Solid engine mount and trans mounts...?

[aggie97]

Ok, so for years, I have read (I think) that if you are running solid engine mounts, you MUST run a stock rubber or urethane transmission mount or you are going to break the bell housing/tailshaft housing on the trans. It's due to something about the torsional loads on the casing that have to be absorbed "somewhere".

so, I am trying to figure out my issue with the cracked tailshaft housing on my T56 so it doesn't happen again. I was speaking with D&D today and they tell me that I should have solid engine mounts and solid trans mount. I made sure I heard him correctly and basically went "huh?"

What is the general consensus out there about solid mounts? This is for a road race car, not a street car or drag car with 6000 rpm clutch dumps on slicks.

Gracias?

[Blackpony]

I have always been told to never run a solid trans mount.

[Sleeper]

same i've always been told solid motor mounts, trans mount should be rubber or poly.

[91CoupeMike]

Solid trans mount would be hell on your hand over bumps.

[aggie97]

Solid trans mount would be hell on your hand over bumps.

not sure I follow your line of thought?

[bobs94formula]

On our dirt cars we always ran solid motor mounts and rubber trans mounts.

[91CoupeMike]

not sure I follow your line of thought?

Maybe it's just my car but when I hit bumps or go over rough roads the shifter will bounce around from rear end movement I guess. I'm having issues with my driveshaft after lowering the car. It seems to be to long and it might be bottomed out in the transmission. Not sure it's related to lowering the car as its an issue that presented itself after a few changes, including solid mounts. I don't think it moves the engine back or down but something isn't right.

[BMCSean]

Hellaflush?

[91CoupeMike]

Hellaflush?

Lol no I have a pretty big gap on the rear tires but not much in the front.

It was a damn mistake.

[BlueCoupeRedVert]

I use solid motor mounts and a stock trans mount.

[dee]

I've always used solid motor and urethane trans mounts. It's just what I've always been told to never really seen the results of not though.

[46Tbird]

Always heard solid engine mounts or a solid transmission mount, but never both.

Maybe your driveshaft is slightly too long and the case cracked during a severe rear suspension movement?

[Strychnine]

What's your cage setup?
Think about how much a frame or unibody twists. That movement needs to be isolated from the drivetrain somehow. IMO, you'd need something tube chassis based (with motor plates) to even think about a solid trans setup.

It's been a while since I've had to draw a free body diagram but I would bet that a three point mount system with solids all around and moment inputs from both the center of mass (engine) and externally (twisting chassis) would create a statically indeterminate system. How's this for a personal rule of thumb: If it's hard as shit [or impossible] to do the math on the system, don't trust it to not break in something you intentionally beat the hell out of.

Even the bridges that you drive over every day have a solid (pin) mount on one side and a roller mount on the other.



"Solid" does not mean impervious to movement. This is a Formula SAE car (w/ single cyl eng)

This is a shot of our rear engine & diff mount (single piece) filmed by Airbus's highspeed camera at FSUK 2010. Obviously single cylinder which explains the huge vibrations. Everything on the car is shaking; the scatter shield, the suspension and much to our surprise the rear bulkhead of the monocoque is also vibrating all over the place. The only thing that doesn't really seem to flex is the engine mount itself, so our conclusion from this movie was that perhaps the engine mount was a bit too stiff.

http://fsae.com/eve/forums/a/tpc/f/1...41#64420339841

[Strychnine]

Semi-related. You've been racing that car for quite a while with a big cage and stuff in it. Have you ever gone over the car inch by inch and looked for small cracks or other signs of stress?

Just curious - I'd like to know how much abuse they can take before they start to show some signs of hating life.

[Strychnine]

BTW, this is a screenshot from a software presentation from LMS. They make high end dataloggers, etc and specialize in mounts, mounting systems, vibration, etc. The last "low end" vibration datalogger kit of theirs I used cost $10,000+.


Notice the disadvantages listed for the "three point focus mount" system. Solid or rubber mounts, these issues are inherent and unavoidable.




They now make software for analyzing things like this, but i'm guessing it's expensive as hell.

Within our company if I had an OEM come to me and ask for a review of a solid mounting system for an over the road application I would not touch it. I'd send it on to someone with decades of experience in engine/vehicle dynamics and with a title like "Senior Technical Advisor – Applied Mechanics." There are people that get paid big bucks to do this kind of work.