404 diffs
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Thread: 404 diffs

  1. #1
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    404 diffs

    Thanks for all the advice on the 504 head. It is now reconditioned and installed and working beautifully. next issue is the 404 diff. Anyone got any clues regarding excessive diff backlash at lowish speeds. Little noise and no vibration, just this annoyng chug when accelerating/ decelerating with lowish revs. Any advice appreciated greg S

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  2. #2
    Guru davemcbean's Avatar
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    Two thoughts:

    -worn tailshaft splines
    -worn wormwheel

    Both will result in total loss of drive eventually.
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  3. #3
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    Yes, the "chugging" sounds a bit more like a worn worm wheel. Also what type of oil is in the diff and how much?

    Graham Wallis

  4. #4
    1000+ Posts Pugnut403's Avatar
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    What type of oil are you supposed to use in a worm diff?
    Dad said they used animal oil in his parents' 203,403,&404 and in his own 403. I have been told EP90 is OK, but I am sceptical of this.
    Pugs Rule!

    403, now sold
    404, project
    2010 Mitsubishi i MiEV electric car

  5. #5
    Gone Fishin' Ray Bell's Avatar
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    It was used, but never before a really good flushing to rid the diff of all traces of the vegetable oil.

    What model diff are you using?

    Jack Nelson used to tell me (I think it was Jack...) that the later (ribbed housing) diffs from 1967 onwards tended to have the bronze wheel go out of round.

    One assumes that all the faulty ones would have shown up years ago, but perhaps a low mileage unit might still be around with this potential.

    My preference is for the '65/'66 diff, large housing, no ribbing, smaller axle spline (I've never heard of one of these axles breaking, so surely they're strong enough?), they seem internally to be a nicer thing than the later one.

  6. #6
    Fellow Frogger!
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    It's certainly a worn bronze crown wheel.

    The only permanent solution is to replace it, flush the axle housing out thoroughly with alcohol and oil solvent and thenceforth use only vegetable oils.

    Esso Gear Oil VT is preferred. It is pink like ATF, but it is assurredly not ATF.

    If it's not locally available, use Castrol R40.

    Any mineral-based oil will destroy a crown wheel in a worm drive car, over time. For one thing, the sulphur in the oil (especially EP) chemically attacks the bronze. In Germany where you might be holding 170 km/h for a few hours at a time, a 404 Injection crown wheel lubricated with mineral oil can be destroyed in one day (the word comes from a service manager at a long-time German Peugeot dealer). Driven more gently, it might take several years for the problem to manifest itself. With vegetable oil, they last forever. Exactly why Peugeot recommended this as a second choice in their owners manual is beyond me. The US 404 owners manuals do not even mention Esso Gear Oil VT. Planned obsolescence? Why did Peugeot not import Gear Oil VT to the USA or Canada?

    Nearly every 404 in North America had mineral oil in its rear axle. As a result, all of them suffer to one dregree or another from this problem. I just bought a brand new 5x21 worm/wheel gearset for my 1966 404 Coupé Injection in France ($250 US including shipping) and I received it last Thursday. I also have some Gear Oil VT and a case of R40 to boot.

    A short-term solution to your problem is to reverse the crown wheel inside the housing, taking care to reverse the shims and bearing races at the same time. I did this on a 404 C I had 22 years ago and it put the unworn side of the wheel in contact with the worm under drive...the backlash was still there but it was not as noticeable, nor was the noise or irritating pulsation under drive at low speed, due to the uneven wear around the wheel's circumference.
    -Mike
    1966 404 Coupé KF2
    1989 405 DL
    2005 smart fortwo cdi cabrio

  7. #7
    Gone Fishin' Ray Bell's Avatar
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    Looks like it's time for anyone knowing where there's a 404 diff lying fallow should snare it and put it into safe storage... those few cars that are still rusting gently away will soon all be chucked onto more permanent and unaccessable scrap heaps and unable to donate their organs to the few still rolling around the roads.

  8. #8
    1000+ Posts Pugnut403's Avatar
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    Is this VT or R40 oil easily available in Australia?
    How often should it be changed?
    Pugs Rule!

    403, now sold
    404, project
    2010 Mitsubishi i MiEV electric car

  9. #9
    Gone Fishin' Ray Bell's Avatar
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    I seem to remember that Castrol made a vegetable oil that was suitable... and I'm pretty sure that Mobil dropped the line they had in the mid to late sixties.

    I must check Cadillac to see what they have... I'd be fairly sure they'd have some good stuff for the job.

  10. #10
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    R40 is made by Castrol and is vegetable based.
    It can only be bought 4 containers at a time for $80 a 4 litre container.
    It is great stuff, less wear,also less friction therefore more performance.
    You MUST drain and flush the diff of mineral oil first.
    Should be changed once a year or so as it tends to oxidise.
    R40 has exceptional lubricating properties and was developed in the 1930s? for racing. It was superceded in this role due to the oxidation problem but is still used in some vintage racing machinery and of course, worm drive diffs.
    I need to buy some more at the moment, if anybody wants to join me in putting in an order let me know.
    SYNTHETIC hypoid oil has also been proved to work well but a friends rally car destroyed its worm wheel using this. So maybe not so good on extreme loadings (this was a very powerful car and driven on the limit).
    Graham Wallis

  11. #11
    Gone Fishin' Ray Bell's Avatar
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    So what is synthetic oil?

    I often wonder, as Peter Brock picks up his piece of real estate saying, "This is where most oil comes from - in the ground!" just what the options are...

    It seems to me, it has to come from 'in the ground' or 'out of the ground' as in from vegetation. Or, as an outside chance, from animals.

    Now last time I looked, stuff from vegetation was called 'vegetable'... so is 'synthetic' oil really all 'vegetable' oil?

    I still didn't get onto George about what he might have. Being a high quality and low volume supplier, he has to have something to cover every need or he risks losing some of his market. His market includes all kinds of things, so there would surely be a 'vegetable' oil range in there somewhere...

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