xschop

Pet project I've started on my 948 has boiled over into the 928 arena. I busted a front cast hub on a 944 a few years back and always have been nervous/diligent about bearing/hub inspections until I could get a set designed in Billet T6061-T6. Now I have an Iron block V8 in my 944 with 18's and larger rotors/brakes, I'm really nervous about aggressive cornering with double the HP and Double the Torque. I've been asked to tackle the 928 hubs in billet as no one makes them. From the majority of 944/hub failures at the base of the inner bearing seat and the fact that the casting is the same on all the hubs in this area, I will build them for the 928 dimensions and chronicle as the project progresses.....

James Bailey

Pretty much a solution looking for a problem......none of the 928 racers have had an issue. And note that more power and torque has NOTHING to do with cornering loads more weight possibly.

xschop

Well I don't plan on this ever happening to me again. From another thread a known 928 hub failure has occured from a racer. And the sand-casting dimensions are all the same. Nonetheless these are coming to fruition....

James Bailey

Some what moot point given there are very, very few 928 racecars......

BC

XSCHOP - I'd like to share a picture, maybe it will help you.







I am interested in your work, but I am wondering what years you are interested in making the hubs for?

Left side is, IIRC, 82-86.5, and right side is 86.5-95

As you can see, we have differences in rear bearing area diameter, as well as total height.

xschop

Nothing moot about about the shelf life of cast alloy under stress.....

You know how to make a cast alloy part weaker?......machine a land for an ABS ring and introduce some macrofissures in the already weak hub.
I will make them for all years once I have all of them CMM'ed and I am going to strengthen them in the ABS O.D. areas on top of the T6 treated billet that is 6-7 times stronger than the cast crap where they seem to fail the most. Another Porsche off-the-shelf brain fart.

To B.C. thank you for posting. I know that the inner and outter bearings are the same for the 79-85 hubs and the outter bearings on the 86-up increased in diameter from my bearing book. I am getting the CMM printout tomorrow for the 85 hub and I mic'd the offset of it to @ 74mm (base of hub to wheel interface). What is that dimension for the hub on the right? This will answer my offset question. I see that the abs signal changed between years there. The I.D. of the ABS ring lands are critical as they are an interference fit. I would take your hubs and interference them myself after the design is done. Thanks alot

Imo000

Can a 928 hub fit a 944?

xschop

No, the inner to outer bearing relationship is larger on the 928 spindle. I will post those dims soon here so others can chime in, this is important info. From everything I've researched the 79-85 spindles are more stout because the outer bearing land on the stub shaft is beefier. contrary to popular belief all 9- hubs/spindles are not machined metric, close but no cigar.

BC

The dimension that you state, for the S4 and up Hub is unfortunately not something readily available to me, as those pics were from around 2005. The assembly is on the car now with the rotor and GTS calipers. The entire assembly is different as the stub axle on the later cars is longer as I recall, and as you can see taller, baring any differences in the picture between the stud lengths.

Imo000

XSchop,

Ok, so wouldn't a modified spindle, coupled with a 928 hub would be a simpler choice?

xschop

You lost me. I wouldn't machine on a cast steel spindle shaft either, why make it more weak? The point is that the cast hubs 924/944/968/928 are all the same base diameter. Not everyone races or sticks in an Iron block V8 to their 944/928 so not everyone will need a stronger billet hub. This is for the hardcore. If my hub busted at 60 mph around a corner on 16's and stock brakes....18's and Big brakes really does make me cringe with 300lb springs for the heavier V8.

xschop

*****My point being that on the early non ABS hubs they are not of a sufficient diameter to machine to then fit an ABS ring****

You answered my next question and confirmed my suspicions about the majority of the Late 944/ 968 M030 hub failures. I had an in depth conversation with a friend (master machinist 36yrs) and we agreed that the Late 944/M030hub failures were happening at the inner bearing race seats due to the weakening of the cast hubs where an off-the-shelf hub is taken and machined on it's outter perimeter for the ABS ring land. We came to the conclusion that the failures wouldn't be as frequent if a new hub was recast with a larger diameter base and then machined for a larger I.D. ABS ring. I don't want to hijack this big brake thread anymore than has been so I'll leave it at that. I will start another thread soon and get more input. The ABS ring land can be retro-fitted. I need to know it's I.D. and they are an interference fit so I would want a hub and ring in hand. Maybe it's the same as the 944/968 one I have on hand. Thanks guys.

danglerb

How certain are you that your hub didn't break from something like a previous owner hitting a curb, and just didn't fully give out until later?

When Jim says they don't fail much, I expect they are not a weak point.

RCinXS

Jim Bailey would know if hub failure is a common problem.

Stronger, for sure.

Any weight savings?

Not to get to far off topic, but I think what the 928 world needs, is a larger selection of thickness choices in hub centric wheel spacers to accommodate a wider variety of wheel offsets.

hacker-pschorr

The #1 problem with wheel offsets and the 928 is in the front, where a spacer only makes the problem worse.