Is there a trans guru in the house?

[J P Stein]

This should about do it for me. Got the backlash checked and it's .006-.007" vs
.16-.20mm (rounded) from the book. A bit towards the bottom of the tolerance.
My tooling is a kind'a makeydo, but functional. .......

[911 tweaks]

can you take any close up pics to post on your set up & what specifically you were checking for us beginers?
Great job from the looks!! Thank you! Bob

[Walt Fricke]

JP

Piece of cake?

Did you have to change any of the carrier bearing shims?

I like the adjustable dial indicator holder. All I have are those rod and magnet base ones. What is yours?

KTL - I've only seen the inside of a G50 once, and that was watching a mechanic change to steel cones or some such synchro stuff out in the open at a race track. Though various tranny fundamentals doubtless are much the same.

For earlier Porsche transmissions there was a Porsche tool which fit the 915 (maybe a couple of others) and was pretty easy to use (because I borrowed one and could use it). And the VW tool which had various adapters so it could be used on more trannies, and is more expensive.

Some folks can set up a tranny just with blueing, but I think it is just too hard to get confident with something like that unless you can play around under controlled circumstances. Spend a day or more assembling things so they are known to be correct and seeing what the blueing says, and then purposely making them wrong in a known direction, etc. There are pictures around of what the pattern should look like, but when I've tried it I have just never felt confident. The guys who really know their stuff that I know often use blueing as a final check.

My understanding is that pinion depth (initially set as you say - to a standard specification) is set acoustically. The ring and pinion are installed in something, and while being rotated the one or the other is moved fore and aft until the desired frequency is reached. Then that offset is inscribed on the set. At least that is the 915 system.

An engineer/mechanic/shop owner friend says he sets up the trannies by measuring, but he doesn't use the factory tools. He must have figured out some other way accurately to locate the centerline of the differential. If you could measure from there to the end of the pinion you'd have it. Or measure to the case by the pinion, and then back with the pinion in to its end, you'd be there also.

What might be fun would be to figure out how to use an old differential housing as the basis for a home brew pinion depth measurer. Old diffs are a dime a dozen, because folks like me and JP have replaced them with somehting else. The factory tools would be a steal, I think, at maybe $1,000. Tough to justify for something you might do once every couple of years, if that often.

Walt

[J P Stein]

Originally Posted by 911 tweaks

can you take any close up pics to post on your set up & what specifically you were checking for us beginers?
Great job from the looks!! Thank you! Bob

Hay, like a bumper sticker that a buddy used to have said:"don't follow me, I'm lost".

This is my first time mucking about with a ring & pinion brought on by being a CSOB.....and wanting to learn how to do it. I spent enough monies on the LSD to ruin what I jokingly refer to as my budget. Tack on an engine rebuild with this...

I'm checking the backlash between the ring & pinion.

The widget on the end of the pinion shaft is to hold it firmly (a poor imitation of the factory tool) while moving the ring gear....stop to stop as it were. It's a 30mm socket over the end of a big effin' bolt back there whose name escapes me, welded to a piece of strapping then bolted to the intermediate plate. I'm not happy with the "firmly" part of this and am gonna try something else.

The aluminum angle face is centered on the axis of ring gear rotation....via eyeball and marked to approximate the radial center of the ring gear & bolted to the axle flange (there is a factory tool for this also).....which is where this mess started.

Were I not a dummy, I woulda checked this as set-up before taking the thing apart. I'd feel much more confident at this point knowing the original lash.

No changes to the shims, Walt. Central Tools Inc. is on the box.....no other marking except "Visegrip". It takes some foolin' around to get the flexible arm.....er...inflexible/stable.

[ChrisBennet]

Originally Posted by J P Stein

This should about do it for me. Got the backlash checked and it's .006-.007" vs
.16-.20mm (rounded) from the book. A bit towards the bottom of the tolerance.
My tooling is a kind'a makeydo, but functional. .......

When measuring the backlash of a gear you want to measure it at the outside edge. Here's a picture of this I found on the Mopar Muscle website:



Obviously, in the case of the 901/915/930 ring gear, the case is in the way so you can't put the indicator on the edge of the gear directly. However, you still need to place the indicator at same distance i.e. the radius of the ring gear. It could just be the perspective, but it looks like your distance is too small.



Just tip when checking the backlash on the ring gear: Make sure there isn't any slop in the flange to diff union (which would skew your readings). One transmission I worked (a friend's 930) on had some slop in the output shaft spines. My friend had to make a tool to bolt directly to the differential instead of bolting something to the output flange.
-Chris

[J P Stein]

Jezze Chris, you're a little late for this conversation. The engine/trans went in the car today.

As Mr. Ledbetter explained it, the gap (backlash) is the same (or should be) throughout the length of the contact area twixt the R & P. The radius of the ring grows as does the radius of the pinion as you move away from the center of rotation.....makes sense to me.

Your Mopar dude has a real bad cosine error with the angle of the indicator to the face of the ring tooth.

[J P Stein]

The new owner of my 914 has carried thru with a trans mod "plan".
10-12 lbs of excess rotating has ben eliminated. It's rather specialized...I figure not many here are rushing to the exits to duplicate this. .....

[Walt Fricke]

Oh you autocrossers. Never need 4th or 5th, do you.

[J P Stein]

Originally Posted by Walt Fricke

Oh you autocrossers. Never need 4th or 5th, do you.

Not often do AXers go over 80 mph.....maybe PCA at Qualcom. Decent 901s are cheep.

A builder still can use ones imagination in the Prepared & Mod classes at Autocross....more so in PCA than SCCA but there is still room at the latter.
You want a turboed twin rotor in a Sprite.....you'll find a class to run in at autocross.