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Transmission trouble last night, weird symptoms. OD gone?

Discussion in 'Vans' started by NeilG, May 4, 2019.

  1. NeilG

    NeilG New

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    I have a 1994 B250 conversion van , it has 135,000 miles on it, 318 with the A518 transmission. I use it mostly to haul my motorcycles around. I also try to drive it to work a few times a month at least if nothing else. We've been using it the last couple weeks a little more since my Durango is down for repairs.

    One thing I noticed in the last few months is that the shift to third seemed to take a little longer than usual. (not sure if that has anything at all to do with what happened last night)

    We had a 15 mile run up a highway that had a 70 mph speed limit, and it was cruising just fine. We got off the highway and about 4 miles later on a twisty road, the van slowed down and seemed to lose power, and like the brakes came on the way it slowed.... I hit the gas pedal and it revved but we were not going anywhere....I thought the transmission failed by the way it sounded and acted...

    I pulled off to the side of the road. After we gathered our wits, I managed to pull off and up the hill, no slipping or anything....BUT,,,as soon as I made it to about 34 mph, the van started slowing abruptly again like it was going to lock up...I flipped it up into neutral and coasted to the side again. I thought I would limp it home but every time I got much above 30 the same thing kept happening.

    I cant remember why I tried it, but I reached over and hit the overdrive defeat switch. No more problems, although of course overdrive was disabled. We made it the rest of the 25 miles home without an issue.

    I drove it today with the overdrive disabled and worked just fine....hit it hard, no slipping no complaining...

    I re-engaged the OD and carefully took it up and at about 35 mph it started it's slow down again...no grinding, no sound, just a super drag like the brakes were on.

    Obviously it has to do with the OD....did I blow it out? Im thinking everytime the OD tries to come on its jamming up or something. 35 seems a little slow for the OD to want to kick in so that also seems weird, but again with the OD defeated it never happens. If I am correct the OD on the A518 is hydraulically controlled, no electronic components yet in 1994.

    So whats it sound like? If OD is shot can that be serviced short of dropping the transmission? Even if I have to drop the transmission I wonder if I can repair the OD....

    Thanks in advance for any input!!
     
  2. NeilG

    NeilG New

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    As I think about it....
    I had an older van, a 1985 that had a torque converter with a lock up feature. That is, when the gearing of the transmission matched the RPMs of the engine at 1:1 it would engage and "lock up" the transmission to the engine...thus taking the hydraulic action of the converter out of the loop...it was a gas saving technique....it was electrically engaged....
    I wonder if the A518 also has this feature and its trying to come on at the wrong time, thus trying to lock up when the ratios do not match which would give me the abrupt slow down.....I dunno the crisis is averted, I can drive it for now, when I get the old Durango fixed I will dig into it properly.... my mind just always runs with the whys and hows..! ;-)
     
  3. ImperialCrown

    ImperialCrown Moderator
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    Is the kickdown cable/linkage free and lightly spring-loaded toward idle? It should move without binding throughout its range and 'flop' back to the idle position. It may be engine braking from downshifting that is the drag you feel?
    A malfunctioning governor could also cause this.
    1994 could be either the hydraulic (46RH) or electronic (46RE) governor transmission.
     
    Bob Lincoln likes this.
  4. NeilG

    NeilG New

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    Thanks, I’ll check out the linkage in the morning. I played around a bit more and it seems to happen just when it should be shifting into 3rd....one thing I didn’t do since the first time is hit the gas when it happens....I want to try that and see if it’s all revs and no go or what or if as you suggest it may have down shifted into first instead of third...
    I drove it around 50 miles today with the overdrive turned off without issues except when l left Walmart because I forgot to hit the overdrive defeat switch ( it reverts every time the ignition switch cycles
     
  5. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    There is no 'ratio' matching with the lockup torque converter. It locks up in 4th (OD) when the temperature is warm and the switch is not engaged, and it also locks up in 3rd when OD is disengaged. It locks up based on vacuum, speed, throttle position and temperature (coolant temperature on older vehicles, then later on transmission temperature). It has nothing to do with matching any RPMs or gears.
     
