Manual Trans. Thud when shifting

[NvrFinished]

Here you go... from post #689

It's called "Stick-slip". It's basically a jerking motion that happens at the interface between the driveshaft and the coupler that allows for in and out play on the transmission end. It all spawns from the friction surfaces at that intersection. I was actually talking about this with a coworker and her mentioned how he published an SAE paper on the study of stick-slip between plunging driveline (i.e. driveshaft in our Mustangs).

Another thing to note: most any RWD, torquey car or truck will have this phenomenon occur. Completely normal and very difficult to engineer a solution to.

One thing I'm curious about is if anyone who has gone to a 1 piece driveshaft has dampened or eliminated the clunk.

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[mada808]

Here you go... from post #689



One thing I'm curious about is if anyone who has gone to a 1 piece driveshaft has dampened or eliminated the clunk.

I'm no engineer so I'm still confused how this happens to some and not others if it's "natural".

 

[Hwy1]

I'm no engineer so I'm still confused how this happens to some and not others if it's "natural".

Its not that some don't have it, all of them have , but different degrees of loudness..

 

[mada808]

Its not that some don't have it, all of them have , but different degrees of loudness..

ah ok makes sense.

 

[woofwoofdroolyface]

Head over to post #689 for a very high level explanation.

Here's a link to the paper mentioned:

http://papers.sae.org/2015-01-2171/

$25, anyone have access? Notice Ford is listed as an affiliated party on the publishing of this paper.

 

[woofwoofdroolyface]

Here's a list of possible solutions mentioned in the thread to reduce the thud (at least apparent to the driver) to summarize:

- BMR BK054 Rear Differential Bushing Kit
- BMR CB005 Rear Cradle Bushing Lockout Kit
- Steeda S550 IRS Subframe Alignment Kit
- Whiteline Transmission Bushing Mount Insert
- Blowfish Transmission Bracket

 

[FordTechOne]

Please everyone, take a minute to google "RWD shifter thud". You will find thread upon thread of people mentioning this same issue on multiple vehicle platforms.

This is an extremely complex engineering issue that is indeed a well known problem with N/S RWD oriented vehicles. Feel free to go berate your dealer and mention how OEMs have terrible quality but if you look closer, this is actually an issue you should take up with the laws of physics.

You seem to be the only person who actually understands that that this is a NORMAL characteristic of almost all RWD vehicles. Seems that a lot people on here who hear ANY noise and assume their vehicle is going to blow up :headbonk:

S550 Mustangs use a 2 piece driveshaft to optimize driveline angles and minimize vibrations, and they do a damn good job of it. The downside is additional driveline lash caused by the long 2 piece driveshaft and center support bearing.

If you want to eliminate a lot of the driveline lash and bangs/clunks, then get an aftermarket 1 piece aluminum driveshaft. Vibrations may increase slightly, but you will have less rotating mass and much less driveline lash. My 04' Cobra came from the factory with a massive 1 piece aluminum driveshaft, and I wouldn't trade the slightly better NVH for a 2 piece unit.

 

[fogus]

You seem to be the only person who actually understands that that this is a NORMAL characteristic of almost all RWD vehicles. Seems that a lot people on here who hear ANY noise and assume their vehicle is going to blow up :headbonk:

S550 Mustangs use a 2 piece driveshaft to optimize driveline angles and minimize vibrations, and they do a damn good job of it. The downside is additional driveline lash caused by the long 2 piece driveshaft and center support bearing.

If you want to eliminate a lot of the driveline lash and bangs/clunks, then get an aftermarket 1 piece aluminum driveshaft. Vibrations may increase slightly, but you will have less rotating mass and much less driveline lash. My 04' Cobra came from the factory with a massive 1 piece aluminum driveshaft, and I wouldn't trade the slightly better NVH for a 2 piece unit.

Is the drive line the bit that goes from the transmission to the rear dif or a part between the engine and the transmission?

