Ok. Let me take a step back here.

I'm using the same ring and pinion that came with the transmission. And I'm using all the same shim packs it came with. The P/S bearing was re-used as it was determined by the machine shop to still be in good condition. The only thing that was changed were the carrier bearing and races.

Based on the above my understanding is that I should not have changed any differential settings.

It turns out I do have a torque wrench that goes as low as 10 ft-lbs. So I torqued the nuts to 18 ft-lbs (which is the higher end of the spec and it was too tight for the ring gear to move).

Is it possible that the bearing races are not fully seated?

"Is it possible that the bearing races are not fully seated?"

This is possible if you think about it logically but if you used a press they should be full home. Even if you didn't use a press you would be able to tell by looking at them. Are the races full seated in the case and side cover? Are the bearings tight against the spacers on the diff? I'm guessing yes to both of these questions.

Hopefully Peter Zimmerman will chime in shortly. (he almost always does on the gearbox posts)

I hope I haven't ruined your day but the reason I made that post is because of other threads I have read on the subject of pre load and backlash. I'm re assembling my troubled gearbox at the moment and here is a link to my thread...

http://forums.pelicanparts.com/porsche-911-technical-forum/462734-915-shift-fork-check-unexpected-outcome.html

I have created a word document with lots of detailed information about this stuff.

I'll send you a message with my Hotmail email address shortly so I can send you this document. It's about 22 pages long with lots of diagrams and pictures.

This is a picture from the Porsche work shop manual. (stolen from another thread)

Please read the section under "Ring gear has to be adjusted, if"

http://forums.pelicanparts.com/uploa...1240402142.jpg

Peter, may I please get a copy of your work also?

Cheers
John

Just sent you a PM with my email address. I'm a bit reluctant to post it here.

Whew, this isn't easy to do via "long distance." FYI: Side cover nut torque will not affect bearing pre-load after the nuts are tight. Using only four (for example) equally spaced nuts to make the measurement might not give you a perfect measurement. Here are my questions:

1. Are you sure that both carrier bearing races are fully seated (one in the housing & one in the side cover)? You can see if they are by simply looking at the back side of each race through the axle flange hole.

2. At this point forget all about pinion depth and backlash, it just confuses this issue.

3. When you removed your old carrier bearings I will assume that you did them one at a time, pulled off any shims under them, and cleaned the shims thoroughly, correct?

4. Did you damage a shim while having trouble removing the one bearing?

5. Did you notice that the shims (not the .25mm super-thin ones) have a square cut on one side, and a bevel on the other. Are you absolutely sure that the bevel is facing the diff on each of the thick shims?

Answer these items and then we'll move on to how you are trying to get the ring gear to turn with the side cover torqued.

In order to correctly measure pre-load you need the following, the washer is homemade and is a snug fit at the ID (35mm), and I had to bevel the outer edge to face the diff because it was a little too wide (7.4mm) and I didn't have access to a lathe (my washer is 2.6mm thick):


http://forums.pelicanparts.com/uploa...1240412895.jpg
http://forums.pelicanparts.com/uploa...1240412935.jpg
http://forums.pelicanparts.com/uploa...1240412958.jpg
http://forums.pelicanparts.com/uploa...1240412986.jpg
http://forums.pelicanparts.com/uploa...1240413016.jpg

Hopefully this will shed some light on things.

The light is brighter!

Sorry, but you might have to pull those bearings back off. This will be very difficult, to not damage them, with the tools you have, so we'll try something else first.

Use a mag light, or similar, to light the area under each bearing. Look at the side/edge of the shims and check to see if they are standing proud from the carrier surface, or if they appear to be firmly seated against the carrier. I have an old diff in the garage (see next post) that I'll look at later to see if this approach will help us...

Matt: Please don't miss post # 48!

Here are a couple of pics for you; I've never experimented with putting the shims on square side down, but I imagine that will only be a few thousandths difference. That said, in this biz even a spec of hard dirt makes a difference.

