72 Riviera with Posi rear end?

Discussion in 'Got gears?' started by jhems17, Aug 16, 2019.

  1. jhems17

    jhems17 Well-Known Member

    Hello, I was dropping the gas tank off of my 72 Riviera to use its sending unit for my 71 and I noticed the rear end had this tag bolted on the differential end cap. So did I luck out and get a Posi Trac rear end? Was this an option for non GS Rivieras? I remember years and years ago if I jacked it up and spun the tires they would both go the same direction but I've read different opinions about this proving it was Posi or not. Also a side question how do i replace the rear wheel bearings? Do I need to remove the whole axle? There is no bearing cap like on the front wheels? Thank you for any help.
     

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  2. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    Posi was available on Rivs. Jacking up both sides and spinning wheels they will go in the same directional way with a posi . Regular open rear one tire will go in one direction and the other will go in the oppisite .

    If I remember correctly axles are bolted in with 4 bolts thru the backing plate and bearings have a retainer spacer pressed onto the shaft that has to be cut off .

    If you change the fluid be sure to add a small bottle of GM axle additive .
     
  3. jhems17

    jhems17 Well-Known Member

    Thanks, cool I thought Posi was only on the GS models.
     
  4. monzaz

    monzaz Jim

    Limited slip was an option on ANY car or truck. IT was more common for a performance optioned vehicle like a GS or a SS or W car etc. Years ago you could build a car and check boxes off of options you wanted.
    NOW everything is a PACKAGE... Suppose to make the manufacturing process cheaper...But really they wanted to make life easier for selling... lol.
     
  5. monzaz

    monzaz Jim

    Axle shafts: you have to pull the tire, pull the drum, then there are access holes in the axle shaft flange to get an extension to thew retaining plate that has 4 nuts that also removes the backing plate and the axle at the same time. You may have to use a slide hammer or some form of removal tool to get the axle out of the tube end as over year rust and debris will pack up preventing a smooth removal.
    Good luck.
    DO check your part stores before removing the axle bearing to be sure you can find them...Some models are very hard to find in the axle bearings. (obsolete)
     
    Last edited: Aug 18, 2019
  6. monzaz

    monzaz Jim

    Be careful with the drum slide hammer I have seen people mess up a drum that way the center got bowed out and it never sat right again...USE an old drum your not intending on using again...Would be a better suggestion
     
  7. jhems17

    jhems17 Well-Known Member

    Hello again, some follow up questions. will my newly discovered Posi have the 3.42 gears or were there other options (an article on buickperformanceclub.com seems to imply there were 4 gear options) ? If I swap it in to my 71 will i have to alter the speedo gears to match the new ratio? How will the new ratio affect freeway RPM's and basic drive ability? Once again thanks for any info you can give.
     
  8. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    It is either a 2.93 or 3.42 for 71 and 72.
     
  9. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    I only know of 3 ratio options . 2.93 , 3.23 , and 3.42 but there might have been a 3.08
     
  10. monzaz

    monzaz Jim

    YOU HAVE TO OPEN UP THE REAR AND READ THE EDGE OF THE RING GEAR THAT WILL GIVE YOU THE NUMBERS TO DETERMINE THE RATIO. or YOU CAN COUNT THE TEETH IN THE RING AND the pinion divide the pinion into the ring tooth count and you will have your answer.
    Sorry about the caps ... Not yelling.
    Jim
     

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