPG 4 spider housings failing because of that?
I am not sure how think the Quaife housing is under the teeth. From the outside it does look very thin, but there seams to be a thick flange ring under there, for the bottom of the cup to bolt to.

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The PPG housing has a tooth OD of 4.210", OD at root to root of tooth is 3.530", with the 4 spider posts, there is only 0.040" of material at it. I know it would be a bit different with the quaife housing, but the PPG housing has a max OD above the teeth of 4.00", if they are using the 3.44" ID, thats leaving 0.280" wall thickness at the top, which would have to have decent wall thickness 1.700" from top of flange to bottom of torsen gear, then subtract 0.230" on the outside for gear tooth profile from the wall thickness of 0.280, gives you 0.050" of wall thickness at root of exterior tooth profile to pocket surface for the lower torsen gears. Not that much to work with, and the torsen gear pocket in the housing overlaps a huge portion of the housing teeth. I would suspect gear tooth failure of the housing.
 
You can definitely see where the cuts for the spider dogs actually went through into the hob runout on the outside. But What I'm having a hard time telling from the pictures is if the cavity for the spider gears extends under the full part of the gear teeth where they actually mesh? Doesn't look like it does. So the teeth are fully supported by material where it counts.

Indeed what I was referring to.

Here is the Quaife ATB drawing

On that drawing it is clearly visible that there will be a problem in-between the bolts where the helical gears are:
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The PPG housing has a tooth OD of 4.210", OD at root to root of tooth is 3.530", with the 4 spider posts, there is only 0.040" of material at it. I know it would be a bit different with the quaife housing, but the PPG housing has a max OD above the teeth of 4.00", if they are using the 3.44" ID, thats leaving 0.280" wall thickness at the top, which would have to have decent wall thickness 1.700" from top of flange to bottom of torsen gear, then subtract 0.230" on the outside for gear tooth profile from the wall thickness of 0.280, gives you 0.050" of wall thickness at root of exterior tooth profile to pocket surface for the lower torsen gears. Not that much to work with, and the torsen gear pocket in the housing overlaps a huge portion of the housing teeth. I would suspect gear tooth failure of the housing.

Indeed 0.050" is just too thin. I guess that does it for the Quaife option. But would there be another LSD option that might have the potential to work?
 
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Good news guys! I got a response back from Ray and it seams like KAAS used to have a Central LSD for Evo 1-2-3 and also a close ratio gear set with 1-3rd straight cut and 4-5th helical gears. Both of which were discontinued about 10 years ago due to lack of demand. They are willing to look into reviving the LSD, but it will need to be handled as a special order, so a minimum of 30 units will be required. I have asked for a price estimation and a confirmation that they can match the PPG teeth profile. So as soon as that is known I can organize a group order.

The best thing would be to jockey ratios around so that the cd gear could be larger in OD.

That will require a custom intermediate shaft as well...

Is someone going to be willing to provide a sample PPG housing to KAAS (which will be returned afterwards of course)? Or at least to support them with some measurements and/or drawings of the PPG gear profile?
I don't have yet a PPG set in my possession yet, so I can't help them with that.
 
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KAAZ may be involved with the organization of the group buy, to make it more trustworthy. I am currently waiting for commitment from their engineering and sales teams. More details on the group buy will will be clarified after getting a commitment.

I have a unistaled ppg 4 spider.

Are you willing to send the PPG 4 spider over to KAAZ so they can take some measurements?
 
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Hey guys, I have got an answer from Quaife and they are willing to look into redesigning the internals of their diff in order to solve the housing thickness issue. They have also asked for a sample straight cut PPG housing (same as KAAZ), so they can take measurements. Once they have that they will provide prices for 10, 20 and 30 unit batch sizes.

This is the point where I need your support if we are to continue with this. I don't have a sample PPG housing or drawings with measurements to provide them.
 
Hello, I am interested, but I live in Brazil. Also I do not check the forum very often. But if it is possible count me in.
 
I do not have any PPG center diff housings here to send in. I only have customer ones for builds I am working on.

You can contact Fernando @ Ostar Performance and ask for a part number and price quote for the 4 spider housing.
 
You can contact Fernando @ Ostar Performance and ask for a part number and price quote for the 4 spider housing.

Thanks Tim, I think I will first try to contact PPG directly and ask them for the specifications and drawings of the housing or at least the planet gear. Of course there is a fair chance they might refuse to provide that. Do you perhaps have a contact person that I can message directly?

Hello, I am interested, but I live in Brazil. Also I do not check the forum very often. But if it is possible count me in.

I believe shipping to Brazil shouldn't be a problem, but those details will be clarified later on when the group buy is being organized. I also saw your comment on the Facebook post, so I'll make sure to message you there when the time comes. :)
 
Any updates please on this from either differential manufacture? I’m totally in for a group buy.
 
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Any updates please on this from either differential manufacture? I’m totally in for a group buy.
Yes, I have found somebody that was able to make one already. However at the moment I don't have much details, only a picture of it. I am currently waiting for a sample.

By the looks of the picture it looks like he cut out the teeth from a PPG spool/diff and welded them on the torsen LSD.

I will be able to give more details once I have my sample :)

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Any updates? Need to get my 2G GST running after an 18 year break. Have an EVO3 transmission and most of the necessary parts for the AWD swap but cannot find a 4 spider center anywhere. If I have to, I will get the PPG gear set but it seems that there's issues finding a decent center dif for those as well. I really want to get this car running as it is becoming quite rare and I've had it since 1996.
 
The center diff cover and pinion gearset, along with pretty much every lower and upper pinion shim are obsolete. Unless you have a new pinion gearset, which Neat Gearboxes in Australia supposedly has manufactured, you won't be doing squat without that or a good diff cover. The PPG 4 spider housing is literally just a bare housing that uses a 90 style lower pinion washer. Those are all obsolete. I use a pinion shim set normally for front diffs and that works for the lower. The upper pinion shims are pretty much all obsolete, and quite expensive from Mitsu, so you machine the cover for a double thrust washer and Torrington bearing instead. On the PPG gearset, you also need to machine the OD of the cover and grind down the bolts to clear the intermediate shaft, along with clearancing the intermediate 4th to the diff housing so you don't damage it.

Like I said by email, my billet cross shafts will be back in stock around March.
 
Tim,

back in the day wasn't like shep or someone doing a torington on the bottom as well? I don't see why that's not a viable option. Might have to pocket the top a little deeper and jockey some things around to make it work.

As for the top cap they have to be pretty torched to not be saveable. Usually that part is machined out for the torington bearing pocket, and then I give it a quick hone and it's usually golden. I've only had a couple that were that bad, and I used em for a welded diff.

Lastly for all. Is the LSD really that big of a deal? I wanted one bad, as I would always spin one front tire, then I got a quaife front lsd and the taller first gear of the dogbox, and tire spin really isn't an issue anymore.

In the past I ran the evo1 final drives, and dsm first, so I had 10% more torque at the tires than everyone else, so it was bad, but I'm anxious to try the front lsd out with a stock gearset and see how it works out. The low first is just so nice for drag use, don't have to murder the clutch to get the car to leave good. Just gotta be ready for that 1-2, it comes quick!
 
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