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Thread: What should a recon diff feel like before fitting?

  1. #11
    SOC Member Tim Proctor's Avatar
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    Quote Originally Posted by jagorstag View Post
    Good luck Louise and enjoy the trip! Earplugs will probably help with the diff whine....

    Cheers,
    Joakim
    Didn't work out too well, Joakim. It was the first real test of the restored car, and once that diff got hot, it began to graunch and create a lot of vibration. I have two slipped discs, acquired during the course of the restoration, and have to avoid vibration to allow them a chance to heal. So, after the first night, we took the difficult decision to abandon the holiday and drive home at 40mph. A real shame, the first half hour of driving, before the diff gets hot, and if you ignore the whine and occasional scrooping noises coming from the back, the car is a gem.

    Undecided about the best course of action now, but it will probably be to buy a recon diff (with new crown and pinion) from Rimmers and send the dud diff back to where it came from.

    Louise

  2. #12
    SOC Member and Moderator jagorstag's Avatar
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    I'm really sorry to hear that, Louise. Sounds though that you are right in that a new recon diff is the way to go, hopefully that one will be better and you can eventually resume your European adventure.

    Cheers,
    Joakim
    1975 Triumph Stag - TV8 & MOD. Still in sickbay...

    Managing Linkedin groups Triumph Car Owners and Enthusiasts & Triumph Nederland

  3. #13
    Taking it slow in 2017 mole42's Avatar
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    Don’t buy from Rimmers. I’m still in the throes of legal stuff about a diff with their parts in it.
    Mabel is a white 1972 Mk1, TV8, ZF 4HP-22 auto,
    2016 RBRR finisher.

  4. #14
    SOC Member Tim Proctor's Avatar
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    Examining the second diff, there are 11 notches per revolution when driving the output shafts relative to each other. I guess this corresponds to a planet pinion of 11t, which I guess would be about right. So, this looks like it is simply a tight initial set-up of the pinions.

    To drive it through the notches needs a 1/2 square drive socket set on each half shaft, one held firm, a boot on the diff to hold it steady and a good push on the other socket drive. If it was fitted and one back wheel jacked up, that wheel wouldn't spin, I doubt, it would stick between teeth, but the wheel would turn with two hands on the tyre, one each side. Best way I can think of describing the level of stickyness. Does this sound OK for the initial set-up?

    Louise

  5. #15
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    No it doesn’t - needs to go back to the vendor. My guess is though there is a lot of swarf kicking around inside it now from the diff section, also it sounds like the diff carrier bearings have been set up badly to generate lots of heat - despite the sun/planets shimming being wrongly set, it shouldn’t whine or get particularly hot. In a straight line the diff section isn’t ‘rolling’ so is doing nothing and therefore not generating heat (unless your back tyres are 2 different sizes, which I doubt)

    You got a bad one. I’ve been very happy with Robsport’s recons when I’ve needed to just get one off the shelf, and I’ve heard good things about Fitchetts too

    I do my own diff repairs now, and know what is in it..

    Russ
    Last edited by kryten; 5th October 2017 at 18:16.

  6. #16
    International Members down_the_plug_hole's Avatar
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    Quote Originally Posted by kryten View Post
    No it doesn’t - needs to go back to the vendor.

    also it sounds like the diff carrier bearings have been set up badly to generate lots of heat - despite the sun/planets shimming being wrongly set, it shouldn’t whine or get particularly hot.

    In a straight line the diff section isn’t ‘rolling’ so is doing nothing and therefore not generating heat (unless your back tyres are 2 different sizes, which I doubt)

    You got a bad one.
    I’ve heard good things about Fitchetts too
    I know what Fitchett puts in his axles, cos Tony told me when he was alive.

    As for the stuff above -sorry most of it is wrong.
    I have rebuilt loads of BRAND NEW old stock axles from the factory inc those for TR6 etc.
    You can't turn the planet gears PERIOD, or usally will be dead notchy if you can.

    IDEM Jaguar ones I have been recently rebuilding with all new bits...brand new stuff, made in Birmingham.

    Also as for carrier preload there is a proper setting for it.
    Did you know it's 3 thou, but makes little difference if you wind it up to 5.
    It won't and can't generate large losses even if you like that theory for the simple reason it's only going round at a few 100RPM max compared with the pinion which is going round at 1000s and 1000s....

    As for power losses in diffs there IS a big loss in a straight line and almost none extra on corners, simply because a hypoid pinion is a cross between a spiral bevel and a worm gear. Hypoid oil is used precisely because the forces are sliding and generate a lot of friction.
    Friction = heat.

    The power losses on run down are a lot higher which is why they put thrust buttons on trucks to give the pinion a helping hand under run down loads especially when using a TELMA.

    Just saying....
    Oh and btw the main reason why repro gears are noisy for stags is cos they've been made wrong...but hey you knew that didn't you??
    Last edited by down_the_plug_hole; 8th October 2017 at 16:16.

  7. #17
    SOC Member Tim Proctor's Avatar
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    The 'notchy' diff, when fitted and with the road wheels attached felt quite smooth with that extra bit of momentum from the wheels. This was both out of gear so the wheel rotated the same way, turning the prop shaft, and in gear, so the wheels contra-rotated against a stationary prop-shaft. On the road, there is just a slight whine when pushing a lot of power through, otherwise silent.

    Two days of hard work, those damn exhaust pipes took some wrestling with, as did balancing the diff to offer it back up. We wanted to celebrate by shooting off up the nearest mountain, but the car had other plans and mischievously dumped her coolant. We suspect the system was air-locked on the last fill, we're not sure yet. We made it to the bar half way up the mountain, and span out a couple of beers waiting for everything to cool down, in the glorious sunshine.

    Thank you all for your advice on this job.

    Louise

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