All;

I really need to replace the motor mounts on my L98. I’m pulling the exhaust manifolds shortly to replace with something less restrictive...would it be any easier replacing the motor mounts if the exhaust manifolds are off, or would that make any difference?

 

Won't make a revolutionary difference, but anything that improves access, can't hurt.

Hardest part of doing motor mounts in these cars though, is the bolts that hold the lower piece to the frame. The control arm is in the way. With that gone, they're easy; but with it there, it's very tedious getting the bolt & nut apart with a wrench up into there.

 

can be done. if you don't care which way the new bolts go through it's a little easier.

 

On a lift with the wheels off and the suspension drooping you can get in there with long extensions and wobbly sockets.

GD

 

I don't see exhaust manifolds/ headers as having any relevance when replacing motor mounts...

 

This is true...
I put the front end up on jack stands, got under there with some extensions/wobblies and was able to get the bolts out fairly easy (compared to some of the stories here). Putting them back in was easier because I put the bolts in from the bottom and fastened the nuts on top. Just take some good super glue or whatever (put it on the bottom of the bolt, then have a bendy wire go thru the hole down through everything and glue to the bolt). When it is dry enough and stuck on there, pull the bolt very easy up through everything and into the hole, slide the nut down the bendy wire to the bolt and fasten with something like lock-tight on your threads so they can't back off. Pull the wire off of the bolt and sand off any glue and call it a day.

 

I just tack welded the nuts to the k-member, no more wrestling wrenches & sockets lol

 

I don't see any point of installing the bolts from under and putting the nuts on top. I've never done it with the engine in place, but with mine, all I had to do was use some extensions (including 1/4"-drive), and a universal socket. To re-install the nuts, I simply put a small piece of vinyl electrical tape over the socket and wedged the nut into the socket end with that, so it couldn't fall out before getting started onto the bolt threads...

 

I was thinking about a little RTV, and glue the washers to the nuts.

 

Should be flange-nuts, so shouldn't be any washers. Put a piece of vinyl electrical tape over the end of the socket, and wedge the flange-nut into the socket. Worked awesome for me..

 

So...i managed to get the 3 bolts off.

Now, the large bolt holding the two halves together won’t budge. The bolt heads are pointed to the REAR of the mounts...I was under the impression the heads were supposed to be facing front. Soaking them now in penetrating oil, but everything is in the way to get access.

Suggestions?

 

From the factory, one of those bolts went one way, the other the other. IIRC the pass side bolt went in from the rear and the driver's side from the front.

If they're in that way, there's not much in the way. The opposite way on either side, ... you'll have to remove some part to let the bolt slide out. The fuel pump for example.

As far as rust and can't get them to loosen, well, that's just luck of the draw. Sucks I know, but comes with the territory. Turn your air compressor up to 150 psi and go for it.

 

Both of mine are pointing toward the back. I’ve been soaking them in penetrating oil for awhile..so far, even my impact wrench hasn’t budged it.

 

I let that big bolt soak for several hours...still can’t get it to budge.

...and to think, I was only worried about the 3 PITA bolts.

 

Must be some serious rust. Hard to imagine a impact gun won't take them loose. You ARE going counter-clockwise, right?...

 

Milwaukee M18 Fuel impact gun (2767)
Literally in the top 3 favorite tools I ever purchased

 

Well, it’s gone from bad to worse.

I let it sit overnight. Got up, while I was feeling my best, and put all the force I could muster.

Heard a satisfying “pop”. Started cranking on it, and while it was turning, realized the bolt wasn’t going anywhere.

Broke the weld that holds the nut in place on the clamshell. Now the entire thing turns uselessly.

Any ideas, now’s the time.

 

Well, I got lucky. Put a large wrench on the nut, to hold it still, and was able to remove the nut. The bolt is FREE.

So, that leads to a couple of questions....

Do I remove the engine mount from the block, and have a new nut welded on?

Or, do I buy a new long bolt, and since I have access to both sides to tighten, simply bolt it back together after I replace the lower mount?

 

I don't know what nut is "welded on" There are 3 bolts that hold the block mounts. Three bolts with flange nuts that hold the clamshells to the K-member, and a long bolt & nut that connect the two. If you snapped the head off the bolt, you'll need a new bolt...

 

I got the bolt out whole. I was under the impression the nut that runs through the mount was tack welded to the clamshell, but I’m not seeing evidence of that.

It looks like what the problem was is that the mount had collapsed, and the “ear” below where the nut goes is bent outward slightly, I suspect the nut was putting extreme side pressure on the bolt, which more or less locked it tightly in place. I’m thinking it would be smart to replace the through bolt and nut with new ones...but I’m going to have to figure out how to bend the bottom of the “ear” on the clamshell to get it flat again.

 

Got all 3 bolts back in the crossmember. Lots of extensions, the electrical tape, and a 15mm Craftsman shallow universal socket, with a long 15mm closed end wrench on the motor mount side means the bolts aren’t installed upside down, like the previous owner did. I went through the lower control arm for the lower one, and through the coil spring for the uppers....turned the wheel hard left to get the upper rear, and hard right to get the upper front. Took about 30 minutes to get the nuts back on the bolts.

 

Cool, you did it the right way. I'm just not sure why you are re-using old clamshells. Were you just installing polyurethane inserts in them? ...

 

No, OEM replacement motor mounts. Polyurethane mounts seem to cause about as many issues as they resolve. The only urethane I’ve installed in my ‘88 is a urethane torque arm bushing.

As far as the clamshells go, the passenger side clamshell is no longer available...and I figured used ones probably aren’t going to be much better than what I already have.

 

No longer available??? I just got some in 2019 for both sides from Classic Industries. 5 bucks each. The clamshells are not side-specific. Only the block mounts are...

 

https://www.classicindustries.com/pr...ts/t83099.html

 

I see the confusion now....I didn’t reuse the rubber motor mounts, just the metal.

I had brand new GM mounts I installed...I’ve had them for nearly 3 years, but due to my late wife’s illness, I haven’t been able to install them until now.