: Engine/Tranny mounts



Skiller.
09-10-10, 05:05 PM
Hi all, and thanks in advance for any help...

Besides the front center motor mount in my car, how many other engine/tranny mounts are there? I am asking because I found out my car was in an accident with a curb/guard rail before I bought it (pass door is repainted, wheel hub failed on that side, tie rod end bent, rim bent)...I have fixed everything so far but the tie rod end. Anyway, I'm wondering whether or not one of the engine mounts could have failed as a result of that collision. What are the chances of that?

I am asking because the car shifts rough at times, even under light acceleration. I think the front center mount is OK (not much movement while brake torquing). I decided to ask about it after last night when I punched it on an on-ramp. It shifted slightly passed 6500 RPM and it was as rough as it has ever been. Usually, it's dead smooth under heavy acceleration and rough under light acceleration if that makes any sense.

Would bad tranny mounts cause a rough shift? The car has no PCM codes.

I am replacing the tie rod end soon and I can inspect the mounts when I do that if someone can point me in the right direction.

Thanks!!

Submariner409
09-10-10, 06:34 PM
Either in the GM shop manual or the blowup parts diagrams in www.gmpartsgiant.com .

johnny kannapo
09-10-10, 06:38 PM
Any bad engine mount can cause movement at shift points when on the throttle. The transmission mount is the engine mount.

Skiller.
09-10-10, 07:12 PM
So the brake torque test is only good for testing the front center mount? There was only about 3/8" of movement in the engine..

With my foot on the brake, the shift from D to N is pretty rough...Along with the shift from R to D...

I'm more confident now that this isn't normal.

Skiller.
09-11-10, 09:49 PM
Does anyone have any ideas?

Thanks

Submariner409
09-13-10, 02:53 PM
So the brake torque test is only good for testing the front center mount? There was only about 3/8" of movement in the engine..
With my foot on the brake, the shift from D to N is pretty rough...Along with the shift from R to D...
I'm more confident now that this isn't normal.

If the engine only moved 3/8", then the front center and other mounts are OK: the whole assembly will rotate a LOT more with bad transmission/cradle mounts.

At what RPM do these "rough shifts" occur ? Fast idle, 900 rpm step, or 650 (warm) idle ?

To check the cradle mounts, you, the car, and a couple of assistants get into a big, deserted parking lot: Open the hood and all windows (hearing ability). Pick a big clear lane and drive the car straight at 6 mph or so and do a quick stop while craning your neck out the window and looking at the top of the engine: during the quick stop the entire drivetrain will rotate toward the radiator about 3/4" due to the braking effort. Any more that that, suspect cradle mounts..................or, absent a large parking lot, get the car up on a chassis lift and go to work with a crowbar.

Skiller.
09-13-10, 03:04 PM
I don't think there is any specific RPM that it happens. It has happened at a shift point of 2,000 RPM, and it has happened at a shift point of 5,000 RPM...

I can prevent it from happening if I slightly let off the gas before a shift, but if I leave steady pressure on the accelerator, even if I keep it below 2,000 RPM, it will shift rough. Most of the time, it shifts smooth if I push the accelerator all the way down and let it shift...Very strange.

Also, I think it takes off rough from a standstill if I romp on it...
I wonder if it could be low trans fluid, or just dirty trans fluid. With 85,000 miles, I'm not sure if that's a possibility.

Thanks for the response, Jim. I just don't want to start a WOT procedure if I have damaged/broken engine mounts.

Submariner409
09-13-10, 03:26 PM
Also, I think it takes off rough from a standstill if I romp on it...
I wonder if it could be low trans fluid, or just dirty trans fluid. With 85,000 miles, I'm not sure if that's a possibility.

You know the butt plug mod and transmission fluid level checking procedure: is the fluid pink and sweet or is it brown and smells burnt ?? At 85K it should look brand new. You could save up $150 and take it to a GM dealer's Fall Special and have the old DEXRON-III changed to the new recommended backwards-compatible DEXRON-VI synthetic. They'll use a vacuum exchange machine which changes every drop of fluid.

Skiller.
09-13-10, 07:38 PM
I'm hoping it's as easy as a fluid exchange...
Can impact cause engine mounts to fail??

Skiller.
09-13-10, 08:55 PM
Another thing I noticed on the way home tonight...I put the car in neutral at about 30 mph approaching a stop sign. I stopped with the car in N and as I came to a complete stop, there was a thud...I did the same exact thing at the next stop sign except I left the car in D. It did not thud. Does that indicate a problem somewhere?

STSS
09-14-10, 10:07 AM
Another thing I noticed on the way home tonight...I put the car in neutral at about 30 mph approaching a stop sign. I stopped with the car in N and as I came to a complete stop, there was a thud...

I throw my car into N as I come down the driveway, and both cars do the thud... not sure what it is (maybe something to do with the reverse lockout?) but I don't think it's cause for concern.

Skiller.
09-14-10, 10:55 AM
Thanks Jonah...I will just have to inspect all the engine mounts to be sure they are OK. How many are there on the car??

STSS
09-14-10, 11:09 AM
There are technically 4.... the front one, one on each side (sometimes these are refered to as "transmission mounts") and one in the back.

Only the front one and the two side ones are fluid filled, the rear one is rubber coated metal. The chances of the sides failing are pretty slim as they don't get loaded like the front mount. I changed the side mounts on my 01 when I first got it (~5 yrs ago) because I was hoping it would help my front mount last longer.... it didn't help.

I have to do the front mount in both STSs right now... I want to rig up a solid mount instead because I'm tired of changing them.

ponyboyt
09-14-10, 11:33 AM
every northstar ive seen thuds like that when i put it in neutral while moving.