If you have one or both shims upside down hopefully you'll be able to detect a space using feeler gauges.
http://forums.pelicanparts.com/uploa...1240426639.jpg
http://forums.pelicanparts.com/uploa...1240426667.jpg

I'll take pictures when I get home.

Peter Zimmerman

You post the best pictures... You should write a book about the 915 gearbox.

PM from Porsche Monkey replied to.

Thank you, sir!

Don't print more than 100 copies. We are the proud, the few, the 915 rebuilders. :)

Ok. I pull the differential back out of the case and looked at the bearings. Here are some pictures...

http://forums.pelicanparts.com/uploa...1240450902.jpg
http://forums.pelicanparts.com/uploa...1240450914.jpg
http://forums.pelicanparts.com/uploa...1240450925.jpg
http://forums.pelicanparts.com/uploa...1240450938.jpg
http://forums.pelicanparts.com/uploa...1240450953.jpg
http://forums.pelicanparts.com/uploa...1240450971.jpg
http://forums.pelicanparts.com/uploa...1240450985.jpg

But I don't think this is where my problem lies...see next post there will be more pictures.

I decided to put the differential back in the case and spin it without the side cover on.

It spun freely, but I would hear it get caught up on something at every cycle. It seemed like the speed sensor was rubbing against something...

http://forums.pelicanparts.com/uploa...1240451163.jpg

What the hell is this?

http://forums.pelicanparts.com/uploa...1240451185.jpg

And this?

http://forums.pelicanparts.com/uploa...1240451206.jpg

And this.

http://forums.pelicanparts.com/uploa...1240451223.jpg

Does that look right?

I'm slowly getting that sinking feeling.

Looks like someone has welded up the crack from the back (inside). It is a really thin bit of alloy casting between the diff magnets and the external sensor... But no reason it can't be cleaned up.

x2... The 915 castings are not perfect. Don't stress about it. If you can clean up that weld without compromising it then it should be fine.

The crack from the outside is a worry but the weld from the inside can be re done and ground flat. This won't cost mush to fix.

Think of it this way. It's so much better that you found this now rather than after it was back together and in the car. So in a way this is a good thing... Well done.

This reminds me of something a Doctor told me when I was in training to become a nurse...

More is missed from not looking that not knowing.

Just a thought... This is an SKF bearing.

Was the old one you removed an SKF? or the original OEM one from the factory?
I just looked at mine and I can't see any marking on it like yours in the photo so I'm assuming it's OEM
and therefore not manufactured by SKF. (or it may be unbranded but made by SKF)

You would assume that the bearings would be the same size externally regardless of the manufacturer but we need to confirm this measurement.

Do you still have the old ones? Are you able to accurately measure their stacked height?

The Genuine Porsche ones are: OEM-999-059-027-00 - $80.25
SKF Part number from our host: 999-059-027-00-M92 - $25.00
(Both available through our host)

Again... Peter Zimmerman should be able to confirm this measurement as he probably has a box full of old OEM and SKF bearings.

What a great thread!

I have to see if I got rid of the old bearings or not. I may still have them. I'm 90% sure they were OEM. I didn't see anything that said SKF on them. I'll take a look tonight to see if I still have them.

I was thinking about the situation again this morning. I don't think that gouge in the sensor plate is the problem. While I'm pretty sure it is rubbing, I don't think it is what is locking the ring gear in place when I torque the side cover nuts. It spun fine before I removed it and the nuts were tight and the side cover was tight.

Another thought I had is, is it possible that I could have not installed the differential straight into the housing? Could it have been tilted and that is the reason it was locking up when I installed the side cover?

I tried looking at the shims, I can see the flat parts are lined up together. But I don't see anything else. I think they look like they are fully seated. It's hard to tell on the ring gear side.

I don't think that's possible... The bearings on the "speedo" side of the diff just drop onto their races in the case.
The side cover centres the ring gear end. You couldn't tilt it and still get the side cover on.

It's good you're thinking this through. Just imagine when you're gearbox is fixed how proud you'll be you did it yourself.

You'll feel that pride every time you drive your 911.

