rear end bump

[Knight5.0]

I can cruise in 6th gear at approximately 50 mph let off throttle and quickly go to half throttle and i get a loud bump from the rear.. Its very similar to the bump i sometimes hear when i shift hard at 6500-7k. is this just drive-line slop? if so will getting a 1 piece drive shaft get rid of it?

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[EXP Jawa]

It sounds like maybe backlash clunk. There are probably several things that contribute to it, so any one fix will probably not solve it 100%, but you can likely whittle away at it. It might help to get under the car and start identifying what's actually playing a role. Excessive lash could be: ring and pinion lash, axle shaft spline fit (on both ends), the 2-pc prop shaft, lash in the differential gearing, etc.

 

[Knight5.0]

I'm going to be under the car today to change over to BG trans fluid so I will check those things.

 

[Knight5.0]

[ame]https://vimeo.com/160897536[/ame]Normal??

 

[Anthony@HTM]

Lol I have the same shit.

 

[Knight5.0]

Lol I have the same shit.

have you been to the dealer yet? i have been thinking about going but knowing Ford they may say its normal.

 

[EXP Jawa]

What are the baseline assumptions here? Is the transmission in gear, or is it in neutral? Are the wheels on the ground, or is the parking brake set? Ford checks the backlash in the rear carrier in the same basic way when they come off of the axle assembly line, though the axle shafts are held from rotation and they apply a fair amount of torque to overcome any hysteresis that occurs. Of course, there's no prop shaft attached in that check either.

If you turn the companion flange like you're doing, and the parking brake is set to hold the axles from turning, you probably shouldn't have more than 5-6 degrees of rotation. Well, ideally, it would be a bit less than that even, but it would have to be above that limit for the dealer to call it abnormal. On the outside diameter of the flange, that happens to be about 5.5-6 mm of movement. So, for rough approximation's sake, let's say that if a point on the flange moves more than 1/4" when you do that, its probably excessive - for a new part. A broken part will probably have a little more movement allowed.

 

[Knight5.0]

Trans in neutral, tires on the ground, parking brake set. It's moving more than a 1/4 inch.

 

[EXP Jawa]

Then that probably qualifies as abnormal, based on the spec when assembled new. But the dealer might have a differing opinion... If you were guessing, how much is it moving?

 

[Knight5.0]

Then that probably qualifies as abnormal, based on the spec when assembled new. But the dealer might have a differing opinion... If you were guessing, how much is it moving?

I'm just remembering how much I moved it and I can judge what 1/4 inch is. 1/4 inch isn't much. Would they rebuild it or replace it?

 

[EXP Jawa]

I guess that depends on what they found. If its R&P lash, they'd probably just reshim the diff. If its slop in a spline joint, they might replace parts that are involved.

A 1/4" might be more than you think, but still, its hard to judge from the video. If you were to do it again, I'd suggest putting a Sharpie mark on the flange, then put a ruler or scale next to it to get a better handle on the movement.

 

[derieuz]

It's normal for the Torsen diff. I know exactly what you are doing and what noise you are talking about.

 

[Knight5.0]

It's normal for the Torsen diff. I know exactly what you are doing and what noise you are talking about.

I do have to PP car. Just seems like a lot of slop.

 

[EXP Jawa]

It's normal for the Torsen diff. I know exactly what you are doing and what noise you are talking about.

I don't know that I'd call it normal; the Torsen doesn't have a spring preload (like the Traction Lok), which masks some of the lash, so it does allow more to be noticed. But that doesn't mean its a bumpy, clunky part. Gear lash within a modern Torsen is quite good, so something else is at play (no pun intended).

 

[El_Centenario]

https://vimeo.com/160897536Normal??

I noticed the exact same slop in my '15 PP GT when shifting and getting off and on the throttle while cruising. I can hear some kind of a thud sound when throttle off throttle on conditions. I checked it out in my garage and I have the same kind of movement. However, I noticed oil seepage around the pinion seal and the both half shaft seals. It's not dripping oil but it is definitely coming out. This shouldn't be normal at only 14.5K miles. I will check with my dealer to take a look at it and figure out whats wrong. EDIT - I did not have this issue on my first S550 GT A6 car, only in my PP GT

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