1991 Ford F-150 Occasional harsh upshift -- and a general qu

ANOTHERMIKEY

MEMBER
1991 FORD F-150
6 CYL
4WD
AUTOMATIC
175,000 MILES

Most of the time the truck shifts smoothly. Occasionally the old F150 upshifts from 1st to 2nd or 2nd to 3rd harshly -- sometimes really violently. Scares the daylights out of my wife. Seems to be worse when the truck is well warmed up, and seems to be worse if I'm intentionally babying it by accelerating very lightly. Am I going to find the transmission lying in the road one of these days?

Now a general question -- when did cars generally change from grounding the POS battery terminal to grounding the NEG terminal?

2 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Sounds like a sticky valve in the trans. When was the last service? Might want to try a couple tablespoons of motor oil when you service it to help lube the valvebody. Not sure about the pos ground. Euro cars used to have "floating earth" ground is that what you mean?

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Wednesday, March 24th, 2021 AT 1:51 PM

ANOTHERMIKEY

MEMBER
3 POSTS

I'm not sure about Euro cars, so we're even, I guess. No, I'm pretty sure our family's 1939 Chrysler had a positive-ground system, as did most early-20th-century American cars. The shift to negative ground happened sometime just after WW II, I think.

As for my transmission problem -- serviced? Dunno. I'm the 2nd owner of this bought-on-eBay beater. Looks like the original owner (RIP) took pretty good care of it in general, though. I think it might be worth getting a general service -- fluids, filters, etc. -- But I don't want to spend big bucks on it. I'll report back.

Thanks.

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Wednesday, March 24th, 2021 AT 1:51 PM