Thanks all…excellent education here on the 915…. I’m about to attempt to change out 3-5th gears myself.

After reading this, I have one question. Is it difficult to ‘press’ off the bearing on the pinion to get to 3rd and 4th gears?

I have never seen damage like that, can't even guess how/why it's there! That said, if your diff was tilted in the bearing race it might have hit because of that, but might not hit after the side cover is on and the diff is centered (as Peter stated). If it were me I would tidy up that weld, and then add a thin layer of JB Weld to prevent a leak. Put a speedo sensor on the diff housing and turn the speedo ring, with an ohm meter hooked up, to make sure it is reading the signal.

About the bearings, you have, generally speaking, two options; (1) SKF, or (2) FAG. Either is OK, but the pre-load spec for each is different than the other. The bearings will measure the same, but if you remove SKFs, and install FAGs, you might need to replace shims to get the proper reading. This should definitely be checked because it's obvious that someone was in that box who didn't know much about it.

I looked at your shim pics, and I think that I can see a space beneath one of them. Did you try to confirm that with a feeler gauge set?

I think that you have the makings for a new thread here. In order to not complicate Matt's thread please open a new one and I'll respond. Cheers!

I'm not much for metal work. Do I just take a file to it? Does anyone have a spare speedo sensor sitting around that I could borrow? Mine is currently on my car.

Here is a picture of the old bearing.

[/QUOTE]http://forums.pelicanparts.com/uploa...1240513142.jpg

I doubt you can tell much from it. I'll look at home to see what the old bearings were. Hopefully I still have them. :rolleyes:

Are you talking about this one?

http://forums.pelicanparts.com/uploa...1240513271.jpg

I did do some checking, but then got side tracked by the speed sensor thing when I saw that. I'll check again with a feeler gauge. Could it hurt to put the differential back on the press and just try to press the bearings some more to make sure they are fully seated? I'm afraid of over pressing. Should I be? This is my first go round using a press.

Thanks for the vote of confidence. Right now I'm starting to feel like I'm never going to get through this.

Sorry, that doesn't help...



Are you talking about this one?

Yes, but the angle makes it very difficult to tell for sure. Can you try to duplicate my photo using the macro setting on your camera?

I did do some checking, but then got side tracked by the speed sensor thing when I saw that. I'll check again with a feeler gauge. Could it hurt to put the differential back on the press and just try to press the bearings some more to make sure they are fully seated? I'm afraid of over pressing. Should I be? This is my first go round using a press.[/QUOTE]

With a press, when they're on, they're on - the press handle becomes tight and very hard to move further. You probably should not attempt to press them again, but only you know what the difficulty factor of the press handle was.

I've got to stress to you one more time that absolute cleanliness is critical - are you sure those shims & surfaces are dry and clean (lacquer thinner or MEK)?

You're almost done... All the hard and expensive stuff is behind you.
Once you fix this problem the gearbox should be back together in a day.

x2 on the lacquer thinners or MEK... I use this all the time on anything that needs to be perfectly clean.

But be warned lacquer thinners is highly flammable and not good for your skin.

SUCCESS!!!! (i hope...)

I looked at my old bearings...they are SKF...same brand as the new ones. So preload should be the same.

I looked at the new bearings installed on the differential and checked for any gaps between the bearings and the shims with a feeler gauge. They were tight. I could not fit any gauge in there. I looked around the whole thing and all the shims and bearings looked like they were seated properly. The space in the photo Pete saw is the bevel of the washer.

I just had this feeling that it had to do with the way the differential was installed into the housing.

So I put the housing on it's side this time keeping it level with wood blocks. I dropped the differential in there and spun it. No noise or rubbing! I tilted the case the way I had it last night and there was the noise and the rubbing again. Aparently without the side cover on, this thing can move around.

So this time I put the side cover on keeping everything level and trying not to move the differential around. One thing I neglected to mention yesterday...when I put the cover on I used a rubber mallet to bang it down flat onto the housing (as it was hard to get on). I must have tweeked the differential inside the case and when I torqued the nuts it got stuck probably due to contact inside the case somewhere. The tolerances in there are really tight.

