What kind of drivability issues would you have is the transmission and/or engine mounts were shot?

Mine is a 5-spped 88 GT. What I am experiencing is when I engage my clutch, which is new with about 200 miles on it, you can feel like a thud type noise, like something is moving in the engine bay. How do I check to see if the mounts are good or not?

Thanks,
Phil

You can use a pry bar to try and move the engine back and forth and look for motion. Are you using the stock dog bone? Watch for motion there too

Are you still using the original mounts? They should have been replaced when you changed the clutch if they are original rubber.

Could even be a loose nut on one of your mounts. Check them all as well.

Good luck

quote Originally posted by phils88GT: What kind of drivability issues would you have is the transmission and/or engine mounts were shot? Mine is a 5-spped 88 GT. What I am experiencing is when I engage my clutch, which is new with about 200 miles on it, you can feel like a thud type noise, like something is moving in the engine bay. How do I check to see if the mounts are good or not? Thanks, Phil

Everything Cam-a-lot said. It's often even easier to diagnose when you have an automatic... with just your foot on the brake, going between drive and reverse without even moving, you'll hear a thunk / clunk.

On the manual transmission cars though, obviously you wouldn't hear this thunk until you started accelerating.


The motor and transmission mounts are, more than anything else, supposed to just hold the engine to the cradle, but they do not prevent forwards/backwards movement. Matter of fact, they aren't even really attached. If you burn away the rubber, you'll find that the motor mounts are just hooks into loops that are isolated in thick rubber to absorb engine vibrations.

There are two things that are likely the culprit... the first is the engine "dog bone," which cam-a-lot mentioned. This is the best picture I could find, but the RUBBER bushings have been replaced with polyeurothane:



You can either replace this "dog bone" / engine strut with either an original rubber-bushing motor mount, or you can buy a replacement one from the Fiero Store with polyeurothane already pressed in: https://www.fierostore.com/.../Detail.aspx?s=52799


The SECOND thing that's likely also failed at this point, is the engine "damper." This is a shock absorber that's mounted on the forward-most part of the engine cradle, and it goes between the engine and the cradle. There's a little bracket that attaches to the engine. I don't know if 88s have these, but my 1987 Fiero SE / V6 Automatic and 5-Speed cars both had this shock absorber. I know my 1985 Fiero GT 4-Speed also had this.

So just checked, they don't make them anymore, and apparently they also eliminated this on the 1988s... I'm not sure why. I guess they didn't think it was as necessary as they originally thought, but if you wanted to, you could easily add one. Just find the bracket from an 85-87 V6 (same engine as yours), and buy the shock: https://rodneydickman.com/p...62b92830eaef8e4a2ae5

I think I'm going to buy one today, apparently they don't make them anymore. :/

I think it already has the aftermarket Dog Bone, just not sure by whom it was made. They look like poly bushings in it..

I know whe has a new clutch, but I cannot speak to the age of the mounts. I am guessing they are like original, or maybe a replacement set.

[This message has been edited by phils88GT (edited 11-23-2023).]

quote Originally posted by phils88GT: I think it already has the aftermarket Dog Bone, just not sure by whom it was made. They look like poly bushings in it.. I know whe has a new clutch, but I cannot speak to the age of the mounts. I am guessing they are like original, or maybe a replacement set.

Yeah, that's the aftermarket polyurethane one from the Fiero Store... and it looks like it's in good condition... so it's definitely not that.

The only other thing I can think of is potentially something with the axles or the suspension. Can you give a little bit more detail as to when / how it happens... and maybe where it sounds like it's coming from?

Well, it mostly happens when I take off in first gear. Depending on how I let off the clutch really. It sounds / feels like it is coming from behind me and down low. I really cannot do it justice, but it sounds / feels like when the clutch first solidly grabs, like something is giving and hitting the chassis. I can't really do much better than that.. Very weird..

quote Originally posted by phils88GT: Well, it mostly happens when I take off in first gear. Depending on how I let off the clutch really. It sounds / feels like it is coming from behind me and down low. I really cannot do it justice, but it sounds / feels like when the clutch first solidly grabs, like something is giving and hitting the chassis. I can't really do much better than that.. Very weird..

Is it a loud thunk, or more like a tap? I just wonder if it could be a sticking caliper that releases suddenly when you remove the brakes. But I suppose it could be the motor mounts. Only thing I'm concerned about is that it's something in the drivetrain that happens when under load. For example... if you have a driveshaft in a rear wheel / longitudinally mounted car, where the bolts from the universal joint bracket to the differential are not torqued down, the bracket will shift and make a clunk when you first start accelerating. Now... you don't have that, because the Fiero is basically a front wheel drive / transversally mounted engine that's placed in the back. But you do have half-shafts... and it could be anything from the CV joints starting to fail, or worse... possibly something wasn't tightened down like it should have been.

Did these problems occur immediately after the clutch job was done on the car? Something like this typically happens because something is not bolted down like it should.

Only thing i can suggest is to check the suspension for wear, check the motor mounts, and see if you can reproduce the sound some other way... either in reverse, etc.

I would suggest you check everything under the rear end of the car.

As mentioned the front and rear transmission mounts. The engine mount was a bigger design and more durable.
So I assume GM eliminated the shock design too. But that was only for 85-87V6 cars. Even if you upgrade with a
fiero store dog-bone, that shock isn't necessary at all.

TFS dog-bone saves a lot of headaches, and prolongs the engine and transmission mounts.
That was the big issue with these cars, and after years of owners driving around like this, failure was deemed
to happen.

Who did the clutch job?

Many things to re-check.
-Cradle bolts (front & rear)
-Suspension lateral (in knuckle, long bolt) tight?
-Did the clutch job include the flywheel bolts replaced with new bolts? (that's a must)
-Check transmission mounting bolts to engine
-Exhaust "Y" pipe for cracks, and if the cat-back exhaust system for movement, all 6 springs on the muffler need to be there
-Cat convertor springs (2 on each side) in place?

Again, its hard to say...without anyone looking at it.

Start with that, and report back.

A lot of people will say, "it looks ok", but have done nothing or tightened, or wiggled, shook anything.
Its no good to assume, but check with your hands.
Visal non-hands on inspection won't get you anywheres.
It can't "look "ok, it "needs" to be ok.

Pictures of those mounts could help us see and determine what shape and condition there in.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

Would love to know what it ended up being once you figure it out. Can you post your findings here?