Mine clunks when i let off the gas and hit it again, hard or soft. If i ease into the pedal it doesnt. ... feels like the engine is slamming down onto the mount if i go over speed bump too fast. my 97 and 98 both do that.

Skiller.
09-14-10, 05:07 PM
Ok, so most likely my motor mounts are fine...Under some applications of the throttle, is some movement in the engine acceptable during a shift (Feels like a slight rough shift)?

Submariner409
09-14-10, 07:23 PM
Ok, so most likely my motor mounts are fine...Under some applications of the throttle, is some movement in the engine acceptable during a shift (Feels like a slight rough shift)?

If that transmission doesn't thump you into the seat back on a WOT 1-2-3, something's wrong. A "smooth shift" at 6300 is bad news.

Skiller.
09-14-10, 07:40 PM
Okay. How do you check the ATF with the car running? I tried to start the car with the top of the air filter housing off, but the car shut off immediately after starting...I don't see how you can check the level with that housing in the way...

I was able to see that the fluid is pink and sweet, but I don't think the reading was accurate with the car off. Where should the level be, halfway between the hash marks in the 'hot' area?

Submariner409
09-14-10, 09:09 PM
Okay. How do you check the ATF with the car running? I tried to start the car with the top of the air filter housing off, but the car shut off immediately after starting...I don't see how you can check the level with that housing in the way...

I was able to see that the fluid is pink and sweet, but I don't think the reading was accurate with the car off. Where should the level be, halfway between the hash marks in the 'hot' area?

There should be NO FLUID on the stick with the engine OFF. Your HOT level guess is correct.

The reason that the engine shut off is because you have a divorced MAF - ANY air leak in that ducting from the air cleaner curved spigot to the throttlebody will set all sorts of mixture and O2 sensor codes. (Your code reader probably will now scare the hell out of you) Either do this mod or temporarily plug the resonator hole with a rattle can paint top, then check the transmission fluid normally......use a Philips machine screw in place of the Torx at the PCM cover tab. (You want intake noise at WOT ??? You're gonna get it now.........)

Skiller.
09-14-10, 09:15 PM
Oh, now I see what you did......I understand now...I'll probably just plug the hole...What do you mean by a "rattle can paint top"?

Submariner409
09-14-10, 09:25 PM
Oh, now I see what you did......I understand now...I'll probably just plug the hole...What do you mean by a "rattle can paint top"?


Rustoleum canned spray paint = rattle ball = "He rattle-canned it". Those tops are just about the exact 2 9/16" diameter of the air duct hole. I'm having a plug with retainer ridge (look at the resonator spigot) made out of aluminum. Simple hose clamp job - trim the skirt to remove gross airflow obstruction.........

Skiller.
09-14-10, 09:53 PM
Ah...I have a can of undercoating in the garage...I'll use the cap of that. It just fits in there without any modification needed? I'm not sure what you were referring to when you said "trim the skirt".

Submariner409
09-15-10, 08:09 AM
Ah...I have a can of undercoating in the garage...I'll use the cap of that. It just fits in there without any modification needed? I'm not sure what you were referring to when you said "trim the skirt".

Different rattle cans have caps of different ODs. Find one that fits snugly to begin with.

"Trim the skirt" = airflow restriction removal. If you completely remove the flex tube, as if to clean the TB, and trial fit the cap in the resonator hole you'll see that about 3/4" of the cap hangs down into the tube. Use a Sharpie to mark around the cap skirt when the top is flush with the flex tube hole - pull it out and trim away the excess using small tin snips.

As a heads-up, after a while the plastic caps begin to distort from heat and band clamp pressure (it does not need to be very tight in the first place). So, until you get the "make it better" bug and have a plug turned out of aluminum, check it once in a while....................:lildevil:

Here's another mod - a cool CAI that I picked up from a ricer at the local high school.......:hide:

Skiller.
09-15-10, 09:21 PM
LOL! So I guess Pringles are good for something...

nzane1
09-18-10, 09:23 AM
shop-Reno, $1000, replace motor mounts (how many-didn't ask, didn't tell), order them from cadillac dealer (!?), cost right at $500, the mounts are causing a engine shift that has cause the refrigerant lines (air conditioning) to rub and have worn them out causing a leak - another $500 to replace them - this includes labor. Question - is this a typical diagnostic? Is this a fair price? No details were given regarding the number and kind of parts. Thanks in advance for any input to this. (could I do this myself - motor mounts?).

Submariner409
09-18-10, 06:52 PM
shop-Reno, $1000, replace motor mounts (how many-didn't ask, didn't tell), order them from cadillac dealer (!?), cost right at $500, the mounts are causing a engine shift that has cause the refrigerant lines (air conditioning) to rub and have worn them out causing a leak - another $500 to replace them - this includes labor. Question - is this a typical diagnostic? Is this a fair price? No details were given regarding the number and kind of parts. Thanks in advance for any input to this. (could I do this myself - motor mounts?).

All depends on your car make, year, model, engine. Update your profile so your login looks similar to others ^^^.

On the FWD Northstar packages the motor/cradle mounts can be DIY, but you should really have access to a 4-point chassis hoist and one or two transmission jacks to support the engine/transmission/cradle. It's a LOT easier to work on these things when you're not flat on your back.........

Skiller.
09-18-10, 07:07 PM
Jim, the paint cap worked perfectly. I checked the trans fluid and the level is right where it's supposed to be. I also visually inspected the two side motor mounts inside the front wheel wells. They look fine. Those are liquid filled and there are no signs of any fluid anywhere...