Join Date: Oct 2007
Location: Fort Bragg, CA
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Whoa, slow down! Usually synchros are EXTREMELY hard to damage to that point. If you were able to do that type of damage you wouldn't have many gears left for the synchros to engage.
First make sure there's nothing contacting the shifter-body lift? Debris? Second, look at your motor mounts. This is a common cause of first popping out on all kinds of transmissions. Driveshaft woes can also be an issue, but I think it's impossible to incorrectly index them on these trucks-you can't on mine.
If it's internal, it still is VERY unlikely to be a synchro issue. The shift rails that scoot the shift forks that slide the synchro sleeves have little indentations on them for spring loaded check balls to hold it in place. A broken spring or severe wear on the shift rails could cause this. Most of the shift detents are usually accessible externally. Often one will double duty as a sensor for neutral or reverse.
One other thing that can make it pop out is anything that prevents it from fully engaging the synchro-from obstruction to bent parts/broken roll pins etc.
Fifth is another story, though. The fifth gear on the nv4500 five speed(that went into some of the first gens and a lot of the second gens) has a somewhat notorious issue of the nut on the 5th gear backing off and allowing the gear to wiggle away from the synchro, until it doesn't engage at all. There are update kits to fix it, but if I understand correctly, the shaft needs to be replaced for a proper repair. Do some searches, you will find GOBS of info on this issue.
Hopefully some more knowledgeable folks will chime in on this. I'd really look to simple stuff first on the first gear thing, though. Especially motor mounts. And especially the driver's side one.
PS some transmissions have a bushing in the shift tower that if worn, will prevent full engagement of gears due to the fulcrum (bushing) of the shifter lever being sloppy. Dunno if the 4500 has one. Never worked on one.
01 100hp tips EZ *hybrid* 4"ss BDbrake &steering brace "t"steer delphi tapped &rammed manual CAD 3.55's LSD, 1.375 nv5600/241HD Valair single pc rear ds 265x70r19.5 big rigs 3rd gen brakes Ugly black and thrashed!
Last edited by totalloser; 11-05-2009 at 11:39 PM.