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Old 10-24-2010, 10:21 PM
Thread Starter
Join Date: Jun 2009
Posts: 69
3 and 4 synchro key failure in rebuild

Tore apart my ax15 this weekend to discover why I lost 3 and 4.

Was shocked to get in and see everything looking good (really good in fact for 140k miles), the only thing wrong was that I found the 3 4 synchro keys in the tranny loose. Nothing like so much grief over a 2 dollar part.

What caused this? If I'm already in here what else would you suggest replacing? I don't really want to spend 350 on a full rebuild kit but I don't want to do this gain either, the bearings are rough but the syncros look okay...gears themselves look great.

So what causes failure of the synchro keys?

thanley is offline   Quote
Old 10-25-2010, 02:35 AM   #2
Join Date: Aug 2008
Posts: 2,473
Are the 2 wire springs behind them still intact?

Forcing it too hard can dislodge or break the springs, letting the keys move into a position where they aren't supposed to be. Then on the next shift they get bent.

Built up crud can also inhibit their proper movement - a good reason to occasionally flush the trans with cleaner like I've suggested many times.

The bearings are rough? Needles and thrust washers are OK? You don't need an entire kit for just bearings. Get the bearing numbers off the outer races, call a Bearing Mart - be sure to get quality bearings. The bearings are surprisingly inexpensive.

It's no wonder the country is falling apart - stupidity abounds!
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Old 10-25-2010, 07:56 AM
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Join Date: Jun 2009
Posts: 69

I will check the springs when I get home tonight. I was exhausted from pulling it yesterday and shocked to see the keys, so I more or less left it and figured I would come full circle tonight and figure out springs and bearings.

The only bearing that really seemed rough was the input shaft bearing (the big one behind the bell housing), and I noticed it because the seal on the bearing pretty much fell right out and was in rough shape. Figure I need to replace that one for the sake of the seal alone.
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