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casor casor is offline
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Join Date: Mar 2007
Location: Boyertown, Pa
Posts: 232
78 911 SC steering rack

Tim - first thank you for the informative post on your st rack. I thought you and other would like to hear about some recent experiences I had when doing what you did to yours.

The rack is a ZF unit #7820900166. When I disassembled it, I found that the grease was hard, the ball bearing had approx 3/32” of radial play and the needle bearing was completely frozen. Both the rack and worm gear (or pinion) had some surface rust also. The main issue however was that the cylindrical upper surface of the worm gear which forms the inner race for the needle bearing was galled and worn. The rest of the rack was in fairly good shape once things were cleaned up.

Although the above bearings are cheap and readily available (needle bearing is part number #HK1712 and ball bearing #6202), the worm gear could not simply be reinstalled since there was significant play between its race and the new needle bearing. The lower end of the worm gear that presses into the ball bearing was fine.

I contacted ZF to get parts and they noted that ZF scraps racks #7820900166 when received for rebuilding and replace them with rack #7820955112 – for about $800. I have seen a number of firms on the internet that allegedly rebuild Porsche racks and sell them on an exchange basis (about $350), but when queried they could not tell me what exactly they mean by “rebuilt”. Gradually painting myself into a corner here, my options at that point were to either replace the worm gear or have the affected area “hard chromed”. Cost of either is about the same at roughly $200, but the parts at ZF are drying up, especially considering that they scrap the original racks as noted above. For the record, the worm gear PN is #7820053127 and the rubbing cylinder, another wear item, is #$7820040200. On this particular rack, I was able to reuse the other parts after cleaning them up. The contact info to potentially get these parts is a ZF distributor:

Northside
Robert Grajkowski
800-247-2491 x1245

It seemed to me that water infiltration, as so often is the case, was the culprit here. The med-hard plastic bell shaped boot that is supposed to seal the exposed top of the rack fits on a bevel on the rack housing and there is no gasket and no postive locking fit here. When I installed the rack in the car, I sealed this joint with a clear, flexible adhesive not unlike “plumber’s goop” and this formed a very secure and waterproof joint.

I could probably write a novel on this one but thought that you would like the short story to shed some light on a very important component.
Rob Caso
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Failure is not an option

78 SC, 06 Cayman S, 74 Targa, 1971 BMW R75, 1975 BMW R90S, 1983 BMW R100S, 2004 BMW R1200GS, 1974 Ducati 750 GT, 1974 Ducati 750 Sport, 1986 Ducati MHR Mille, 1995 Ducati 916, 1994 Bimota DB2, 2005 MV F4 Ago, 2001 Tri 955 RS, 1970 Norton 750, 1975 Hon 400 F, 1971 Hon 750, 1967 Duc 250, 2016 Tri Thruxton
Old 09-30-2008, 04:39 PM
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