rear axle upper bushing

[Freddyman]

I needed to replace my rear axle upper bushing, and I found there are a couple options from Ford (OEM parts). There's the regular bushing (PN BR3Z-5A638-B) but the 2014 GT500 got a different bushing (PN DR3Z-5A638-A). I ordered both, expecting the GT500 one to be heavy-duty, visibly more stout. Not really the case- the only difference appears to be the center sleeve. On the regular bushing, it's flat steel, rolled into shape. On the GT500, it's a tubular part with serrations. Maybe it's stiffer? I have no way to know, holding them in my hands.

I'm not a big fan of poly in that location, so I'll put in the GT500 (it was only a couple bucks more), but it doesn't look like a huge improvement. In the pics, the GT500 is on the left.

 

[Freddyman]

 

[Norm Peterson]

Those nubs are there to positively locate the UCA in a rotational sense on the sleeve. This sets zero preload at static ride height when installed correctly, and keeps the sleeve from slipping one way and allowing the rubber bushing to be overstressed (think failure in torsional shear or tearing here) when large suspension travel in the other direction happens.

I imagine the reason the GT500 gets that design while the rest of the Mustang lineup gets the plain-ended design is linked to the power/torque levels.

It's a standard OEM approach to guaranteeing that the bushings remain properly clocked, so I'm not sure why there even is a plain-ended version in this instance. One bushing sleeve on each of the OE LCAs that I took off of my 4.6-liter car also has the nubs.


On edit, the GT500 bushing probably is made of firmer rubber, which would be more likely to tear if over-strained by too large a range of suspension travel.


Norm

 

[Grant 302]

so I'm not sure why there even is a plain-ended version in this instance.

It’s so some nickel-hoarder at Ford can justify employment.

 

[67GTA]

@Freddyman - here’s a similar discussion from a while back when I replaced this bushing. If you haven’t tackled the job yet, take a look at the tool that I pieced together to press the bushing our and back in. Makes this a really easy job. Let me know if you’re interested in the Rotunda part #’s or any info.

S197 Upper Control Arm (UCA) Bushings

Recently there was a very informative discussion on the benefits (and limitations) of the different types of UCA's available in the "3Vs...We're Not Dead Yet!" thread (link below). Aftermarket vs OE, fixed length vs adjustable, poly vs spherical bearings, etc...

trackmustangsonline.com

 

[Freddyman]

I should have searched! 67GTA, you already did the leg work for us. Thanks for the offer, but I already spent an hour on the lathe turning some spacers, but I did use 1/2" threaded rod like you did. Norm, you perfectly articulated why I don't want poly in that spot.

 

[Norm Peterson]

Actually, a poly bushing is better equipped to cope with large amounts of two wheel bump suspension travel than a rubber bushing, as it will slide at the surface of the sleeve rather than tear. Meaning that the sleeves for poly bushings can get away without incorporating any means of mechanical interlocking.

That does come with a significant caveat, however. If the poly is longer than its inner sleeve, it's the poly that receives the first compression and the sleeve ends up being not as tightly clamped as the fastener torquing leads you to believe. As soon as the suspension moves, sliding occurs at the faces of the poly and total resistance to the bushing and sleeve moving in the control arm axis direction drops off (usually with a 'clunk' as the bolt to sleeve clearance is taken up).

What polyurethane really hates is to be forced to accommodate rotation about either of the axes that are perpendicular to the sleeve axis. The same stiffness that locates it more accurately for rotation about the axis of the sleeve gets in the way of allowing easy rotation about the other two axes, and large forces are developed in the poly as it is forced to distort. These forces can and will beat up on the brackets and local structure, and will induce generally un-tuneable amounts of roll resistance and wheel loadings that wouldn't be present otherwise.

OE rubber, being much softer, accommodates the same amounts of distortion without generating forces nearly as high. There's no getting around this, given that all of these suspension pivots really need 3D rotational freedom as provided by spherical pivots. Cylindrical bushings can only approximate a spherical - to varying degrees depending on material and other design decisions - because you can't get away from the distortion issues. Not completely.


