Rubber vrs. Poly rear bushings

[1987stangman]

Hi guys, for what ever reason as of late I have been interested in improving my Fox again and been busy getting to all the small stuff that it has needed for a long time.

I bought a set of Prothane rear poly bushings about 2 years ago and over the weekend I got to installing them. At this point I have the whole rear out and have already removed all the bushings including the ones on the diff and I spent some time while it was all out to sand blast, clean, and paint everything.

I spent some time searching on here and noticed that some people like the poly's over the stock and some don't and there are some that say there is a binding issue. Before I go installing these and put everything back together I wanted some feed back from others that have gone full poly.

Keep in mind too this car has never seen any track time and is mostly a weekend nice day to work street ride but I do run it hard.

 

[stang&2Birds]

Simple answer: Anyone that gives you a definitive answer with the info you gave is FULL OF *****!


More detailed:
Your doctor went to school, so did I. So, I say you need a full open body surgery and I can do it in my garage next to my dirt engine parts. WTF??????????


The point: Saying "Poly" and "rubber" MEAN *****!! And, the people generally that blast or praise either often have their head up their ****.

There is a VERY WIDE range of firmness ratings for bushings. So, like I said "Poly means *****"!
Also, there are MANY MANY MANY LCA designs. Some are designed for light QTR mile only use. Many designs are just pure CR*P!


However, in general, if you want to go with ANY "poly" in the rear, then YOU MUST HAVE BATTLE BOXES INSTALLED!

Again, I'm sure there could be some soft ploy LCAs, but they are stiffer than stock. And, you know that even the soft rubber in the Fox LCAs can result in the POS torque boxes being ripped the ****ed out of the body. Sigh.


And, as I said, the designs for ALL REAR SUSPENSION COMPONENT UPGRADES VARY MASSIVELY! Many should never ever be used for a street car.


Summary:
If you want better handling, the safe bet is BATTLE BOXES and the lighter duty MM LCAs.
If you want better QTR mile performance, the safe bet is BATTLE BOXES and the Heavy Duty MM LCAs. If you care mostly about weight for a qtr mile car, then others can suggest what light LCAs are a good choice.


FWIW: My choice is battle boxes and MM adj LCA and BBK rear UCA. Yea, I went with BBK for the rear UCA because I felt they were more compliant. My goal was to replace the old stuff that was worn, and get a sight handling upgrade.


Good luck, and IMHO, even a 100% stock rear should have battle boxes installed. It won't hurt, and could save a huge repair bill for if/when the rear torque boxes decide that to go. It's a well know weak area on the Fox chassis. So, IMHO, it's better to deal before it becomes a problem.


Last: Yea, most doctors don't know what a "full open body surgery" means. So, that's more proof that you need me to operate NOW! BTW, I take only cash and do my operations in some 3rd world country that has basically no laws. See, people like me help to keep down health care costs!

 

[Noobz347]

Geeze 2birds... I'd no idea you were a doctor too!?!

 

[danond]

If you use poly in both ends of the upper control arms, you will get binding. Binding is bad.

Use polyurethane in the lowers, both ends, and get aftermarket arms. They normally come with polyurethane.

I recommend a matched set of control arms, upper and lower, with polyurethane bushings in the lowers and uppers, but use spherical bushings on the axle-side bushing of the uppers.

Big +1 on the torque box reenforcement kit. Necessary stuff if you plan to drive it hard.

Maximum Motorsports has everything you need. Spend time on their site and read their product descriptions. Great info.

--
Dan in ND

 

[1987stangman]

Simple answer: Anyone that gives you a definitive answer with the info you gave is FULL OF *****!


More detailed:
Your doctor went to school, so did I. So, I say you need a full open body surgery and I can do it in my garage next to my dirt engine parts. WTF??????????


The point: Saying "Poly" and "rubber" MEAN *****!! And, the people generally that blast or praise either often have their head up their ****.

There is a VERY WIDE range of firmness ratings for bushings. So, like I said "Poly means *****"!
Also, there are MANY MANY MANY LCA designs. Some are designed for light QTR mile only use. Many designs are just pure CR*P!


However, in general, if you want to go with ANY "poly" in the rear, then YOU MUST HAVE BATTLE BOXES INSTALLED!

