915 Trans - Mainshaft ball bearing

Shawzy · 07-30-2002, 04:39 AM

Thanks to some great threads on this board (Tony and Jim's), and the Bentley and Haynes manuals, I ripped apart my 915 tranny for the synchro rebuild. So far so good!

However....when dissassembling my mainshaft (or input shaft as some call it) the ball bearing seem to...well... dissassemble itself. Luckily the balls didn't roll far! The inner brass(?) race seems fine (no cracks) and the balls seem fine (no evident wear), outer housing seems fine too. Can I re-use this bearing without sweating? I expected to have the bearing come off the shaft intact, but as I haven't done it before I can't be sure. Is there a red-loctite trick for this one or must I drop $250CAD on a new bearing

?

Many thanks

Jim Sims · 07-30-2002, 08:31 AM

I am a bit dismayed about these ball bearings coming off in pieces. First Janus's and now yours. Did you press only on the inner race to remove the bearing; this is really the only sure way to get most bearings off "intact". I personally wouldn't reuse a ball bearing that came apart. It may work fine upon reassembly but it may not. Ask yourself if it is worth C$250 to take the transmsission out and apart again to replace that bearing when and if it starts "whining or howling" in the future? Only you can answer that question. Have you attempted to locate an equivalent bearing through another source beside the OEM Porsche parts system; without the Porsche "tax" I would expect a bearing of this size and type to cost between US$50 and US$75. Perhaps John Walker will come in here with his more experienced opinion. Cheers, Jim

tbitz · 07-30-2002, 09:51 AM

Where in Ontario are you located? I'm in Ottawa.

I'd try and source another place for the bearing. When I had the motor out for my tranny rebuild, the main bearing in the altenator was shot. I found an equivalent replacement for $5.

Tony

Tim Polzin · 07-30-2002, 10:27 AM

Jim:

A few years ago, I rebuilt the 901 transmission on a 914 I had at the time. The intermediate plate bearings both needed replacement. I provided the FAG bearing numbers to a large local bearing house who was a FAG dealer. Without telling him what the bearing was from, he indicated that the bearing was proprietary and was only available through Porsche.

Was I handed a line of BS, or is this have some element of truth to it?

Tim

Jim Sims · 07-30-2002, 12:10 PM

Tim, I haven't actually tried to 3rd source a 915 transmission bearing so the following is speculation but based on my experience in obtaining replacement bearings for other equipment. The bearing house's statement is probably legitimate. Porsche could have made an arrangement with FAG to put a special number (could be a simple as a single character added to the usual FAG number) on a standard FAG bearing and sell it only to Porsche. What is more likely is that a standard FAG bearing was modified slightly (probably one or both of the races) and it became a special for Porsche. It is unlikley the entire bearing is custom as the internal features are expensive to tool for and there are so many standard bearings available that one can usually be found and slightly modified to suit any given application. One may be able to still cross-reference to another FAG bearing or another brand of bearing if the races are not too special. However, one would need to determine the quality, style, load and speed rating of the special Porsche bearing. This is not always obvious as ball bearings have different ball/race contact patterns depending upon how they are to be loaded. One would have to carefully inspect and measure the bearing and then have access to bearing manufacturer's design and catalog information. It is probably not worth the effort (if FAG is trying to keep the bearing proprietary) unless one is trying to prove a point or is in a corner. I've had to do this with obsolete equipment for which the bearings were no longer available from the OEM. Cheers, Jim

Shawzy · 07-30-2002, 05:07 PM

Thanks for the input guys!! I'm so glad to hear from you Tony and Jim as I have read your threads in detail before my attempted rebuild.

Tony - I am within 1 hour of Toronto in Dundas, Ontario, just north of Hamilton. I was in Ottawa last week actually grabbing a UK Visa - I actually thought of emailing you to talk shop but I thought we should meet here on the board first...

I am tempted of course to re-use the bearing as it appears fine. My instincts say replace however - to be on the safe side. I would like to find a suitable replacement bearing by SKF or another manufacturer. I assume that if I bring the bearing in, tell them the application, they will specify one that will meet all requirements. Unless of course, they can't due to proprietary info! That's when I go to another manufacturer I guess. I assume there is no substantial radial load placed on the bearings, and a moderate axial load. If I picked bearings out of a catalogue, I would use a safety factor of 2.5 to ensure good wear and performance capabilty.

I priced the bearing from Porsche at $265. Not too bad, but I am sure if I hunted I could find a replacement for less than 100. Is it worth it? I must ask this. Worst case is that my replacement bearing wears more quickly than the Porsche one and I am into another project. Because I am a telecom contractor for Nortel Networks, I HAVE HAD LOTS OF TIME ON MY HANDS LATELY. (Stock now at $1.50CAD from $120 18 months ago - ouch) That's just fine when working on my baby of course, but one can only play with other projects for so long. I keep busy on the lathe - turning a synchro hub removal tool and building a shop press right now to do things right. I used your hammer and chisel trick Tony - worked well although took a while and almost lost a thumb doing it.