Norm

 

[Grant 302]

Rubber bushings promote grip largely due to longitudinal compliance of the link. Something that spherical bearings do not provide much of.

The tighter it’s ‘controlled’ at the lower trailing arms, the more the effect can be ‘seen’ at the 3rd/upper link.

 

[302 Hi Pro]

As for the upper control arm axle housing Bush, I used a 5 piece Energy Suspension busking kit. Works great in my application and it’s quiet, no more clunk noises & Zero axle hop.

 

[Grant 302]

And I liked the OP’s first post for showing us the differences in the two parts. One of which is that the GT500 unit has larger voids. I’d choose that one for that reason alone. Higher durometer rubber would still be a benefit, IMO. How much so would depend on what’s being used in the front of the link.

 

[Stangra]

Or... delete that bushing entirely and install a torque arm

 

[Grant 302]

If only they could be easily tunable down to the ~50% ‘calculated’ anti-squat range. My understanding is that wouldn’t be possible.

 

[Grant 302]

Not that most would want to go this low, but my calculated anti squat for the stock Boss is only around 35%.




So I’m keeping my 3rd link and the rubber bushings, thanks.

 

[Stangra]

And I thought we wanted more anti-squat, without negatively affecting roll steer. What am I missing?
____________________________________________________

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cortexracing.com

 

[Grant 302]

And I thought we wanted more anti-squat, without negatively affecting roll steer. What am I missing?

I’d gladly discuss further in an appropriate thread.

 

[Norm Peterson]

Not that most would want to go this low, but my calculated anti squat for the stock Boss is only around 35%.

View attachment 59893


So I’m keeping my 3rd link and the rubber bushings, thanks.

That's only a couple percentage points higher than what I measured my '08 up to provide, at OE ride height, with the shorter early UCA.

I suspect that acceleration launch performance wasn't all that high on Ford's list of priorities. If anything, it's easier on parts (and warranty expense) to let spinning tires act as a fuse to limit loads and stresses on everything involved.


Norm

 

[Grant 302]

That's only a couple percentage points higher than what I measured my '08 up to provide, at OE ride height, with the shorter early UCA.

I suspect that acceleration launch performance wasn't all that high on Ford's list of priorities. If anything, it's easier on parts (and warranty expense) to let spinning tires act as a fuse to limit loads and stresses on everything involved.


Norm

And I suspect they left it mostly alone on the Boss because of its ability to put down power on corner exit.

 

[Norm Peterson]

And I suspect they left it mostly alone on the Boss because of its ability to put down power on corner exit.

Yeah, I think there's something to the notion of using the least amount of whatever it takes to get what you want, so that it doesn't hurt something else too much.


Kind of off-topic, but I'm surprised that Filip seemed to only be looking at LCA inclination for achieving his anti-squat goals - if you play around with the UCA inclination instead, you can increase antisquat without hosing the axle roll steer. I thought the whole point behind the 3-link + PHB arrangement was to be better able to isolate longitudinal tuning from lateral tuning.


Norm

 

[Grant 302]

Kind of off-topic

Pick or start another place to discuss. Sounds like you and Stangra are interested.

 

[EF1]

I needed to replace my rear axle upper bushing, and I found there are a couple options from Ford (OEM parts). There's the regular bushing (PN BR3Z-5A638-B) but the 2014 GT500 got a different bushing (PN DR3Z-5A638-A). I ordered both, expecting the GT500 one to be heavy-duty, visibly more stout. Not really the case- the only difference appears to be the center sleeve. On the regular bushing, it's flat steel, rolled into shape. On the GT500, it's a tubular part with serrations. Maybe it's stiffer? I have no way to know, holding them in my hands.

I'm not a big fan of poly in that location, so I'll put in the GT500 (it was only a couple bucks more), but it doesn't look like a huge improvement. In the pics, the GT500 is on the left.

Did you consider going with a spherical bearing in place of the rubber bushing on the diff end? I don't like poly on both ends. It tends to bind, but poly on the front with a spherical bearing on the rear works well.