Let's analyze this together.

Forget about the wheels, what is moving vertically in the center of the vehicle between 2 and 3 seconds into the video?

 

OK, I too have been reading this thread with interest as I am actually a person that installed the Pfadt component. My intent wasn't necessarily to limit the sometimes excessive wheel hop but, was to better stabilize the rear end when exiting corners while in the lower gears. Anything that improves my track day performance and experience is beneficial, cost limiting of course.

Other than the fact that I am getting too old to squirm around under the car to fit this component, my personal experience and road testing clearly indicates an improvement and a rather significant one at that. Engineering analysis aside, road testing revealed that the rear end is less prone to the loading/unloading of the wheels which certainly appears to happen as the drivetrain reacts to torque rotation under accelleration. Throttle response and corresponding engine output to the wheels in first and second gear is more precisely felt as reduced "flex" in the rear end. This translates into far better oversteer response especially with higher grip tires which one can easily detect. Vehicle feels equally more secure/rigid in higher speed cornering manuvers.

What other metrics do I have? None to be exact. I will better evaluate this component soon at another track day. Until then, keep up the academic arguments going on here. In my previous work environment I witnessed so many students of engineering argue for days and weeks on end over who is correct. Does it help? Sure to a certain extent but not just to prove who is "right." It typically resulted in way too long of a delay to a solution. At least folks like Pfadt racing are willing to apply their real world expertise along with obvious engineering to bring products out for our use. Whether we decide to use them is entirely our decision, right or wrong. And, I don't work for nor know anyone at Pfadt. Trust this is helpful now have at me...

A1

 

A1,

My Pfadt Racing transmission mount will arrive Monday via UPS. I will have it installed by Tuesday evening.

 

I have viewed the video again, and I believe that the components moving vertically between 2 and 3 seconds on it are the exhaust pipes.

Now, if those are the exhaust pipes moving so violently vertically, they are not attached to the differential. They are attached at three points to the vehicle: 1) at the exhaust manifold pierce points 2) Slightly aft of mid vehicle to the springs coming off the floor 3) At the rear of the vehilce through the mufflers.

What's causing this vertical displacement ?

Your thoughts ?

 

I'm not quite following you, Pumba.
I don't recognize the view under the car, so I can't be sure what's moving. Since this is a video showing a change from replacing motor mounts, and I don't recognize any rear end components, I assumed it was a shot of some part of the engine.

To answer your question about what would cause such violent motion if they're exhaust pipes, I guess any violent vibration in the car, since the exhaust is mostly spring mounted.

If someone can explain exactly what that camera angle is, and what we're looking at in the left screen of the video, I'd be grateful.

Why do we want to forget about the wheel hop? It's the biggest known destroyer of drivetrain parts.

Not trying to be difficult, I just really don't understand the scenario that's being presented.

 

I believe that the picture in the right frame is coming from a camera that is attached to the C6 Z06 underbody just ahead of the front crossmember. It is pointing to the rear.

Can someone help me with the picture on the left frame? What am I looking at, and where is the camera mounted?

 

Since it's already been established (I think) that the drive train doesn't roll to one side like an ordinary drivetrain when engine torque is applied, and since any such motion wouldn't be communicated to the suspension anyway (they're connected by CV joints which will bend in any direction and also telescope), and since the differential performs no suspension support function, do you have any thoughts on why the car feels different with the differential brace?

 

Don't recall that the "drive train doesn't roll to one side like an ordinary drivetrain" had been established (at least for my simple mind). If that were the case, it would seem to make sense that the transmission/differential could and would be rigidly fixed to the aluminum subframe that supports this assembly -- it however, is not. For someone that believes otherwise, fabrication of a rigid mount would be very simple and a non-believer should be willing to "volunteer" their vehicle as a test bed since the cast-in differential mount bosses should not break, right? Further, perhaps someone can explain the presence of an "anti-vibration damper" on the left side of the differential which appear to help offset some of the harmonics associated with movement of the assembly. It is not needed when the Pfadt component is installed.

