P258a Mandrel - differential tool; can it be recreated?
 

Gang,

I'm trying to get my hands on a tool set allowing me to adjust the R&P clearance in a 915 Diff. According to the Workshop manuals, the big expensive beast I'm looking for is Porsche tool P258 (sometimes denoted P258a) - the documents I have are very poorly reproduced, so it's hard for me to tell what this tool is really doing. From the description I am assuming that it is really a precision machined piece which fits within the axle mounts in the differential case and allows a dial gauge to be used to determine the spacing between the centerline of the axle to the pinion on the drive.

My very unsucessful queries at locating this tool have garnered mostly "that tool is too expensive for the hobbiest" type replies, a couple quotes of >$2K, but I can find no one with actual prices.

My thought is that with some machine shop time (which I can get) and some detailed drawings/dimensions, this tool may be reproducible.

So, on to my questions:

1) Are my assumptions correct on the usage of this tool?

2) Is a new one really that hard to find - and that expensive?

3) Would anyone that owns one be willing to send me (or post here) photos/dimensions/etc? Or perhaps I could borrow a tool for a week or so and dimension it myself?

Thanks,
<josh>

Apparently, Gary Fairbanks offers a very neat alternative to the factory pinion depth tool, made from an old diff housing. Accurate and easy to use --

I'll call over to Gary tonight - thanks for the tip!

Let us know what you find. I would like to do the same for a 901/911.
I have an old case/diff housing to use for making one up.

Haven't heard back yet - I'll give him a few days before releasing the hounds ;)

Anyone else? I can't believe there isn't more interest in coming up with an alternative to this expensive (but necessary) tool.

I've been trading voicemail with Gary - but apparently this isn't something in "production".

I'm still looking for any info on the original Porsche tool. Anyone?

Hello there.

I have a very simple method.

I use an old diff carrier , the cross pin for the planet gears is made a stiff sliding fit in the bores. and I brazed a ball bearing inot the end of the pin.

This is to be rotated till it rubs the end of the pinion, then the whole lot is removed and measured with a big micromter.

A few sums and I have the pinion protrusion.

Not a slick as the factry tool..

Kind regards
david

Thanks David! Any chance of some pictures?

Here are some photos of the tool Gary Fairbanks made up some years ago. I've had this one for some time. Parts and the box for storage (which was included):

http://forums.pelicanparts.com/uploa...1139618627.jpg

Closeup of the machined Diff carrier:

http://forums.pelicanparts.com/uploa...1139618886.jpg

Dial indicator mounted inside:

http://forums.pelicanparts.com/uploa...1139619004.jpg



EDIT: More photos posted on 5/13/07

I know VW tool #385 will also work...at least for the 901.
I have been searching a P&P depth tool too with no luck. This is something most people do not want to loan out.
David, your way sounds very simple. Could you post a picture?

Jim, It looks like your tool is machined to accept the dail indicator, a knurled handle is added to rotate it in position? and the bearing surfaces are turned down slightly so the bearings slide off and on?
I have a couple of diff carriers. Who has a lathe??
Thanks
Lyn

Dave,

That tool is literally a work of art! My simple brain can't quite come to grips on how it works however. Would you be able to describe the operation?

Hello guys.

I'll need to get some tech stuff to get pix.

It is indeed terrifying in its crudity..

The old planet carrier pin is cut in half..ech half has a big ( 12mm) ball brazed on the end..they are ploished to make a tight sliding fit in the carrier...rotate, remove, measure repeat, to be sure..thats it.

The big side plate bearings also need to be easily removed to shim to suit..

Kind regards
David

Jim,

I mis-posted on the "work-of-art" comment - that is your tool. Would you be able to describe the operation of it?

David,

Even a rough sketch or drawing may prove invaluable if you have the time.

Others,

Baum tools (the source for many Porsche tools) lists the P258 as discontinued and the replacement is described as:


PINION ADJUSTING MANDREL Tool #385
Universal pinion measuring mandrel for adjusting ring and pinion depth.

A quick phone call reveals the ugly truth: MSRP $2400


Is there any fellow pelicans that would consider loaning/renting this tool out?

Regards,
josh

Oh John, you are such a tease.

So, when can you send that out to me ;)

Wow - it IS a nice looking tool. Too bad there isn't something less "industrial" for us home mechanics.

Josh,

The operation of both the Factory tool (picture by John Walker) and the Fairbanks tool (picture by me) is essentially the same. Briefly, the tool is inserted in the case and the distance between the centerline of the diff carrier and the end or face, of the pinion gear is determined. Then the distance the face of the pinion gear protrudes in the diff case is adjusted to satisfy the numbers marked on the pnion face.

The details of how to do this covers several pages in the factory manual. The P385 tool is different in the way it is made, but the concept is the same.

http://www.continentalimports.com/porsche_part.html
http://www.longenterprises.com/specials.htm
do a find for 385

Will any of these work?

Jim,

Thanks for the info - that does make sense, however what I'm not getting is how the "Gary" tool accomplishes that with the needle gauge mounted in the center of the differential case. If it meant to contact the bottom of the pinion, shouldn't the gauge be located where the ring gear normally sits?


Huh,

That indeed is the "VW" equivalent tool - I just can't afford to buy one. :(

Anyone know of a rental place based on the 'net?

Josh,

Remember the ring gear has it's teeth on the side of the gear, and the pinion gear has it's teeth on the side, so the gear teeth don't mesh on the center line of the differential case. But the end, or face, of the pinion gear is in the center. The tool is supposed to measure out to the face of the pinion gear. That is why the dial guage pin is in the center. If the dial guage was in the same place as the ring gear normally sits it wouldn't have anything to touch against. The factory tool of John's does the same thing as the "Gary" tool.

The pupose in adjusting the pinion gear is to center up the "mesh" of these two gears, for lack of a better term. The "play" of the gears is a separate measurement and adjustment.

Maybe you will find a place to rent such a tool, but I have my doubts. I can't imagine anyone owning an expensive piece like this who would rent it out, without a deposit in the amount of what a new one would cost, *if* they could find one. A moment of carelessness resulting in a bounce off the garage floor....... well, you get the picture. But....... good luck in your search.

[slaps head]

Umm yeah - duh. I see it now.

Thanks Jim!