Is my motor mount (s) broke?

Sealion · 05-02-2008, 08:55 PM

Hi.

The engine has been "shaking" the last few days during STARTING (while the key is turned). All shaking goes away soon as I release the key and the engine starts. But it seems to run fine, tho maybe some weird vibration.

Today coming out of taco joint, I noticed the muffler on left/driver side was hanging down ~ 2-fingers worth.

A friend who knows a little about 911's said my motor mount might be broke, or a bolt loose, or something similar.

Car is '84 Targa, original engine. 175K miles.

My questions:

1. Safe to drive?

2. What do I look for (where)?

3. What's involved in the repair?

My friend seems to think it no big deal to replace a broken motor mount, tho not sure.

Any advice/insight appreciated.

BrokeMyCar · 05-02-2008, 09:03 PM

Open the engine bay, look at the big round things at the corners towards the back of the car (front of the engine). A bolt should go through those round things (they're the motor mounts), into a metal cross-bar that goes from left to right. If its the cross-bar that's broken, it could be at where the cross-bar meets the engine mount, which may require a mirror to see properly.

Involved in the repair... not too bad. Depends on what's broken. You can replace the cross-bar (~$120) and the mounts ($30 each) in an hour or two easy. Don't even need to lift the car, just put a floor-jack under the engine (use a wooden block) and lift just the engine a bit.

Let us know what you see, I'm sure folks will walk you through all of it.

Good luck!

Babak

slodave · slodave's Garage

Motor mount could be worn out. Look at each corner in the engine bay and look at the condition of the rubber. The bracket that holds the muffler in place, could be broken as well. My muffler was a bit low and when I had the engine out again last summer, I had to take the muffler off for the repairs and noticed mine was broken.

Dave

EDIT: Babak beat me to it and has better info too.

Sealion · 09:24 PM

Okay, it's dark. 10PM. I will look in morning.

You guys are fast. This forum rocks.

What about "safe to drive"?

I been driving it a few days since I noticed "shaking" during engine cranking/starting.

I am supposed to go places tomorrow. Should I cancel?

Wouldn't the shaking engine bode more for broken MM than muffler bracket?

slodave · slodave's Garage

Since Babak mentioned the possibility of a broken cross bar, I would not until I made sure it was OK at both corners. Worn mounts will be OK as will a broken muffler mount.

Sealion · 09:44 PM

Sounds like a broken cross-bar is worst case scenario (so far). And I have been driving it a few days. If it *is* broken cross-bar, what other damage might I have caused by driving?

Would worn MM's yield symptoms I described? (muffler hanging down 2 fingers)

How about broken muffler bracket? (engine shakes during cranking)

It's okay to drive with broken muffler mount?

This is encouraging:

"Involved in the repair... not too bad. Depends on what's broken. You can replace the cross-bar (~$120) and the mounts ($30 each) in an hour or two easy. Don't even need to lift the car, just put a floor-jack under the engine (use a wooden block) and lift just the engine a bit."

slodave · slodave's Garage

Sorry, a long time neighbor was just taken to the hospital with chest pains.

Nothing bad should happen, but if the other side goes, you will have serious problems.

I suppose worn mounts will cause the muffler to sag, but the you could also have a broken muffler bracket - this would definitely cause the muffler to sag. Broken bracket should not cause engine 'shakes'.

Yes, OK to drive. I did for many years - unknowingly.

Dave

al lkosmal · 05-03-2008, 06:06 AM

Just had this happen to me. Same symptoms of engine shake. My problem was simple. One of my motor mount bolts lost a nut and I just had to tighten it. I believe that you have either a loose motor mount or a broken motor mount crossbar (typically they break at the weld for the bolt tube). I would not drive until repaired. All the weight, at the rear at least, will now be transferred to a single rear mounting bolt. If that side breaks too, you will not be a happy camper.

regards,

al

Sealion · 05-03-2008, 06:54 AM

Hi.

Thanks for your helpful responses.

I've just inspected, and can't find anything obviously wrong. (except the muffler on the left appears to hang down a few inches).

I see where you said the MM were. Both sides have a big-center bolt, and two smaller bolts outside of them.

I see where the crossbar you mentioned connects each MM, underneath. The weld-joints at each MM seem fine.

Not sure what Al meant in last post by "lost a nut". The only nuts I can see are those underneath, connected to the two small bolts. I see no nut attached to the big-center bolt. It appears the big-center bolt screws down into the bottom-side of the MM.

Moreover, there is only a small gap (unable to get my pinky finger in gap) between the crossbar and the frame where the MM bolts into. So that it appears the crossbar (and therefore the engine) could only be raised a small distance (less than width of pinky). Altho I may not fully understand how everything goes together.

Underneath the car, it appears everything is level. In other words, it doesn't appear that one side hangs lower than the other.

I could see no obvious broken parts connecting to the muffler. I tried pushing up on the muffler to see if there were any give, and if felt very solid.

