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Constant Velocity Joints – 1985 Porsche 911

Constant Velocity Joints – 1985 Porsche 911

BACKGROUND: My 1985 Cabrio has 175K miles on it. I have owned it since 17K and kept all records so I am sure the CV’s are original and never serviced. A clonking noise led to the replacement of the outer joint. Here is what I found.

INFO: In model year 1985 there was a mid-year change in CV joints. This creates difficulty in verifying the correct parts and how to go about this repair.

There were three models in 1985; Carrera, Turbo, and M491 (Turbo look-alike). All three had mid-year changes relating to the half-axles. My CV’s are the Carrera type so my comments focus on these.

To make matters worse, there have been problem with bolts coming loose and GKN/Lobro (the OEM manufacture) changed the thickness of the metal plate which holds the boot. This last change necessitates bolt length change (at least on the outer) if these boots/axles are used.

Early 1985 Carrera
Transmission; G15.67/68 (915)
CV joints (2) size; 100mm (inner&outer)
Factory Bolts; M8x50

Late 1985 Carrera
Transmission; G15.72/73 (915)
Inner CV joint (1) size; 108mm
Factory Bolts; M10x50
Outer CV is integral part of half-shaft.
Notes: Inner CV was changed to Turbo sized CV.

The Carrera CV joints changed early to late by going from smaller inner/outer detachable CV’s to welded outer with larger detachable inner CV. The Turbo continued to use the larger inner/outer CV’s but some change (flange?) causes bolt size change from 60 to 50mm in 1985.

RECOMMENDED: Get a parts diagram (PET) from Porsche website. (https://techinfo.porsche.com/techinfo then: select USA _worhshop info_catalog 7. See pages 131,132, & 136. Also see http://forums.pelicanparts.com/porsche-911-technical-forum/ search on ‘constant velocity joints’. Also see www.type2.com/bartnik/cvjoints.htm and http://volksweb.relitech.com/cvjoints.htm.

BASIC PROCESS: The early Carrera and Turbo/M491 CV’s can be replaced by removing the six bolts on each CV joint. The same is true with the inner late Carrera but it’s outer CV requires removing the wheel nut which ‘extremely’ tight. On my early ’85, I was able to remove ‘only’ the outer without removing inner CV. It required removing lower shock bolt to gain sufficient clearance. See picture

PLAN YOUR ATTACK before ordering:

1) Identify the CV and replacement strategy
2) Determine if BOOT replacement is needed
3) Determine BOLT strategy
4) Determine washer, loctite, and/or wire strategy

Identify CV – The early Carrera used 100mm diameter CV and M8 bolts (6mm hex). The later Carrera used 108mm inner CV and M10 bolts (8 mm hex). You can also verify the later Carrera outer CV does not have bolts.

Early 1985 Options – You have the option of replacing CV only, CV with BOOT, or entire half shaft. The new Lobro replacement half-shaft uses the thin boot plate requiring shorter bolts. The same is true of their boot although boots with correct flange thickness appear available. You ‘may’ be able to retain the original thicker flange and replace the rubber boot only (there may be some precautions like a sealant required).

Overall, replacing the complete half shaft on the early ’85 Carrera may make sense for you. The assembled CV/boots are grease packed and unit price is not much more than the individual parts.

Late 1985 – Again, this is a much different procedure for outer CV since the CV is part of the half-shaft. The inner CV replacement looks clean since the boot is replaced separately from the flange.

SOURCING: This situation is complex and difficult for suppliers. Many potential sources have only partial information on ’85 CV’s or don’t show any CV’s for ’85 at all. I like to investigate multiple sources so search on 1984 model year if early and on 1986 if later. Any notes should be clear and consistent.

BOLTS –The original M8 Porsche bolts I pulled were 12.9 hardness which is required. They are DIN 912 dimensions, normally available in 5mm length increments and appear to be reusable if in good condition. You may want to pull the bolts and inspect for scoring. The hardness is stamped on the bolt head. Some bolts come painted with Loctite on them & this seems like a good idea. Also, racers have been drilling holes to put safety wire in and there may be aircraft bolts with holes. Pricing ranges from $0.50 to typically $2 each for standard bolt depending on your source.

LOOSENING BOLTS – Read the numerous posts on Pelican Parts Forum (search for “constant velocity joint”). There may be moon plates on this year according to PET diagram but mine had nothing. Some people recommend adding Schnorr (VS type preferred) or other locking washer such as Belleville. There may have been a TSB from Porsche on this. Consider the impact on bolt length if adding washers. The debate on use of Loctite or not continues.

For normal street driving it appears ‘very’ clean bolts and holes with precise torque (M8-31ft/lb, M10~60ft/lb.) may be the best approach. This means mating surfaces and thread holes cleaned with something like brake cleaner or lacquer thinner using cotton/swabs. Bolts washed with soad & water. All mating flange/CV surfaces should be absolutely clear of grease. I did “re-assemble as removed” and will watch for problems afterward.

I have never had a bolt problem in 160K miles including three transmission removals using, I believe, original inner CV bolts.

GREASE – Use CV type only. I got some Febi/Bilstein hi-temp in a plastic 120g tube when I ordered from my source. I injected grease without disassembling the CV joint. It was thin to moderate viscosity with a dark moly appearance, not thick & pasty. The flat grease bags or cans may be more difficult to use when packing by hand.

GASKETS – Early ’85 requires one (1) gasket per CV according to PET info*. I found the outer flange has an indentation for the gasket allowing for a CV/flange metal interface. The gasket I got had adhesive on CV side. Late ’85 inner CV does not require gasket due to dome cap but may require a sealant, if used consider impact on bolt tightening.

*I found a second gasket on the flange side (recessed) while doing final assembly. This was undocumented.

CIRCLIP – My new CV joint came with one. These are hard to remove/install so get astrong tool.

NOTE: After 500 miles check bolt tightness and periodically thereafter.

PRIOR REPAIRS – It is worthwhile to verify existing bolt length in a 1985 while planning a repair as things may have changed since it left the factory.

CONCLUSION – I left the inner CV intact and replaced only the outer CV with new gasket, grease, and bolts for $86 in parts.

FOLLOW-UP – Cleaned original bolts were used during reassemble. After 500 miles I check for looseness (there was none) and replaced each bolt individually with new bolts. Rechecked after another 500 miles.



Last edited by glenncof; 06-06-2007 at 07:44 AM..
Old 02-08-2007, 07:07 PM
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