Solid motor mount impressions

[stomachmonkey]

Installed solid motor mounts over the weekend, ran out of time to do the sport mounts on the tranny so that's this weekend.

I do not know if the old mounts were original or had been replaced so let's assume they were original. They were worn but were not completly shot.

The goal is to improve shifting as much as possible. Have done shifter bushings which helped a bit, did Swepco which is a nice improvement.

I don't notice any real shifting specific improvement with the solid mounts.

What I do notice is drastically improved driveability. The car feels more solid and stable.

Low speed situations, rolling in traffic in 1st or 2nd is much easier, the car no longer bucks.

Low speed rolling starts from 2nd is great.

Clutch engagement from a standing start is smooth and precise, overall more responsive and predictable. The occasional shudder is gone.

Gear changes are better, not neccesarily from improved shifting, it's more like the whole drivetrain feels solid, not sloppy.

I was concerned about increased vibration and noise. I have only noticed an increase at around 4k and it is completly acceptable. The trade off is no more noise from the drivetrain moving around. Even with the minimal vibration increase at 4k overall the car does not feel like it is 20 years old, feels solid like a new car.

I recommend the mod, cheap, basically a 1 hour project and does make a difference.

Scott

[RickM]

Scott is there additional stress at the mointing points that may be detremental?

[stomachmonkey]

Rick,

Stress is not an issue. The factory use rubber mounts for creature comfort.

Solid mounts transmit engine vibration to the chassis, the rubber helps absorb some of it making the ride more palatable to the average Joe.

Probably every dedicated track car out there has solid mounts and they endure much more abuse than a street car.

Scott

[bigchillcar]

Scott,
This thread is giving me new hope. I've been trying to track down a sloppy play symptom for months now. I replaced my rear axles (cv boots were goners anyway), hoping the play was there, but apparently it wasn't. I can't tell by looking if my mounts are worn, but I suspect them. The bolts are all tight and when I rev the engine, a friend says he doesn't think the engine vibrates, but I just don't know. Your symptoms sound an awful lot like mine. Already in gear, just rolling along (unloaded) and blip the throttle...you feel some play then the drivetrain loads up, particularly noticeable in lower gears...very annoying. I don't hear any groaning/whining which would indicate internal tranny woes. Only other thing I've wondered is the clutch itself, although under load it doesn't slip (thouhgt this was the clutch test).

What do you think? Unless it's suspension related, like spring plate bushings or maybe motor to tranny bolts, ect. I'm not sure anymore.
Ryan

[island911]

Originally posted by stomachmonkey
Rick,

Stress is not an issue. The factory use rubber mounts for creature comfort. . . .

I'm call'n BS, on that.
Stress *is* an issue. Every time you slap 2nd gear, you induce a huge torque spike thru the drive-train. Solid mounts make this spike worse. Rubbermounts, attenuate the pulse, and thus lowers peak forces on gear-theeth, CV-joint and such.

Also, how can anyone say solid motor mounts are better for shifting, when they haven't compared them to new OEM mounts? (which work just fine, btw.)

[William Miller]

Scott,

I was thinking about my mounts this morning as I was following a parade of cars a few miles long to get to that one stop light that is the choaking point in my commute.

I was trying to think of how to describe the "bucking" you talk about.
Worse, my car is a cab. The mount bar that goes across the back of the engine is also made so the engine can twist. It has a little shock absorber that I assume is supposed to dampen the twist.

The 83 is the first year cab and I don't know if they kept this engine mount bar in later years. It was probably a good idea for the cab to make it more of a touring car.

I just installed the engine I rebuilt last week. This is the first time the car ran well since I bought it. Now that it's running well I am starting to notice other things that I didn't have time to attend to or care about.

My engine mounts are in pretty good condition so I don't think they are worn. The little shock is however probably not as stiff as it probably was.
A new shock is expensive and I am thinking about the alternatives.
I could replace the shock with something solid to make it more like a solid mount bar. I could find a solid mount bar, or maybe weld the one I have solid. Then maybe go to solid engine mounts.


I'm really intrested in hearing from anyone who has done this on their cab. Like you said above is this to prevent dammage to the tub or simply for comfort?

Good topic! Just in Time!

[Eugene at Pelican Parts]

Since moving to solid motor mounts, I have not noticed any more vibration or resonance perceived within the cabin. Keep in mind that the motor mounting crossbar absorbs much of the vibration in the pitch and yaw direction (w/ respect to the orientation of the vehicle), but still hardly any in terms of roll.

I cannot comment on shifting improvements since I had done my shifter bushings and some tranny work at the same time, but I think the solid mounts gave me a slightly better throttle response. Stress is definitely induced and it feels like a hearty shout of "giddyup" as I floor it in first and brace my neck to prevent whiplash.

EDIT: William, just read your post. Do you have a picture or diagram of your mount crossbar w/ shock? That's interesting.

"The mount bar that goes across the back of the engine is also made so the engine can twist. It has a little shock absorber that I assume is supposed to dampen the twist."

[island911]

If you want solid mounts, then I would suggest what Porsche did, and get these: (tic)




The engineers at Porsche have some repsect for the need of compliance in the system.

[Elombard]

I love my solid mounts, very similar impression to yours. I cant wait to put the sports in the tranny. I still wonder what was behind that big add PMO put out about the solid mounts being such a bad Idea?? I sold a spare set recently to Eric Mckenna, I am interested in his impressions. He has newer sport mounts on his now so it should be an interesting comparison. Island does have a good point, but my old mounts did not look that bad and it was a huge improvement with no trade off in my car.

