915/62 Reseal and Inspection

[blg5035]

While Bruce Abbott is rebuilding my engine, I am resealing and inspecting the trans since it was leaking.

These are my notes on how it was shifting.

1. First can be funny. I typically put it in second before going in to first. Sometimes I’ll get a "sproing" feeling through the shifter. Feels like I have to “go around” something to get in to gear.
2. Hard to get into 2nd sometimes. Have to use a lot of force and then can be hard to tell whether it went in.
3. Sometimes can feel some clash when go in to 3rd, but no noise
4. Have to yank out of 5th. A tech thought it was catching on the reverse lockout
5. Shifter making noise (rattles) at times in 2nd. Touching it makes noise stop
6. Had a time period when very difficult to not crunch gears 1-3, but yanking out of 5th one time seems to have reset it.

I have the gear housing off. These were my disassembly process sticking points:

• The transmission needs to be in neutral for 5th/R selector fork to “just pull out”
• I had to pry on the 5th/R hub to get it off. The pry bar was against the 5th big circlip which doesn’t look like it contacts anything, so I thought it was OK.
• Also had to pry on the bigger 5th idler (gear on pinion shaft) to remove. It seemed like there was some carbon buildup on the inside. Make sure to not pry on the gasket surface.

Parts inspection pics to come in a second.

[blg5035]

A couple chips on the reverse gear idler. I don’t think I’ll do anything about this since it is reverse.



5-R Idler Washer. Can feel the 2 concentric circles in the righthand pictures with my nail


5-R Idler Thrust Washer. Can barely see some wear marks on the rollers. The needle bearings looked good. The cages were in one piece and the only “crack” I saw was what I thought was where I assume it was fused closed.


5-R Selector Fork. Some wear at the tips.


5-R Selector Fork. Which side are you supposed to take the measurement on or is it both? Both sides were in the .1-.3mm new range. .5 is wear limit


5-R Slider. The inner groove that sits on the synchro threw me off at first. I thought the dog teeth looked good.


For comparison, Bruce gave me some spare parts. I’m not sure what new looks like, but Bruce’s inner groove (on right) is about half as deep.


5th dog teeth


5th Inner Race


The circlip on 5th gear has a pretty deep nick (7 o'clock), but I’m assuming it is ok since the surface doesn’t contact anything.

[blg5035]

Wear pattern on 5th gear ID


5th gear washer


5-R Hub had an interesting wear pattern on the not straight teeth (left of top pic). There is a deeper groove on one side of all the teeth (bottom left) compared to the other side.


The selector shaft had some build up I could feel. What would you recommend to polish the shaft? I have some grey Scotchbrite (600-800 grit) and some higher grit paper.


There are some interesting cracks on the inside of the gear housing that don’t go all the way through. Almost looks like crazing that happens in plastic.


The bearing racings in the gear housing can be wiggled a little in and out axially, but they don’t spin. I wasn’t sure if this is OK. Input on left, pinion on right. Is the wear the shiny part or not shiny?
The cage on the input shaft can be wiggled some, but the inner race doesn’t move. Is this an issue?



What are your thoughts?

[blg5035]

Your input would be appreciated. Thanks!

[blg5035]

bump thanks

[kevingross]

You'll probably get more of a response if you ask some specific questions! Cheers,

[blg5035]

I was trying to get input on what people think about the amount of wear and what needs to be replaced since this is my first time rebuilding a transmission. I've looked through the many rebuild threads and didn't see much on needle bearing wear patterns for example. There are some specific questions sprinkled in there such as:

5-R Selector Fork. Which side are you supposed to take the measurement on or is it both? Both sides were in the .1-.3mm new range. .5 is wear limit

[kevingross]

I don't see much that looks horrible in your photos. The bearing outer races do look pretty worn -- but the focus in the photos makes it hard for my tired eyes to see whether there is significant pitting. Synchros are worth taking some better pictures of, looking for shiny or patchy surfaces.

On the selector forks, I would focus less on measuring with a feeler, and more on the condition of their brass tines. If the tines look like they have material worn away where they engage the shift sleeve, that would be a concern.

If you can move the bearing outer races at all, that needs to be addressed. They should have a solid interference fit with the housing.

Hope this helps!

