Overdrive slipping question
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Overdrive slipping question
I have a 92 F250 4x4 with a 7.3 diesel and a4od tranny. The tranny seems to slip in/out of OD once in a while. This will happen at highway speed of 60mph and back road speeds of 45mph cruising at a constant speed and no hills. I changed the tranny fluid (it looked good) and filter, but no difference. Is there a solenoid for OD that I should look at to see if it is operating Ok? Thanks for any info.
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From: Powell River B.C.
Get a 30 dollar OBI code reader from any parts store to check for trouble codes. Check the connector plug on the pass side aft of the tranny that the heat sheild is in place, and for corroded or bad electrical connections. Bad grounds in the lights can send a signal back down the brake light wiring, which tells the PCM to unlock the torque converter as well FWIW.
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From: Campbell River, B.C.
Its not likely to be a shift solenoid. There are only two shift solenoids that are switched on and off in different combinations to produce the four forward gears. Overdrive (4th gead) is produced by switching both solenoids off.
There is also a coast clutch solenoid, and a TC lockup solenoid, I think what you may have is a TC lockup problem. What sort of difference in RPM do you see when the tranny begins hunting?
There is also a coast clutch solenoid, and a TC lockup solenoid, I think what you may have is a TC lockup problem. What sort of difference in RPM do you see when the tranny begins hunting?
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it will happen at @60 mph, motor rpm will be 1700 in OD then it will jump up to 1900 rpm when the gear is lowered, kind of hunt (in /out of OD)there and eventually go back into OD and down to 1700. I can not tell you the exact mph because someone before me put way oversized tires on it and I have @ 13% error in the speedometer. No idea of the rear gear ratio.
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From: Campbell River, B.C.
Originally Posted by DarylZ
it will happen at @60 mph, motor rpm will be 1700 in OD then it will jump up to 1900 rpm when the gear is lowered, kind of hunt (in /out of OD)there and eventually go back into OD and down to 1700. I can not tell you the exact mph because someone before me put way oversized tires on it and I have @ 13% error in the speedometer. No idea of the rear gear ratio.
The difference in RPM you are showing, is not enough to be the overdrive kicking out, since the OD ratio is 29%. But a slipping torque converter clutch will cause that amount of RPM change.
Something to try is to drive the truck under the same conditions, and when it "drops out of gear", press the OD cancel switch, if there is no change, then its the OD thats the problem, if there is still a further increase in RPM, then its the TC.
Have you noticed hard shifting yet?
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From: New Jersey
Mine started doing this when I would use my turn signal. Turned out one of my brake lights was burned out. It cleared up after replacing the bulb. Still trying to trace the electrons on that one.
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Thanks. I will try the OD switch tomorrow. I have not had hard shifting recently. I had it a long time ego when I hauled some gravel and it shifted hard afterwards for a few miles once I dumped the gravel off the bed.
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The BOSS HOG Torque Converter
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Nelson
If you have any questions, call me @888-267-7464
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Nelson
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From: columbia river gorge
since the brake lights are connected to the cruise control which also unlocks T/C any voltage difference can cause up and down revs. everything is connected nowadays and finding the problem can have you running in circles. brake light switch was one problem of mine that caused the RPM up and down.
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From: Manitoba
have @ 13% error in the speedometer
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