8.5 rearend

Discussion in 'Got gears?' started by buick350, Sep 16, 2004.

  1. buick350

    buick350 Well-Known Member

    in the old corporate 8.5 rearend can you use gears from the newer chevy trucks?? theyre both 8.5 but i think the chevy trucks are 30 spline while the corporate is 28 spline am i correct??if you can can the posi also be used??j
  2. 70 gsconvt

    70 gsconvt Silver Level contributor

    You are correct about the spline count. I don't think the posi's will interchange.
  3. monzaz

    monzaz Jim

    posis 30 28

    The posi are the same you just need to buy or find the same length axle that are 30 spline to use that posi unit . Moser can make them just give them the same dimensions from your old axles and tell them you what 30 spline Then the axles will be tough as the rest of the rear. Will be great for whatever you want to do. Jim
  4. buick350

    buick350 Well-Known Member

    can i install the gears without any modifications??or ring spacer??
  5. monzaz

    monzaz Jim


    If you are installing the exact items that came out of the truck(gears and matching posi in the truck the gears came in then yes they will fit right in but if you get a posi here and gears there then you need to make sure of the 8.5 posi series like 2 or 3 series. 2 series is 2.56 and down and the three series carrier is 2.73 and up so most of the 30 spline units I would say are 3 series just because the overdrive enables the cars/trucks to use a steeper gear with over drive trannys... get it? a lot of the 28 spline older 8.5 posis are 2 series because they need to be with only 3 auto matic gears and only 4 speed manual so when you want to put a steep gear like 3 series (3.08 -3.90) or 4series(4.10-and up) you need to use the spacer to make up the difference the 2 series is from a 3 series posi case. I hope your getting all of this... lol If not email me and we candiscuss over the phone ...my fingers are tired. :Comp: Hope this has help a bit. Jim
  6. buick350

    buick350 Well-Known Member

    yeah i get what you are saying and thanx :TU: i just was wandering after going through the summit catalog that they sell the 8.5 gears together 30 spline and 28 spline.and here in cali there are many mid 90s chebby trucks in the junkyard and was thinking of taking some good gears like 3 something out of one and buying a spool for a 28 spline 8.5 and putting it together in a corporate 8.5 so i could have a budget rearend and some serious :3gears: just wanted to save some money cause going to college.ill see what i can do and thanx again :TU:
  7. monzaz

    monzaz Jim


    I would suggest NOT doing the spool thing if you already have an open rear just put the lock right unit in it It rachets but will not harm your axles tires and gears barking around corners on the street but is very strong and the posi is very aggressive and they are down to around 200.00 about the same amount as a race spool at 179.00 plus you need to buy the special spool bearing that go on them for another 30.00 so where are you... see Trust me I do alot of these and everyone around here likes them because we race too and street drive. Give that a thought too. Jim :TU:
  8. oPh

    oPh Well-Known Member

    All factory posis used in '71 to early 90's Chevy & GMC 1/2 ton trucks & Blazers were of the Eaton governor-lock variety. These carriers are ABSOLUTE JUNK in a performance application. The gov-locks were designed to lock in or lock out, basically to help a pick-up if on wet grass or in a small amt of mud (not mud bogging). In building rears, have removed more of these type of posis which have grenaded & took out the ring & pinion, than any other design. Often when they do blow, they violently lock up the rear & occasionally cause the lh cap mtg area in the housing to be destroyed. Now not only will one need a new ring & pinion & carrier, but also a "new" housing :rant:

    Unknown quality used 8.5 gears...
    Personally, I can no longer afford the time in warranty comebacks to properly set-up what appear nice used 8.5 gears out of unkown useage pickups & vans. Mention this as we pulled & used hundreds of 3.42 & 3.73 ring & pinions out of well worn 1/2 ton trucks in the mid to early '90's. As the pickings got older, & such donor vehicles had more & more miles, it finally got to the point, it was just smarter to buy a new set of US Gear-Torqueline or US Gear-Strange Gears. The $100 we were charging out in a r/e build when using use what appeared nice condition used 8.5 gears was missed, but the profit did not offset the labor in occasionally chasing ring & pinion noise in flawlessly patterned & set-up r/e builds. Just something to think about.


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