One thing that did seem weird was that there was a bolt connecting to the A/C unit that was actually RESTING ON the frame (painted) part. I know that shouldn't be like that, cuz then you couldn't turn it.

Another observation in that the rubber parts of the MM are SQUISHED FLAT.

What else can I look for?

I recall yesterday, on the way over to the taco joint, the car *did* bottom out in back as I crossed a street with a sudden steep clmb. Didn't think anything of it at the time.

Yesterday was the first time I noticed the low-hanging muffler.

Where in particular would I look for broken muffler mounts?

How would I tell if a MM was broken, or a nut was loose or missing?

Are the big-center MM bolts supposed to have nuts on the other side, underneath?

Sealion · 05-03-2008, 07:08 AM

I am going to take some pictures and upload.

Sealion · 05-03-2008, 07:55 AM

Okay, here they are. Maybe they'll help figure out what's goin on:

http://radified.com/carrera/muffler_level_view.jpg

http://radified.com/carrera/underneath.jpg

http://radified.com/carrera/finger_gap.jpg

http://radified.com/carrera/ac_bolt.jpg

http://radified.com/carrera/tailpipe_gap.jpg

What do you make of this?

On the other side of the car, everything looks normal.Nothing hanging down.

slodave · slodave's Garage

The A/C bolt should not be hitting the frame. I'd check to see if the engine mount bolts are tight.

JP911 · JP911's Garage

There should be 2 metal straps that hold the muffler up against the engine. They should be close to the center of the muffler, roughly 8 inches apart. I'm guessing that one or both of these have rusted/cracked/failed, allowing the muffler to sag. The other possibility is that the mount that the straps attach to on the car has failed. Have a look under the back of the car.

Sealion · 08:49 AM

Re: "The A/C bolt should not be hitting the frame. I'd check to see if the engine mount bolts are tight."

Probably dumb question, but do you mean the small outside bolts, or the large center bolt?

I was able to tighten the small outside bolts somewhat (on both sides) .. maybe a complete turn or so, but this did not lift the AC nut off the frame.

I was not able to budge either of the two large-center bolts, but I did not give it my all. Should I try more here?

slodave · slodave's Garage

The one in your pic...

The two small bolts on the motor mount, secure the mount to the frame and drop in. You should not have to worry about these bolts.

Gotta run.
Dave

Sealion · 05-03-2008, 08:57 AM

RE: "There should be 2 metal straps that hold the muffler up against the engine. They should be close to the center of the muffler, roughly 8 inches apart. I'm guessing that one or both of these have rusted/cracked/failed, allowing the muffler to sag. The other possibility is that the mount that the straps attach to on the car has failed. Have a look under the back of the car."

I believe you're talking about the two metal straps at the rear of the car, in the center, under the license plate.

Those two straps are there, and appear intact.

I should add that pushin UP on various parts of the muffler allows NO GIVE, no matter how hard I push. I mean, it seems very solid, no sagging or loose, or allowing for any play.

Does that muffler side-picture seem as if the muffler is hanging low?

Sealion · 01:40 PM

RE: "The two small bolts on the motor mount, secure the mount to the frame and drop in. You should not have to worry about these bolts."

To labor the obvious, it seems like you're saying I should try to tighten the large-center bolts, yes?

I tried moderate torque, but could not budge. I will try harder.

Edit, I tried very hard. Could not budge either. Used a 1-foot long socket wrench (3/8-inch). Would have to use cheater to apply more torque.

Cdnone1 · 05-03-2008, 09:25 AM

I would recommend that you pack the car on a level surface and take some measurements to help you pin point your problem. Measure from the top the distance between the MM and crossbar on both sides where you stuck your finger in. Then get under the car and measure both sides from the engine and crossbar. Then measure both sides of the muffler.
This will help us help you trouble shoot.
I have never heard of it happening but if you experiencing a shaking while starting you might want to check and make sure your starter motor hasn't some how worked loose.
Steve

Cdnone1 · 09:26 AM

I would recommend that you park the car on a level surface and take some measurements to help you pin point your problem. Measure from the top the distance between the MM and crossbar on both sides where you stuck your finger in. Then get under the car and measure both sides from the engine and crossbar. Then measure both sides of the muffler.
This will help us help you trouble shoot.
I have never heard of it happening but if you experiencing a shaking while starting you might want to check and make sure your starter motor hasn't some how worked loose.
Steve

al lkosmal · 05-03-2008, 11:07 AM

There are two types of crossbar mounting tubes. One is threaded and one is not. I.E. one uses bolts that thread into the crossbar mounting tube itself and one design the bolt goes all the way thru the tube and uses a nut to fasten the crossbar to the motor mount. Just reach inderneath, to the other end of the large mounting bolt and feel/see if the crossbar is still connected to the mount or has dropped below, signifying that you have lost a nut or the tube weld has broken. It will take you two minutes to verify it.

Here's a pic of the crossbar/mount/bolt connection. You can see the nut holding the crossbar up. Check this connection to verify that the crossbar is still connected here.