So this time I put the side cover and pushed down as far as I could go with my hands keeping it straight. Then I tightend the nuts to seat the cover down and torqued them.

And the ring gear spins!!!

The only thing now is I wasn't expecting this to work 100% so when I reinstalled the cover I didn't oil the side cover seal again. I oiled it last night though. I probably need to pull it out and re-oil it right?

The oil on the o-ring is only for ease of assembly. Just be warned that in many transmissions the pre-load will change over time due to normal stresses, and should be checked.

Thinking ahead a little, have you cleaned/checked your metal shims that are used to set pinion depth? A loose pinion bearing often damages those shims to the point that they have to be replaced. Also, the clamping plate for the pinion shaft must also be checked for wear at the point that it contacts the pinion bearing race.

I have cleaned the pinion depth shims...but I'm going to take a picture of them for you to look at because I want to make sure they are re-usable.

The clamping plates were checked by the shop that did the P/S sleeve. They determined the M/S plate needed to be replace and gave me a good used one and the P/S one was good.

I think these are shot...what do you think?

http://forums.pelicanparts.com/uploa...1240534768.jpg

http://forums.pelicanparts.com/uploa...1240534798.jpg

http://forums.pelicanparts.com/uploa...1240534830.jpg

http://forums.pelicanparts.com/uploa...1240534863.jpg

Too damaged for my liking...

I really don't like being obvious but this is a precision item that sets you P/S depth so they need to be better than good.

Anyway, If it was mine I would buy new ones. At around $10 bucks each why wouldn't you?

Check the thickness of all three with a good calliper at several different points.
Double and triple check the thickness... Make sure you're 100% of their measurements... Then buy three the same as when you have.

0.10 mm – 915.302.268.03
0.15 mm – 915.302.268.04
0.20 mm – 915.302.268.05

Great news on the differential...

Man, you got that right!!!

Find a metric micrometer somewhere and measure those shims on a section that's as undamaged as possible. They are available from the P-car dealer in three different thicknesses (.10mm, .15mm & .20mm).

To be clear, your R&P settings will be OK if:
1. The pinion depth shims removed from the trans were correct
2. Your replacement shims match the old shims exactly
3. You didn't mix up the diff carrier bearing (pre-load) shims, and you have them correctly installed, as they were, with the bevels toward the diff carrier
4. The pre-load shims were correct to begin with for both pre-load and backlash...

Now why would they just mark on the shim what the thickness is so there's no guesswork????? Too easy I guess.

I have a micrometer, but it's inches not mm. I think I should be able to figure it out though since the incriments are 5mm apart. I'll give it a try.

Pete as for the R&P settings...I can only assume that everything was set up from the factory and not changed down the line. All the bearings/shims etc. seem to be original and I have no reason to believe they were removed or changed for any reason. I've put everything back just as it was and I'll make sure I get these new shims right.

It's all good from here... Good luck with the final assembly.

Post some pics when you're done.

If you can it would be great to see a video of your car when she's going again.

Try and you show the shifting from within the car as your driving.
Maybe get someone to sit in the back and take the video as you drive.

New to this 915 stuff.. and I have a simple / dumb question..

How does one 'hold' the M/S in place and thighten the 41 mm nut the factory way?
I'm missing some thing here with this 915 education..thanks all;)

This is a good place to start. It explains this and other challenges in rebuilding one of these legendary gearboxes...

http://www.pelicanparts.com/MotorCity/marcesq3/TrannyRebuild.htm

There is a wealth of information in many threads here.

Just search for threads titled "915 gearbox" or "Differential" or whatever you need.
Have fun

If you have the 8th Edition of my book (The Used 911 Story) check out page 30, where a few of the factory transmission repair tools are pictured. The "holder" is the top left picture, the "tightener" is the lower right picture.

I measured my shim plates.

I came up with two at .0035" and one at .0055".

So I'm figuring two .10mm and one .15mm.

Everyone concur?