Engine Bad engine shaking at idle

Hello everyone,
So a couple weeks ago I replaced the old tired T5 in my 89 GT for a new Z spec and while doing that I changed the engine mounts and obviously put a brand new transmission mount on as well. I replaced the transmission for reasons unrelated to the shaking so I won’t go into that.

I thought the mounts would help with the shaking since the old engine mounts were either original or very old as they were completely delaminated from the metal and one was even missing a nut that secured the metal to the block of rubber. I replaced them with the vert style mounts. The trans mount is rubber not poly or any harder material.

I’ve been having the shaking issue for a while and I had a new ford performance 50oz balancer put on a couple of years ago since my bottom end is bone stock and when I rebuilt the top end and put a cam in I verified that the balancer hadn’t slipped by checking where the pointer was with #1 cylinder at TDC.

The car has a TFS 1 cam in it and I know some shake is to be expected but with the TFS 1 cam being as mild as it is I don’t think it should be shaking nearly as bad as it is. I have the idle set at 950 with a QH. The car idles pretty good aside from wanting to shake my teeth out. Also worth noting that the shaking was there and pretty much just as bad before the heads/cam/intake

When driving the car is pretty smooth and no driveline shakes at least from the trans and back.

Here are two videos I took a little bit earlier. The car is up to temp and had been driven for a little bit before hand

In the second video, the shaking becomes very apparent towards the end of the video. I honestly am running out of ideas at this point. Is it possible that the balancer slipped already and is causing it to vibrate? I was thinking it could be my flywheel but when taking off there’s absolutely no chatter or vibration. The shaking happens whether the clutch is pushed in or not.

The car passes the cylinder balance test although I’m not sure how accurate it is since I’m only running the passenger side O2 sensor due to running a wideband for the quarterhorse tuning.

Let me know what you all think and let me know if there’s anything I should check or try before throwing the parts cannon at it.

AeroCoupe said:

Is your tensioner moving all over the place or is it pretty steady? Has it always been like this or did this develop over time? Honestly I don't think the shake is that bad either but if it was smooth as silk at one point then started doing this then I get it. If there isn't vibration in the drive train through idle to redline when under load then I wouldn't be to concerned.

When you say you checked to see if the balancer had slipped I am assuming you put the #1 cylinder on TDC by physically verifying the piston was at the top of the compression stroke.

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Tensioner is pretty steady but in the video it looks like it’s bouncing because of the way the engine was shaking. The videos kinda don’t do the shaking justice because it’s very pronounced in person and in the car. The car wasn’t always this shaky. It was never silky smooth but it just had a little shake at idle.

Before I did the heads and cam job the car had been sitting for a while and when I got my interior all back together and started it I noticed it was knock your teeth out shaky but I didn’t think much of it since I already had everything ready to go to replace the entire top end. After the top end job the car was a whole lot worse until it was tuned and then it mellowed out for a little while and then came back even worse.

Yes that’s how I verified it. I had the heads off and put the #1 cylinder at TDC on the compression stroke and the balancer was dead on the money at 0 degrees. I wanted to enjoy it a little before I tear it down again for the new AFRs and the FTI custom cam that should take the shake out. I’ll drive it a little more and make sure no vibration is in the driveline and if not I’ll just run with it until spring

AeroCoupe said:

Have you verified the plug wires are good? Distributor cap in good shape and not cracked at one of the cylinders? Are all the injectors firing? Have you done a leak down test on the cylinders? What I am driving at here is it sounds like a dead/weak cylinder.

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Plug wires and plugs are brand new but I won’t rule them out because I for some reason keep getting bad parts out of the box. I’ll do a compression test here soon and verify that all cylinders are participating then I’ll do a spark check.

I also have another new cap and rotor I can throw on. I actually found something yesterday that helped reduce the shake a little. The day that I made the original post I had brought the car to an exhaust shop earlier that day to get my catalytic converters put on and get some new bungs welded in for my widebands in prep for my Pro M system. I saw a wire dangling and it turns out they had unplugged my neutral sensing switch for some reason and didn’t bother to secure it so it fell onto the new catylitic converter. Once I fixed it the car behaved much better.

CAMTWO1070 said:

I had the same shaking problem as you..........

It turned out the old owner found a way of installing the flywheel wrong and ruining 2 bolts in the process..

The flywheel was literally off 180*

Luckily it was repairable by using a forming tap w/ new bolts as the flywheel was the culprit that damaged the threads............

In another vehicle I forget the brand of the flywheel but it was from Summit and it came from the factory with a bad balancing....

Had I read the reviews I would of found out before actually finding out it didnt conform..........

