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Borg Warner 35 in 3500 - weak reverse when cold, no reverse when warm..

Discussion in 'Gearboxes and drivetrain' started by Peter Simpson, Jan 18, 2018.

  1. Peter Simpson

    Peter Simpson New Member

    Good evening. I'm hoping someone on here can help with a slightly odd automatic gearbox fault. The car in question has recently been recommissioned after being unused since 2011, and having very little use - under 100 miles a year - from 2006 to 2011. Basically it goes into forward gears fine and with a reassuring slight thud. However the reverse engagement is always weaker and needs a lot more revs to go backwards and won't go up more than a slight incline. However when the car is warm it all-but loses reverse completely. In all other respects the box seems fine - it goes into top at about 36-40mph even when fully warm, and feels no more 'clonky' than any other bw35 I've driven. Any ideas - is there an easy fix, possibly something sticking or leaking - or am I looking at another gearbox... Thanks in anticipation
     
  2. harveyp6

    harveyp6 Well-Known Member

    If you have TOP gear then it's a rear servo or rear band fault. The rear servo can come loose, and the seal can fail, which could be causing it to have some drive when the oil is thicker when cold, and then lose it as the oil thins with heat.
    I think I'd make sure that the rear band adjuster on the outside of the casing hasn't worked loose, and if that's not the case, drop the sump and have a look to see if there's a fault with the servo.
     
  3. Peter Simpson

    Peter Simpson New Member


    Thank you very much for that - much appreciated. As I don't currently have a garage/workshop, i'll be asking my local (old school and very classic-friendly) local garage to do this - can i trouble you further as to where/which side on the box is the adjuster on, and whereabouts under the sump is the servo? The ATF fluid looks clean by the way..
     
  4. harveyp6

    harveyp6 Well-Known Member

    The adjuster is on the O/S of the main casing.

    [​IMG]

    Go straight upwards from the "l" of "cyl" and you'll see it.
     
  5. harveyp6

    harveyp6 Well-Known Member

    [​IMG]

    The rear servo is the bowl bottom left retained by two bolts. There is a strut that will fall out when it's removed, this needs to go back in properly otherwise the band can be permanently applied if it gets jammed in the wrong place, and if that's the case the box will lock up when it changes into SECOND gear.
     
  6. Peter Simpson

    Peter Simpson New Member

    Fantastic!!! Many thanks for that Harvey; I can print these off and show them what's needed - did I see elsewhere that you can supply parts - if so I'm kind-of thinking it might be prudent to get hold of a seal now so I've got it to hand if needed...
     
  7. harveyp6

    harveyp6 Well-Known Member

  8. badrover

    badrover Member

    Mine was doing just that. It was the reverse servo rubber o ring in the end. This was identified as ever by Harvey. I can't find the original thread but there's an explanation in this one.

    Gw 35 no reverse P6 3500 1970
     
  9. Peter Simpson

    Peter Simpson New Member

    Good evening - just want to say a great big Thank You to Harvey and everyone else who gave advice - and to Colin Gould for doing the work -my P6 3500 auto now once again has a fully-functioning reverse gear - the fault turned out to be, as suggested, the reverse servo o ring; as soon as we dropped thesump we saw bits of it in the bottom, then looking up at the servo we saw a bit of the seal hanging out. About an hours work a 45p o ring and 3.5 litresish of atf.
     
    Chalky likes this.

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