I thought it was agreed, or perhaps not, that the entire engine/torque tube/transmission/differential are basically one unit thus subject to torque flex due to varying rotational forces of the engine. Yes, the CV joints function in multiple planes and yes the differential and halfshafts do not support the suspension. However, it strikes me that the shifting of the entire mass of the transmission/differential along it's centerline contributes to loading/unloading to varying degrees one side of the suspension or another. Beyond this simple explanation/theory, I have no interest in dissection of the Pfadt engineering logic because I am not that intelligent and I am retired. FYI, Pfadt doesn't advertise this as a "differential brace" to my knowledge.

And finally, I just drove my vehicle 20 minutes ago and by golly it is now fun to "act up" exiting slow corners with a heavy foot! Not trying to make light of your questions or show any disrespect however, I again state; no one has to agree with the design/engineering and the best way to show that is don't install this on your vehicle. And, I am not here to defend my decision or their product -- Pfadt seems to be very capable of doing that. Besides, hasn't this thread topic lived it's full life and needs a headstone?

Time for a nap and the comments are only my opinion, nothing more...

A1

 

 

In the other Pfadt thread on this brace, someone just installed it and is impressed with the difference. So it appears to be doing something positive.

 

BACK FROM THE THREAD DEAD!!!!!

I just installed the VBP mount. I don't know how it could get any better as far as just a mount is concerned at transfering all forces into the rear K member or whatever you want to call it.

There won't be any movement and I'm not sure how any more elaborate configuration, given you have to connect the thing to the stock mounting points, could make any better difference.

I'm very pleased and this will compliment solid motor mounts very well. I wanted to change both because I didn't want one to twist more than the other.

 

I JUST installed this mount:



After only a day of driving it was squeaking uncontrollably, very audible from outside the car. Granted, I do not have the torque specs (PFADT guys, please supply?) for any of the involved bolts but they weren't supertight when i took them off, so I did it hand tight going back on. Fastforward to today, driving in a hilly/bumpy area of San Marcos has caused many squeaks and terrible noises. I've been under the car literally once a week checking that the bolts were tight, etc. They're tight onto the subframe, but I'm noticing today that the studs themselves are backing out of the mount. I'm assuming with a mount designed like the PFADT one, where the studs/bolts are (I'm assuming) splined/welded into the steel lower portion of the mount that this will not be an issue.

 

Summary:

Eric: Awesome person, who 'gets it.'

ajg1915: A bitter douche who must've bought one of these before doing his research.

Josh: While being super helpful by answering everything he can, is clearly just a sales rep and not an engineer. It's apparent that the transmount DOES work, but not in the capacity that the sales reps are trained to say. It has a function to stabilize the differential based on lateral movement of the chassis and NOT engine torque.

I don't want to flame a supporting vender, but do I have a couple of legitimate questions for PFADT Engineering. How many licensed PE's does PFADT employ? I appreciate the 3D CAD image of the product that your sent to the CNC guy for manufacturing, but did a PFADT engineer also model the C5 powertrain in real-time and produce an accurate model of the forces generated on the differential housing using something like Pro-E or Solidworks? If not, how can you claim the brace reduces the torque load on the half-shafts? Can you provide the models and calculations that prove this statement?

Sorry if I came off wordy, but I am also a Mechanical Engineer and I always feel the need to fully understand a concept that's not quite sticking for me.

 

Ryan,

What does taking a PE exam have to do with being a competitant engineer? What automotive OEM are you working for in Florida? Oh yes, there isn't an OE automotive company that uses Pro-E or Solidworks.

Why don't you draw all of us a force diagram, with Vectors of the LS powertrain, with the standard differential mount versus the Pfadt mount.

If you are able to understand how Pfadt's differential mount limits half-shaft angular displacement, don't flame on Josh, Jordan, or anyone else.

