J&M polyurethane rear upper control arms discussion. - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 13 Old 09-08-2019, 12:27 AM Thread Starter
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J&M polyurethane rear upper control arms discussion.

Ok, I know that putting poly bushings in the upper control arms could rip up the torque boxes because they do not allow any type of flexing or movement. My question is would the J&M upper control arms with the large flexible spherical polyurethane (not the metal bushings) actually be a better choice and offer more movement/flex than the stock rubber bushings?

My car currently has the J&M upper control arms with Maximum Motorsports lowers. My car is a 1995 mustang GT with Maximum Motorsports full length subframe connectors, Eibach pro kit springs, Tokico blue shocks, poly sway bar bushings with lower MM k-member brace.

The car seems to handle pretty good with this very basic set up. The car dyno's at a very conservative 327 rwhp, and 357 rwtq.

I live in an area with extremely curvy roads, and it's very fun to drive this car on them. However I'm left wondering if the J&M uppers are actually damaging my torque boxes. I've looked at the rear end, and everything seems fine for now.

So basically I bought these control arms as an handling experiment. I just hope my experiment isn't ruining my car. At least maybe they will hold me over until I can get a torque arm.

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post #2 of 13 Old 09-08-2019, 12:41 AM
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post #3 of 13 Old 09-08-2019, 05:01 PM
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The primary reason Ford used the rubber bushings for all the rear control arms was to allow the suspension to twist and "grow" during articulation. This is especially necessary for the uppers because they perform two functions: (i) control axle roll during acceleration/braking; and (ii) control lateral axle movement during cornering. At times, the rears are performing both functions at the same time. With stiffer bushings in the uppers, these functions cannot be performed as designed. Moreover, bind occurs earlier which causes the wheel rate to go to infinity causing unexpected handling issues (e.g., snap oversteer). This is why MM recommends not replacing the uppers with anything but stock bushings or better yet, removing the uppers altogether and replace with a T/A.

When I was faced with this dilemma I first put on the MM PHB and their lower arms. I replaced the stock uppers with the Ford upgrade arms (still rubber bushed). This didn't dramatically improve handling nor ride comfort because bind still occurred. But the RLCAs and PHB provided me with a base for removing one of the uppers otherwise known as a poor mans 3 link (PM3L).

With one upper removed and the other replaced with a one-off custom arm using spherical bushings at both ends not only did cornering and traction improve but ride comfort went way up. The PM3L requires a greater rear spring rate to account for the removed bind designed into the stock converging 4-link. But even higher spring rates, the handling and ride comfort were so dramatically improved I try to push guys in this direction as often as I can. You will not believe the improvement on so may measures. And the PM3L is a relatively cheap solution assuming other rear suspension pieces are already on the car or soon will be. But PM3L is not without it's own issues. The results, however, are pretty amazing.

With the above said, any poly in the two uppers will likely not result in what you are intending short of a dedicated drag car.
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post #4 of 13 Old 09-08-2019, 06:20 PM
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sn95gts331,

It looks like you are referring to the J&M 23970B Upper Control Arms. These arms have a 3-piece poly bushing, similar to the bushings found in the Steeda UCAs I used on my autocross cars for years. I havenít personally used the J&M UCAs, but aftermarket manufacturers use the 3-piece bushing design because itís considered easier on the torque boxes than a 2-piece bushing (and for other reasons).

Iíve done over 100 autocrosses with my Steeda UCAs and the torque boxes look as good as the day they left the factory.

Unless you are doing something illegal and ill-advised, you will not damage your torque boxes by cruising curvy backroads with the OEM or the J&M UCAs.
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post #5 of 13 Old 09-09-2019, 10:10 PM Thread Starter
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Thanks for the replies everyone!

Quote:
Originally Posted by qtrracer View Post
When I was faced with this dilemma I first put on the MM PHB and their lower arms. I replaced the stock uppers with the Ford upgrade arms (still rubber bushed). This didn't dramatically improve handling nor ride comfort because bind still occurred. But the RLCAs and PHB provided me with a base for removing one of the uppers otherwise known as a poor mans 3 link (PM3L).

With one upper removed and the other replaced with a one-off custom arm using spherical bushings at both ends not only did cornering and traction improve but ride comfort went way up. The PM3L requires a greater rear spring rate to account for the removed bind designed into the stock converging 4-link. But even higher spring rates, the handling and ride comfort were so dramatically improved I try to push guys in this direction as often as I can. You will not believe the improvement on so may measures. And the PM3L is a relatively cheap solution assuming other rear suspension pieces are already on the car or soon will be. But PM3L is not without it's own issues. The results, however, are pretty amazing.

