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I have a 1988 GMC Sierra 4x4 truck, and I recently bought a rebuilt NV3500 transmission from a 1995 chevy truck (I picked this year, because from 1993 onward, this particular transmission used a single shift rail and a better bearing design as opposed to the older designs which were prone to early failure), which should bolt right up to my truck. The transmission bolted up to the engine fine, but I noticed that when shifting, there was a slight delay before the transmission would shift into gear. It's like when I am shifting, I am temporarily being blocked out of each gear for a few seconds (especially 1st and 2nd gear) before it decides it wants to go into gear. Keep in mind, there is no grinding noises or anything like that.

At first I thought maybe the hydraulic clutch system was faulty, which shouldn't be the case, since everything is new. I bled the master/slave cylinder of all air bubbles, but it still did nothing. The clutch and pressure plate are also new, along with the pilot bearing, clutch fork, release bearing, etc.

I had a mechanic take a look inside the transmission and he said all of the synchros were new. So I am basically at a loss ... what could it be?

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 31, 2018 at 13:18

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There may not be anything wrong with the transmission. I believe what might be going on is when you shift, the transmission is RPM matching itself through the synchros. When the power side (from the engine) of the transmission slows down enough so it matches the driven side (to the drive train), it allows it to go into gear.

This could be a factor of one of two things: the fresh rebuild on the transmission needs to get fully broke in or you need to change how you shift gears. Double clutching may do the trick for you or rev-matching for the transmission.

There is one other thing this could be ... with a brand new clutch, it may not be releasing completely. If you find it hard to shift into first/reverse from a dead stop as well, this could be a sign of that. Since it's a hydraulic clutch, the only adjustment factor you might have is break-in of the new clutch. Once it gets about a 1,000 miles on it, it may release more fully and give your transmission the ability to shift easier.

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  • Thanks for the reply. Yeah someone else mentioned that to me before as well. Is it normal to have a break-n period for rebuilt transmissions? I've talked to some people who say that there is, but others who say that the moment the new transmission is in, it should drive fine. I wouldn't even describe it as "hard" to put into gear, but that there's just a delay...an abnormally long delay to the point where the truck slows down substantially before I can shift, which makes the driving experience pretty painful. So you're saying I basically should just keep driving it and it might get better?
    – William
    Dec 31, 2018 at 19:21
  • @William - Not a break in period for the transmission, but for the clutch, which is very normal. There is what's called a "bedding" period. Once the clutch gets broke in, things may be a better ... no guarantees.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Dec 31, 2018 at 19:54

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