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allison problem

Discussion in 'Chevy Trucks' started by t.i.b, Jan 24, 2011.

  1. t.i.b

    t.i.b Senior Member
    Messages: 140

    my 02 2500 8.1/ally is acting up. i went to pass a trash truck the other day and the truck banged and wouldnt shift passed 3rd and the ses light came on. i shut the truck off and started again the light stayed on but shifted fine. the comp says incorrect 2nd gear & 1st not detected by computer. i checked the fluid (it was chenged this fall) it was full but smells burnt. anyone have any ideas as to the problem? thanks.

    RBRONKEMA GHTFD 2000 Club Member
    Messages: 2,592

  3. t.i.b

    t.i.b Senior Member
    Messages: 140

    so its warmed up to -1 out so i went out & poked around @ the truck. now the prnd321 is no longer lit. is that likely the nbus? and would that cause the other issues? i wouldnt be so concerned but the burnt fluid has me worried. i dont beat the truck & the trans temp hasnt gotten hotter than usual so im hoping its nothing to major/expensive.
    Last edited: Jan 24, 2011
  4. stacks04

    stacks04 Senior Member
    from ct
    Messages: 119

    I would suspect the neutral safety switch on the side of the trans. They are very common and cause all sorts of issues. The fluid usually doesnt get the traditional burnt smell like in a normal trans if it is getting old and worn. Some do if they are really really fried but thats mostly an abuse situation.
  5. ticki2

    ticki2 Senior Member
    from NH
    Messages: 175

    It might also be one of the shift solenoids , there are 3 , all can be replaced from outside the tranny . Do some reading at Dieselplace to check your symtoms .I had a similar problem and it was a solenoid and not the NSBU switch.
    Last edited: Jan 24, 2011
  6. ticki2

    ticki2 Senior Member
    from NH
    Messages: 175

    If you go to Dieselplace do a serch for "Allison mystery" , that's my story , see if it sounds familiar .
  7. bmacd1

    bmacd1 Junior Member
    Messages: 7

    when u did your fluid change did you use genuine allison filters with transynd? the transynd is the important part here...its allison's full synthetic trans fluid and runs like $35-40 a gallon...atf tends to help burn up clutches without proper lube...i work at a detroit diesel/ allison cert shop.. they are great trans' but can be finiky sometimes
  8. 496 BB

    496 BB Senior Member
    Messages: 789

    This is most likely your prob. Make sure you get the updated one. Go here or equivalent as the dealer will RAAAAPE you. Trust me I know. http://www.merchant-automotive.com/allisonnsbuswitch2001-2004.aspx

    If not that then Id check solenoids by a professional shop dealing with Alli's.

    CT-TILEMAN Member
    Messages: 61

    Find a local NAPA store and buy it for less than $40 !

    Part description will be for a 4 speed Automatic, they do not count the OD as a gear in the part description.

    It will be a two-plug connector.

    You will need a heat gun to warm to original connector up as it has an epoxy that seems to glue itself to the wiring connector and with some heat it softens the epoxy so it will pop right out.

    Takes about 20 minutes to change, Good Luck
  10. woodchuck2

    woodchuck2 Senior Member
    Messages: 304

    X2 on this.
  11. tuney443

    tuney443 PlowSite.com Addict
    Messages: 1,847

    Granted,it is the opinion of many including myself and Allison that Transynd is one of the very best TES 295 fluids,but let's remember Castrol makes Transynd for Allison as part of their licensing agreement.There are other TES 295 fluids and clones out there that are just as good as Transynd.The point I want to make though is that you certainly do not have to have Transynd in your Ally as GM put Dex3 in the OP's truck when it was built and GM doesn't even recognize Transynd as a possible fluid to use.Only Allison does.Case in point is my 2006 LBZ--furnished with Dex VI--went 108K miles on it with regular 14K external filter change outs and just recently changed out to Transynd. I sometimes tow heavy,it is my plow truck and the original fluid served me fine.
  12. t.i.b

    t.i.b Senior Member
    Messages: 140

    thanks for all the tips. the switch is changed and the guts of the tranny were checked. so here are the new symptoms. theprnd123 was lit for 6 outa 12 hrs plowing when shifting from p to r the r isnt highlighted r to n r blinks and acts like neutral shift again and its in n eutral shift again and it will go into d ,3 & 2 but wont go down into 1st. i will try to find allison mystery over on deisil place but im not so good on the computer, thanks
  13. t.i.b

    t.i.b Senior Member
    Messages: 140

    pinhheads @ the tranny shop dindnt put the switch in right:realmad: after hrs of reading random things on diesil place(thanks for the link & suggestion) i found someone with the exact same issue. so i'll try adjusting that on saturday. guess its true "if you want something done right do it yourself. again thanks for all the help.
  14. t.i.b

    t.i.b Senior Member
    Messages: 140

    1 more question. would driving the truck with the switch improperly adjust possibly fry the new switch? the dash lights are out again wich is making it very difficult and irritating to try to adjust.
  15. t.i.b

    t.i.b Senior Member
    Messages: 140

    so im on my 3rd nsbu. 1 instaled wrong by" pros" 2 black 1 installed by me & and every thing worked fine from 10 am yesterday threw 10 am today then the prnd123 went out and the trans would pop outa gear when plowing. the "pros" put the 3rd in and still no lights and pops outa gaer under load. would the switch cause the truck to come outa gear? any help would be great.