  6. AllanC

    AllanC Well-Known Member

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    I found this link which describes the functionality, components and trouble shooting for the A500 / A518 / A618 Chrysler rear wheel drive overdrive automatic transmissions.

    https://shop.ukrtrans.biz/wp-content/uploads/catalogs/42RH.pdf

    Scroll to pages 25 & 27 and the discussion about the direct clutch and overdrive clutch. The direct clutch is always applied through spring pressure in reverse and the forward gears 1, 2, 3. The direct clutch is even applied when vehicle is not moving. When the PCM determines overdrive engagement is permitted, the overdrive solenoid energizes and allows hydraulic fluid to pressurize appropriate components. Simultaneously the overdrive clutch is engaged and the direct clutch spring pressure is overcome to release the direct clutch and the transmission goes into 4th gear overdrive. I believe the shuddering and slow down you are experiencing is the direct clutch is NOT RELEASING while the overdrive clutch is engaging. You cannot have 2 different gear ratios applied to the output shaft at the same time as this creates a mechanical conflict. Thus the strange behavior. I am thinking the overdrive unit needs to be removed, checked and possibly rebuilt (guess on my part)???

    In 1994 model vehicles the A518 / 46RH transmission was hydraulically controlled, hydraulically shifted. The only electronic control component was the 4th gear overdrive solenoid. When engaged by the PCM it allowed hydraulic pressure to flow to the appropriate components so 4th gear overdrive would engage. The 42RE / 46RE / 47RE transmissions with electronic control did not appear until the 1995 or 1996 model year.
     
    valiant67 and Bob Lincoln like this.
  7. NeilG

    NeilG New

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    Well ok. I think I was misremembering the 1:1 ratio in the converter itself, I thought the 1:1 was between the engine and the input shaft of the trans....but then again if the converter is locked then the crank and the trans are at 1:1. Thanks for the info!

    The temp sensor hasn’t worked in 6 months. I’m sure that hasn’t helped!
    I looked at it and it’s literally broken, no connection.

    It is also doing some other weird things, not always shifting back into 1st at a stop, taking too long to shift into 3rd. I put some Lucas additive in it... I’ve been back and forth with the detent cable with appropriate results tho. Sounds like a lack of pressure overall..as you said,. at some
    Point the components activated by the overdrive are Pressurized to defeat the direct clutch and maybe there’s not enough pressure to do that.
    Thanks again!!
     
  8. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    I don't see anywhere posted where you have checked the transmission fluid level and quality at hot idle. You definitely need to do that. Also, have you ever changed the fluid and filter? If not, or not done in the last 50K miles, I'd change them, using ATF+4 and a good brand of filter.

    When my truck sits for more than a month, sometimes it won't shift into OD for 10-12 miles of driving, until the fluid gets hot enough and the viscosity changes. That tells me I should change the fluid and filter, hasn't been done in many years, despite only driving a few thousand miles a year.
     
  9. AllanC

    AllanC Well-Known Member

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    There are 2 separately located engine temperature sensors on the Magnum V8. One is a 2 wire sensor near the thermostat housing. It provides input to the PCM (powertrain control module) which is used to set the proper air - fuel ratio for the engine. See attached image.

    Magnum V8 Coolant Temp Sensor.gif


    A separate single wire sensor is located somewhere else on the intake manifold and provides a variable resistance signal to the instrument panel engine temperature gauge. So which electrical connector is broken: 1 wire or 2 wire? The instrument panel tempperature gauge sensor (single wire) has no effect on the running and performance of the engine or transmission.
     
  10. NeilG

    NeilG New

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    Thanks... the single wire unit is the one that’s broken, I didn’t know there were two! That explains why when I bought a new one it had 2 connectors and wouldn’t plug in.
    Sounds like that one would not affect the control then.
    After thinking a bit and driving it some more, I think it’s a general case of low pressure. There are other things going on with the transmission. .at a stop, it doesn’t always shift back to 1st. .when I get the chance I’m going to do the filter and fluid and go from there.
     

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