cabmustang

iTrader: (3)

maybe someone can help me with this, i have an 88 pontiac firebird 2.8. when i first got it there was a vibration coming from some part of the drivetrain and was told the engine was not balanced well. i didn't fix it because they told me there is no way to fix it besides tearing the motor apart. anyways the vibration would start becoming really bad at around 3000 rpm, and lately i've been getting around 18 mpg (which BTW i would love to increase). so last night i decided to throw in one of those fuel injector cleaners and suddenly when driving it this morning the start of when the bad vibration kicked in has dropped to around 2000 rpm. is there a reason for this drop? is the engine vibration something that can be fixed besides rebuilding the already rebuilt motor? someone help please. also i think 18mpg is pretty bad, what do you think? what do you get on average?

Thanks

forkvoid

iTrader: (1)

Check the flexplate/flywheel for warping(remove dust cover, have someone watch it while the car starts and is slowly revved; if it moves in any direction that isn't perfectly in a circle, it's warped). Check the damper for being loose(grab hold of it and move it side to side and front to back, see if there's any play). Check your motor mounts and transmission mounts to see if they're still good.

Is the vibration only while driving or does it occur in park as well?

Derickab

Def the flywheel needs to be changed. I had the same issue when I swapped in the 3.4 in my car and put the wrong flywheel on. Would start vibrating really bad around 3k rpms.

2.8RS

iTrader: (5)

Do what forkvoid said but also remove the belt and run the car for a minute to see if the noise is still there. Also spin each accessory by hand and feel for anything rough and if they make any noise. I'm in the same boat as you right now, have a real bad rattling that can only be a couple of things now.

Also when you pull the inspection cover off the tranny cehck and see if the torque converter bolts are tight on the flywheel. You will have to spin the motor by hand wich isn't to hard. 3 15mm bolts I believe.

forkvoid

iTrader: (1)

A neat trick to check your accessories is to run the car with the belt on and put a long solid pole(or even a screwdriver) to the accessory and put your ear on it. A good accessory makes a quiet whirring sound. A bad one is rough, grinding and loud. They will also make that noise if the the bracket is not entirely secured.

The same trick can be used to listen to an engine(stick the pole on the heads or engine block), but you gotta have a fine-tuned ear to make sense of what you're hearing(assuming it's not perfect).

cabmustang

iTrader: (3)

wow, i wasn't expecting so many replies so quickly, but that is awesome thanks guys. maybe i can narrow it down a little more, it's a manual trans car (also rebuilt) the vibrations are somewhat there when sitting, but you can really feel it while driving. i thought these year motors were internally balanced? i'd be very happy if this is something that can be fixed. do i need to drop the tranny to inspect the flywheel? oh what belt is it that i should take off? and i'll definately check the damper hopefully sometime today. any more suggestions or questions for me? thanks guys

forkvoid

iTrader: (1)

The belt we're speaking of is the serpentine belt, or the various v-belts if so equipped. For the flywheel, there should be a small dust guard between the transmission bellhousing and the engine block. Crawl under, unbolt it. No need to drop the transmission. When the dust guard is off, you can watch the flywheel spin when the engine is being revved. And yes, your year engine is internally balanced. The damper and flywheel are all neutral balance with no counterweights.

cabmustang

iTrader: (3)

ok i will take a look at that tonight. from the sounds of it though it could just be the motor is just that far out of balance? or is that just not possible? i'll let everyone know my findings. again thanks for all of your help, at first i thought i would just have to live with the vibration, you have given me hope haha.

forkvoid

iTrader: (1)

Engines aren't something that need rebalancing from time to time like tires. It's either balanced correctly or it's blown. No in between. Your vibration is from something else in the drivetrain, such as the damper, flywheel, etc.

cabmustang

iTrader: (3)

i wasn't saying it needs rebalancing, but the engine was rebuilt and i was told with a lot of cheap rebuilds the parts aren't balanced which could cause the vibration. anyways i checked the damper and it was solid as a rock, no play side to side in and out or up and down. i even started the engine and just watched the belt and it seemed to track normal. i haven't checked the flywheel yet, but mechanic told me it's highly unlikely because of just how heavy and thick it is, not saying you're wrong because believe me i would love if you were right. oh i was also thinking maybe the motor mounts need replacing, like maybe it's sending the vibrations throughout because they are just shot. if they are how hard are they to replace them yourselves? is it possible or do i just needc to take it in. saves alot of money if i can do it myself .

forkvoid

iTrader: (1)

A flywheel/flexplate can easily be warped. Mine was. That's how I know about it. Dave has had one shatter on him entirely.

Motor mounts could be it. They're a lot of work to get done; I did mine with the engine out and it still took two people and a lot of busted knuckles.

bl85c

iTrader: (2)

If it was assembled using mismatched parts then the engine is out of balance. I'd like to know what it's been doing to your bearings. Only fix is dissasembly, balancing at a shop and reassembly.

cabmustang

iTrader: (3)

well found out what the vibration is... the person who installed the transmission installed it off center and wrong which eventually cracked the bellhousing, and then destroyed the transmission mount. i was told i'm going to need a new transmission. so now another 1100 in the car if i want to fix it. i still haven't decided whether i will or not. thanks for all your help guys.

forkvoid

iTrader: (1)

A bellhousing can be found used, as well as the transmission mount. Was the transmission destroyed as well?

project89

iTrader: (1)

prolly shewed up the front bearing on the input shaft, should be an easy fix though if it did,but im not sure ive never had a t5 apart

cabmustang

iTrader: (3)

they didn't say anything about the trans being junk, but i think they may think other damage to the trans may have been don't because of it. the 1100 is a used trans with new clutch and flywheel, i'm being charged very little in labor, the trans alone is 570. but what worries me, and is the main reason i may not keep the car, is that this could have caused considerable damage to the engine which may not be seen right now, but may have compromised it none the less.