911racer

Tony,

By agreeing with the break in period, I ment I was agreeing with you. My typo.

They should shift as good the first time (ok, maybe the 3rd time), but I have never experienced a break in period.

Ed

Peter Zimmermann

Tony G. said all the majic words in his above post. "Slider, brake bands, dog teeth, anchor blocks..." I was fortunate enough to receive formal training from Porsche in April, 1976 - one solid week of intensive training on how to repair the Porsche manual transmission. I've been doing them ever since, and I'll tell you a few things here. When a synchro ring is replaced its slider (aka sliding sleeve or selector) MUST BE replaced. A Porsche synchro ring, used through 1986, wears in over time - so does its slider. It is fruitless to hope that a new synchro ring will be compatible with a worn slider. The result of a new ring and old slider is a car that must be shifted with two hands, and if you can figure out how to do it, both feet. The inner surface of synchro rings are grooved. Those grooves will produce miniscule wear on the parts Tony mentioned, anchor blocks, energizer blocks and brake bands. Those parts must be replaced to insure that when the slider engages the ring they work properly to stop the gear from turning. Dog teeth, the ring of teeth in which the slider's teeth mesh, should almost always be replaced. Many times they have obvious wear/damage, sometimes they can be warped just enough to force that new synchro ring to hang - not good. Tony stated little or no break-in was required on his. He's correct, about the longest "break-in" period, sometimes due to a slight imperfection in the coating on a synchro ring, is about 100 miles. Even then the trans should feel wonderful within 10 miles of installation, and will continue to get buttery smooth over time. There is much to know about the Porsche manual trans, which is why some "rebuilds" cost $1200, and some cost $3500, more if ring & pinion replacement is required. Tony relates the cost of just his 1/2 parts, and he isn't kidding. Trans parts are expensive, and so are the tools. A quality rebuilder should have everything needed in his tool chest (see the new 8th edition of my book), without those tools a good result is virtually impossible. I've re-repaired 915s done by authorized dealers, other shops, even DIYers, which is testimony to the greatness of the 915 - all those re-repairs drove into my shop! A rebuilder must understand the processes of determining the usability of a gear needle bearing, how and why ring gear backlash must be set, why and how to set pinion depth, the need for quality dial indicators, etc. He also needs to know clearly the difference between a race box, where noise is not critical, and a street box. He needs to know, and care, about trying to achieve 100K miles with every trans he does. Some re-repairs I've done were lucky to get out of the parking lot when they were picked up following repairs. I've seen synchros grenaded by valets, some damaged so badly it was more cost effective to rebuild a core for the customer. Time is required to repair a Porsche trans. Every new synchro ring must be measured with a precision vernier caliper (or comparable tool) - yes, I've found bad ones out of the box. The clearance for the reverse idler must be set, as well as the shift forks. Many times that is done wrong, sometimes producing the subject of another current thread. A rebuilder must have access to a high quality machine shop, so when bearing race sleeves are needed they can be done to as-new measurements. Quality rebuilds aren't cheap, the last time that I checked labor rates around the country were in the $80-110/hr range. Twelve hours plus ring & pinion work (includes R&I) will get that bill up there. Need a new 2nd gear? Add another $600!
Yes, you can get a cheap one, with luck it'll be better than the one Brian is stuck with.
Pete

BRB-83-911SC

Pete - yours are words of wisdom, and it all makes good sense. Everyone else here has also added tremendous insight, and offers to help in any way they can. Thanks!

One question regarding my situation - if my transmission shifted well (no synchro issues, "buttery" smooth shifting) before taking it apart, and all parts pass inspection, would it make sense to simply have my case repaired and re-use all existing moving parts? Is this foolish economy since it is already apart? I am not looking to spend money I don't need to, yet I don't want to be in there again in the near future.

Also, would the R&P need to be removed to re-sleeve the bores on the diff case? I understand the reason to set up the R&P, but is this required only when parts are swapped out, or every time it is apart?

Thanks again for the input. Keep in mind, I am not doing the work - just trying to learn. I am sure I will have a few more questions before this saga is over.

TonyG

Gary R.

>>>Tony - I'm about to start a 3.6L conversion, did you go with an LSD when you did it? I was told (by a VERY reputable source) that it was the way to go..<<<

No I did not install a LSD. I wanted to, but I did not, and still do not, know what to expect concerning reliability and the 915 box when coupled to a 300RWHP 3.6L engine.

The thing about the 915, is that it's easy to do after the fact. I just didn't want to spend the money.

The other reason is that I have a couple of G50 transmissions in the shop and I was very seriously contemplating installing one into the SC. But again... I'm already WAY to far in to the SC financially. Doing a G50 with a Quaif/Torsen would be another $5k deal by the time the dust clears...

I will say that so far the 915 box I rebuilt has done good and has no problems. And the lack of LSD has not been a problem for me at to date. It may if I start running on a tighter track though.

The other thing... I may not even have the car long enough to worry about it. Toys come and toys go around here pretty fast. :-)


TonyG

TonyG

Peter Zimmermann

Gotta say that the only reason I decided to get into doing my own gear boxes is because of the bad (and expensive) experiences I've had.

I just couldn't take it anymore.

