915 Bearing Questions

[gregwils]

I have been buying up parts to rebuild my transmission. I intend to make this a DIY project, but will likely ship the pinion out for someone to check it along with any machine work needed. I'm still another year or so away, but it's coming.
My car is a fairly late '86 (02/86 MFG date) with just shy of 100k miles, so I know the transmission has the late changes to the 915. I don't track it, and today I usually double clutch up and down just to reduce any stress on it. However, it has all the classic symptoms of needing a rebuild.

My question is related to the bearings. I have read that Porsche changed the intermediate plate bearing to a smaller bearing to maximize the amount of material in the plate itself supporting the bearing (I think I have that explanation correct.) in an effort to reduce the issue with the bearing becoming loose in the race.

I have scoured the various transmission threads in search of any answer. What I am having a difficult time reconciling is that most of the application charts that I see list the same bearings from 74-86. It doesn't seem to me that both can be correct - one size fits all and the later trans using a smaller center bearing(s). What am I missing?

Part Number______Part Description

930-302-391-01___Mainshaft Bearing (Rear)
999-052-030-00___Mainshaft Bearing Intermediate
999-110-025-00___Mainshaft Front Bearing (Front)
999-110-146-00___Pinion Shaft Bearing Flywheel (Rear)
999-052-043-00___Pinion Shaft Bearing Intermediate
915-302-399-00___Pinion Shaft Front Bearing (Front)

[DRACO A5OG]

Bearings wise, you look good to go.

If I may suggest, get the 1 piece CMS bearing bracket:

https://californiamotorsports.net/collections/porsche-915-transmission-parts/products/cms-915-bearing-retaining-plate

You will find some of the needle bearings may drop out on disassembly, so be careful.

[gregwils]

Thanks. I saw some of your threads referencing CMS. I am planning buy their bearing plate. I also purchased Rauch & Speigel dog teeth for 1st & 2nd, but am thinking of selling those and buying dog teeth from CMS.

PS - For the record, Wayne is my first stop for parts, but as we all know on occasion there are some select items that need to be purchased from other sources.

[Jack Stands]

A local Porsche expert has been cautioning about quality issues with the bearings available today. Has anyone with transmission rebuilding experiences noted any problems as well?

[Trackrash]

Ship out the pinion? Not sure why you would need to do this. The condition of the R&P is not so hard to determine. If it doesn't make noise, a simple visual check should suffice, I would think.

I would be more concerned about the condition of the differential bearings. If they are to be replaced you will need to reset, or at least check, your backlash and pre-load settings.

+1 on the one piece bearing retainer. The originals are prone to wear and don't support as well as the one piece replacement.

[gregwils]

Originally Posted by Trackrash

Ship out the pinion?

I would be more concerned about the condition of the differential bearings. If they are to be replaced you will need to reset, or at least check, your backlash and pre-load settings.

Thanks. This is what I was referencing. I knew there was some procedure that required the backlash and preload settings. I don't notice excessive noise at this time.

All of the bearings I have purchased are Porsche brand, so hope I don't have any quality issues. They should be on top of quality for their nose bleed prices.

[Tremelune]

I may be rebuilding my 915 at some point (I want different gears), and I'd like to build as good a 915 as can be built (well, for my needs). I don't know much about Rauch, Speigel, et al, but I'm interested in what upgrades are available and what benefits they provide over stock...If you happen to have your research and conclusions written down, I wouldn't mind taking a look.

Such as not much love for R&S:

How is Rauch & Spiegel Quality?

[gregwils]

Agree. I find it interesting that Wayne continues to carry their products. The ones I may sell I purchased through here, so am at bit disappointed that I may take a hit when I sell.

[Matt Monson]

R&S actually got the message on their teeth. They now have the 9 degree backcut on the 915 teeth. Don't know of any changes to their syncrhos though. They seem to be a bigger problem.

[gregwils]

Matt - Thanks for weighing in. I bought the teeth two years ago, so not sure if I have the latest ones or not. Is it possible to see the backcut when you look at them?

Also, I have read a ton of your posts, including those discussing syncro quality. All the syncros that I purchased are Porsche brand, seemed like an area where Porsche part number premium may actually pay off. There may be other good aftermarket sources, I just don't know them.

You had an excellent post where you listed what parts you considered essential to a rebuild. It was super helpful to me, so thank you for giving back to the board.