tips on rebuilding a posi unit on a 72 buick skylark

Discussion in 'Got gears?' started by 72gsBuick, Jul 5, 2009.

  1. 72gsBuick

    72gsBuick Never Say Never..

    Will be installing the posi unit i got with the new bearings and hardware, just wondering if there are any special tips or tricks i can do to put it back together, i have done posi swaps before but never by installing a different pinion.. i know they have to be precisely ligned up so just wanted to ask the experts, also do the axle bearings need to be sent to a shop for removal of the bearing and seal or can one change them. i know it would of been easier for me to send it to a shop but what good is it if you dont try it firsthand.. thanks guys.. by the way i will be intalling the 3.08 gears suggested
     
  2. GStage1

    GStage1 Always looking for parts!

    Not worth your time for the work involved. There are some special tools. The bearings must be pressed on and same for the carrier and pinion.

    Local shop here charges me $200 + parts to rebuild the entire rear with new bearings, seals, install posi and carrier.......usually runs me about $350 and well worth it.

    The pinion has to be set with a specified depth and there is a little more than meets the eye when shimming the carrier to get the proper gear pattern.
     
  3. 72gsBuick

    72gsBuick Never Say Never..

    thanks George... Didnt really explain myself right..i will be taking the carrier to a local shop i know which charges me 20 bucks to intall the bearings on the pinion and carrier. i know i have to get the right clearances for the pinion and gears, which is why i will be using a dial indicator for the right clearance.. my main concern would be the pinion crush sleeve installation...like i said before i just want to learn how to do it right, i have done this in the past and spent numerous hours and money getting it right but i think knowledge is well worth it.. guess i just like to do it the hard way no matter how many times it takes, when i removed my first tranny, just for the heck of it i removed it about 3 times in a role, and then set myself a time limit in which i had to do this.. did all this in about an hour and ahalf, just to do it as fast as possible while still doing it right. any tips would be great.. another question..about the bop bolt on axles, since im ussually dealing with chebbie axles without bearings in them, how are those removed/installed. aswell as where can i get them..i go to kragen and ask them for that, and they give me the :shock: when i tell them my differential is different than a chebby..thanks
     
  4. GStage1

    GStage1 Always looking for parts!

    I seriously doubt that any auto parts store will carry rear axle bearings...those usually are found in a rear axle builders' inventory.

    The bearings are pressed on and require a commercial floor press.....another tool you won't have. Like I said before...take it to a pro and have him set-up the rear....no need for you to bother with it since you will only be doing it once.
     
  5. 72gsBuick

    72gsBuick Never Say Never..

    might concider that but i doubt our prices here are that cheap..i called in a while ago to different shops and they wanted to charge anywhere from 350-1500 to rebuild a 8.6 differential, i then asked how much to install a new gear set and they wanted $500 bucks.. dont know why their prices are so rediculous here but either way good idea to compare elsewhere..on the mean time what should i look for as far as parts i need, i want to buy the parts myself instead of getting overpriced parts from shops
     
  6. GStage1

    GStage1 Always looking for parts!

    Contact Monzaz here.....he is a rear axle rebuilder and will have all the parts.
     
  7. speed70

    speed70 Henderson Driveline, Grafton OH

    If you are wanting to do it right then you won't have the new pinion bearing pressed on by the local shop or you won't be able to set your pinion depth.
    Maybe some shops are farming out their work and then adding a little extra to line their pockets but as a professional rebuilder i don't think my price of $200-250 labor + part$ = too much? A customer of mine pays for a disassembled and cleaned housing/center section, complete inspection of parts to be reused (if any), my experiance and my guarantee the job is done right the first time with quality parts. I'm all for learning how to do your own work as thats how i've learned much myself. Its just to me anyways that some things (like re-roofing my house) may be better off done by a pro as i don't like spending more than i have too especially when i may not do it right the first time and have to do it over again. On the upside if you can find a pro in the line of work you need done and he/she can work along side you and give you pointers while you're learning thats even better! :beer
     
  8. 72gsBuick

    72gsBuick Never Say Never..

    ok, thanks either way im writing down some shop numbers and giving them a call.. hopefully i dont get the 1500 dollar price again.
     