PS> glad it wasn't a G50.


TonyG

TonyG

BRB-83-911SC

My opinion is that if you plan to keep the car, you should step up and do all the 1/2 parts (not the actual gears, but the parts I listed), then do the case and obviously the bearings that meet the case.

It's almost always the 1/2 that have problems. By spending another $700, you will guarantee that the trans will shift very nice for a long time to come. Plus, there's no additional labor from where you're at right now.

Send the case to Wevo! (I wanted to, but I didn't have to pull the gear stacks out to do the 1/2 stuff...)

TonyG

Peter Zimmermann

Brian: Before doing your case you must attempt to establish exactly what the "noise" you speak of was. Nothing substitutes what can be learned during an actual drive, but let me know what you were hearing and I'll try to pin a cause to it. In your situation every gear must be examined, and verify that each gear set is indeed a matched pair. The next thing is to examine each gear's needle bearing, make sure that it turns properly and it's bushing (race) is good. Each gear must be examined for wear-through in the root area of the teeth. The case needs an expert repair to assure the distance between the sleeved bearings is correct. Your ring & pinion, because your trans is certainly not a virgin, must be completely reset as though it's a new unit. Remember, the same guy who installed that diff also put the trans together using the sloppy housing. Anyway, in order to sleeve the bearing bores in the diff housing the diff needs to be removed to safeguard it from debris. The carrier bearings should be replaced anyway, so you will be replacing the 6 primary bearings, and possibly needle bearings/bushings. What you're facing is a much tougher job than repairing a never been apart virgin, but it can be done. Best of luck with the project.
Pete

jet911

I had the same experience as Tony G. Had my box rebuilt three years ago by a "reputable" shop that came recommended. The only problem was downshifting from 2nd to 1st (syncro/slider/dogteeth), everything else was smooth as butter. I was told that while we are in there, let's do a total rebuild as the only additional cost would be parts. I agreed. The wrench replaced all 5 sycnros, 1/2 and 3/4 sliders, dog teeth, bearings (all bearings, main, pinion, needles, etc.), etc., etc., cost me over $3.5K including a new clutch. When I got it back, the car shifted worse in all gears except downshifting from 2nd to 1st (wouldn't down shift into first except at a dead stop before). The wrech said it needed to break in the syncros. Bull****! After 20K miles on the rebuild, it still shifts like crap (I mean crap for a 915). It shifted much, much better up and down prior to the rebuild except from 2nd to 1st. Now, half the time when upshifting from 1st to 2nd, it won't go in no matter how slow and easy I treat her. Down shifting from 5th to 4th is a joke as is 4th to 3rd and 3rd to 2nd. I've talked with the guy over time that did the rebuild and he just can't figure out why it has not "broken in."

I've learned to live with it, however I am disappointed. It keeps me from driving the car the way I know it can be driven. In a few more years, I will do the rebuild again. When I checked the paperwork for parts, I did notice there was no new brake bands or blocks. I've always wondered if that is the reason it shifts so poorly...the cheapest parts of all.

Good Luck!

Regards,
Jim
'86 Coupe (95K miles)

BRB-83-911SC

First off, I want to thank everyone for your advice and offers to help. After considering the options and the current state of my transmission, I will be getting a fully rebuilt 915 from Gary Fairbanks within the next week or so. He has been working directly with my mechanic and we all feel this is the best route to go. I feel confident in his work, and his goegraphic proximity to me is also helpful. I will post again once I go for a drive. Fingers are crossed. Thanks to all who posted, I now have a better understanding of how the 915 works, and the ability to make an informed decision.

Peter Zimmermann

Jim: I hate hearing stories like yours, there just isn't any reason for it. Many years ago I worked with a guy who would "flip" synchro rings and put the trans back together. (I don't know if he charged for new ones!) His theory was that all of the wear was on the upside of the ring that was compressed by the slider, so if he flipped it the effect would be the same as a new synchro ring. Strangely enough he actually got away with it on a few early (901) transmissions, but I figured out in a hurry that what he was doing was flat wrong. The un-worn side of the synchro ring was forced to work with the old, worn-in, slider. Bad situation, similar to using an old slider with a new synchro. Also, if the inside surface is worn where the brake bands contact it, it really screws everything up. Instead of giving you all new parts, I can't help but wonder if the shop "flipped" your synchros, instead of replacing them. Whatever they did, they certainly didn't do you any favors.
Pete

TonyG

jet911

Sorry to hear about your experience. Been there, done that.

I was able to all the 1/2 parts without pulling the gear stacks or touching the shift rods. You can can do the same for 2/4 as well.

What this means is that unless you have a bearing problem, or an actual damaged gear or have to mess with the ring & pinion gears/bearings, it's pretty easy for anybody with basic mechanical skills to do the rebuild. It's very straight forward and difficult to screw up. I was surprised.

You might be better off starting with a used 915 box that shifts well that has never been opened up, then doing a rebuild yourself from there.

TonyG

jet911

Thanks for the input gents.

Pete: I did receive all the parts back, however I don't know if those parts came out of my box or not. I do suspect there was some BS going on though.

Tony: Actually I was thinking when the time came, I would try it myself. After that experience, I do nearly all the work myself.

Regards,
Jim