Getting Ready for 915 Rebuild - It's my turn.

[arbita1]

Originally Posted by Porsche_monkey

How much play do you have? And (Peter Z) why do you say no to the loctite? Concentricity issues?

No play. But I can rotate it and slide it in and out. The gap I measured to be .076mm between the race and the housing. Although its kind of hard to say for sure, since I'm trying to measure a round gap with a flat feeler gauge. You can see photos above.

[Porsche_monkey]

That's 0.003", quite a bit. I'd still be tempted to try Loctite.

[Peter Zimmermann]

Originally Posted by Porsche_monkey

How much play do you have? And (Peter Z) why do you say no to the loctite? Concentricity issues?

The problem is complicated enough that I'll do my best to explain. Sometime during Carrera production, beginning with '84 3.2 cars, Porsche attempted to fix the pinion shaft bearing problem by modifying the diff housing. It's like they didn't have total confidence in their "fix," so they only did the mod to some, not all, of the transmissions.

Through the end of SC production Porsche used a 62mm OD bearing for the main shaft (the bearing that sits next to the troublesome pinion shaft bearing), but Porsche reduced that bearing size to 55mm OD for "some" Carreras (it's probably safe to assume that all '86 cars got the 55mm bearing). That change effectively increased the thickness of the support material between the two bearings by 3.5mm. Guess what? The change worked, I've had a number of the small bearing diff housings apart and have yet to find a loose pinion shaft bearing race in one of them (and have not found a failed smaller bearing).

That leaves us to think about why the pinion shaft bearing gets loose. Hole flex is probably the answer, and I've had a number of 915s apart that had been fixed by others, including bearings secured with Loctite, and those bearing races are always loose. I would guess that if the diff housing at the pinion shaft bearing was as structurally strong as the bearing race, perhaps Loctite might work.

That is not the case because I know from experience that the pinion shaft bearing opening doesn't just move a fixed amount, its condition continues to gradually deteriorate. I've seen housings where the bearing race could just barely be turned by hand, and housings that were so bad that I could spread apart two fingers inside the race and simply lift it out of the housing. The bearing race in one trans that I repaired came out with the bearing (the oil lock was enough to overcome the housing) as I removed the shafts from the diff housing. As I moved to the bench it fell off, hit the floor and rolled away.

The stresses on that bearing position are so great that the precision-machined diff housing flexed enough to allow the bearing to get loose, so in my mind I can't picture how peening, or Loctite, sometimes both, can possibly do the job; neither solution is as strong as the original housing. You have a combination of flex, expansion/contraction, and torque loads all acting against an insufficiently supported bearing. A steel shim precision machined for the housing, installed at a correct press, provides the needed support.

It's kind of like constructing a building on sand, sooner or later the building is going to start to move. Add a row of cement blocks, with no mechanism to anchor them internally, around the perimeter for the walls of the building to sit on, and you have the illusion that the building is stable. But at some point the sand outside of the cement blocks starts to move, which allows the cement blocks to move, which allows the building to move. The builder bought a little time, but a little time, in my mind, is not enough.

[arbita1]

So here is my current status:

I ordered my replacement parts for the 5th gear and pinion shaft work. I'll have those probably early next week. I'm waiting for my special tool to be made so I can start disassembling the main shaft. And I'm still trying to decide what I should do about the pinion shaft bearing race. (I'm currently leaning towards sending it out to be reinforced.)

This weekend I'm going to start removing the dog teeth from 1st and 2nd gear. I bought some exhaust clamps and am going to try that method. Hopefully it works for me.

How do I go about putting the new dog teeth on the gears? Do I need a press?

[Peter Zimmermann]

Originally Posted by arbita1

This weekend I'm going to start removing the dog teeth from 1st and 2nd gear. I bought some exhaust clamps and am going to try that method. Hopefully it works for me. (1)
How do I go about putting the new dog teeth on the gears? Do I need a press?(2)

1. Tread carefully, the last few dog teeth rings that I've replaced would have treated exhaust clamps very rudely! Hopefully yours won't be as tight!

2. Pressing the new dog teeth on is highly advised, if for no other reason than to keep the pressure against the ring equal all the way around so you don't tweak it. The important thing is to keep the new ring square to the gear hub.

[arbita1]

So it sounds like I need a press. Norther Tool has 6 and 12 ton ones for not too expensive. I don't know if they will work though. Can anyone tell me.

However if I only have a couple of parts that need pressing maybe I could just find a shop to do it for me. What else will need to be pressed on/off?

[Porsche_monkey]

Originally Posted by arbita1

This weekend I'm going to start removing the dog teeth from 1st and 2nd gear. I bought some exhaust clamps and am going to try that method. Hopefully it works for me.

How do I go about putting the new dog teeth on the gears? Do I need a press?

Last ones I did had to be ground off, and then broken away with a chisel. They can be a real bear. Be prepared to use other means than the clamp.

Don't know anyone with a press? They are pretty handy, someone nearby must have one.

[Peter Zimmermann]

Originally Posted by arbita1

What else will need to be pressed on/off?

Depends how far you go with your repair. If you have the P/S bearing reinforced you might want to replace at least the bearing that was spinning. That means that you will have to remove everything (with a press) from the P/S. Likewise with the M/S, if you're going to check everything (highly recommended because you said that the castle nut was actually loose so you might find the same with the large M/S nut), a press makes it much easier to do that work.