 

The drivetrain is rapidly loaded and unloaded when the car wheel hops. If the drivetrain is rapidly loading and unloading then the transmission mount is rapidly loading and unloading. During load it's put under compression as the differential pushes down and then when the wheels hop it's unloaded and the differential "jumps" back up.

The rubber mount is similar to putting a heavy short spring under the differential. Under changing loads the differential will start to "bounce" on the spring.

I didn't post this theory before but I'm personally thinking removing the compliance of the rubber mount will greatly improve the situation. The Pfadt mount has a very nice looking round poly bushing in the middle that most likely doesn't allow the transmission to move up and down at all as the drivetrain loading changes.

Eric D posted that transferring the engine power to the road does not cause any side to side twist in the drivetrain. I was thinking a stick axle car lifts the drivers side the same as the engine meaning that a Corvette would have some rotational force in the drivetrain since both the diff and engine try to rotate the same way. But, the diff actually tries to lift the passenger side, the opposite of the engine torque. So, when the engine and diff are directly connected the torque does cancel out.

However, when the drivetrain mounts are subjected to wheel hop maybe the drivetrain still shakes side to side to a certain extent. It doesn't seem to when I'm holding the shifter though because I don't feel any side to side shake. Overall, I just don't think wheel hop results in drivetrain rocking.

Overall, I now think a mount with very little bushing compliance (hard poly) without the side arms would show very similar performance. It would hold the transmission from moving up and down as the drivetrain loading changes. This will also lead to a more positive feel when going on-off the throttle since you don't have the lag caused by the rubber mount compressing and stretching.

I've never seen a C6 transmission mounting arrangement so discussing the possible similarity of the Pfadt to the C6 doesn't really help me. Are there just 2 mounts on each side of the transmission/differential somewhere or does it use more than 2 mounting points?

Peter

PS. I do get wheel hop with cold tires. Once I drive a mile or 2 they are good and don't usually hop.

 

Not sure what you are trying to say? I use the generally accepted definition of angular displacement as the measure of how much, in degrees, a body has been rotated about an axis. In this case, I would call the angular displacement of the half shafts the amount, in degrees, that the half shafts rotate around their axis. Since the half-shafts are 3 pieces I would assign an axis to the center of rotation of each piece. I'm not really sure what any of this has to do with the transmission mount or how it limits this though. But hey, that's just me.

Could you please post where Pfadt has claimed this mount limits half-shaft angular displacement? I missed that claim and would like to see the whole explanation for myself.

Peter

 

I'm not bitter at all. Just tired of a bunch of guys like you making comments about something that you never did any product testing of and making off handed remarks like the ones you made above.

Just show your true colors.

 

I have this mount presently in the car, no noises at all. Not sure how you installed it.

Torque is 37 ft lbs

 

I asked if PFADT employed any PEs since they license this as an 'engineered product.' Even if an EIT designed it, one would still work under a PE. If we found out who the engineer was, then we could ask the source for information ourself and this whole debate would be settled. What's wrong with asking that question?

Assuming this was designed by a real engineer, they would have done some sort of vector analysis on the part in question or else they wouldn't have a need to design a new product. I'm not sure why you are asking ME for a vector analysis model since I didn't design the product. That's why we are asking PFADT for the information and not some random CF member.

That's the whole reason why we are asking questions about the product. If we designed the product, why would we ask ourself these questions?

I don't know if you were asking me or not, but I saw the claim on PFADT's website.

"Our brace will reduce the loads on your half-shafts and other driveline components."

http://www.pfadtracing.com/catalog/p...2dcb8d1743cf7e

 

Your really good at paraphrasing others comments to you and then slanting your reply comments.

BTW, you act like a two year old calling people names.

If these guys were so interested in this products engineering why didn't they come out and say "Hey were automotive engineers and were really puzzled on how this product works" instead of trying to blind side the OP.

I'm all for trading ideas and thoughts but not for bashing someone like you do and the few others in this thread.

Heck theoretically, helicpoters can't fly but they do. Go figure.