If it's the former, then I don't see how it's mass is relevant: we experience this with the clutch in and at a standstill. Wouldn't any drive line mass be dominated by being tied fairly directly to the road?

 

[WeinerDog]

You seem to be the only person who actually understands that that this is a NORMAL characteristic of almost all RWD vehicles. Seems that a lot people on here who hear ANY noise and assume their vehicle is going to blow up :headbonk:

S550 Mustangs use a 2 piece driveshaft to optimize driveline angles and minimize vibrations, and they do a damn good job of it. The downside is additional driveline lash caused by the long 2 piece driveshaft and center support bearing.

If you want to eliminate a lot of the driveline lash and bangs/clunks, then get an aftermarket 1 piece aluminum driveshaft. Vibrations may increase slightly, but you will have less rotating mass and much less driveline lash. My 04' Cobra came from the factory with a massive 1 piece aluminum driveshaft, and I wouldn't trade the slightly better NVH for a 2 piece unit.

We aren't talking about driveline lash! This is a completely different sound. Damn, this is so frustrating. I've had plenty of RWD manuals and none did this. I still have my 2010 GT and it does not do this.

I'm NOT worried about it blowing up, the sound is what bothers me. Why is this so hard to understand? I'm not calling you out but it just seems some folks are talking about something other than the issue.

I hear lots of slop and lash in my 2010...that's not what we are talking about here. There's very little slop/lash in my S550.

The weekend is here, I will try to get a video of what is going on. I don't know if I can capture the sound though, it is so low like a subwoofer turning on. BOOM! NOT driveline lash.

 

[fogus]

We aren't talking about driveline lash! This is a completely different sound. Damn, this is so frustrating. I've had plenty of RWD manuals and none did this. I still have my 2010 GT and it does not do this.

Yeah. I think you're right. When I first got this car it was my first RWD car and first manual. I got lash a lot because I couldn't control the clutch well. Now I don't get it anymore. I get thud though.

 

[FordTechOne]

We aren't talking about driveline lash! This is a completely different sound. Damn, this is so frustrating. I've had plenty of RWD manuals and none did this. I still have my 2010 GT and it does not do this.

How do you know it's not driveline lash? Did you place the car on a loaded dyno and observe the driveline as the vehicle was accelerated? Did you use a vibration analyzer or chassis ears to determine which component was inducing the clunk/noise? A 2010 GT is a completely different car. You need to compare apples with apples.

 

[fogus]

How do you know it's not driveline lash? Did you place the car on a loaded dyno and observe the driveline as the vehicle was accelerated? Did you use a vibration analyzer or chassis ears to determine which component was inducing the clunk/noise? A 2010 GT is a completely different car. You need to compare apples with apples.

Uh, you did just say it was a normal characteristic in almost all RWDs.

Now a previous gen mustang is an invalid comparison?

 

[FordTechOne]

Uh, you did just say it was a normal characteristic in almost all RWDs.

Now a previous gen mustang is an invalid comparison?

Yes, because a completely different car is going to have different characteristics. It's not that hard to understand.

All RWD cars will have more driveline lash than a FWD car because they have a longer driveline with more components. The extent of the noise/lash is entirely dependent on the model.

 

[WeinerDog]

Yes, because a completely different car is going to have different characteristics. It's not that hard to understand.

All RWD cars will have more driveline lash than a FWD car because they have a longer driveline with more components. The extent of the noise/lash is entirely dependent on the model.

Do you have one of these cars and/or have you heard in person what we are talking about?

 

[WeinerDog]

How do you know it's not driveline lash? Did you place the car on a loaded dyno and observe the driveline as the vehicle was accelerated? Did you use a vibration analyzer or chassis ears to determine which component was inducing the clunk/noise? A 2010 GT is a completely different car. You need to compare apples with apples.

How much of this thread have you read? It's not lash because it happens BEFORE you engage the clutch/transmission. It happens clutch IN...no way for lash in that condition. Unless we differ on the definition of "lash".

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