Transmission bearings...cheaper options?

[Pazuzu]

I have my 915 torn apart right now, and I'm having a fainting moment looking at the prices for the 6 bearings.

$950? For 6 freaking bearings???

Why can't we just go down the street and get some $50-70 Timkin bearing and be done with it? Are these bearings (which surely were not built by Porsche) not standardized at all? I need to sit down maybe tonight and measure them, but I'd be surprised if they were not standardized sizes.

Convince me that I need a $300 roller bearing for my pinion shaft.


Full disclosure, I'm not 100% convinced that I need any new bearings, but if I can find them for less than $80 each, I'd just buy all 6 for the sake of it.

[KTL]

Unfortunately these bearings are not common sizes and thus the price on them is high. Sorta crazy high.

The bearings that are important to replace are the four bearings at the diff housing. There are the two ball bearings that are captured in the retaining plate. These see a lot of wear and should be replaced. The two roller bearings that are actually within the diff housing are also subject to wear- especially the races. The pinion bearing seems to take a major beating and you can see that from the wear in the race (becomes quite gray/silver in color) from all the loading, as well as the race loosening in the machined bore.

The two bearings in the mid case are often in pretty decent shape and it's not uncommon for people to reuse these. These are also quite expensive, despite them appearing to be a basic roller bearing.

EBS Racing often has a promotional email they send out for price reduction on some of the air cooled classic parts. Worth a call or email to them to see if they'll give you the low low price. PM me your email and i'll forward to you the last email I got that had the discounted bearings.

[kevingross]

Unfortunately few if any of the bearings are generic, as Kevin L notes. You can take the numbers off the bearings you have and try to locate them from a bearing distributor as original FAG/INA, SKF, Timken, etc. parts. If you do so, be sure you dive into the weirdness of identifying and figuring out the modifiers on the parts you find, eg, -CL7A for tight tolerance pinion bearing service, C3 for shaft fit, ... yuck.

I am pretty sure you'll feel better about the bearing costs, though, once you inspect and measure the synchros, and learn what it's gonna cost to replace them, the sleeves, and dog rings!

(BTW, I have gone the distributor route to locate NLA parts for other transmission types. It saves the day, but it's a huge hassle and not worth the time, to me, if you can source the bearings pre-vetted as legit Porsche transmission service parts by SSF, Pelican, etc. I keep a spreadsheet where I track versions of bearings I find in older transmissions because there are different numbers used by different makers. Pretty weird but it works for me!)

Good luck with the project.

[Pazuzu]

Oh, I've already jumped in that hole, I'm replacing 1 and 2 dog teeth, 1-2 slider, both syncros, both brake bands and the anchor/stop blocks.

3-4-5 will just get the syncros swapped around.

[KTL]

Mike,

I wouldn't recommend flipping the synchros. The synchro friction band actually functions on both sides, not only one side.

Obviously the primary side goes into the slider. But the other side sits in the dog teeth and establishes the installed dimension of the synchro band and it also has a frictional effect since the band actually rotates a bit within the dog teeth. I know flipping the synchros has been done before but probably not a good idea if the side you're installing into the dog teeth is severely worn. Just my opinion and not an expert on the 915 by any means.

[Pazuzu]

Actually I was thinking of swapping 3 to 5 and vice versa, instead of flipping them. 4 might be flipped, might be left alone. I might also change my mind once I open them up.

1 and 2 for sure are toasted. 2 had broken dog teeth and 1 is worn down to nubs.

[Trackrash]

My $0.02. FWIW. Look on the bright side. As 911 owners we have the ability to rebuild our cars with the availability of any parts we need. In your case, if you do it right, you will have a transmission that will never need to be repaired again. It helps that the basic parts are of the highest quality to begin with. Rarely do we have to replace worn gears or shafts. Try saying that about anything English or Italian.

The fact that Porsche used special, and not off the shelf bearings, does add to the cost, but at least they are available.

From time to time these bearings will be discounted, so it pays to shop around before buying.

As far a flipping synchros, as mentioned, the only time you might consider doing that is if there is very little wear, and when flipped they still measured in spec. I have done this a couple of times without problems. I have also moved them around, considering that 5th gear is not very demanding on the synchro.

But it is very important to measure every synchro when installed to make sure it is in spec. Even new parts can be way out.

[kevingross]

To me, flipping synchros is penny-wise-pound-foolish, as would swapping 3 and 5 for example. I realize it's your money and time, and YMMV of course. I would hate to get it all back together only to find that, oops, things ain't working as hoped. But that's just me, I am fussy and I try really hard to avoid doing the job twice!