With the above said, any poly in the two uppers will likely not result in what you are intending short of a dedicated drag car.
I'm assuming you designed the control arm yourself? This seems like a great idea actually if a Torque Arm is not in the budget.


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Originally Posted by Warhorse Racing View Post
sn95gts331,

It looks like you are referring to the J&M 23970B Upper Control Arms. These arms have a 3-piece poly bushing, similar to the bushings found in the Steeda UCAs I used on my autocross cars for years. I havenít personally used the J&M UCAs, but aftermarket manufacturers use the 3-piece bushing design because itís considered easier on the torque boxes than a 2-piece bushing (and for other reasons).

Iíve done over 100 autocrosses with my Steeda UCAs and the torque boxes look as good as the day they left the factory.

Unless you are doing something illegal and ill-advised, you will not damage your torque boxes by cruising curvy backroads with the OEM or the J&M UCAs.

I had no idea Steeda's upper control arms were 3 piece. I remember seeing them and thinking they were the standard 2 piece so I passed them by. Anyways it is good to know that the 3 piece upper control arms seem to be much better than the 2 piece. At least this gives me a little peace of mind now.
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post #6 of 13 Old 09-11-2019, 09:34 AM
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Quote:
Originally Posted by sn95gts331 View Post
I'm assuming you designed the control arm yourself? This seems like a great idea actually if a Torque Arm is not in the budget.
Nope. The design was developed by Mathis as noted in his Mustangs 2 publication. The arm was fabricated by a guy on CC.com from whom I purchased the piece. He used it on his race car for a couple of seasons. I used it for 3 seasons on my A/X/OT/DD.

As for torque box (TB) damage, I failed to fully address this in my initial post. Upper TB damage occurs because the uppers are trying to move in two plains at once during articulation (roll/lateral axle control). In order to do this Ford used a channel designed arm to allow twist, and softer rubber bushings meant to allow lengthening of the arm through deflection. At some point maximum twist and length are reached causing bind at the bushing. At bind the TBs and axle mounts are stressed since these are the next mounting points. Since the axle is cast iron and the TB is stamped steel, you can guess which is likely to take the biggest hit from a damage perspective. But rubber does not shock the TB all that bad since oversteer generally results in an off-throttle response. The design is to provide time for the driver to correct before bind. Oversteer, especially suddenly and unexpectedly, is a very dangerous situation on the street.

When the upper arms/bushings are replaced with after market units and/or with poly bushings (even 3 piece), Ford's design is compromised. This is because the new arm won't twist, and the poly bushing will not allow the required lengthening during articulation. This has two results: (i) the stress is directly transferred to the mounts where the TB is the most fragile and not designed to carry these kinds of loads, and (ii) snap oversteer occurs much earlier and more suddenly in the turn.

For a drag car these issues are not that much of a concern since lateral axle control (cornering) is where most of the problems are generated. Drag cars reinforce the TB because the shock of axle roll on launch is intense. On the other hand, for a street car cornering happens all the time. And when spirited cornering is involved, the TB is taking a beating with poly bushings, not to mention the oversteer issue. Just my 2 cents.
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post #7 of 13 Old 09-14-2019, 07:31 AM
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Curiously, what if spherical ends are utilized on all points of the 4-link system over the bushed ends?

Essentially articulation would be far greater with reduction or potentially elimination of the binding/snap associated with rubber or urethane.

Yes, the upper geometry would still be off a little and yes there would be more road noise.........

Though a panhard bar and torque arm is ideal, could this be a suitable option for AutoX or road course?

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post #8 of 13 Old 09-14-2019, 10:40 AM
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I don’t think spherical ends can be used at all four points because they will not control the axel laterally. Maybe with a panhard rod.
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post #9 of 13 Old 09-14-2019, 03:37 PM
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Spherical bearings used in all eight locations of a Mustang 4-link rear suspension will result in a lot of binding. I cover why in section 3 of the post below.

