why is my car jumpy in 3rd and 4th gear at about 30 mph

Discussion in 'Fox 5.0 Mustang Tech' started by 91 HATCH, May 19, 2007.


  1. 91 HATCH

    91 HATCH Banned

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    i was wondering if anyone knows why my car bucks or how to fix it. it only happens in 3rd and fourth gear while trying to cruise at about 30 mph:shrug:
  2. TheUser

    TheUser Active Member

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    because you're probably in too high of a gear. What rear end gears do you have? Shifting normally (2000 rpm), with 2.73's, I shift to 2nd about 20mph, 3rd about 30, 4th about 40, and 5th about 55 or so.

    I don't know exactly why the car is bucking, but I would assume that being at such a low mph in that gear puts it very low on the rpm's, which lacks torque. This is all an assumption though. My car does the same thing, which is why I don't run under 1500 rpm...I'd assume most other people don't either.

    What rear end gear do you have? What size are your rear tires? What transmission are you running?
  3. 91 HATCH

    91 HATCH Banned

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    i have 3.08 gears t-5 trans and 225/60r16 tires i know they should be 225/55r16.
  4. TheUser

    TheUser Active Member

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    so, according to a spreadsheet I have, after entering your variables, you should be right around 1550-1600 rpm at 30mph in 3rd gear. In 4th gear at 30mph, you should be right around 1200rpm. My point is that your RPM's are too low and that's most likely causing the bucking.

    Try to stay above 1500-1600 rpm. 30 mph w/ your setup should be about 2300 in 2nd gear, so just stay in 2nd or speed up a little and hit 3rd at 35mph, which should put you at about 1800 in 3rd (at 35mph) and you shouldn't have those bucking problems.

    Run 3rd out until about 46mph (2300 rpm) and hit 4th, which will drop you to about 1800 rpm in 4th at 46 mph.

    Run 4th out until about 60mph (2300 rpm) and hit 5th, which will drop you to about 1800 rpm in 5th at 60mph.

    I never get out of 4th gear in town with my 2.73's. W/ my GT w/ the 3.73's, I'll hit 5th in the city if I'm around 50mph or so, which is speeding, so of course it's not often:) My speedo is wrong in the GT though, so I really have no idea how fast I'm going.

    I'm not trying to tell you how to drive, I'm suggesting how you might get rid of your bucking problems, because the most likely thing I can think of is too low of rpm. You can shift higher, but I wouldn't shift much lower.
  5. slappy9090

    slappy9090 New Member

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    I personally like to ride just around 2000rpm whil cruising, sounds a little better, and I get a little better pedal response ya know???
  6. 85_SS_302_Coupe

    85_SS_302_Coupe it sucks (I know) to be on the receiving end

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    Yeah you don't need to be in 4th gear at 30mph....hell i'm not even in 4th with 4.10 gears at 30mph and 265/50/15s.
  7. modusmortis

    modusmortis New Member

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    if you have a hot cam it can change low speed driveability as well.
  8. 91 HATCH

    91 HATCH Banned

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    ok guess i was not getting enough rpm`s i will just have to drive in 2nd i drove it like that it seems fine.also after about 35 it doesnt do it in 3rd or 4th thanks for the help i thought something was wrong with the car
  9. 1988WHTGT

    1988WHTGT Member

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    Mine was doing the same but it was really bad.....I ended up having a busted rear upper control arm
  10. 91 HATCH

    91 HATCH Banned

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    mine wasnt lite im going to look over my control arms

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