Mike, what's up with the brake bands, anchor and stop blocks that has led to your replacing them? Cheers,

[oldie44]

Some of the 915 transmission bearings are standard sizes under the German DIN numbering system. The roller bearings and the differential bearings are standard but the ball bearings are specially manfactured for Porsche to include the flange on the outer race.
Take a look in the FAG or SKF websites and you will find the bearing specifications corresponding to the numbers engraved on your old bearings. You won't find the roller bearings listed though because they are nonstandard.
The problem with roller bearings is that even though they are standard sizes, they apparently not used by by anybody but Porsche and are not commonly available. The differential bearings are widely used and are available in bearing supply houses.

[Jon B]

Be aware that bearings of similar dimensions can have vastly different applications, from caster wheels to machinery to electric motors.
Bearings are rated for load, capacity, speed, temperature, lubrication, tolerance, alignment, etc.. they're marked with codes to identify these various aspects.
Don't assume that any bearing you can source cheaply is appropriate for your transmission.

[Pazuzu]

Originally Posted by kevingross

To me, flipping synchros is penny-wise-pound-foolish, as would swapping 3 and 5 for example. I realize it's your money and time, and YMMV of course. I would hate to get it all back together only to find that, oops, things ain't working as hoped. But that's just me, I am fussy and I try really hard to avoid doing the job twice!

Mike, what's up with the brake bands, anchor and stop blocks that has led to your replacing them? Cheers,

I'd rather buy all of the pieces and parts inside the gear assembly, then return what I don't use than not buy it and have to wait. There's too many pictures and descriptions of cracked and chipped anchor blocks, and no way to diagnose problems with them until you pull the snap ring and yank them out.


I'm not sure I'll even open gears 3-5, because opening them up means (a) risking damaging something that isn't damaged when you remove the massive snap ring, (b) potentially getting some external junk in there accidentally while opened, (c) being too critical and replacing a syncro that doesn't need it, and (d) damaging something while wrestling getting that snap ring back in place. SO many changes to break something, versus just leaving the whole lying dog alone.

Transmission has 185k on it, daily driven for 10 years, I know how it feels and sounds and the only problems are the damage between 1 and 2 which was getting worse.

Oh, and...

I am fussy and I try really hard to avoid doing the job twice!

I know where you're coming from, but I'm almost the opposite, I LOVE to do stuff like tear into my transmission, so maybe leaving something for next year gives me a reason to crack it open again. I drop my engine at least once a year, opening the transmission again in a year will be a fun weekend for me and maybe i'll spend the last of the money then.

[BlueWing]

I buy bearings at the local Kamen Dealer in Newburg N.Y.. Now the bearings I buy for say my old Harleys are a fraction of what the dealer charges. They are standard bearing for what maybe considered lighter service.

Now go to their more precise and aircraft bearing sections and see the different prices as opposed to the lighter duty section.

Kamen is owned by Sikorski Helicopter, they purchased Kamen to assure a supply of bearings for their stock.

Harley - Timkin Bearings say 8 - 60 bucks
Precision/Aircraft Bearings say 200 - 800 bucks

So even a bearing supplier might no be a "cheaper source, best to purchase a known quality and application for generally similar costs.

Even my Dodge Ram Pickup 5 speed manual cost 2500. for a rebuild so if you want a tranny that will see it's last rebuild in normal service pay now or pay again.

A proper rebuild with correct parts will follow the cars value. Would you keep your car or sell it with receipts from Fastenal or Ebay or from one of our top notch Porsche suppliers/rebuilders?

Terry

[RedCoupe]

Terry, many Ram pickups use a Getrag transmission that is related to the G50 unit in 911's. I think it's called a G53. Mustang, Camaros and Corvettes are also using German manual transmissions, so there just aren't any cheap transmission overhauls any more, European or domestic.

[Trackrash]

It's really hard to know, and I don't know how you would even figure out the differences between "precision", or heavy duty bearings of the same size.

I went through this a while back when I was rebuilding my alternator. The problem I found is beyond the standard numbering system, the manufactures will have their own codes and everyone shrugs when you ask about the specifics. No one who responded to my posting at the time was much help, and the manufactures charts don't go into much detail.

Sorry the hijack, at any rate, I think any of the bearings that are specified for the 915 should be OK to use in a rebuild.

[Matt Monson]

I once inquired with SKF about making a replacement for a Porsche FAG proprietary bearing. It was going to cost me $325 per bearing with a 100 bearing minimum. I suspect at this point in the life cycle of servicing these gearboxes whomever is making them isn't making more than a couple hundred at a time. I see lots of old tranny parts that US distribution has zero on hand and only a small handful of them showing in Germany.