https://forums.corral.net/forums/16630714-post11.html

All 4-link suspensions used on a solid axle, bind to varying degrees. A "4-link" with equal length upper and lower control arms which are parallel to each other in the side view and not quite parallel to each other in the top view, will bind the least, but it is really a 5-link because there must be a link added for lateral control of the axle housing under the chassis. The only reason to ever use a "4-link" or 5-link is if the car already has one or the rules require it. In every possible respect you can get better performance from a 4-link ("3-link" plus Panhard bar or Watts link).
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post #10 of 13 Old 09-14-2019, 10:31 PM Thread Starter
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Quote:
Originally Posted by Jack Hidley View Post
Spherical bearings used in all eight locations of a Mustang 4-link rear suspension will result in a lot of binding. I cover why in section 3 of the post below.

https://forums.corral.net/forums/16630714-post11.html

All 4-link suspensions used on a solid axle, bind to varying degrees. A "4-link" with equal length upper and lower control arms which are parallel to each other in the side view and not quite parallel to each other in the top view, will bind the least, but it is really a 5-link because there must be a link added for lateral control of the axle housing under the chassis. The only reason to ever use a "4-link" or 5-link is if the car already has one or the rules require it. In every possible respect you can get better performance from a 4-link ("3-link" plus Panhard bar or Watts link).
Very good information in this thread. However I'm still very curious to the effects of a 3 piece poly urethane upper being the same as a solid two piece upper control arm. Warhorse says the 3 piece poly joint did not damage his torque boxes. Others seem to state that the 3 piece causes the exact same punishment to the torque boxes as a solid 2 piece bushing.

Now I've seen a diagram of a 2 piece polyurethane bushing sheering metal, because it has virtually zero movement. On the other hand the 3 piece bushing should technically have more give than a 2 piece, or even a stock squishy upper control arm bushing. I know the upper control arm design is not ideal, but I wonder if there have been any tests that show movement between arms. I could indeed see how the 3 piece could still tear the torque boxes while drag racing, because the the spherical bushing does not move with forward acceleration.

I also would like to know what kind of rear axle set ups were involved on the 1994-1998 World Challenge Saleen Mustangs with 9 inch solid axles which beat Acura's NSX and the C5 Corvette's in the late 90's. That is of course if anyone knows or remembers.

The IMSA Turbo Mustang GT's and Capri's from the late 70's and early 80's seemed to use a Parallel 4 link design, and put the Porsche 935 on edge with its solid axle set up. I don't think the World Challenge Mustangs used a Parallel 4 link because that would require removing the rear quarter panels, and replacing them with wider pieces.

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post #11 of 13 Old Yesterday, 08:29 AM
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@Jack Hidley, though I can understand where your logic lies, I must disagree with your statement that the design of a spherical 4 link will result in a lot of binding. In a mustang fox body with the factory geometry of the upper arms there will be binding. The point of bind will depend on many variables, torque input, articulation, load, and traction will play important factors.

I'm not disputing that the panhard bar and torque arm system (which Maximum Motorsports is really nice and will be the next upgrade when I'm finally assembled) is superior for AutoX or round course handling (I actually quite like the torque arm for drag as well) when using the stock mustang geometry.

A properly designed triangulated 4 link will offer very little to no bind in the operating ranges its subjected to, again if properly designed.

My curiosity lies in how far off the geometry is with the upper arm in a mustang fox body, and would the majority of bind occur from articulation only, torque input only, or combination of torque, and articulation?

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post #12 of 13 Old Yesterday, 08:35 AM
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I should add that for most (inclusive of myself) loosing the rear seat to correct rear arm length and angle really isn't an option. If it were a race only autoX type car, and the rear seat was removed or rendered pointless it might be a different point of consideration

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post #13 of 13 Old Today, 01:40 AM
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GTS331,

Referring to section 3a of my post above. The main problem with a two piece polyurethane bushing (used in a 4-link suspension) is that with only two pieces (split down the middle), each halve is going to have a constant durometer. This causes a problem because you need the thrust surfaces to be soft to avoid binding from 3a, but the center portion of the bushing needs to be fairly stiff to stop significant changes in the length of the control arm so there isn't wheel hop. With 3-piece polyurethane bushings, it is possible to mold the center portion of the bushing of of a harder material so that the control arm length does not change too much, while using a softer material for the thrust surfaces to minimize binding. See sections 6 and 11 at the link below for a comparison of these two cases. Case 11 uses a 2-piece polyurethane bushings in the RLCA.

Corner-Carvers Forums - View Single Post - Roll bind numbers?

Mr. Heavy,

Post a side and top view of your proposed triangulated 4-link geometry. If it is what I think it will be, it binds significantly. I can prove that fairly simply.

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