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M46 OD deceleration grumble & slipping 200 1985

posted by  someone claiming to be acd483 on  Mon Jul 30 05:44 CST 2018 [RELATED]

Hi all,

I've searched the Brickboard forums hoping to find someone with a similar issue, but haven't found one...so here goes:

I've got a 1985 Swiss-market 245 GLT, B230E, M46 with 240,000 KMs (150k miles). Excellent mechanical condition overall, but I've got an issue with the overdrive unit. When I'm decelerating from 120km/h (75mph) down to 100km/h (62mph) the unit starts to grumble (slight vibrations, audible groan) as though it's going to slip out of OD. If I accelerate, it will take 2-5 seconds to work itself out. Revs do not jump during this so I'm pretty sure it's staying in OD. If I let the car continue to decelerate under 100km/h it will drop out of OD. It also seems to complain if I'm driving down hill, drop throttle. It's as though the load on the unit is stressing it. In my part of Switzerland we have a lot of hills and long incline/declines on the highway, so the conditions vary when trying to diagnose the problem. Furthermore, it doesn't seem to matter whether the car is cold or hot...but I can do more extensive testing to see if there are any significant differences. Also, decelerating from 140km/h (87mph) to 120km/h doesn't have the same effect. The OD seems happy between these speeds.

Other background info. I've just had the car in for service. Oil change, etc. and asked the garage to check the functions and replace the oil in the OD. Apparently it's fine although I have not asked the garage to fully road test and diagnose the issue - yet. All the electrics function (gear switch, wiring, solenoid). The previous owner included another OD unit in the sale. He's a mechanic so I think he wasn't pleased with the OD operation either - just didn't get around to swapping the units.

I'm looking for your expertise on the existing OD issue but also what to do with the replacement. Since it's already separate from the car I could have it looked at with the intention of simply replacing the current one. Honestly though, I'd rather keep the original OD unit that came with the car. At this point either one would probably need to be opened up, overhauled, etc. It doesn't seem worth having the garage replace the units without doing any inspection or service first.

I look forward to your insight and opinions.








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    M46 OD deceleration grumble & slipping 200 1985

    uid 46171's pic
    posted by  kittysgreyvolvo on  Mon Jul 30 17:52 CST 2018
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    last visit: Sat Oct 18 15:23 CST 2014
    [RELATED]

    FAQ:

    https://www.brickboard.com/FAQ/700-900/TransmissionManual.htm

    https://www.brickboard.com/FAQ/700-900/OverdriveRebuild.htm
    --
    Give your brickboard.com a big thumbs up! Way up! - Roger Ebert.








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    M46 OD deceleration grumble & slipping 200 1985

    posted by  Volvodad on  Mon Jul 30 11:06 CST 2018
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    last visit: Thu Oct 23 16:18 CST 2014
    [RELATED]

    My 1983 with M46/OD (300,000km) shows some similarities, but at lower speeds, and only when at full temperature on a warm day. It will vibrate (chatter) and feels like it is disengaging when backing off the throttle and coasting down to about 80km/h (50MPH).

    The consensus on the BB when I posted about this a few years ago was that the piston seals were worn and allowing fluid to slip by (loss of pressure) when the fluid thins out at high temperatures.

    My temporary fix was to replace the factory original fluid with Redline MTL synthetic fluid, which has a higher viscosity when hot. It definitely helped but the problem still lurks. So I only engage the OD at speeds above 90-100km/h.

    The proper solution is to rebuild the unit with new piston seals before damage occurs. Apparently there was a rebuild kit which included an improved seal design. You could try a search at the usual online suppliers of old Volvo parts.
    --
    Son's XC70, my 83 244DL, 89 745 (Chev LT-1 V8), and XC60. Also '77 MGB and four old motorcycles. Long gone: 1981 244, 1994 940 and 1998 S90.








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      M46 OD deceleration grumble & slipping 200 1985

      posted by  CH245GLT on  Mon Jul 30 14:24 CST 2018
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      Thank you Volvodad. From the hunting around I've done, this seems like the most reasonable answer. I've got to do some more temperature testing. I'll try when its cold and the car is cold.

      Luckily, I drive on the highway rarely, and when I do I drive relatively fast. This car seems perfectly happy at 140km/h.







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