[roblav]

When friends of mine were designing uprights for racecars, the consensus was to use Made in Japan bearings. FAG or SKF were not even a choice. NTN or NACHI were it. Some of the 915 / G50 bearings may have a crossover number.

[fanaudical]

This won't make you feel any better.

My rebuilt 915 had the main pinion shaft bearing fail in less than 2500 miles. This was a factory bearing from the Porsche dealer. Inner race cracked. We (myself and the shop) were never able to confirm an installation or fit-up issue and suspect it might have been a counterfeit bearing that made its way into the supply chain. (It's more common than you think.)

On the bright sight, Porsche transmission bearings are much cheaper than some of the specialized bearings I used to buy for large metal forming equipment. (Those bearings were ~$5k each, qty 4 per crank, ~10000 hour max life...)

[914efi]

Are your bearings known to be bad? My trans was quiet but rough shifting, I just did the 1-4 synchros and sliders and all is well. I didn't even upset the R&P, no need, especially since this is a fair weather low mile car for me and most others I would guess.

My races showed a bit of gray, but since they were quiet, let it run!

[Pazuzu]

OK, I have everything apart. Now, I need advice on what is considered wear.

First gear brake band, anchor and stop block:


No chips, no darkening, no discoloration. Some shiny points on the anchro and stop block ,but small sections along one edge.

First gear brake band surface:



No cracking or chips, but the outer surface is ground mostly flat, the ridges are maybe 70% gone along the whole surface.

First gear syncro:



1st and 2nd gear syncros are bring replaced, but is there specific damage I should be looking for? Are the ridges on the inner surface caused by the brake bands, or do the syncros come that way? None were broken or chipped, all showed some wear, 3rd 4th and 5th all came into spec when tested (76.2-76.4mm).

Second gear brake band and accessories:



Again, no chips, cracks, discoloration

Third gear brake band:



3rd, 4th and 5th shows no damage, but all (especially 3rd) showed grinding/scuffing where the ridges were worn down and took on that matte look of the syncro rings. This was not everywhere.

So, what is "damage" when it comes to brake bands, anchor blocks and stop blocks? I don't have clear damage (chips, cracks, discoloration, burned spots), but what is "you need to replace that part" damage? I mean, I'm looking at $150 extra in parts if the 1st and 2nd stuff needs replacing, that would get me the 1 piece bearing retainer instead...

[KTL]

Brake bands and blocks are typically reused. The bands don't seem to experience much wear since they are subjected to partial rotation, then stop, when the synchro friction band engages the slider ring and starts the braking/engagement process. Both blocks are there to manage the brake band(s) and they too don't seem to experience any discernible wear

The friction material-coated bands are grooved on the inside and the brake bands are smooth on their outer surface. So you can see that internal grooving slightly transfers to the surface of the brake bands but nothing of major significance. Brake bands worth replacing are those that somehow get misshapen by something gone wrong, like when a synchro comes apart. The large bands like 1st and 2nd can sometimes get a bit misshapen but it's easy to see because they should be a nice progressive curve. If they look bent then they should be replaced.

The crescent-shaped bands in 3rd-4th-5th seem to be in good shape almost all the time. I have a bunch of old 3-4-5 bands in a plastic bag and on several occasions i've compared their shape to new bands. I can't ever see a shape difference- even when comparing discolored (excessive heat?) bands to new. I haven't checked any difference in thickness between old and new because they don't seem to show much wear on their surfaces.

These brake bands act much like a spring and they wedge against the inside of the friction ring to transfer the stoppage of rotation via the openings in the dog teeth hub and in the opening in the friction band. Even though you might think a spring eventually fatigues and could break, this doesn't seem to be the case. They are completely safe to reuse.

Gordo2 here on Pelican put together a nice demo video, just like his nice detailed threads here on the forum, to show how it works in operation.

https://www.youtube.com/watch?v=BbBxR8stYRE

He also has a short video that is a great demonstration why the two separate bearing retainers are often not doing their job and and it's money well spent to use a one-piece billet retainer instead. The one-piece retainer is basically a modern billet recreation of the original 930 transmission bearing retainer

https://www.youtube.com/watch?v=YkPxoIxFUSo

If those ball bearing housings are allowed to move around within the retainer as shown in the video, that allows shaft movement to eventually distort the diff housing bearing bores. The roller bearing in the diff housing leans against its race in a non-uniform manner and that wiggles the bore out of round. The bearing race is supposed to have a precision press/interference fit in the housing, but that shaft movement destroys that fit and you end up with a race that is free to spin in the housing like this

https://www.youtube.com/watch?v=xmNmxm_AT0c