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true or false

MTN4X4

NAXJA Forum User
i heard that if you install a poly trans mount like daystar
you also must intsall poly engine mounts, if you dont you will
crack your bell housing. true or false
 
Not to argue, and again, I'm not 100% sure about jeeps, but I have seen automatic transmissions crack through the bellhousing before because of a new poly mount on the transmission and old, soggy, soft motor mounts. 3 cases in person, several more hear-say. Motor mounts are more important than tranny mounts, unless your tranny mount is broken in half.
 
Not sure if that could happen in a jeep, but I definitely agree that the motor mounts are more important than the tranny mount.

If you've got poly motor mounts, I wouldn't worry too much about the tranny mount, unless it's totally f'ed.
 
it seems that if you had poly mounts on the trans, and rubber on the motor, the motor would be able to torque more than the tranny, making it a hell of a lot more likely to crack your transmission. poly in the motor would probably be fine...
 
not just vibrations... rev the engine with the hood open, watch it torque side to side... it moves a good deal. then add the torque of turning the wheels to that, and you really got something there!
 
from what i heard, poly has too less of give, there really really tight so when u have it in gear and give it gas theres no give at all and puts alot stress on stuff, the rubber mounts has a little more give so its not as much as stress on stuff, just my opinion....... i dont know about mixing them, but i was always told not too, never had a good reason why.... tho
 
basically... poly is hard plastic... not compare that to rubber... rubber gives quite a bit, where poly doesn't. so yes, XBoBJ you are right.
 
Sorry to bring up an old thread...really old..but i figured better than starting a new one. Anyways, i had basically no trans mount before, the rubber had basically desintigrated, so intalled a daystar poly mount. While searching to see if the vibes were normal i ran across this. my motor mounts are in good cond. but are stock rubber...so am i gonna run into problems? A cracked bellhousing would kinda ruin a good day. O and to add to the problem i have little to no $ due to the holiday season..Got the poly mount for next to nothing. Im basically just looking for reassurement. has anyone actually see it happen? and under what loads? sorry in rambling. Thnks.
 
You should not get cracks from running mixed mounts - unless the rubber mounts are on the way out anyhow.

This has a lot to do with why you should always replace all mounts if you're going to replace one - the new mount will "fail" the old mounts, and they could take other parts with them. Does that include metal bits? It's possible. Likely? Hard to say.
 
So then the question is can i go with MORE's or should i go poly? Id like to go more if possible.

"Aftermarket performance" mounts (like M.O.R.E) tend to use a stiffer elastomer (synthetic rubber) than OEM or OEM/Aftermarket replacemens - so M.O.R.E. mounts should work neatly with your poly slushbox mount.
 
O.k.. 1 more question. Those mores are expensive as Sh1+..how about rusty's. i know they arent known to be as good but its a motor mount how can you scew it up? By the way thanks 5-90.
 
im sorry, im far from loaded, but fox 3.5 bypass shocks are 'expensive as sh1+', but more motor mounts are far from expensive.

BUT.... if theyre not in the budget, you might want to look into brown dog motor mounts, lots of people run them and are happy (i prefer my zinc coating on the m.O.R.E.'S.... , and find the american flag out of place in an engine bay, and painted parts in that area unacceptable... but whatever), the brown dogs are time tested, trail approved as well.
http://browndogindustries.com/c2572-0jeepmotormounts.aspx


...unless the rusty's are like, $15, i would go with the brown dog stuff in a budget minded build.
 
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I've gone through 1 and 1/2 motor mounts so far. Not bad for 100k+ miles I guess..

Anyway I read that if you put poly motor mounts on a cherokee you would get some vibes, actually a lot of vibes from the motor to the unibody.

Is this true? I'd like to have better motor mounts, but the dental work could get expensive.
 
I've gone through 1 and 1/2 motor mounts so far. Not bad for 100k+ miles I guess..

Anyway I read that if you put poly motor mounts on a cherokee you would get some vibes, actually a lot of vibes from the motor to the unibody.

Is this true? I'd like to have better motor mounts, but the dental work could get expensive.

Poly mounts on anything are going to give you vibrations, simply because the poly is stiffer than the elastomer (it's not actually "rubber" - it's also synthetic) that is used on OEM engine mounts.

Recall that OEM parts are a compromise, and much of what is done is driven by NVH (Noise, Vibration, Harshness) because people are turning into wusses (I tend to think.) While that's okeh for a Caddy or a Lincoln - I'd expect one of those to be smooth and quiet - it's silly for a truck.

The softer you make a mount, the more torque you'll lose in compressing the thing.

Enter polyurethane. Like using poly suspension bushings, you'll have less "give" in the poly, because it is stiffer than the elastomer used in OEM and OEMR mounts (probably Viton, come to think on it. Or possibly Buna-N.) Since there's a stiffer coupling between the engine and the chassis, there's going to be more vibration transmitted through the mount. Not as much as if you were to, say, machine one out of solid mild steel (I've seen that done,) but more than if you were to make one out of sponges.

The OEM elastomer has to be able to hold up the weight of the engine, handle vibration with minimal transmission, respond to torquing of the engine, and not deteriorate in the presence of oil, grease, fuel, heat, and general crud. Poly does all of those rather better than the OEM elastomer - except for "handle vibration with minimal transmission" - stiffer means stiffer. It's really that simple - there's only so much you can trade off.
 
Its taken me about 3 days to get used to the vibes of the poly trans mount and its not even that bad. just sitting in gear at a light or somthin is the only time its openly noticable. Im ordering brown dog poly mounts as soon as i get paid next. And thinking about it, i kinda like the vibes compared to my brothers wj, i can tell the damn thing is on. Just my thoughts.
 
Its taken me about 3 days to get used to the vibes of the poly trans mount and its not even that bad. just sitting in gear at a light or somthin is the only time its openly noticable. Im ordering brown dog poly mounts as soon as i get paid next. And thinking about it, i kinda like the vibes compared to my brothers wj, i can tell the damn thing is on. Just my thoughts.

I don't mind a little vibe I just don't want to have it vibrating so bad I have to switch back to the other mounts. Those OEM mounts are crap. I'd rather have something more beefy.

Thanks for the info, this is what I needed to know.
 
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