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truck doesnt clunk in overdrive

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MudRebel350, May 28, 2000.

  1. MudRebel350

    MudRebel350 1/2 ton status

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    I was driving my truck usually in drive not overdrive around town and in overdrive on the highway and it would clunk when I'd slow down when the speedometer was at around 15. I put in overdrive when i was going around 55 down the highway and didnt put it back in drive when i slowed down and it didnt clunk. It doesnt clunk in overdrive so i decided to drive it in overdrive and not have to worry about something falling out of it. If anyone knows whats going on here shed some light on the subject.

    J.D.
    88 Gmc Jimmy
     
  2. dumbfounded

    dumbfounded 1/2 ton status

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    I'm a little puzzled with auto's It seems like it shouldn't matter b/c the tranny "usually" knows what's best with the exception of overdrive. It may just be a fluke in the valve body where it downshifts harder and makes some slack in the drive line make a clunk... I believe if you had any slack in the tranny it would do it either way and if it was tranny slack hold on to your wallet b/c a normal rebuild wouldn't cover it I don't believe. Look back on other posts there was a site somebody posted where someone said it explained alot about trannys I checked it out and answered alot of questions. I believe it explained the same symptoms that happen in the gm 4T60 in the front wheel drive 3.1's and I think it said it was a modulator adjustment that had to deal with engine vacuum. Don't know if this relates but I'll find the site then post back.

    Blood, sweat, tears, and lots of money is what keeps my K5 alive.
     
  3. dumbfounded

    dumbfounded 1/2 ton status

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    the site is www.thegrid.net/thedrivetrainpage/ if I typed something wrong type in 700r4 in the search then look in the posts

    Blood, sweat, tears, and lots of money is what keeps my K5 alive.
     
  4. MudRebel350

    MudRebel350 1/2 ton status

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    the previous owner had the tranny rebuilt about 5000 miles ago. In overdrive there is a little downshift pull but not a big clunk feeling and the noise to boot. I don't want to put up my truck in the tranny shop. Im not going back to drivng my grandpas old car the Chevy Celebrity, although it was a good car i love my truck.

    J.D.
    88 Gmc Jimmy
     
  5. MudRebel350

    MudRebel350 1/2 ton status

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    i read it, its kinda confusing unless i can totally see what he is talking about. Im one of those hands on people who couldnt learn it in writing and then try to do what it says. I think i have an idea whats going on though. thanx

    J.D.
    88 Gmc Jimmy
     
  6. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    You're doing the right thing by driving at city speeds in drive and saving overdrive for the highway....I'd advise you not to start using overdrive all the time unless you really want to replace your tranny. Overdrive at low speeds makes your tranny "gear hunt", which makes it run hot and will really speed up the deterioration of your already weak 700r4. I don't really understand why it wouldn't clunk at low speeds in overdrive...maybe it has something to do with your shift modulator or your kickdown adjustment. Auto trannies are still a mystery to me!
     
  7. Kiblsnbits

    Kiblsnbits Registered Member

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    Just wanted to say that I have the exact same problem, so you're not alone!
    -Steve

    Blazer: A hole in the air, surrounded by metal, into which one pours money
     
  8. CrazeeBush

    CrazeeBush 1/2 ton status

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    Same thing here! There is a pronounced downshift in Drive that isn't present in Overdrive. I've wondered it myself, but I just thought that since the tranny has 150,000 on it and the previous owner didn't take care of it(The filtering medium in the filter was nonexistant when I did a fluid filter change for the tranny), that I was looking at just driving it until the dang thing fell out.
     
  9. Topher

    Topher Registered Member

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    Hi. I have an 85 Jimmy and I too experience the downshift clanking noise while in drive, but not in overdrive. It's been there pretty much the whole I've owned my vehicle. I guess I just never thought it was a big deal; seeing as how my 700r4 is one of the, ahem, "troubled" units of the mid-80's w/ ~140k mi on it I just figured it was being its normal self, hehe.

    Mine also occurs around 15 mph or so; or usually when I'm slowing down to come to a stop or something.

    Anyway I plan to do a rebuild and then add a shift improver kit, or maybe just get a whole new tranny from B&M, TCI, or Jet one of these days.

    Take care!

    (p.s., I keep it in drive all the time. When on the highway I usually keep it in drive until about 65-75 mph and then throw it into OD if it's a relatively flat run.)

    Chris Southerland
    topher75@airmail.net
    DFW, TX
    85 Jimmy & 78 K5
     
  10. River

    River 1/2 ton status

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    I think dear is a little play in your driveline or rear dif. and the th700r4 when driving in overdrive will (when slowing down) shift down very late to save fuel, but when you drive in drive it will shift down just like a th350 and the car brake`s also on the engine that`s when you here the clunk.

    Greetings from Amsterdam,

    River
     
  11. jarheadk5

    jarheadk5 1/2 ton status

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    This thread piqued my curiosity, so I did a little experimenting to and from work today. My 700r4 seems to downshift a little firmer while coasting down in D versus OD. No brakes applied, level ground, 35mph down to 15mph a few times each in D and OD. I don't get it, either. I guess it's one of those quirks we have to get used to!

    [​IMG] Semper Maintenance!
     
  12. Eagle86K5

    Eagle86K5 1/2 ton status

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    you also have to remember about the lock-up...when I first got mine I thought I had a 6 speed cause it will do the lock-up thing in 3rd as well as 4th or overdrive...

    <font color=green>[​IMG]Eagle86K5[​IMG]<font color=red>
    Masonry...It's a Good Thing
    2B1ASK1
     
  13. Blazer1970

    Blazer1970 1/2 ton status

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    Mine definently downshifts harder when in D too. I like it that way. Glad to know it seems to be normal.

    Tim

    1970 Blazer CST 4X4 350 SM465 NP205
    1987 Suburban 4X4 350
    1988 Chevy Pickup 4X4 350
     
  14. 87JIMMY

    87JIMMY Registered Member

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    Add mine to the clunk list too. Mine started after a rebuild @ 180k.and had a Corvete servo and beefier clutches put in. My driveline was all rebuilt at the same time, so it is definately the tranny. I had the tranny guy and my driveline guy look at it and they said it was normal. The driveline guy even rebuilt his the same because he liked it. So I guess I gotta believe it's ok.

    Scott 87JIMMY
     

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