nsogiba

What's out there currently? I'm doing a refurb on my drivetrain and was shocked to see how much play is in the stock differential mount when removing the cradle/diff/trans/torque tube assy. The stock mount did not look damaged, just very floppy.

My application is a 2000 FRC 6 speed that is driven mainly on the street/highway with a couple track days in the summer.

NVH going to be unbearable with a solid mount? I think the best happy medium is a poly mount of some sort, just can't seem to find one online right now.

C5 Pete

Hinson has a good piece. Engine mounts and diff mounts.

nsogiba

Is it true that there is a W-Body part that can be used on the C5 as well? Rockauto shows a cross reference between the stock replacement part, implying that the geometry is the same...

Buyer's Guide : DEA/MARMON RIDE CONTROL A2712HY Transmission Mount
BUICK REGAL 1994-1996
CHEVROLET CORVETTE 1997-2004
CHEVROLET IMPALA 2000-2011
CHEVROLET LUMINA 1991-2001
CHEVROLET MONTE CARLO 1995-2006
OLDSMOBILE CUTLASS SUPREME 1991-1997
OLDSMOBILE INTRIGUE 1998-2002
PONTIAC GRAND PRIX 1991-2007

C5 Pete

Personally, I would not trust rock auto info to be correct.

If you go to a parts store and actually hold the part in your hand to confirm, then I guess it could work.

LoneStarFRC

As they often do, it appears as though RA has re-posted/listed information that the manufacturer (DEA/Marmon in this case) provides as to which applications that particular part number (A2712HY) mount fits.
Like Capthuff says the best way to know for sure is to get one in your hands, but I think you also may be able to tell more by doing a simple Google search of that part number and check the "images" listings and compare all the results.

Btw, I checked the RA listing and that mount is "hydraulic", meaning there is a fluid inside (very common, btw) that helps to suppress NVH. While checking, I noticed another manufacturer also offers that same mount in a non-hydraulic version for cheaper money. It's the Pioneer 622712 (note the last 4 digits of the part number are the same as the DEA). I doubt the non-fluid version is any stronger or better, just cheaper.
I would stay with the stocker.

TastyBacon

Yep, I'm using that one, it fits. If "floppy" isn't what you're looking for, though, you should probably skip it...

nsogiba

Yeah, looking at the concept of how the mount is placed (in the center of the drivetrain underneath the diff, you'd need an extremely stiff or even solid mount to really minimize the movement of the drivetrain under load. That's going to increase NVH to a point that I'm not comfortable with.

In lieu of replacing the mount with something stiffer I think I'm going to install a differential torque limiting mount. It uses the stock mount but prevents the drivetrain from twisting. My theory is that keeping the stock mount will keep NVH at an acceptable level.

LoneStarFRC

That looks like a good option for you.

I'm sure this issue of a central location for the mount being more conducive to rotational forces, is what led GM to completely change the design for all the C6 cars, which uses two rear mounts that are widely separated. Better design.

nsogiba

I agree! This was the first time I had seen a C5 drivetrain up close and personal. I am an engineer by trade and my eyes almost popped out of my head when I saw how they had mounted it. It is the weakest way to combat drivetrain twist! The C6 setup makes far more sense.

kirk tarrant

zz performance makes a urethane w body mount...

TastyBacon

I looked into that but read a lot of reports of them cracking. I think Hinson's is better.

nsogiba

Found a Pfadt mount for a song and got it mounted up. Needed to file the holes in the cradle a bit to fit the studs in, I wonder if they warped during welding (they're tacked). Really looking forward to getting it back together!

Patches

I found a used Pfadt mount and had it pc'd to match the rest of the underpinnings. Realize that if you use a used unit, you may need to shim under the pads to ensure any play is eliminated. The original mount package included shims for the installation. Also, I found replacements from an online vendor for the center urethane bushings as the ones in the mount I bought were shot.

nsogiba

Patches, good call - I did a mock up last night on the mount to cradle and found that the Stainless Steel studs actually contacted the corners of the slots in the cradle when inserting. Some quick work with a file on the slots and they fit fine. After snugging up the nuts underneath, I saw that there was a bit of play (probably 1/16" or less) in the unit. It rocked back and forth about the center axis. I placed a thin washer between the Pfadt mount and the rubber pad on the left hand side to "shim" it out against the cradle. No more play. I am curious to see if the constant contact between the rubber and the cradle causes any undesirable NVH while cruising.

My center bushing was in very good shape so I left it as is.

lionelhutz

Except the C5 drivetrain doesn't twist. The torque tube setup means the reaction torque when accelerating lifts straight up on the nose of the car with no twisting imparted into the chassis or drivetrain. This is THE reason GM switched to a torque tube instead of continuing with a driveshaft.

The heavier and wider C6 mounts were to make it more stable and solidly mounted to try and avoid the drivetrain shuddering on the mounts. Also, if you put sticky tires on a C5 and manage to pick the nose off the ground or even come close to picking the nose, then all that weight is put onto the single mount. The C6 design is much better since it has 2 mounts out closer to the frame then one mount in the middle of the aluminum crossmember.

99blkfrc99

What if you get a piece of square steel, bolt it to the diff and cradle and put a few hockey pucks on each end?

nsogiba

The hockey pucks make no difference at that point. The diff is hard mounted to the steel which is hard mounted to the cradle.

On the Pfadt/DTE/whatever mount there is a round rubber bushing that gives some compliance between the diff and cradle. The "arms" act like outriggers to counteract the rotating motion, and the rubber bump stops act as a cushion when contacting the cradle.

99blkfrc99

I see. How bout if you bolt it to the diff, hockey pucks on each end with thru bolts to the cradle. I know it sounds ghetto but I'm trying to engineer one myself in hopes of saving a couple hundred.

nsogiba

You might be able to send thru bolts through the hockey pucks, when you tighten them it will make the puck squish out. There's no "hard contact" there so you run the risk of the nuts underneath coming loose.

You can sometimes find the Pfadt mount used for under $400. I think I got mine for $325. Mine didn't entirely solve my wheel hop though, I'm going to try Pfadt engine mounts next.

99blkfrc99

I'm not a good artist.