Good Luck

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I think that will be my go to here soon because it’s time for for a new TOB soon anyway I can hear it making funny noises now that my exhaust is quieter. Thanks for the recommendation I’ll probably tear into all of that here soon

CAMTWO1070 said:

When you go do the throw out bearing it might actually be the pilot bearing which was an issue on another vehicle I obtained as it turned out that owner didnt stab the trans in straight and must of used the bolts to pull the transmission to the bellhousing because the roller bearing got pushed out of the bushing which gave zero support for the input shaft ....In the AP store the whole roller bearing/bushing assembly is $50 and just the roller bearing is $15...

In my case the TOB was good but had to replace the front input shaft bearing in the T-5 along with the pilot bearing..

Theres a special way to install the pilot bearing too if you buy the roller bearing alone as one side is slightly more open than the other to allow for slight installation misalignment...............

As for the flywheel ...If you happen to remove it take pictures of the backside of the flywheel .............Im curious like that & Thanks ..

Good Luck

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I ordered a new clutch kit with all new bearings which is what i should’ve done before stabbing my new transmission lol. I’ll be sure to include pictures of anything I find when doing it all here in the near future. Thanks for the suggestions!

Mcmahst said:

I second the compression test before you blow it apart. And a leak down if the results are not to your liking.

I wanted to ask about the shaking: does it feel like it goes through a cycle of vibrations? In other works, does it have a harmonic that seems like it gets stronger, than weaker, but in a predictable manner? If it does, that helps to point to likely culprits. Exhaust systems can be the source of vibrations that you can hear and feel. To see what I mean, put your hand on top of the intake, if it isn’t too hot, for like a minute, and see if you feel a cycle to the vibration/harmonic. Just my 2 cents.

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I’ll check that out sometime this week and get back to you. From memory it almost seems rhythmic and it can be seen and heard in the second video towards the end. Although it could’ve been rhythmic because of the neutral sensing switch not being hooked up thanks to the exhaust shop.

I will definitely be doing a compression test and a leak down test if need be. Even if I don’t find a smoking gun it’ll still be nice to have some baseline numbers to compare to for my new heads going on soonish.

CAMTWO1070 said:

When you go do the throw out bearing it might actually be the pilot bearing which was an issue on another vehicle I obtained as it turned out that owner didnt stab the trans in straight and must of used the bolts to pull the transmission to the bellhousing because the roller bearing got pushed out of the bushing which gave zero support for the input shaft ....In the AP store the whole roller bearing/bushing assembly is $50 and just the roller bearing is $15...

In my case the TOB was good but had to replace the front input shaft bearing in the T-5 along with the pilot bearing..

Theres a special way to install the pilot bearing too if you buy the roller bearing alone as one side is slightly more open than the other to allow for slight installation misalignment...............

As for the flywheel ...If you happen to remove it take pictures of the backside of the flywheel .............Im curious like that & Thanks ..

Good Luck

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As requested, here is a picture of the back of the flywheel and some pictures of the rest of the clutch assembly. I haven’t found anything out of the ordinary so far.





One thing is for certain though. I was definitely lied to about the clutch that was in the car. I was told it had a center force clutch in it and from what I’m seeing it looks to be a stock replacement clutch. Also the bell housing had no alignment dowels in it at all. I’ve got a guy local that’s got some spares I’ll be picking them up tomorrow.

A little update I found after I cleaned up for the night. The throw out bearing was absolutely shot which I already figured since I could feel it in the pedal and I could hear it making awful noises. Hopefully if I can get the dowels early enough tomorrow everything will be back together.

AeroCoupe said:

Yeah man that flywheel is a 50oz unit but it need to be resurfaced badly. The pressure plate has hot spots, the pilot bearing is junk, and the clutch plate is suspect as well.

I would take the flywheel to a machine shop and have them resurface it and get a clutch kit for it. That would never go back in one of my cars.

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I should’ve mentioned I’ve already got brand new everything sitting in the house waiting to go in tomorrow or whenever weather permits. Everything seems to have been done in such a bad way it really makes me curious as to the life this car had before me.

Also, has anyone ever seen a pivot stud like this? I’ve got a new one and while the top part looks identical I’m not sure what the cylindrical piece below it is. It also seems a little too wobbly which I was under the impression that the pivot stud shouldn’t move at all.

AeroCoupe said:

Agree, someone tried to shim it or rig it or whatever its not right. Good thing you are replacing it. You have a new clutch fork? If not inspect for wear where the throw out bearing makes contact with it. This was what mine looked like when I replaced it.



Also, is there a Ford part number on that bell housing? If so post a picture of it please.

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Yes I’ve also got a new clutch fork as well. I assumed everything was in terrible shape so I bought it all.

This morning I’m going to remove the old pivot stud to make sure that the threads aren’t cooked and the cylinder piece wasn’t used as a band aid or something.