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Replacing the Rear Differential

Discussion in 'Omega How to and FAQ's' started by Vectrolosys, Dec 20, 2007.

  1. Vectrolosys

    Vectrolosys Club Barge VxON Regional Co-Ordinator

    Messages:
    3,468
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    17
    Location:
    Bristol/UK
    I completed a Diff swap back in the summer.

    Basically, take your time. Don't bother with ramps, as already stated, you need to rotate the wheels to get the driveshafts off. Here's a quick run down.

    Jack the car up as high as you can and support the rear of the car on axle stands.

    Soak the following in plus gas or WD40 at least 12 hours before attacking the job.

    - The bolts holding the diff up, there are two at the rear and three on a mounting near the front.
    - The pinion bolts
    - The bolts at the wheel hubs

    I personally left the exhaust in place will the last minute, so worry not about this for the moment.

    Using some blocks of wood, wedge the wheel in turn as you remove the 6 bolts holding the driveshaft to the hub. You'll need a breaker bar, extension and a Torx to undo these. Keep these bolts, and the shims that come off (three in total) safe.

    Once the shafts are loose, remove the bolts on the pinion, if I recall, the nuts come off but the bolts don't come out completely, keep the nuts safe. The prop should pop off with a little push, its best to tie it up or support it in an axle stand so it doesn't just dangle, as this puts additional strain on the centre bearing.

    I managed to get one driveshaft out and had to leave the other one in, if I do the job again in the future, I'll use a crowbar to carefully prise it shaft out, I found it easier than wrestling a heavy diff complete with arm like driveshafts out from under the car!! Label each shaft left and right, so you know which ones which on refitting.

    Lower the exhaust, possible even remove it from the cats back if you want it out the way completely.

    At this point, I placed my jack at the rear of the diff (the heaviest part) and had a block of wood stretch out thus supporting the whole diff. I jacked up to take the weight and remove each large bolt, remembering where each came from.

    Lowering the diff is interesting, I held and lowered very slowly guiding the diff down.

    I pulled it out from under the car. Now is a good time to touch up any areas of rust with hammerite, perhaps even break out the waxoyl.

    In an ideal world, we'd all have one of those massive three tonne jacks, with the big cup. This would allow us to mount the diff onto the cup and just jack it into position. In the real world, I used my 2.5 tonne halford jack and another jack, with a block of wood, effectively making a bridge for the diff to sit on. The diff was placed on and carefully wheels under the car. Ever so slowly, this platform was raised, till the rear of the diff was in position to get the bolts in at the rear, the two large ones. Lower the diff ever so slightly so it sits at an angle with the pinon facing downwards. At this point I placed the prop nearish the diff, slowly jacking up allowed the prop and pinion to mate together. You can now put in the three large bolts on the flexi mount, and tighten all bolts to the specified torque, USE NEW BOLTS FOR EACH OF THESE.

    Now, I popped the driveshafts in and made sure that the circlip was present, I then check they should not be pulled out with a hard tug, and put all six bolts back in of both sides. Pinion nuts and bolts, all to torque values, using new bolts all round.

    At this point, with the exhaust back on and everything together, but the car still in the air, I topped up the diff oil. With the car still in the air, I started her up and drove through the gears up to around an indicated 2500 RPM in 4th. This allowed me to listen for any undue noises from the diff.

    A quick test drive revealed all was well.

    [​IMG]

    The old diff, just after I had dropped it down.


    [​IMG]

    The void, sans diff, exhaust in place but lowered off rubber mounts at the rear.

    [​IMG]

    New diff in place, awaiting the driveshafts


    [​IMG]

    The old diff, crownwheel was in fair condition, but the magnets had collected a lot of swarf, pointing to a collapsed pinion bearing.
     
  2. lotusman

    lotusman New Member

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    Location:
    mountain ash south wales
    thanks a lot.with the help of your pics and text,it looks like it shoud'nt be too hard(hopefuly).
     
  3. lotusman

    lotusman New Member

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    Location:
    mountain ash south wales
    thanks again guys,have just fitted new diff and have now got nice quiet motoring again.
     
  4. Andy McKay

    Andy McKay Guest

    Rear diff problem diagnosis

    Hi there, I've got a rattling noise coming from the back, thought it was a loose exhaust mounting or maybe loose baffles in the back box but can't find anything obvious i.e. no rattles when I shake it and all rubbers still in place plus the exhaust is only two years old so don't think this is the problem. Friend suggested it might be diff problem but he's not sure. What made you suspect yours i.e. rattling noise or something else. Looks like quite a big (and expensive job) so don't want to go down that road unless I'm certain this is the probblem.

    Andy
     
  5. Jaybooze

    Jaybooze New Member

    Messages:
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    Location:
    Penmaenmawr,Wales UK
    Diffs dont rattle when they are effed,they whine,graunch,clang,bump,make horrible crunching noises and finally dont transmit drive.
    It will be something loose,I would have suggested exhaust baffles,but you have eliminated that.
    Perhaps loose diff mounting bolts,brake backplates,plenty of things.Just drive it until it becomes obvious unless it is really bad.If so stick it on a ramp and have a good shufti( Arabic for look,usually combined with a couple more words regarding female anatomy).Jerry
     
  6. Andy McKay

    Andy McKay Guest

    OK thanks for that. Will wait for it to stop raining then get out under there again. Omegas certainly keep you busy with all these minor irritations. Glad I didn't pay big bucks for this but it's defintiely a high maintenance car and is starting to really p**s me off due to one irritation after another. Andy
     
  7. Andy McKay

    Andy McKay Guest

    Sorted

    The rattling turned out to be a cracked weld on the inlet to the back box. Walkers replacement exhaust. Only 18 months old when it started to rattle and guess what I'm not covered by the warranty. Tried liquid metal etc. but it didn't last very long before it shook itself free. Garage didn't want to weld it in situ and reckoned it was too much effort to take it off an repair it. Looks like I'm going to have to strip it down myself and get a mate to weld it up for me. Maybe I should have got a genuine Vauxhall part but they're a wallet attack.
     

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