changing 930 transmission synchro hubs - grind the nubs off??

b930 · 07-08-2017, 07:59 PM

Hi
I am rebuilding my 930 transmission. I have removed the old synchro hubs using a dremel and the original gears have these bumps or nubs on the tops of each spline. I have read and seen youtube videos of where guys grind these off and make a slight taper to more easily press the new synchro hubs on.

It looks like the factory had them on to retain the synchro hubs. Should I just freeze the gear/heat the new synchro hubs and press over these nubs?

Thanks.

b930 · 07-08-2017, 08:07 PM

It could also be the case that the factory had a process of creating these upsets to lock the syncho hubs on after they pressed on the hub, may be special press of some kind that was used to create the upsets after the hub was on thereby locking it in place. The measurements to the start of the nub from the face of the gear suggests this is the case as they start at the same point that the hub spline ends, i.e. with the defined line on nubs essentially measures the same as the hub spline height from the face of the gear.

It seems logical then that I should grind back the nub so the spline is a constant OD and then press the hub on. Am I on the right track here?

cheers.

boosted79 · 07-09-2017, 05:36 AM

I just rebuilt my 930 trans, have 600 mi on it. Yes, you want to grind those nubs down, even put on a slight taper so the dog gear presses on easily. You know you have to heat the dog gear right? Also, after the new one is pressed on, measure the ID of the gear to make sure it is the same across the length of the bore, eg. the ID under the dog gear is the same as the ID under the actual gear. As long as you heat the dog gear and grind the nubs you should be ok but double check. It's a good idea to TIG the dog gear to the gear hub in a few spots if it's a track car just to make sure it doesn't back off. Then check ID again. I didn't on mine but I'm just street. I put in some Walmart 75-90 for break in of the synchro rings and will dump it this week for the Swepco good stuff.

Mark Henry · 07:05 AM

I stopped using Swepco, shifts 100X better with cheaper stuff, I like Kendall.
You can really notice it in a 901,914,911 trans which is little brother to the 930.

Use the cheap stuff and because it's cheap frick'in change it more often.

But I still swear by Swepco 101 grease.

Matt Monson · 07-09-2017, 09:05 AM

If you grind off those peens you need to be sure to tack weld the new dog in place. Easy on is easy back off once rebuilt and driving.

boosted79 · 07-09-2017, 11:24 AM

Now you've got me worried. I ground the nubs off and heated the dog and froze the gear for a shrink fit. I thought TIG'ing it was for boxes that get used hard on the track, should I take it out and tear it down again and TIG the dog on? PITA but not as much as if it comes off. I thought Swepco was the go-to lube for these, now you are saying I should use any old gear oil? I've already got the Swepco.

Matt Monson · 07-09-2017, 05:35 PM

Swepco is fine. It just warms up a bit slowly.

If you don't thrash on your car I wouldn't lose sleep over it. When/if is starts to walk it will start popping out of gear. It won't allow the slider to throw far enough to lock the detent. It usually gives fair warning to issues and rarely comes all the way off.

boosted79 · 07-09-2017, 07:05 PM

Great, thank you. I may be giving you a call for my next build for an LSD install, I don't want to set up this diff.,Dana and 9" no problem but not this one. Used to get to Loveland for business, beautiful place.

Porschephd · 07-13-2017, 02:02 PM

If you grind those off you need to Tig it back on. You are asking for trouble down the road. Then again I am not one that likes to ever create a chance I have to be back in there before it's time. FWIW I have built hundreds of these and I have never ground a taper on it. Freeze one side, heat the other, line up and press on.

boosted79 · 07-13-2017, 03:31 PM

How many did gears boxes did you see where the dog actually came off?

Porschephd · 04:31 PM

On ones that people ground off and in street cars..5. But 90% of the ones I took apart hadn't been ground off. No failure on the ones that hadn't been ground.

I never understood why people do that. That lip is there for a reason and putting it back on is not hard.

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boosted79 · 07-13-2017, 04:50 PM

Here's a pic from mine when I did it. The 3-4 slider is locked into 4th. You can see the slider hub that the slider ring slides on and is locked to. Looking at 3rd gear, it seems like if the dog ring does start to walk the slider hub will stop it from coming all the way off?

Porschephd · 07-13-2017, 05:11 PM

Yes, the hub will stop it but the damage to the dog teeth and hub/slider is done. And maybe the gear. It may be fine but trying to second guess what a transmission does under TQ and heat is questionable. I have always been conservative when building things. I simply caution in the practices that have been suggested and now that the ridge has been ground my professional recommendation is to tig it down. I get to pull it apart is a pain, however I have been known to pull a customers motor down simply because I couldn't recall a nut that I tightened. I apologize I caught this post too late.

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boosted79 · 07-13-2017, 05:34 PM

OK, thanks, well I think I will drive it this summer and drop it in the fall. If it feels like it's not going into 3rd right then I'll do it now. It's a day to get it out and tear it down, 15 min to TIG it and another day to reassemble, couple to the engine and put back in the hole. Should have done it when I had it apart, live and learn..