Do gearbox rebuilds require a significant "break in"?

deputydog95 · 01-08-2017, 06:35 AM

My box in the 85 was shifting kind of meh... Especially 2nd and 4th. Had the shop open it, ended up replacing a lot of stuff. Ring and pinion (was on its way out), a couple gears, some syncros, dog teeth. Lots of stuff. Very expensive.

Got the car back, didn't think it shifted all that much better. Brought it back. They did some break in time on the lift with conventional oil, then switched back to syn. Shop still isn't loving it.

They want to put conventional oil back in, let me drive it till it feels right, and then switch to synthetic.

Is this normal? It doesn't feel right to me. With so much replaced, I expected a little break in, but this is giving me concern. It was a very expensive job and I was expecting the 915 box to shift like butter afterwards. There's a new clutch in there too.

Am I worrying too much? Thoughts?

yelcab1 · 01-08-2017, 06:38 AM

no break in needed.
they did not do it correctly

RedCoupe · 01-08-2017, 07:07 AM

The gearbox experts on this site say to always run non-synthetic lube in the 915.

Crude Rudy · Crude Rudy's Garage

I had the same symptoms as you on my '84 box with 140K on it. After Rob at Dutch Treat rebuilt it shifted like new right away, "like butta"

Run the dino Kendall 75-90 gear oil as Porsche recommends.

deputydog95 · 01-08-2017, 07:44 AM

It's a bit of a sensitive topic for me and the shop. They have 40 plus years of raicng/building vintage Porsche. I'm struggling on how to approach them as it's not some random place that works on all sorts of cars....

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deputydog95 · 01-08-2017, 07:46 AM

It's still not shifting as it should according to the shop with the convential oil. Is there a possibility it will shift better with time using that oil or should I ask that they open the box back up at their expense to review their work?

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SoyRacer · SoyRacer's Garage

If assembled correctly then there's nothing that needs to "wear in". You don't want anything that comes into contact with hardened street to "break in".

Conventional gear oil only. Some cheat incorrect alignments and noise by using heavy synthetics.

If it's not right by now it won't get any better, it'll just damage very expensive parts that "someone" will have to pay for.

Good luck.

Crude Rudy · Crude Rudy's Garage

OK, good point. But did the guy w/ 40 yrs experience rebuild your box or the latest guy off the blue bus? Your box should shift like new, that's what you paid them for, they should fix it.

deputydog95 · 01-08-2017, 08:56 AM

The shop is basically managed and run by a father / son. They routinely build engines and gearboxes. Not sure how to start this conversation with them being that they're the experts and I'm just some guy with no mechanical knowledge.

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Jdub · 01-08-2017, 09:51 AM

You must be sure all your peripherals are in good shape and adjujsted correctly - from your left foot to your right hand (U.S. spec. here!). That is, your shifter bushings, to coupler, and adjustment are perfect, and the clutch pedal via Bowden cable to clutch adjustment lever are also spot on.

Those were the first things I did (rebuild pedal cluster, new cable and omega spring, bushings, coupler) before I spent any money on opening the gearbox. It was rebuilt by John Walker who is one of the very best in the business. Still shifts like it did when it left his shop.

john walker's workshop · 09:55 AM

Simple. Tell them it doesn't work properly and call me when it's fixed.

deputydog95 · 01-08-2017, 10:46 AM

Quote:

Originally Posted by john walker's workshop

Simple. Tell them it doesn't work properly and call me when it's fixed.

What are your thoughts on the topic John?

If there are a significant amount of new components, should it be crisp and shifting correctly right out of the gate?

Is there a break in period?

Thoughts on conventional versus synthetic oil?

I've already had the conversation with them about wanting the car perfect but I would like to educate myself more on what my expectations should be. It was an expensive job....

fanaudical · fanaudical's Garage

+1 for no synthetic lube (conventional only in the 915) and there should be no break-in required.

