93_five_oh

on my way home i noticed that in 4th/5th gear when i apply much throttle my mustang starts to "buck" or shake... like something is slipping or the rotors are very warped.
if i drive at low rpm (in any gear) and apply the brakes to load the engine and apply throttle it does it too.
now i know it's not the brakes. i just replaced the rotors, pads, drums, and shoes. those work just fine.

it's really weird and out of the blue. i wasn't driving hard or anything.
if it's the clutch slipping the rpm should jump up and down, no? rear end maybe?
there's not any unusual noise either.

any help would be greatly appreciated!

centipede3001

Do you have after market gears in it ?

nacanitihs

how low of rpms? and why the hell would you go in low rpms and apply the brakes and open the throttle?? that makes no sense. its bucking because its trying not to shut off on you. keep it above 1500 when driving.

a manual trans has a direct coupling to the engine unlike an auto car which is a fluid coupling.

it will buck in any gear at very low rpm. put it in first and let drive at idle speed. it will buck like crazy. all standard cars will do that

enix187

^^^^^^^^^^^^^^^^^^^
I have to agree with him, mine doesn't buck until 800 but non the less

If we're totally off on what your problem is try and explain it again, it really just sounds like driver error the way you're describing it

93_five_oh

it's not driver error. lol i've had the car for 5 years now and i know how to drive it.
i applied the brakes to load the engine to recreate the problem.

and i'm pretty sure it's the clutch.
the normal bucking at low speed is caused by the tolerance in the gears. i know.

on my way to work when i applied much throttle cruising down the highway the rpms would jump up a bit until i let off. so probably clutch.
but above 3k rpm it doesn't slip. i don't remember if my clutch has centrifugal weights or not. it's a king cobra clutch.

edit: stock gears btw.

USMC1775

Its bucking like the drivetrain is slipping or like the engine is stuttering?? If the engine is choking, check your fuel pressure and pump, if not, look at your rear end bushings, or nut up and drop the trans for the clutch

93_five_oh

ok so since i don't have a whole lot of experience troubleshooting...
my dad said he's sure it's a miss. (bad clutch didn't make a whole lot of sense since it's not very old)

i did replace the sparkplugs the other day with autolite 24's... i had 25's in before.
it ran fine with them until yesterday though.

i also cleaned the cap and rotor. again, it ran fine for a week until yesterday.
i checked timing (10 deg.), all the plug wires are on right (haven't been replaced in forever though), tps is fine, too.
it really misses under a load, e.g. 5th gear at 60 mph (approx. 1500 rpm)
i'm not sure why the fuel pressure would be messed up, but i'll check it. the pump is only a year old.
any other ideas? I think i'm going to get new plug wires just to get new ones.
Any brands you'd recommend?

Thanks for all the input!

nacanitihs

what color is your spark? is it bright blue/white like it is supposed to be?

93_five_oh

As in pull a plug and turn the engine over and watch the sparkplug?
Not sure. I'll check when I get home. how much resistance should be in the plug wires?

nacanitihs

yea do that. it should not be orange if it is you are getting weak spark. you want it white/blue.

as for resistance i dont kno the answer to that

also, how come you put autolite 24s in instead of 25s?? if it were me id run Motorcraft SP-445 (stock heads) or SP-447s (GT40s)

did you gap the plugs to .052" ?