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91 Ranger wont shift into OD, HELP!!
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cabech984
New User
Jun 28, 2008, 11:56 AM
Post #1 of 4
(4052 views)
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91 Ranger wont shift into OD, HELP!!
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Hi everybody,
I own a 1991 Ford Ranger XLT with a 2.3L 4cyl and a 4speed Automatic tranny. Ive never had OD in the truck as long as Ive owned it!! I what could cause all the gears to be fine except overdrive(4th)? I found a vacuum leak going to the Modulator on the side of the tranny and fixed it, but still no OD. Its got me stumped! It has shifted into OD a few times for me(going downhill with little to no throttle), but will slow down and shift back into 3rd.
What could cause a tranny to not shift into 4th?
Thanks, Chris
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 28, 2008, 12:03 PM
Post #2 of 4
(4049 views)
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Re: 91 Ranger wont shift into OD, HELP!!
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Sounds like that vacuum leak is still leaking somewhere - either the device at the trans or the underhood end. It's probably getting just moderate vacuum instead of an acutal vacuum which is a trigger that engine load is low and it can engage overdrive,
T
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cabech984
New User
Jun 29, 2008, 6:40 AM
Post #3 of 4
(4043 views)
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Re: 91 Ranger wont shift into OD, HELP!!
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Well, I blew into the Vacuum line going to the tranny, I cant blow through it anymore, I'll hook a vacuum gauge up to the engine to see whats going on there. Someone on another board suggested the Torque converter, because it could possibly be Overdrive when it goes into lockup. Makes sense but Idk what kinda tranny I have!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jun 29, 2008, 8:04 AM
Post #4 of 4
(4041 views)
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Re: 91 Ranger wont shift into OD, HELP!!
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By any chance got one of these? It's a hand vacuum pump with gauge and adaptors - handy suckers. You could put vacuum to the trans line and see if it holds and measure engine vacuum with it running using the "T" in line to manifold vacuum.
Just basics but three main things allow an engine to upshift. Throttle position, load on engine and RPM. Manifold vacuum has been used forever as an accurate indicator of load on engine. When going down hill or anytime engine is acting as a braking force the vacuum exceeds what it would at idle! Most will read about 18hg at idle.
Overdrive is really just locking the converter to achieve a 1 to 1 ratio there and is enabled electrically but with the same three criteria as its guide and some have a selector to defeat it if desired. That could be an issue if your shift indicator isn't right on with the gear selected.
I'm not a real "tranny" head but it was part of the whole training program back when, when cars were like Fred Flintstone's!
T
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