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Thread: Clunking Differential - play/ backlash?

  1. #11 Re: Clunking Differential - play/ backlash? 
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    Quote Originally Posted by dogoncrazy View Post
    Might seem like a daft question but has it got oil in it? Don't assume anything - CHECK
    Now you’ve said this I’m definitely going to be checking haha! Do I just take out the fill plug and stick something in to see if the level is just below the plug?
    If this is the case, will a refill likely solve the clunking? Or is it too late if the noise is there? (The cars only done a few hundred miles, but I have no idea on the history of the diff).
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  2. #12 Re: Clunking Differential - play/ backlash? 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Do all the checks to eliminate other causes and then accept that the diff has probably had it! Adding oil now if its empty won’t fix the damage. The filler plug is difficult to reach on the Cabrio as the fuel tank is in the way. Probably why it doesn’t get checked! I cut the end off an allen key to leave just enough sticking out to fit a flat ratchet type combination ring spanner on the end.


    To remove the diff you need to jack the rear of the car onto axle stands under the rear of the chassis. Then you can undo the rear brakes and pull out the drive shafts. Get hold of a Haynes Sierra workshop manual as it tells you how to do all this. THE DIFF IS HEAVY! I made up a jack to swap mine! There is a post on this forum showing how I replaced my rear diff mounting which may help you. Once the diff is out of the car you can remove the rear cover plate and check for damage. Rebuilding one is not a diy job! Best source a used one in good condition. I obtained mine (replaced for ratio change) from John at Kitfit. I have his phone number if you need it.


    The diff ratio will be stamped on the edge of the crownwheel. The following link is invaluable for identifying Sierra diff types / sizes and ratios. Peter.


    http://www.super7thheaven.co.uk/comp..._differential/
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  3. #13 Re: Clunking Differential - play/ backlash? 
    club member Club Member dcunn's Avatar
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    Mornin' charlh94

    If you're really lucky, there may be a tag on the back of the diff to tell you it's ratio - like this one !

    Please send details/pics of the car to my email as in Pitstop magazine

    Rgds Dave Cunnington Archivist
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  4. #14 Re: Clunking Differential - play/ backlash? 
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    I was aware of the backlash as seen in the video. My suggestion of checking the oil was on the premise of if none is present then you really don't need to look any further as the unit is probably beyond redemption.
    I know of one member who having installed a reconditioned axle in his Roadster had it blow itself to pieces on the A38 out of Derby. He either assumed it had been filled with oil or just forgot to make the check. An expensive oversight !
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  5. #15 Re: Clunking Differential - play/ backlash? 
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    Update: Had a look today and the oil is low!

    Looking for a source of a leak I found the rubber boots around the cv joints are full of oil (should just be grease, right?) and there are a couple of tears where it can seep out.

    The paperwork I have shows the diff oil was done in 2016 which was only a couple of hundred miles ago.

    I’ve ordered a Sierra Haynes.

    Does anyone think if I replace the seals going to the cv joint (not sure how feasible that is), then I might just be lucky enough to not have to source a new diff?
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  6. #16 Re: Clunking Differential - play/ backlash? 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Quote Originally Posted by charlh94 View Post
    Update: Had a look today and the oil is low!

    Looking for a source of a leak I found the rubber boots around the cv joints are full of oil (should just be grease, right?) and there are a couple of tears where it can seep out.

    The paperwork I have shows the diff oil was done in 2016 which was only a couple of hundred miles ago.

    I’ve ordered a Sierra Haynes.

    Does anyone think if I replace the seals going to the cv joint (not sure how feasible that is), then I might just be lucky enough to not have to source a new diff?
    There is no path for diff oil to reach the inside of the cv boots. The diff oil seal runs against the outside of the metal “can” that contains the inner tripode joint. The rubber boot is clipped around the can and the drive shaft so it completely and separately contains the grease. CV grease is black and runny so may look like oil. Diff hypoid oil has a distinctive smell. How did you check the oil level? If using an improvised dipstick (bent wire or finger) what colour was the oil? Were there any small shiny metal flakes in it? If so that means something is seriously worn inside.

    Sorry to say that in my opinion, with both the clonk and the scraping noise you mentioned earlier, the diff is u/s. As you need to remove it to replace it I would take it out and get the back cover off and all will be revealed. Fit all four new rubber boots while the drive shafts are out. Search this forum for how to do that without trying to dismantle them. Peter.
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  7. #17 Re: Clunking Differential - play/ backlash? 
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    Totally agree with Peter's analysis above but if you really have got oil (instead of grease) in your CV joints then that could explain the 'scraping' noise.
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  8. #18 Re: Clunking Differential - play/ backlash? 
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    Ah I didn’t realise there wasn’t a path! Can’t see any other source of a leak so can only presume it wasn’t filled properly or the oil came out years ago.

    I first tried the check the level with an Allen key, but the oil was lower than it could reach. So in the end I got a long screwdriver in at an angle that touched the oil so hard to workout where the level is other than lower than it should be!

    The magnet on the plug definitely had some filings in the sludge: https://drive.google.com/file/d/1ZC8...w?usp=drivesdk
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  9. #19 Re: Clunking Differential - play/ backlash? 
    club member Club Member kahawi's Avatar
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    Given that there is no drain plug, what is the collective opinion on top-up vs drain and refill? Our diff’s probably haven’t done many miles, but the oil is going to be at least twenty years old.

    What’s the best option:-

    1. In the car with some kind of vacuum:
    2. Loosen the end plate and drain:
    3. or remove the whole diff assembly?


    Cheers, Colin B
    Last edited by kahawi; 27-07-2020 at 01:58 PM. Reason: 'Tab' option adds its own numbers, no need for A,B,C
    Marlin Hunter R500 ULA 1997 Ford-Based Hunter with 2.3 DOHC L4 engine, chassis/kit No. 157
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  10. #20 Re: Clunking Differential - play/ backlash? 
    frequent forum contributor Club Member greyV8pete's Avatar
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    Quote Originally Posted by kahawi View Post
    Given that there is no drain plug, what is the collective opinion on top-up vs drain and refill? Our diff’s probably haven’t done many miles, but the oil is going to be at least twenty years old.

    What’s the best option:-

    1. A) In the car with some kind of vacuum:
    2. B) Loosen the end plate and drain:
    3. C) or remove the whole diff assembly?


    Cheers, Colin B
    Option 1. I bought a jumbo syringe thing on ebay years ago. Use a long piece of clear plastic tubing so you can get right to the bottom. You will be able to replace about 90% of the oil like that. You can always repeat the process after a few hundred miles to further purge the old stuff.

    Option 2. Not an option on the Cabrio. There isn't enough space unless you take the fuel tank out. Don't forget that the crownwheel protrudes beyond the joint face, so you have to get the cover past that. Also having oil still dripping out as you try and remake the seal isnt a good idea.

    Option 3. Not unless you really need to for other reasons.
    Peter.
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