GregBBRD

Now you are getting it.

Once those little engaging teeth wear off the edges that keep them locked together and start "slipping apart", the problem goes downhill, very quickly. What might start as a linkage problem, quickly becomes an internal transmission problem.

The amount of material present, which keeps the teeth engaged, is very, very minimal and very critical. So minimal, that I'm not sure that I can tell, by looking at a gear, if it will stay in gear, or not.

The VW transmission rebuilders (for old bugs/busses) have (still) a huge problem with this. They routinely assemble a transmission that will "pop" out of a gear and will then have to take it apart and use alternative pieces. They "accept" this as a part of "the job". I worked part of my way through college rebuilding these transmissions. You could use a brand new gear and a brand new slider that would still "pop" out of gear. Frustrating.

GregBBRD

I charge $1200 labor to rebuild one. Plus whatever pieces you need. Track cars tend to wear the syncros heavily. Syncro wear is also very dependent on gear oil type. Pour in a GL-6 and you might as well pour in $1500 into an envelope for new syncros.

The really costly stuff is the actual gears. Finding used gears for these things is getting really tough....especially used 5th gears and used 1st/2nd gears with shafts. Finding used gears that are good enough to be used in a race transmission with higher torque output....that's really tough.

Pieces that used to be "standard replacement parts" are now a huge problem. There are no longer any new 5th gear bearings for any of the 1985-1995 transmissions. A high wear, standard replacement piece, in the past. Now a look around for thebest used one you can find" replacement part.

The big springs that go inside for "side" to side" preload are also gone. These break on a routine basis. I used to put a new one into every rebuild I did. Now all I can do is put the old one in and tell the customer that he is on his own....or search around for the "best used one you can find" replacement part. When it breaks (and it will), it breaks.

The roller bearings that the intermediate shaft spins on are NLA. These also were/should be a standard replacement part. Huge loads on these bearings....with, like all bearings, a "limited" life span. I have "sourced" these and have replacements...for the time being.

Porsche has a few gear sets left in stock.....very limited. Also very expensive.

The "problem" with gear sets is that they also have a "design life span". They work harden (they suffer from hydrogen embrittlement). Not to mention that they suffer from torque loading....which is generally increased, in a high output environment, with sticky tires. Putting an increased amount of torque on a 20 year old gear set is unpredictable, at best.....remember that all of the torque has to go through the 5th gear set, before it ever gets to the other gears. 5th gear has a true life of "hell" and is the gear that suffers from fatigue, the most.

I have no idea how many 5th gears Mark Anderson broke, in his race car......but it certainly had the highest failure rate of anything else in the entire vehicle.....many times higher.

These 5 speed transmission parts are going to be the "long term" problem with keeping a 928 "active" on the road, much less, on the racetrack.

What year is the "Holbert" transmission?

Rob Edwards

Greg, are the 5th gear bearings you mention 999 201 402 00, which (I think) come inside a 5th gear, or something else?

EDIT: Or are you talking about the input shaft bearing 999 052 138 00? Duh, sorry.

GregBBRD

No, the big "input" ball bearings that go onto 5th gear....spin all the time the clutch is engaged, at the same rpm as the engine......very high wear items.

928 302 152 10 ('85/'86) and 999 052 138 00 ('87 to '95).