Motor mount condition

I've wondered this. Do they sag? I don't hear of too many getting changed, or issues with them. The top mount strut bushings get heat soaked from the rear header, crack and start to look ugly.

 

Sadly I think the answer is that like everything else made of rubber at 10 years they are past their prime, by 20 they are sad and by 40 they are dangerous. 308 mounts (and I assume gt4 mounts) have springs and rubber and the springs hold up really well so its pretty near impossible to tell when the rubber has failed but the rubber is their to act as a damper so as it fails the engine bounces more and more.....but I'm unclear about what issue that could/does cause exactly?....it could lead to broken springs in the mount I guess?

 

All the ones I've taken apart the rubber is simply a dust/debris cover. The internal is a tuned spring with a metal mesh damper. So the big killer is rust. The rubber doesn't play a role that I've seen other then to keep it clean.
They're tuned isolation dampers, so spring condition is critical.

 

[QUOTE="smg2, post: 149703240, member: The internal is a tuned spring with a metal mesh damper.[/QUOTE]
Metal mesh damper? My brain just isn't processing that, how does that even work?

 

So how would you know they have problem? Can you see rust? Can they be opened without cutting apart? Will engine vibration be more harsh?

Thanks!!!

 

When I first started tracking my 77 coupe, I experienced difficulty downshifting from third to second at thunder hill, coming up the hill, braking and truning left, then right, (forgot the turn number, been 6 years). I surmised that the mounts were loose, allowing a poor alignment of the chassis, shift linkage and tranny.
One of our more experienced guys suggested replacing the mounts, with his poly urethane units. Worked like a charm, the chassis/tranny relationship stayed more constant, allowing the shifts to happen much more easily, particularly under braking and turning.
As with most all hot rod parts, there are tradeoffs, in this case, the stiffer mounts allowed a noticeable increase in engine vibration in the cabin. Not objectionable, but perceptible.

Looking forward to getting back to T Hill, great track, but first, i need to fine tune my dad's Porsche 911, 2.8 twin plug hot rod and let it rip. Will bring good buddy, for shake out that helped me finish the car. dyno set up first.

Cheers,
chris

 

That really (to me) sounds like the shift bushing. Coincidentally, mine just acted up last week, and shifting suddenly went 'goofy'. I knew of that little rubber bushing being a common issue, so first chance I got, I looked at it and noticed it was pretty bad. I had a relatively fresh new part, so in 20-30 minutes, all fixed. Took her for a good drive and then changed the oil.

How we love them so!

 

If you're pulling the engine & the car has its original motor mounts, I can't think of a good reason NOT to install new ones. There's no better time.