[William Miller]

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_enginD_main.htm

[William Miller]

That doesn't get you all the way there.
Click on mounts and Cabrolet engine support.
The shock is another picture.
I couldn't find one with it all in one place together.

[stomachmonkey]

Island,

I could be wrong re: the stress but I don't drive my car on the street in an aggressive manner 100% of the time. Asked my shop about it before I did the swap and they had no concerns. I decided on the solid/sport combo because of all of the positive threads on this board, I don't recall seeing very many if any negative threads and certainly none that cited stress as an issue. Then again maybe I just did not see them.

Also I was very clear that my OEM mounts were most likely the original 20 year old mounts and was not comparing the solid mounts to new OEM mounts.

I was clear in stating that I did not notice much improvement in shifting but that the overall feel and driveability of the car had improved. BTW, have you ever compared solid mounts to new OEM? If you have then your opinion on that would have been a very welcome contribution to this thread and may have helped some of the others who have questions/concerns.

Was just giving my impression of the change it made in my car and based on some of the responses it looks like I may have addressed an issue of concern for other members of the board.

Bigchillcar, cool name, I get it.

I was getting drivetrain slop, kinda like a car with bad universal joints in the drivetrain.

Your description of your symptoms are identical to what my car felt like last week.

It's all gone and the car really feels a lot better. I like it this way.

Scott

[dd74]

I acquired a pair of aluminum motor mounts specially made by TRE. To say the least, they improved handling and response quite a bit. Additionally, the mounts smoothed out and quickened my shift action to the point that it now seems effortless.

Vibration is near nil, although there is a slight "whirring" which was not present when the last mounts were in. My rear windshield vibrates a little as well; again which I equate to the mounts. But to me that's a vague (and entertaining) trade-off for a tangible increase in better overall driveability.

BTW: this is in city driving, where solid motor mounts are most frowned upon.

[island911]

Scott, My only point, was that "ride comfort" is not the only reason to have rubber motor mounts. (though, many have propogated that simplistic notion. . . mechanics included.)

More detail here.

[john_colasante]

Solid mounts make the car *much* louder inside, if we're talking about the same thing. The sounds transmit through the whole chassis now. Also, solid mounts will cause lots of bolts to loosen, you are going to need to check things much more often now and nut&bolt the car regularly. In my opinion solid mounts should be reserved for a racing application only where the car is regularly teched top to bottom before each outing.

[dd74]

So one should check the nuts, bolts, and whatever else for tightness, hope their CV boots stay together, and also smooth out their shifting.

Solid mounts are still a good trade-off as a 911 should be shifted smoothly anyway. And if harshness is a concern, what are larger torsion bars, lower profile tires and weight lightening doing toward "harshness?"

[1fastredsc]

Actually, i think that ride comfort IS the only benefit of the rubber mount. That and to not shake the rear window loose as dd74 discusses. Because althought the instantaneous "buck" of shifting when you let out the clutch is a spike in torque, which technically would be bad in the case of a chassis with no elasticity. Steel has a decent amount of flex before reaching it's peak stregth. A good examble is the front part of the chassis where the strut tower "flex" under load without a cross brace (of course this is under extreme conditions). Therefore, i doubt the chassis will be hindered by a slight "peak" of torque under clutch engagement, but i've been wrong before.

[doug petty]

william
i've got an 85 cab with 145000 on it. when i rebuilt my motor last summer my rear mount shock was shot. replaced with a piece of 1/2" allthread rod, firmed up but still shakes on take off. next took off mount & removed the center rubber ring & welded the two piece mount together plus replaced all four rubber mounts and things are nice & smooth now. i was concerned about excess vibration at the windshield with the top down, but now its a lot less than before.
go for it!

[bigchillcar]

Bigchillcar, cool name, I get it.

I was getting drivetrain slop, kinda like a car with bad universal joints in the drivetrain.

Your description of your symptoms are identical to what my car felt like last week.

Scott,
Sounds like you know the movie (I watch it for the car...fast forward through all the mid-life angst).

I've often described it like worn u-joints...used to have them in a jeep cj-7 and it reminds me a lot of that. I can feel it in my hand transmitted through the gear shift...rolling along in gear, tap pedal hard enough to induce and i can feel something moving in the drivetrain through the lever.

The engine mounts LOOK ok...they're tight enough and revving the engine, it doesn't seem to vibrate like i'd expect with worn mounts...i've watched it from the engine compartment and laying on the ground looking underneath. But, damn, it sure sounds like you've discovered the problem...wish i had ANYONE in arkansas to help confirm. oh well, lucky to have shoes, running water and a book in the library...
Ryan

[stomachmonkey]

bigchill,

If they are the original mounts I'd just go and replace them.

My mounts looked OK as well, but how can you tell by visual inspection if they are shot? My shop told me to replace them and I'm glad I listened.

If someone out there has the answer please pass it along.

My brother called while I was changing the mounts, he's a shop foreman for the largest Toyota dealer in S. Fl.

Asks me why I'm bothering, am I getting vibration? Said, I don't really know, I've only owned the car for a year, I know how it feels and drives but I don't know how it SHOULD feel and drive.

It's possible that the solid mounts induce a lot more vibration than new OEM, but my benchmark is how it felt with the old mounts and I don't notice that much difference so in retrospect maybe I was getting vibration from the stock mounts but did not know it.

Anyway, after reading some of the replys and paying attention to the car on my ride home last night and back in this morning my impressions have not changed. The car feels like it had 15 years shaved off it.

Scott