  9. 72gsBuick

    72gsBuick Never Say Never..

    just an update...did the rebuild myself on the rear end, took the car and bam..great job.no problems at all, overal i think i did a very good job..and outdid myself while saving 275 bucks. :bglasses: and gained lots of experience, let me tell you it was a pain ligning up the pinion and gear but overall good experience hope nothing happens later on
     
  10. TimR

    TimR Nutcase at large

    Just curious if you replaced the axle bearings yourself, if so did you punch the bearings off or use a press or ??

    Glad to hear you had fun and it all worked out good, nice feeling to do things yourself. :beers2:
     
  11. BrianTrick

    BrianTrick Brian Trick

    Most auto parts stores usually stock the axle bearings & seals,or they can get them from another store within 24hrs.The bearings are SET-9 or also known as A-9. The seal # is either 712146 or 2146. Timken had both,but now everything is 2146 for them. The 712146 seals were a hair wider.
    As for setting up the gears,yes,they have to dead-nuts.Don;t be real concerned with the pinion depth number that might be scribed onto the pinion head.It is only a suggestion,& what the company got with their fixture.The MOST important thing is the pattern. The pinion shims will be trial & error,so you might want to find an easy way to get the large pinion bearing off each time.You can either polish the bearing journal on a lathe,or hone the inside of the large bearing.If you polish the pinion,just do it enough that the bearing still fits snug,with light tapping to get it on.If you hone the bearing,get a duplicate,so you have one for the final assembly,to press on.Pick a pinion shim to start with.I suggest something between .030"-.040" to start with.You don't need the crush sleeve for the trial fittings.Install the pinion,yoke,& nut,& tighten until there is a light drag on the pinion.Now move onto the carrier/ring gear.You will want to set your backlash at .006"-.008".Shim the carrier to achieve the desired backlash,& at the same time have enough shim to put preload on the carrier bearings.You don't want the carrier to just fall-in.You want some resistance or pressure.Once you your backlash set,torque the carrier caps down to 50ft-lbs,for your trials. Now brush on your gear marking compound on both drive & coast side.Do about 5 teeth,then skip over a section & do about 5 more,etc. Do that for both drive & coast.Once you have done that.put some resistance on the carrier,to simulate wheel drag,& rotate the pinion 3 or 4 complete cycles,& see what your pattern is.Your pattern will tell you if you need more or less shim,for the next trial.If you need help reading the pattern,post some pictures,& we can help,or you can e-mail them to me.Once you get the desired pattern,you can take apart for the last time.Reassemble with your crush sleeve,place some white thread sealant on the pinion splines,install the yoke,& dab some red lock-tite on the pinion nut. You will need something to hold the yoke,like a yoke wrench,or a very large pipe wrench.Some people use an impact gun for the pinion nut/crush sleeve,but I use 3/4" drive ratchet set.The crush sleeve will take some balls to squeeze it.You will need to check the pinion periodicly to check for play & preload on the bearings.You will want a light resistance,just as before,when it's all done.You should not be able to freewheel it.Once that is done,put the carrier back in,with your selected shims,& place the carrier caps back in & torque to 65ft-lbs.NOTE: The carrier caps should go back to the same side that they came out of,& the arrows face outward.Do a final pattern check with some compound,& if it's still good,you're done.
    If you don't have a large press,I would take your shafts with the new bearings/seals,& have a machineshop swap them.Just make sure they place the new bearings on the correct way,with the rib facing outwards.there are directions in the box,but I have seen many shops put them on backwards,as well as the carrier caps.If you have any other questions,just ask.
     
  12. TimR

    TimR Nutcase at large

    I have done a few diffs (about one every 10 years..LOL) but was mostly just curious how he did the axle bearings and seals. I do have access to a press at work but not sure if its big enough. Guess I'll find out, will have to make the plates too that fit the bearings to press on and off.

