Engine bucks when shifting [Archive] - GrandAmGT.com Forum

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lomn13
06-02-2008, 07:12 PM
It started last fall. When the car would shift gears, the engine would literally rear back and then with a loud "clunk" it would shift and the engine would go back into place. I ran codes on it and the only thing that came up was a bad thermostat. I replaced that, and it continued. A friend mentioned the TPS, so I replaced that and it seemed to be fixed for about a week. It started to gradually come back, until the temp bottomed out for the winter. It was fine all winter, and now that it's warmed back up, it's bucking again. I tried the TPS again, but nothing came of it this time.
It's a V6, 2001 GT, just over 130,000 miles.
Ideas?

AaronGTR
06-02-2008, 07:53 PM
Could be a torn engine/trans mount. Check those.

TmaXx
06-02-2008, 08:19 PM
My 2001 SE does the same thing. It's most apparent when shifting from 1 to 2 when under torque.....when it's warm out. It was fine all winter also. I'm guessing it's the tranny, so I baby it until I can get the money up to have it rebuilt.

DISCLAIMER: YOU COULD RUIN YOUR TRANNY IF YOU DO THE FOLLOWING

If you're brave and you want to test that....start to do a brake torque when it has warmed up good. If the engine starts bucking, it's actually the bands slipping in the tranny. Stop doing it immediately ! Thats a cheap, old school way to test a tranny when buying a used car. It didn't take a whole lot of rpm's to get mine to act up.

MarineCoprsGASE
06-02-2008, 08:25 PM
i had the same thing in my 96 5 speed, so i replace the motor mount to poly mounts and it all went away not sure it it would work the same but thats what i did.

lomn13
06-02-2008, 09:21 PM
....start to do a brake torque when it has warmed up good.

I could be dumb, but how does one do a brake torque?

Thanks for the help!

cardude007617
06-02-2008, 09:33 PM
its actually pretty simple bro:
1. Pick a nice empty street.
2. Come to a complete stop.
3. Put your left foot on the brake firmly
4. Use your left foot to put some pressure on the gas pedal

and thats how ya do a brake stand/torque etc.

lomn13
06-02-2008, 09:36 PM
Ah, ok. Here I was thinking too much into it.

cardude007617
06-02-2008, 09:37 PM
ya, sounds like a motor/tranny mount too......

lomn13
06-02-2008, 09:58 PM
Any ideas on why outside air temp would matter?

MarineCoprsGASE
06-02-2008, 11:18 PM
the cold weather will make things expand and firm up. i would say it more likely a motor mount or trany mount more like a motor mount tho i would say, but in hte winter rubber is firmer and less flexable. in the summer when it gets warmer rubber is softer and more flexable so you will see a difference in the seasons., just go with poly mounts trust me there worth anymoney there bad ass. and they really help to.my motor used to really move now i have barely any movement, the torque is great to. i noticed that in 3rd gear the RPMs only drop 750 RPM, it used to be 1000 every time. then in 4th it drops 650 RPMS, andin 5th it drops 500 RPMs they really help in the long haul.

MarineCoprsGASE
06-02-2008, 11:20 PM
hey how do you post, post, i can figure it out i have a few ?s but can figure out how to post.

hass
06-07-2008, 09:52 PM
Is there any definite way of knowing if a mount is broken or not without taking it out?

Because my engine shakes quite a bit when brake torquing if you look at the motor. [moves front/back].. and there's a longish shift delay when switching from P -> R -> N -> D...

I'm not sure if there's supposed to be a delay or not.
I know with my mom's car, it just pops right in to gear with no hesitation at all.
and mine takes a few seconds to get in gear.
and if i hit the gas before it gets in gear, the engine just revs up with no power to the wheels... then it will finally snap in gear and the car will fly off at whatever rpm it was at.

All the mounts look fine by my standards.
Aamco said the front motor and rear transmission are broken... But when I asked them to show them to me they wouldn't.
I took it to another shop [my cousin works there], and that shop said they are all fine.

So I'm not sure.

lone_wolf025
06-07-2008, 10:43 PM
Is there any definite way of knowing if a mount is broken or not without taking it out?

Because my engine shakes quite a bit when brake torquing if you look at the motor. [moves front/back].. and there's a longish shift delay when switching from P -> R -> N -> D...

I'm not sure if there's supposed to be a delay or not.
I know with my mom's car, it just pops right in to gear with no hesitation at all.
and mine takes a few seconds to get in gear.
and if i hit the gas before it gets in gear, the engine just revs up with no power to the wheels... then it will finally snap in gear and the car will fly off at whatever rpm it was at.

All the mounts look fine by my standards.
Aamco said the front motor and rear transmission are broken... But when I asked them to show them to me they wouldn't.
I took it to another shop [my cousin works there], and that shop said they are all fine.

So I'm not sure.

A certain amount of movement is normal and acceptable. The brake torque test is the easiest and fastest way to test the mounts. Do it once in Drive and Once in Reverse. Have a helper handy cuz its hard to see the engine through the hood. But the gist of it is if the movement one way is about the same as the other you should be fine.

As for hesitation, with an older tranny it does take a slightly longer amount of time to slip into gear as compared to a brand new one. However it should take no more than a second or so. If you have to stop and wonder about it...its taking too long. At that point its not so much a mount issue as most likely a tranny issue. Have a good shop do a pan drop and check it out.