Bad Motor Mounts?

I’m getting a clunk as I let out the clutch from a stop. As I was looking around for the cause I noticed that the rubber from the motor mounts look like it I extruding out quite a bit and it looks like there is a bit of space above the rubber in the metal loop. So that doesn’t seem right but I can’t say Iv ever really looked at them before and the only other MM failures that I have dealt with the rubber was clearly falling apart. So my questions is, am I correct that the MMs are failing and if so what kind should I get to replace them? I wheel my truck a lot and in hard conditions but I also put a lot of freeway miles on her. Rubber, poly, brands?

As I recall, there is a bit of space between the stock motor mount rubber and the metal loop piece.

Look at your rear brakes and make sure they are well-adjusted and that the slip-joint is well lubricated on the rear shaft. These will make some serious clunk-type noises if not correct.

Just to clarify how could the brakes be clunking as I let out the cluch? Also I was not aware of a way to lubricate the slip-joint (slip yoke)

I have replaced the motor and transmission mounts on my 88 XJ. Like you I was able to see daylight between the top of the rubber and the metal banjo housing. On the driver's side I could slide my index finger between the rubber and hte housing.

The replacement mounts will have rubber filling the whole area inside the metal. If it has drawn back then it is partially degraded. If there is day light then the rubber can move and cause the engine to roll a few degrees, you will feel this when you rev the motor.

I installed new mounts which I purchased at the dealer. I do drive my XJ on 6-10 hour drives at times and isolation of vibrations out of the passenger cabin is VERY important to me. I am willing to replace mounts over having vibrations wear on me.

Everyone will have an option on what material, to me vibration isolation is #1, long life is more important to others. You have to make up your own mind. I choose dealer mounts because I knew they had the objective of making the XJ a pleasant vehicle to ride in.

My dealer told me they replace all 3 mounts at one time if one if found bad. If you don't the remaining older ones will fail more quickly.

To change the mounts you will need to do one side of the engine at a time. I recommend you jack up the XJ, take off the front wheels and let the axle drop down. Support the chassis on jack stands, do not put jack stands under the axle.

Then you will have to jack the engine, put the jack under the bellhousing, no the oil pan, and jack up the engine to take the load off the mount. Then remove and replace the bad mount. do the same on the other side. On my 88 XJ I had to remove the oil filter mount so you may want to pick up a set of O rings at the dealer.

If you don't take off the wheels and support the chassis then when you jack up the engine with the weight on the wheels, the entire chassis will lift until you are at the end of the suspension travel THEN you will begin to lift the engine. I did not want to use a 6 ft step ladder to change mounts.

To do the transmisson mount you have to drop the crossmember to change it out. I used a jack under the transmisison pan. I had a 2 x 10 between the jack and the pan. I lifted up the aft end of the transmission once the bolts and nuts were removed. Not a bad job. All of this goes better if you have use of a lift.

I did try to buy mounts at a part store, they were anchor brand and the rubber was already shrinking. I went to the dealer and their mounts looked very good, rubber filling the cavity and the look of quality.

Some day I'll have to change mounts again, but not anytime soon.

My rig if fairly far from having a Cadillac ride but that’s not to say I want it to be worse. Can anyone who has gone from OEM to Poly jump in with a how much difference report.

Martin - I'll have to go look at mine with OEM mounts tomorrow; I was positive there was a gap between the metal loop-thingy and the rubber. I haven't paid much attention to them since installing them two years back.

The reason I asked about the clunk as you let out the clutch is because most of the time when I let the clutch out I also let off the brake. When coming to a stop in the XJ, it isn't unusual for the back end to lift up and 'unload' the springs a bit. When you hold the brake the back end settles and that preload is then transferred to the slip-yoke and the brakes. When you let off the brake there is often a rapid unload that goes *clunk* and feels like you've been hit in the rear bumper... The rear brakes will do that or the slipyoke shaft will if it isn't greased a bit

Jim

Anyone using the M.O.R.E. MMs they look like they might be a good compromise between stock and Poly

I recently replaced all my mounts with rubber replacements from NAPA. They also have the gap between the upper hoop and the rubber. The factory ones I removed had this gap as well. I don't believe it is an indication of shrinking rubber, but rather "as designed". The mounts are functional without the metal hoop, but it is federally mandated as a safety catch to contain excessive motor movement if the mount fails. You might recall the reto-fit chains GM dealers installed in millions of their cars a few decades ago. Same deal.

Bronco, I've never used the poly mounts, but have read numerous reports on this board of guys that tried them and where stuck with a major increase in NVH. I've ran solid welded mounts on a competition vehicle, but would never consider using anything but rubber on a primary street vehicle.

Yucca-Man I know what you are talking about. I picked up that aftermarket mount and it had a gap about 1/2 as much as the one I was replacing. I went to my dealer and asked about mounts, they pulled me two which they had just taken delivery on that day. I remember how "full" the mount seemed with rubber, there was no shrinkage. I thought to myself "so this is what a new/good mount looks like."

If you think about it that rubber is supporting the weight of the engine 24/7/365 so after a while you will compress and cause a gap to appear at the top.

I was just saying brand new mounts are full of rubber, and I am sure after 3 years mine have some space above the rubber now. I think it a good thing to replace mounts on a periodic basis. When I did it I was moving 450 miles to a new town and still commuting back to my old home. I was trying to make the ride a better one. The new mounts did make an improvement but the XJ is no luxary car.

Remember what we call mounts are technically called "insulators" since they insulate the passenger cabin from engine/drive system vibrations.

Another thing I have done is replace all the suspension bushings to include sway bar bushings. It made a huge difference in how the XJ rode and drove. When the control arm bushings were replaced what I thought was wonder from over boosted AMC power steering turned out to be sloppy control arm bushings. I also recommend monroe Reflex shocks. I guy at the parts store told me Monroe matics and sensatraks were the same shock, just different color paint on the outside. I installed a set of monroe matics and they were much better then stock shock with over 100K on them. After 30K I replaced those with the Reflex and much improved ride. My next set will also be Reflex on this XJ.

I put the M.O.R.E. torsion rubber mounts in. Do I feel more vibration? Yes. Is it as much as poly mounts? Don't know, never tried poly. Would I go with the M.O.R.E. mounts again over stock? Probably. Do I notice the vibration much? Only at idle or starting out.

I went from a stock engine with rubber to a mild 4.2 stroker with poly mounts. It was not that bad, I did have the crank ballanced so that might help. But I would not due the solid mounts unless you are going to race(and there is not much of that here).

After fan munching two radiators I realized that instead of one bad mount I had three bad mounts. After spending $300 on radiators I vowed it would not happen again. I put on the currie motor mounts and daystar trans mount. Way noticable increase in vibes. Just at idle though. I've had solid mounts in other vehicles and while not that bad its close. IMHO.

I installed the m.o.r.e. mounts a couple of weeks ago and I am extremely happy with them. you get a little extra buzz at idle but who cares. I called m.o.r.e. about a rubber mount for the tranny ( theirs are poly) and they said the best one was mopar, so I went with that. there is almost no rocking with the motor. it used to sound like a box of loose parts shaking when going over a speed bump before, now its total silence. I love it. also, it's more responsive as its not flopping around like a fish anymore.

Cool guys I think I may try these things. Thanks for all the input.