I will check out some bearing folks and post my findings here on the board if you guys are interested. I may even try and get them to explain why I shouldn't re-use my old one. When properly assembled on the shaft, there's no way the balls would find there way out, even if the inner race shattered.

Wish me luck...

Jim Sims · 07-30-2002, 05:24 PM

Shawzy, There are both radial and axial loads on the ball bearings. Helical gears produce both types of loads. The synchronizers/operating sleeves also produce mixed loads. Cheers, Jim

Shawzy · 07-30-2002, 06:03 PM

Radial and axial loads agreed, but I wonder how substantial they are? Enough to cause what happened to mine I guess! I know little of helical gears and perhaps my assumption of loads is incorrect and that the bearings need to stand up to more punishment (I knew I shouldn't have slept through those stress and strain classes damn it).

You ask me Jim how I removed the bearings - I used the good ole inertia method (man was that a blast) because my shop press hasn't been welded together yet. I was careful about how things came off, i.e. I was holding everything in my hand when it finally separated from the shaft. The bearing fell apart when I placed it on the workbench. The two 'washers' on each side of the bearing appeared to be separate. I almost thought the bearing was designed to come apart when it did, but then realized it wasn't so after reading in the Bentley to 'press off the inner race' if necessary.

thanks for the bearing loading info...

Jim Sims · 08:32 PM

If it came apart in your hand it may be okay, but I would think if the ball cage or separator was good, the balls would not come out of the inner race. From an old 1997 catalog: 72-86 915 mainshaft (input shaft) four point ball bearing (yes, the outer races are loose or separate but matched to balls and inner race); Porsche Part No.: 999.052.030.00, Mfg. Part No.: 526406. '97 price was reasonable. Cheers, Jim

Shawzy · 07-31-2002, 07:20 AM

I am now wondering if the bearing can be 'rebuilt' with a new inner race, assuming of course that it took the majority of the wear and not the balls. It may not be worth it if I can't rebuild it myself. If a new inner race can be simply pressed into the housing, fine. I am confused as to how the balls stay in the bearing themselves. What keeps them in there when the outer races are separated? I have another similar 4-point bearing on my pinion shaft I may take off and look at today.

I don't want to wait for too much longer so I will likely track down the porsche part or talk to the mfg about a suitable replacement. I might talk to the mfg about re-using the old one with a new inner race. They will likely tell me some more details as to why I should not, which will help me jusitify the $ on a new one.

Thanks for the part no.!

PS. I wonder if Tony or JanusCole had similar issues with their bearings?

Wrecked944 · 07-31-2002, 07:59 AM

"PS. I wonder if Tony or JanusCole had similar issues with their bearings?"

Well, I think we may have stumbled upon a weakness in the "Inertial Gear Removal Procedure". I agree 110% that it is fun as all heck. Of course, next time I'll be sure to wrap a few shop towels around the shafts so I won't beat up my hands so badly.

In any event, I guess we've found that the interia method is pretty hard on input shaft ball bearings. Mine actually exploded and sprayed ball bearings all over the floor. And I also searched around for inexpensive replacements. But since I am a novice I played it very safe and ordered the OEM bearings. I got them from PowerHaus II and they were not cheap. I think it was about $180US. The number at PowerHaus is (641) 469-3063. I've been calling them almost daily asking for advice and parts and they've been very helpful.

And please keep us abreast of your progress !! I am currently in the process of removing the ring gears from my differentials (stock and donor) in order to attach the 7:31 ring gear to the SC differential. Let us know about your project. The folks on this board love to hear that stuff (I know I do).

Good Luck !!

Jim Sims · 07-31-2002, 11:30 AM

Stephen, I sent you an e-mail message, Jim

Shawzy · 08-03-2002, 08:15 AM

I now have my new bearing, and of course compared it to the old one. I was surprised to see the inner brass cage spining freely (I realize now that's the intent of the design). The difference is of course between new and old are the 2 inner races holding the bearing together. They are on there pretty tight and won't come off easily. I am sure if they were removed the new bearing would fall apart like the old one. I am wondering then, are the inner races worn on my old bearing or can they be pressed on in order to keep it together?

The diagram of the mainshaft with it's pieces (Bentley manual pg ?) shows the ball bearing off the shaft with the 2 inner races separated. Why do they not show the bearing intact with the 2 inner races still holding the bearing together?? The Bentley states the inner races are to be heated and then pressed on as if they are to be treated separatley from the bearing (I assume they mean pressed onto the shaft and not pressed onto the bearing - it isn't clear). The diagram implies to me that it is expected for the bearing to come apart, and be re-used.

From the board, I know that the bearings do come off intact (i.e. inner races remained in bearing). My Bentley is confusing me damn it.

I hate confusion!

If this was a $50 part no big deal. I don't want to spend $250 on a part that may not need replacing, agreed? We have all been there I am sure.

