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Brown Dog Ultra-Flex Rubber vs stock vibrations?

md21722

NAXJA Forum User
Location
TN
Hey all,

On my 97 XJ AW4, I made the change to the Brown Dog Ultra-Flex Rubber motor mounts along with their engine support brackets. I've got new vibrations. Its really no different at idle than driving, but I suppose I don't notice it as much driving. Not only does it make the steering wheel vibrate, but sometimes the dash and headlights can be seen vibrating. My old mounts were relatively newer dealer motor mounts. For install I tightened per instructions to tighten the through bolts just until the washers stop turning, then back off 1/4 turn.

I am wondering if these vibrations are normal with this style mount, or if I should make an effort to reduce the vibrations.

I will say that the engine feels very solid in place.

Thanks!
 
I have the same ultra flex rubber brown dog mounts and my wife won't ride in my XJ with me anymore. When I have AC on and am stopped at a red light, it feels like it is going to blow. Lots of new vibrations. I guess when you hold a stock mount, which is some pretty thin steel wrapped around a pretty large clump of rubber, next to the brown dog, which only gives a really thin layer of rubber it makes sense.
 
My DB rubber mounts "toned" down some over time, plus I've gotten use to them. They certainly are a lot less "buzzy" than when I first installed them about 3 years ago.

I was replacing a cracked header, so I decided to do the motor mounts a long as access was easier. That, and I am of the firm belief that the snugger DB motor mounts keep the engine from torquing over as much; thereby reducing stress on the header, and hopefully prevent future cracking...
 
I have the brown dog rubber mounts, and yes there are a bit more vibes at idle. At idle only, but its nothing awful. I have a rattle or two from the dash that I hadn't had time to track down and fix yet. Not as bad as what the two people here are experiencing... especially with seeing stuff vibrate. Perhaps there is a problem with your engines that the mounts made obvious?
 
After further diagnosis, mine may be helped by rehanging the exhaust. Between the engine support and mount I have a small gap towards the radiator side, but the rubber is somewhat compressed towards the rear (towards the transmission). I found no way to resolve this during the install, and I tried repeatedly. If I try to pull the engine forward, there is no way the crossmember at the transmission mount will bolt up.

Dash vibes are kind of interesting. In my other Jeep, that does not yet have the Brown Dog mounts, and is otherwise stock, I expected more vibrations after pulling the dash to change the evaporator, but its actually quieter than it has been in a while. I used no special tape/foam/rubber to try to quiet it back down.

My main goal was the engine supports with 15 rather than 6 bolts, so I'm tempted to put back the dealer mounts...
 
Do you also have the the thru-bolts "adjusted properly"?
Too tight = vibes.
 
Mine have a little vibration after a couple thousand miles. Its not that bad anymore, but it was hard to handle at first.
 
Night and day difference, even $10 cheapo Anchor brand mounts were much much smoother than BD rubber.
Go after market if you need the strength and can tolerate vibrations, rubber or poly.
 
They soften up after a few thousand miles. I ended up tightening them down further as well. I recently replaced the trams mount and it helped a lot.
 
Thanks for the comments. I'm pretty sensitive to vibration. I'd say the Brown Dog is "tolerable" but "not preferred". Rehanging my exhaust may help. I'll let you all know if that helps when I get to it.
 
Does your exhaust contact the x member at idle ? Ive got poly brwn dogs and poly stinky trans mount and no vibes at idle
 
No, not at all. The transmission mount is pretty new and in good shape. Exhaust hangers in the rear were replaced recently as well, but the band clamp between the cat and muffler allows the exhaust to rattle a bit.
 
I had two sets of mounts from Rustys, rubber and poly, and they drove me insane. I tried everything to get them to reduce vibrations. I ultimately swapped them back out for a good set of Mopar OEM mounts and never looked back. Yes I have had to swap them out again a couple of times over the years but I couldn't stand the vibrations. I will say this however, I now have a rebuilt engine in my Jeep and it was decently balanced before assembled. I have had my 97 since it had 75,000 miles on it, it has 269,000 miles now, new engine at 265,000 miles. The rebuilt engine runs 1000x smoother than the original. In my research into engines and rebuilding them and building strokers, apparently Jeep didn't do the best at building well balanced 4.0s so they had some vibrations. With how smooth the Jeep runs now, I would probably try an HD set of mounts again and see how they do.
 
I have the BD rubber motor mounts and the Vibration has either smoothed out a bit or I've just got more used to it. If I were to do it over I'd just get a good set of OE Mopar rubber mounts. The vibration is not smooth at all considering my rig is a Daily Driver. I've adjusted the thru-bolt many times and to be honest it's backed off so much I was leery it would back out all the way. None of that helped for me... and if I hadn't dropped so much $$ on the mounts and if they didn't look so good I'd just go back to an OE Motor Mount.
 
I kept the Brown Dog engine support brackets but reinstalled my dealer rubber mounts. I was mostly concerned with braking off the mounts from the block anyway.
 
IIRC, Daystart or Energy susp. make an "upgrade"/replacement bushing that installs in place of the failed stock mounts. Takes a little effort, but a friend of mine has them in his heep and they seem to be fine.

For those that want something better than the chinexican replacement, stock style mounts.. consider StinkyFab. They use a larger bushing than the BD mounts. I have no issues with vibes. I am currently running them in my MJ with stock engine side mounts.
I have BD rubber in my XJ, a little vibe, but feels much more solid than stock mounts.
 
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