    Excellent write up for everybody, and the info on the bearing and seal p/n's could save a lot of grief.:beers2:
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Brian,
    I had a problem with the seals when I did my 1971 8.5 10 bolt. I at first used the 2146 seals, and I had a lot of axle end play. I had to disassemble and use the 712146 seals. The 712146 seals were almost 1/8" wider, and that solved my problem. There are some threads on this on V8 Buick. Others have had the same problem. I remember posting this at least once. According to a search I did, the 2146 is .375" wide, while the 712146 is .490"wide.
     
  14. BrianTrick

    BrianTrick Brian Trick

    Larry,
    Your seal measurements look right.I always get the 712146.That way I know everything is seated properly.I recently noticed that Timken is making(or trying to make) the 2146 seal ONLY,so I have since sourced-out to Federal Mogal to get the 712146. I think Timken might be trying to make a width in between the two,so they can drop one line,but not sure.
    Yes,any of these bearings/seals are available at your local AutoZone(Timken),or AdvanceAuto(Federal Mogal,BCA,National). I also have Erie Bearing where I live,which carries all brands,and they have anything & everything.
     
  15. monzaz

    monzaz Jim

    2146 is used in the AMC cars with the a-9 bearing alot. 2146 and 712146 are a huge difference in thickness major disaster will happen if you mix them up. ALWAYS measure them...BECAUSE the maroons in the parts store sometimes will pull parts and shove them back in the wrong BOXES!!!!!

    Another thing on the set-up info your giving...NOT trying to step on toes ...BUT Taking down the pinion shaft diameter to make a bearing fit with less press is a BAD idea...NOT GOOD... This is a press fit and needs to be this way. Do not modify the pinion shaft diameter.

    ONLY hone a bearing that will NOT be used in the final assembly to set up the rear. If the bearing race of the cone bearing spins on the pinion shaft while in use the bearing WILL FAIL from heat build up and could over heat the pinion shaft and cause pinion failure also. PLEASE be careful with this practice.... I would only do the set-up bearing honing...then once the correct depth is located in the housing press the new bearing on and double check the pattern once more ...I say this because I have actually had bearings that were NOT the same specs from same and different brands same part number and the pattern actually changed some from bearing to bearing buy a few thousands.... NOW that was very few and in between but it does happen in the imperfect world we live in. LOL Good luck on all the rear diff set-up out there.

    Cold winter is coming.......AGAIN....:eek2:
     
  16. BrianTrick

    BrianTrick Brian Trick

    Yes,I have a bearing that is honed,for my trials,but I have seen plenty of big-named shops polish the pinion shaft.No,you would not want the bearing to fall on there,so they must be taking a very minimal amount off. I think if someone did do that,I would suggest puting some locktite behind the bearing,for final press assembly,to make sure it does not spin.
    Also,Yes,check the bearings if you get them at the parts stores,as I have found the narrower 2146 in a 712146 package.I have also found the A-9 bearings without the lock ring,which is a must.
     
  17. monzaz

    monzaz Jim

    ADMITTEDLY I would tell ALL BUICKV8 and other forums... NO modifying of the original size of the pinion shaft that removes press fit at all... NEVER.

    Just because they are big name shops does not always mean they know what they are doing and that they are doing it right. :error: :error:

    There are quite a few practices that I can let slide...BUT this ain't one of them.

    PLEASE .... THIS is a bad idea. please only hone the set-up bearing. lock tight will not work on smooth surface of the pinion bearing... This is a recipe for disaster so much so I will not post this thread any more on that subject of honing the pinion shaft...:error: :error: :error:

    AGAIN, I do not want to step on toes here but this is a wrong thing to do.

    Jim Mitschke
    J D Race
     
  18. BrianTrick

    BrianTrick Brian Trick

    Their pants are bigger than ours,so they can get away with it.
     

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