: Factory strut tower brace and "dogbones" - can i do better?



fubar569
06-16-07, 10:56 AM
i have an itch to weld something today, and cant finish the exhaust because it doesnt make sense to redo it when i go duals with the X pipe in a month or whenever...

so im staring at what seems to be a pretty flimsy stock front strut tower brace in my 97 deville

now these cars will never flat out handle, and thats not what i bought it for anyways...just wondering if it would be worth the time to fab up a bigger/stronger one out of steel...

ALSO, is it normal to be able to move the "dogbones" by hand? i bet i can move mine a good 1/8" of an inch. at a minimum i think its time for new bushings BUT i had another idea...

solid heim joints and a stronger bar - no bushings, no give...should equal more power to the ground...prolly one one billionth of one hp but o just dont like the idea of these suckers moving at all. they are meant to be a brace...not a decoration

thoughts?

Dadillac
06-16-07, 12:49 PM
Not sure about the brace, but if you solid mount the dogbone set-up, you will transmit engine vibration into the car body. How much? There is only one way to find out. The dogbine needs to give a little to stop the vibration effect.

Don

fubar569
06-18-07, 08:43 AM
i figured it would transmit some vibration back into the body...thats almost a given...but i think these things just move way way too much...like i can grab them and move them with my hand (actually 3 fingers) - this just cant be good. if anything with that much slack it's just one more thing to vibrate...

one thing i can see them doing is limiting engine movement to a set maximum, but anything less and it's about worthless...

perhaps i could include poly bushings in a new design? though something is telling me to say screw it, straight Heim it and be done with it.

the other option could be a heim link bar, but with a couple of "enhancements" - like order a larger joint than needed, slide a metal sleeve over the stock bolt, slide a poly sleeve over the metal sleeve, and thats what the heim joint would ride on...so it would have some give to it but much much less slack then the setup thats there now...with no direct metal-to-metal contact it should limit transmitted vibration vs a solid link while greatly reducing engine movement...

thoughts?

jadcock
06-18-07, 02:44 PM
If your upper engine mounts wiggle that much, the bushings are shot and you should just replace the mounts. I would not want to go with solid mounts. You don't know what else you might be affecting when doing that. During high torque maneuvers (like WOT from a stop, etc), if the upper mounts don't flex, you might be putting more pressure on the lower mounts, and break them. Who knows. Remember that everything is designed in harmony with its neighbor.

Simply slap a new set of mounts on there and be done with it.

fubar569
06-18-07, 06:26 PM
If your upper engine mounts wiggle that much, the bushings are shot and you should just replace the mounts. I would not want to go with solid mounts. You don't know what else you might be affecting when doing that. During high torque maneuvers (like WOT from a stop, etc), if the upper mounts don't flex, you might be putting more pressure on the lower mounts, and break them. Who knows. Remember that everything is designed in harmony with its neighbor.

Simply slap a new set of mounts on there and be done with it.



the only thing i can see these mounts doing is limiting movement so the lower mounts dont get damaged or snap from those maneuvers you described...if the mounts were stiffer than stock the movement would be reduced, and that power would have to go somewhere which usually is the ground...at the expense of some vibration transmitted into the body...

it really could go either way...given no one has done it i figured i would solicit some opinions before i become a guinea pig...

at a minimum i would want to replace the stock rubber with poly and leave it at that....

jadcock
06-19-07, 12:07 PM
the only thing i can see these mounts doing is limiting movement so the lower mounts dont get damaged or snap from those maneuvers you described...if the mounts were stiffer than stock the movement would be reduced, and that power would have to go somewhere which usually is the ground...at the expense of some vibration transmitted into the body...

Think of the engine mounts being designed as a system...meaning some movement is allowed, but it's distributed across a number of mount points, to isolate harshness and vibration into the body structure. When you solidify one or two of those mount points, that rotational torque has to be taken up somewhere. It won't be taken up by the body structure -- it's much too heavy. It won't manifest itself into more power to the wheels because, again, the vehicle is heavy. It'll take the path of least resistance, which is through the one or two rubber mounts you have remaining.

It's not uncommon for guys with older RWD cars (70s and 80s) to replace their two engine mounts with solid or poly mounts, leaving their rubber transmission mount in place, then snap the tranny mount because it effectively has to take all the abuse. They end up having to replace ALL the mounts with a like material. As it's often said, the chain is only as strong as its weakest link.

The front lower engine mount on these cars seems to be fragile already. Front engine mount replacements seem to be rather common these cars, regardless of generation. My '97 had it replaced once, and my '01 twice. I wouldn't want to be transmitting even more rotational torque to those mounts. If you could change ALL the mount points over to polygraphite or polyurethane, I think you'd be on to something there. You would be solidifying the structure, but you'd be distributing the rotational torque over multiple mount points of like material, so in theory, it'll be taken up evenly throughout the system.