[blg5035]

Thanks Kevin

Here's some better pics of the bearing races. There seem to be some very minor pitting, so I think I'll replace them while I'm in here. The pinion (top) seems to have some chattering.




I wasn't able to get really good pics of the 5th synchro, but there are no shiny spots like I am seeing on 1-4's synchros. On 5, it almost seems like there is more wear on the dog teeth side. The worst spot is circled in red.



Worst dog tooth is right in the middle with the dust on it. My overall conclusion is to leave 5th as is, since I didn't have any issues previously.



I was trying to do this feeler gauge measurement from the Bentley. Is it not a useful measurement? In the bottom two pics of the fork, I can feel a lip with my fingernail, but it doesn't seem bad based on my limited knowledge.

[kevingross]

Synchros and dog teeth visually ok. I would (always) measure the installed diameter of the synchro to make sure it's in spec.

Bearings look tired and ready for replacement. I agree: they don't have horrible pitting, but they are well on their way there.

I assume Bentley takes their diagnostic protocol from the Porsche WSM. Which includes a lot of measurement specs that, while fine and dandy, in my experience aren't terribly useful. From your photos, your shift forks look just fine to my old eyes.

I hope this is helpful.

[blg5035]

Kevin, yes, very helpful!

I've haven't been able to make much progress until this week, but I finally got the gear shafts disassembled and may have gotten to a big stopping point.

There is some serious-looking pitting on the pinion teeth. The one side's wear isn't on all the teeth, where as the other side's wear at the base on the tooth is pretty consistent on all.

Does this wear warrant a new ring and pinion?

Worst tooth on convex side

[blg5035]

Had some issues uploading .png's

2nd Worst tooth on one side


Other side wear consistent on all teeth

[mepstein]

At my shop, we would call it trashed.

[blg5035]

Bummer, thanks for the feedback

[mepstein]

I’m sure you could put it back together and get some miles on it. How much is anyone’s guess. As a shop, our goal is to build a trans that shifts like new and last 120k +. If it only last 10-20k, it would be a problem. It just depends on your expectations.

[Mark Salvetti]

Be really careful not to mix up the thrust washers. They are not all the same thickness, and I think they are pretty hard to find. Here is a thread:

quick 915 pinion shaft qusetion

You have Pete Zimmerman's wiki? Porsche 915 Transmission

Mark

[kevingross]

As others have commented, your ring-and-pinion set should be replaced. I would not rebuild with erosion to the pinion teeth as seen in your photos.

Regardless of the erosion being on the coast vs. drive side of the pinion tooth, it is a substantial stress riser on a part that, because of the hypoid tooth geometry, is heavily stressed.

Sorry to be the bearer of bad news! Good luck with the rest of the project,

[blg5035]

Originally Posted by mepstein

I’m sure you could put it back together and get some miles on it. How much is anyone’s guess. As a shop, our goal is to build a trans that shifts like new and last 120k +. If it only last 10-20k, it would be a problem. It just depends on your expectations.

Thanks for the clarity. I'm going to replace it.

Originally Posted by Mark Salvetti

Be really careful not to mix up the thrust washers. They are not all the same thickness, and I think they are pretty hard to find. Here is a thread:

quick 915 pinion shaft qusetion

You have Pete Zimmerman's wiki? Porsche 915 Transmission

Mark

Thank you for the reminder, I've been using zip ties to keep everything in order.

Yup, Peter Z. has been one on my very good references. It doesn't give much guidance on wear, which is driving a lot of my questions here.


Thanks for the extra detail, Kevin, learn something new everyday.

[blg5035]

Since new ring and pinions are looking to be around $5k, is it worth looking at used? Of course, the tradeoff is how long do you want it to last.

With the ring pinion having to be reset, I'll probably be sending the whole trans to CMS since I was already planning on shipping them the cases to having the pinion bearing races fix.


Finishing the tear down and inspection, 2nd gear is starting to have some erosion too. Do you recommend replacing this too? It looks like my trans has already had 1st gear replaced in the past, which on the input shaft is just starting to erode too

[mepstein]

You can find good used r&p’s that should still have many miles left in the bank. There are never any guarantees but neither is there if you buy new. There are many new parts that don’t have the quality of the original ones.
We regularly overhaul trans with 150-200k miles with good r&p’s.