Rebuilding the 915

[NY65912]

OK, I have pored through countless threads on rebuilding the 915 transmission. I have decided to rebuild mine in the future. I have access to a press and mucho tools of my own, a tech buddy and my shops.

My car has just shy of 80K on it and it has never been abused. My complaint is the 1-2 shifts, especially into 1st.

The question I have is, is it necessary rebuild the diff at the same time? Is this common/best practice or up for interpretation? Or is it the “while you’re in there” syndrome?

After reading the threads I have full confidence that I can do the job.

Thanks, advice and thoughts welcomed.

[notfarnow]

I didn't touch my diff. My car has 120k miles. Doing just a 1-2 synchro job is a fair bit easier than doing all 5 gears, although I opted to do all syncros while I had it apart.

You tried all the usual suspects before deciding it was internal? I had a buddy rebuild his 915 last year to address a progressively more balky 2nd gear. Shifted exactly the same afterwards... replaced the transmission mounts and then it was fine

[NY65912]

I have not replaced the mounts. I do have new shifter bushings, Siene gate shift kit and a Stomski coupling.

I am changing over to Kendall and dumping the Swepco, hopefully it will help. But, I am pretty darn sure its the 1-2 synchros.

I am not trying to cheap out on a rebuild, I am trying to learn what is absolutley necessary and what might still be servicable. Thanks

[Trackrash]

I'm not sure what you mean by rebuild the differential. I'm assuming you don't have a limited slip.

The best practice would be to inspect the diff bearings and then decide on replacing them. They are relatively inexpensive, but you will need to check and possibly reset your pre-load and ring gear's back lash.

Most would say that if the ring and pinion looks good, you probably are OK leaving it be.

[Jdub]

I'm the last to help on the trans, I had JohnW do mine. But I can say you would do well to renew all of the mechanisms that actuate the trans. This means from the clutch pedal to the trans, and from the gear shift to same. A rebuilt pedal cluster, new Bowden cable and for the shift lever new bushings all the way to the coupler, plus proper adjustment (see Peter Zimmerman's post at this site) will do wonders.

Good luck!

[johnsjmc]

worn out first gear syncro is typically going to require replacing the 1-2 shift hub/drum and both 1st and second syncro. once opened up its hardly more to do the other 3 syncros. I have only done one with 110 mi on it but the diff portion was near perfect looking.

[MARISOL78sc]

just did a rebuild on my 915, synchros, sleeves new clutch and while it was apart a couple more. rebuild what needs replacing, only opening it up will tell

[NY65912]

Thanks for the input. I guess only opening the patient up will tell.

[kevingross]

If you have a limited slip diff, yes, it needs to be rebuilt, absolutely. It is worn, it is out of spec, and it ain't doin' its job in worn condition. Follow the factory procedure. Prepare yourself for a long wait for some of the parts (which is why I keep a deep inventory). Not described by the factory, but consider replacing the cup springs which have almost certainly lost "height" and pre-load pressure. Check the thrust washers carefully for cracking next to the pressed-in tab, use a diopter inspection lamp to look real close.

If you have an open diff, by all means tear it down, inspect, reassemble. It's easy and quick. And while they rarely have issues or fail, it would really stink to have one crop up a year or two from now. On an open diff, check the spider and side gear teeth and backsides for any damage, cracks, etc. Check the cross-shaft ("bolt") for excessive wear where the spiders turn on it. Replace the two circlips, or at least have replacements on hand in case the old ones show signs of distortion.

As Gordon says, make sure you reestablish proper preload (turning torque) and backlash via shimming under the differential bearings. No, you CANNOT simply reuse the original shims, don't even think of doing that.

BTW, Pete Zimmerman's how-to is wonderful. I don't do things 100% the way he does, but we all have our own little techniques and Pete's process is excellent. Good luck with the rebuild!

[Speed Buggy]

Don't do it, it's the entry drug...before too long you'll want to rebuild your engine...get professional help now...haha

[NY65912]

I've been addicted for the past 50 years. I'm already screwed

One way or the other, it has to be done.