How do I test motor mounts?

[Otter74]

I've recently noticed that I sometimes have a slight 'clunk' coming from the rear when I let out the clutch. Not always, just occasionally. This may or may not be related to the clunk I sometimes get when slowly backing out of the garage over the concrete lip.

Given the clutch-out clunk, motor/trans mounts seem an obvious candidate to check, even if I am skeptical that there is anything wrong with them, as the PO put in new sport mounts a few years ago. However, I have no idea how to test them. On my other cars it's pretty easy, as you can get a good idea of the state of the rubber and whether it is bolted in correctly or not just by looking.

[Oh Haha]

No way to "test" them other than inspecting the rubber for cracks and deterioration, especially around the center where the sleeve is. For the gearbox I would support it with a jack and remove the mounts to get a good view instead of having them attached. Be careful when removing the bolts and make sure to not cross-thread when re-installing them.

You could use the same method for the engine mounts but don't remove them all at the same time.

Of course, support the car safely on jackstands when doing any work under it.

Have you checked your sway bar end links regarding the clunk?

[KTL]

Agreed with Wayne's last sentence. I would take a look underneath the car, ahead of the rear tires. Look to see if a sway bar mount has broken. Not the links at the ends of the bar where they attach to the trailing arm behind the wheel. Look ahead of the wheel where the bar mounts to the chassis with the U-brackets.

[Otter74]

I should probably clarify what I meant by "test". First, I think I meant test whether one is loose. Jack powertrain up just enough to take the load off the mounts, then put a wrench on it to see if bolt is tight?

Really it does seem unlikely (the PO refreshed nearly everything mechanical on my car during his ownership, and the mounts aren't very old), but I am struggling to think of what else can cause a clunk back there when I let the clutch out. Again, it only happens sometimes.

As for the a/r bar, I looked through some of the POs posts and there was a mention of a possibly cracked a/r bar mount, though it doesn't appear he ever did anything about it. I've looked at the mounts and they do not look obviously cracked - is this something I have to look really closely for? The end links look fine, and I think they are also newish. I imagine a cracked a/r bar mount would cause both clunks, but wouldn't I see witness marks somewhere? If so, where?

[911 Rod]

Put a jack under the engine and if the engine moves before the car it's the mounts. You can see if the bolts are tight when the load is off the engine. Could be a stripped bolt.

Ya I'd be looking at the sway bars.

[KTL]

The engine mounts can come loose. A simple test of jacking on the engine in a safe location will show you if the mount itself is loose in the chassis crossmember (mounts are held in place with two M8 bolts for each mount) or if the through-bolt passing through the mount itself is loose. If the mount is loose, it'll rise up off on the crossmember when you jack the engine. If the center bolt is loose, or the rubber within the mount is compromised, you should see the 19mm center bolt head rise up quite a lot when you jack up the engine.

The sway bar mounts usually break in one of two ways:

1. The M8 bolts that secure the U-bracket to the mount will pull the nuts (tack welded to the underside of the mount) thru the mount base.

2. The curved section of the mount, where it transitions from horizontal to vertical, fatigues over time and severs.

Jack up one rear corner of the car at a time and look directly where the U-bracket attaches to the mount. It will be very obvious if the mount is broken because the U-bracket will pull away from the chassis. The U-bracket must stay fixed in order for the sway bar resist the suspension travel.

[SCadaddle]

I've had instances where my 82SC, after hard acceleration in 1st gear when going to select 2nd gear I get a "rowing" motion feel in the shifter for a few seconds before engaging 2nd gear. Almost like the entire engine and gearbox are swaying forward and aft. Is that an indication of the mounts being toast or?

[Otter74]

KTL,

Thanks for that - very helpful. I'll check this on Saturday.

Originally Posted by KTL

The engine mounts can come loose. A simple test of jacking on the engine in a safe location will show you if the mount itself is loose in the chassis crossmember (mounts are held in place with two M8 bolts for each mount) or if the through-bolt passing through the mount itself is loose. If the mount is loose, it'll rise up off on the crossmember when you jack the engine. If the center bolt is loose, or the rubber within the mount is compromised, you should see the 19mm center bolt head rise up quite a lot when you jack up the engine.

The sway bar mounts usually break in one of two ways:

1. The M8 bolts that secure the U-bracket to the mount will pull the nuts (tack welded to the underside of the mount) thru the mount base.

2. The curved section of the mount, where it transitions from horizontal to vertical, fatigues over time and severs.

Jack up one rear corner of the car at a time and look directly where the U-bracket attaches to the mount. It will be very obvious if the mount is broken because the U-bracket will pull away from the chassis. The U-bracket must stay fixed in order for the sway bar resist the suspension travel.

[hangar21]

Found it! Reason for my "clunk".

[DRACO A5OG]

OP, your clunk could be your rear wheel bearings.

Find a safe road where there is a slight side street/road burm, drive the car horizontally to it and swerve up and down the burm. If the bearings, you will be able to reproduce the "clunk" at will.

[Otter74]

Originally Posted by DRACO A5OG

OP, your clunk could be your rear wheel bearings.

Find a safe road where there is a slight side street/road burm, drive the car horizontally to it and swerve up and down the burm. If the bearings, you will be able to reproduce the "clunk" at will.

Do you mean a soft curb, and drive up and down it or against it at an APB
Inquest angle?

Gotta say, it would never occurs to me that a wheel bearing would cause a clunk rather than a hum/roar. Or make a noise when I let the clutch out from a stop. But I will test this! Thanks.

[DRACO A5OG]

Yes, a "soft curb" or "burm" ( I use to race YZ80's as a kid :-P )

Yes, once it hums or roars they are toast. Sharp turn right or left from stop can re-produce the dreaded "clunk" too. The lateral movement tends to do it.

[Otter74]

Sway bar mounts are definitely fine. Now to find a berm to drive against!

[DRACO A5OG]

Doh, that's right "berm" :-)