[arbita1]

So I took a better look at my spun bearing and also checked the area for any cracks. Luckily there were none. However, I was a little less timid this time in checking it out and realized that I do have some side to side play and I can easily remove it.

So....





I guess it's going to the west coast. The case is still heavier than I had hoped. This is going to suck to ship. I'll probably send the side cover as well since they clean it. Might as well have it all cleaned up.

On another note, are the bearing races in the intermediate cover supposed to spin?

Also, I noticed that the threaded hole that the throttle linkage attaches to is all chewed up inside for some reason.





Do I need to find a new cover now???

[arbita1]

Originally Posted by Porsche_monkey

Don't know anyone with a press? They are pretty handy, someone nearby must have one.

Can you tell me what least expensive one that will work here.

http://www.northerntool.com/webapp/wcs/stores/servlet/NTESearch?storeId=6970&N=0&Ntk=All&Ntt=shop%20press&Nty=1&D=shop%20press&Ntx=mode+matchallpartial&Dx=mode+matchallpartial

http://search.harborfreight.com/cpisearch/web/search.do?keyword=shop+press

[Peter Zimmermann]

Originally Posted by arbita1

So I took a better look at my spun bearing and also checked the area for any cracks. Luckily there were none. However, I was a little less timid this time in checking it out and realized that I do have some side to side play and I can easily remove it.

I guess it's going to the west coast. The case is still heavier than I had hoped. This is going to suck to ship. I'll probably send the side cover as well since they clean it. Might as well have it all cleaned up.

On another note, are the bearing races in the intermediate cover supposed to spin?

Also, I noticed that the threaded hole that the throttle linkage attaches to is all chewed up inside for some reason.

Do I need to find a new cover now???

It sounds like you bought a fairly "rough" trans. The center housing bearings usually only get loose after the pinion bearing condition gets to extreme wear. There is far less load on those two bearings than the big P/S one, and depending how loose they are if the P/S bearing gets reinforced sleeve retainer will usually work on the other two bearings. How "loose" are they? Of course, if you have a chance to buy a center housing with tight bearings you will be better off.

EMS can also fix the threaded throttle linkage hole if you send them that part of the housing.

Definitely send the side cover with the diff cover - the machine shop will use it to stabilize the housing during machining. Remove the bearing races from the housing and cover - you should plan to replace them anyway. Also, remove the throw out bearing guide tube and re-install the missing studs for the side cover (or ask the machine shop if they have new studs for the housing).

Originally Posted by arbita1

Can you tell me what least expensive one that will work here.

I use a 20-Ton press that I bought from Harbor Freight in 2000. I never dreamed that I might get 10+ years of use from it, but it's still perfect and the jack does not leak.

[Porsche_monkey]

I think the H/F 20 ton looks like a pretty good deal.

And since I just keep agreeing with Peter you should ignore me and just take his advice.

[arbita1]

How about the 12 ton version. Do you think this will do the job?

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=33497

[Porsche_monkey]

Yes, but for $100 more I would go with the 20 ton. But I like overkill

If the $100 is an issue buy the 12 ton.

[arbita1]

Originally Posted by Porsche_monkey

Yes, but for $100 more I would go with the 20 ton. But I like overkill

If the $100 is an issue buy the 12 ton.

Not so much that as the 20 ton looks huge and I'm already cramped for space in my garage.

Plus...after I'm done with this...other than my transmission that is currently still on my car (which I'm thinking of rebuilding as a spare or selling)...I can't think of what I'm going to use this thing for.

[BReyes]

Great thread. The definition of no fear! Of Pelican working on 911.

Good luck.

[arbita1]

Originally Posted by BReyes

Great thread. The definition of no fear! Of Pelican working on 911.

Good luck.

LOL. Thanks but far from it. My biggest fear is going through all of this getting it into the car and finding out it doesn't work properly!!!!

So Pelican delivered my parts for the P/S, however, I'm stuck because I had to order the new P/S bearing. I also can't send the differential case out to EMS for the same reason.

I found out my special tool to remove the nut on the M/S is ready. So once I get that I can start the M/S disassembly.

I found a good intermediate case on Ebay. The race bearings are supposed to be tight. So I'm waiting for that now.






I'm still contemplating what to do about a press and the exhaust clamp method doesn't seem to be working. I'm really fighting having to buy a shop press. Maybe I can just find a shop to do all the pressing, however depending on what they might charge it may almost make sense just to buy one.

[Porsche_monkey]

You can carefully zip-cut the dog tooth part and get a chisel under each side to get it off.

And you might be able to re-instal the new one with a vice...carefully. Or just take it to a machine shop, they should press everything you need done for $25.00 cash.

[coollx]

Matt, I have a 15 ton press that resembles the 12 ton one you are looking at that I've had 20 years. It has handled everything I've ever needed it for including pressing dog teeth off and on as well as any of the bearings on the 915 main and pinion shafts. The bearings in my 915, and I suspect most, only have a slight interference fit and can be pressed off and on cold with very little effort. The dogs are a tighter fit but I was able to get mine off with the press and a bearing separater in about 5 seconds. I think the 12 ton would be fine for what you'll do with it. You could always sell it after you are done and get most of your money back. Dom

[arbita1]

...at least not for dog teeth!

I used the Dentist's method with a heavy duty exhaust clamp.



However, I felt my problem was the socket I was using was the weak link. So I made a modification...



I gave it a few good whacks...



and off they came. Then I put the gears in the freezer for about 2 hours. And started the new dog teeth on by hand and then used the vice to press them on.



It went much easier than expected.