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Thread: Shifting Issue

  1. #1
    Electronic Ignition!
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    Shifting Issue

    Just a little background...

    I have a TBI truck with a new vortec 350 motor, and rebuilt nv3500 swapped in place of the original 700r4. All is going well for the most part, except I'm having a shifting issue. The clutch for whatever reason doesn't seem to want to disengage quick enough. Keep in mind these are all new parts(clutch, flywheel, pre-bled slave/master cylinder kit, etc).

    When I'm driving(this usually happens with gears 1, 2, and 3) I'll press the clutch in, and there's always a delay before I can fully put it into gear, kind of like lockout, but if I wait long enough, I can eventually shift. So if I'm in first gear, I'll press the clutch, and then it seems like it doesn't want to come out of gear when I want it to. It will eventually come out of first, but then I have to delay a couple of seconds before it will go into second.

    I actually removed the transmission at one point and had a mechanic look at the internals to see if it was rebuilt poorly, but he said it all looked good, new synchros and all.

    I'm thinking it might be the slave/master cylinder system, but it doesn't leak, it's new, and it was already pre-bled from the factory. I'm at a loss considering everything is new. If you guys have any ideas they would be greatly appreciated.

  2. #2
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    what kind of fluid are you running?
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  3. #3
    Electronic Ignition!
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    I'm running Penzoil Synchromesh at the moment, apparently it's the factory equivalent to the fluid GM used to make. I've tried Royal Purple Synchromax as well, but it's even thinner than the Penzoil and the transmission didn't feel as good shifting.

  4. #4
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    well, there goes my guess.... it's amazing how many wonky shifter issues I've fixed by dropping cheap 80-90 that a lot of people pin in their transmissions and getting the specified fluid into a transmission/transaxle.

    does the tach respond like the clutch isn't releasing? and you mention 1-2-3, does it happen for the 3-4 or 4-5 shifts?
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  5. #5
    Electronic Ignition!
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    For whatever reason, 3-4, and 4-5 seem to be okay...my guess is because the rpms are usually lower by the time I'm going into 4th gear.

    When I press in the clutch, the rpms and tach immediately go down as they should, but there's a short period of time where the rpms are going down and it doesn't want to let go of the previous gear in a timely manner(keep in mind I'm a pretty steady driver). And after I pull it out of 1st gear, there's a slight delay before I can put it into 2nd gear. None of the gears grind or anything, but it's like I'm getting temporarily locked out until it decides it's ready to go in gear.

    It's great because I have a good point of reference, considering I have an chevy s-10 5speed as well. It shifts smooth as butter.

  6. #6
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    perhaps try holding 3rd longer before shifting into 4th, see if elevated RPM there also causes it to happen in higher gears?

    I would think if the hydraulic system were acting up, all gears would be effected equally.

    what happens if you double clutch?
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  7. #7
    Fuel Injected!
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    Congratulations. You've found that annoying difference in a light-duty transmission and a medium-duty transmission. The larger gears (both in diameter and mass) mean the synchro's job is MUCH harder, and it takes a finite amount of time and friction to spin up/slow down those big gears. There are ways around it though-and it will "wear in" and get better with time.

    Basically the friction surfaces on the synchronizer cones doesn't have enough contact area with the friction surfaces on the gears themselves. These two friction surfaces are essentially a wet clutch-and just like clutches, they need time to "mate" together.

    The situation is worsened by loose tolerances on the synchro stack-most shops do not measure the synchronizer engagement distance to make sure the friction cones are properly mating up prior to the selector collar engaging the gear. They just rely on the parts suppliers to send them synchro rings that are "close enough" and normally they're a little too small-so they take a long time to "wear in" but they are rarely oversize enough to allow a newly rebuilt transmission to grind going into gear.

    10-15 thousand miles and an oil change at the 7500 mile mark will help considerably. I see this in NV3500's, NV4500's, T56's and TKO's in Ford/Chevy/Mopar, FS5R30A and FS5R60A transmissions in Nissans, and some of the older heavy-duty Ford transmissions.

  8. #8
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    RobertISaar
    Hm, I haven't tried double clutching yet, I'll have to try that when I get back into town.

    Xnke
    I was actually thinking that it might need time to break in a little, but I wasn't sure. I heard from a few people that the syncros need to break in, but I've heard from many others that rebuilt transmissions shouldn't need to "break in". When you install them, they should just work. And that any driving done on a transmission that seems faulty could cause even more harm to the internals.

    When I removed it last summer and the mechanic opened it up and looked at it, he said all of the synchros were new. I really hope the synchros just need to break in, because otherwise, this almost seems like a insolvable mystery.

  9. #9
    Fuel Injected!
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    What Xnke says is true. Blocker rings are similar to brake pads, they will create a wear pattern once "broken" in.
    If it don't fit force it, if it don't force fit f&%@ it!

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