Wrecked944 · 08-03-2002, 08:52 AM

I received my new bearing yesterday and put it on the input shaft last evening so I may be able to help...ain't the internet a wonderful thing? Where else can you find a dude in another freakin' country who *just happens* to be 1/2 step ahead of you in rebuilding an identical exotic european sportscar?...(laughing)...

Anyway, enough of the Pelican Love Fest...I also have a Bentley and I agree it is pretty lightweight regarding the input shaft ball bearings...so I examined mine and compared old to new and this is what I found...

From outside to inside the assembly consists of: 1) An Outer Ring, 2) Ball Bearings, 3) An Inner Brass Cage which holds the Ball Bearings against the Outer Ring, and finally 4/5) Two Inner Races on either side which hold the entire assembly against the input shaft.

When I examined my new bearing assembly, the Two Inner Races (i.e. #'s 4/5) fell easily off the assembly and into my hands. Following the Bentley (sort of), I heated and pressed these little guys onto the input shaft (first one, then added the rest of the bearing assembly, then the second race). The rest of the assembly (i.e. (#1) Outer Ring, (#2) Bearings, and (#3) Brass Cage) seems to be pretty solid and would not come apart. My guess is that the impact of the Inertial Gear Removal procedure ripped the (#3) Brass Cage from the (#1) Outer Ring allowing the (#2) Ball Bearings to spew all over my floor.

Can the old assembly somehow be repaired? I have no clue and I was too cautious to try. I posed the question on this BBS and it was suggested that ball bearings are manufactured to pretty close tolerances and so hurling them all over the floor might disqualify them for future use.

I hope that helps.

Shawzy · 08-03-2002, 10:17 AM

That helps tons actually.

You are saying then that with the inner races removed on your new bearing the balls and cage stayed intact? I.e. the balls and cage didn't fall out?

I thought the inner races held everything together....

Tell me something, with the inner races removed, did the cage and balls spin within the outer race and still not come apart? That is the key for me. I am shocked if that's the case as I don't know how the balls would be kept in the cage with the inner races out (unless the oil in the bearing provided enough 'stickyness' to keep it all togther).

My inner races on the new bearing won't come off easily. I am thinking that when I heat up the whole thing in the oven the inner races may pop off and cause the dissassembly of the bearing, depending on how things expand relative to each other.

My balls did not fall onto the floor but rather into my hand, so perhaps they can be salvaged.

Can you check out my thrust block thread JanusCole? I just posted it recently and would love your input.

Good luck with the reassembly - hope it goes well!!! I'll be there Wed hopefully.

Too bad we can't have beers together when it's all done over the net - that will be the next tech generation hopefully.

Wrecked944 · 08-03-2002, 12:29 PM

"That helps tons actually."

I'm very glad to hear that. I have a lot of good karma to return to the folks on this BBS for helping me out a zillion times.

"You are saying then that with the inner races removed on your new bearing the balls and cage stayed intact? I.e. the balls and cage didn't fall out?"

Yes, exactly. And since I have already installed the new bearing assembly, I took a picture of the old bearing assembly (sans balls) laid out the same way the new one was prior to installation just so there can be no confusion...

"Tell me something, with the inner races removed, did the cage and balls spin within the outer race and still not come apart?"

Yes. Spun pretty freely.

"I don't know how the balls would be kept in the cage with the inner races out"

I don't know either. I am a total novice at this stuff. The first question I posted when this tranny project began in April was, "What is a floor jack?" So definitely consider the source.

"when I heat up the whole thing in the oven"

Dude, get yourself a heat gun. The oven may work better, but the heat gun is way more fun.

"My balls did not fall onto the floor but rather into my hand, so perhaps they can be salvaged."

But what does the disassembly say about the condition of the inner cage? Again, I'm just making ignorant questions here. Jim Sims defintely knows this stuff a lot better than I. Actually, nearly everyone here knows this stuff better than I.

"Can you check out my thrust block thread JanusCole? I just posted it recently and would love your input."

Whoa, way over my head. JohnWalker is definitely the undisputed expert on such matters.

"Too bad we can't have beers together when it's all done over the net - that will be the next tech generation hopefully."

Suds-around technology?

Jim Sims · 08-03-2002, 01:40 PM

I reviewed our assembly notes and our 4-point ball bearing had separate inner races and a one-piece outer race that held the balls and cage. When pressing off the end roller bearing the ball bearing and it's two inner races were also pressed free. To reinstall the forwardmost (as installed in car) inner race was heated with a hot air gun and just slipped on followed by the balls, cage and outer race (balls and race lightly coated with Swepco). The rear most inner race hung up even though heated so it was pushed into place with a hydraulic shop press. If the inner races of the replacement bearing are integral to the bearing assembly and the bearing cage is metal; I'd heat the whole thing to 300F or so and slip it on. There is an orientation, flanged lip towards the rear of the car or towards the clutch disk. Don't forget to have the bearing clamp plate (bearing retainer) in place first. Cheers, Jim