ReconTrojan · 01-08-2017, 12:07 PM

I wrote several threads on my 915 experience. I replaced...everything. I did experiment with some WEVO components that were to make it a better gearbox and ended up going 100% OEM. It shifts better than when I started but sometimes 1st is tricky ( tight) and Reverse requires me to play frogger once or twice and it slides in. While driving though other than the long throw each mile is finding it getting better.

On my thread ( feel free to find them) people said 1k miles is a good break-in. The two shops that worked on mine serviced my other 4 Porsches with zero problems. This is my only 915 car and it's unique. If I had it to do over I would have probably tried to find as good a 911 but a G50. the 915 is just a weird transmission. My mechanic worked at VP in Hermosa when they were new and he said they were like this new and customers with newly purchased 86's complained about shifting. Some people will tell you that is wrong that they ALL shifted like " butta" I know for a fact this not the case. Each car is unique, each rebuild is unique and certainly all the surrounding components are as well. But since we replaced about everything from cables to every slider/synchro I knew mine would probably be a bit tighter than most. It is taking me time to put miles on it but it is getting better with each mile/shift.

I have to chuckle though as I have an identical year 951 as my 911 and wonder how one is such a great gearbox and even modded with 100 pounds more torque it shifts like my more modern Porsches. 1986 was the transition year and Porsche knew it. It is what it is, my 911 is great and I've done everything I can with the 915 to make it better but drive it and learn it more which is next.

Give it sometime if you can. But if you are having gear selection issues...short shifter installed?

deputydog95 · 01-08-2017, 01:07 PM

I do have a renn shifter installed but that isn't it. We left it at stock throw length to avoid any shifting issues.inahve the renn shift on my 79 race car and it shifts magically. Adds a wonderful feel and centers with reverse lockout. Great piece of engineering but pricey.

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MARISOL78sc · 01-08-2017, 01:21 PM

My 915 shifted perfectly after my rebuild this summer.

DanielDudley · 01-08-2017, 01:57 PM

I had a crappy shifting 928 box with the Porsche syncros, and I eventually ran Redline NS in it. It made a huge difference. That box was rebuilt twice, FWIW.

I have been told that synthetic can coat the syncros, and it can take time to wear off, but there are only a few guys I would have build my box these days, and most of them post on this forum.

One of them already gave you his opinion. Also, if the clutch or the pilot bearing are dragging, it will feel exactly like your transmission is screwed up. Cold weather can also make the transmission feel stiff until the oil warms up. IMO, Redline is very good in the cold.

It gets cold here.

deputydog95 · 01-08-2017, 02:01 PM

Quote:

Originally Posted by DanielDudley

I had a crappy shifting 928 box with the Porsche syncros, and I eventually ran Redline NS in it. It made a huge difference. That box was rebuilt twice, FWIW.

I have been told that synthetic can coat the syncros, and it can take time to wear off, but there are only a few guys I would have build my box these days, and most of them post on this forum.

One of them already gave you his opinion. Also, if the clutch or the pilot bearing are dragging, it will feel exactly like your transmission is screwed up. Cold weather can also make the transmission feel stiff until the oil warms up. IMO, Redline is very good in the cold.

It gets cold here.

I'm in Florida... Temp isn't really an issue.

Should I be asking them to open it up again and review their work?

Ironically I brought it in because 2nd and 4th were shifting badly. 2nd and 4th are still an issue.

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Matt Monson · 01-08-2017, 02:40 PM

928 has Borg Warner synchros like a G50. Not comparable to a 915 and it's Porsche synchros.

I'm guessing some new synchro teeth went on the gears? Did they have proper back cut and were the new synchros measured after being loaded on the gear?

deputydog95 · 01-08-2017, 02:42 PM

Quote:

Originally Posted by Matt Monson

928 has Borg Warner synchros like a G50. Not comparable to a 915 and it's Porsche synchros.

I'm guessing some new synchro teeth went on the gears? Did they have proper back cut and were the new synchros measured after being loaded on the gear?

I have no idea... Way above my pay grade. I can ask though.

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