Again, I'm sure there could be some soft ploy LCAs, but they are stiffer than stock. And, you know that even the soft rubber in the Fox LCAs can result in the POS torque boxes being ripped the ****ed out of the body. Sigh.


And, as I said, the designs for ALL REAR SUSPENSION COMPONENT UPGRADES VARY MASSIVELY! Many should never ever be used for a street car.


Summary:
If you want better handling, the safe bet is BATTLE BOXES and the lighter duty MM LCAs.
If you want better QTR mile performance, the safe bet is BATTLE BOXES and the Heavy Duty MM LCAs. If you care mostly about weight for a qtr mile car, then others can suggest what light LCAs are a good choice.


FWIW: My choice is battle boxes and MM adj LCA and BBK rear UCA. Yea, I went with BBK for the rear UCA because I felt they were more compliant. My goal was to replace the old stuff that was worn, and get a sight handling upgrade.


Good luck, and IMHO, even a 100% stock rear should have battle boxes installed. It won't hurt, and could save a huge repair bill for if/when the rear torque boxes decide that to go. It's a well know weak area on the Fox chassis. So, IMHO, it's better to deal before it becomes a problem.


Last: Yea, most doctors don't know what a "full open body surgery" means. So, that's more proof that you need me to operate NOW! BTW, I take only cash and do my operations in some 3rd world country that has basically no laws. See, people like me help to keep down health care costs!

2Birds, Thanks for the advice. To be honest, I have read a ton of threads on here over the years and some of your post make me laugh, some I wonder where your head is, but this one made me understand the topic a bit better. No flame intended.

On to the topic at hand.
As far as the tourqe boxes, I'm in the proccess of installing a set of battle boxes and a set of weld in SFC. My tq boxes are in perfect shape and I'm the second owner (owned the car for over 10 years).

Gonna head over to Racer Walsh on the morning and price out some MM adj. LCA's. I did not intend on spending that much on this deal, but I want it right.

I'm going to change direction here and ask another question. The Prothane kit comes with a thurst washer. The instuctions claim this helps side to side movement, would that not compensate for binding?

 

[srtthis]

**** bushings...

SOLID FOR LIFE!

 

[Sharad]

I recommend a matched set of control arms, upper and lower, with polyurethane bushings in the lowers and uppers, but use spherical bushings on the axle-side bushing of the uppers.

Big +1 on the torque box reenforcement kit. Necessary stuff if you plan to drive it hard.

This part I can agree with!

**** bushings...

SOLID FOR LIFE!

My brother from another mother.

 

[SVT32VDOHC]

Install the poly bushings and be done with it.

 

[tunedin302]

Certainly an area to spend some time and research before buying. I found the best setup to be spherical bushings on the LCAs, no UCAs, torque arm, and PHB. Second best suspension setup for me was spherical bushings on the LCAs, FMS UCAs with soft rubber, and PHB. I would advise you stay away from poly on the UCAs because it will cause binding issues.

On the LCAs, the spherical are great for not wearing like poly in high HP applications, better handling, but increase a bit in the NVH; however, if you have moderately loud exhaust you'll never realize the difference in sound.

Good reading: Mustang Rear Lower Control Arm Tech : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

 

[Sharad]

I would advise you stay away from poly on the UCAs because it will cause binding issues.

I've been into Mustangs for 25 years and I've owned literally dozens of them. I've never seen anyone have "binding issues" with poly UCAs. I'm beginning to think this is an urban legend, like sasquatch or something.

 

[rd]

Did the polys everywhere but on the diff back in the 80's. Got more noise, and the poly's wore out in 50k miles. Next time I replace any, they will be stock.

My other Fox has all 1980 original rubber, and they work ok at the track for a 12 sec car with just some band aids. That one has boxed upper and lower arms, air bag, and old school traction bars. And upper torque boxe reinforcements.

 

[myslo50]

Maximum Motorsport. i did a ton of research on control arms for my last stang, found MM bouught a set and never looked back

 

[tunedin302]

I've been into Mustangs for 25 years and I've owned literally dozens of them. I've never seen anyone have "binding issues" with poly UCAs. I'm beginning to think this is an urban legend, like sasquatch or something.

Drive a fox with a t/a setup - big difference.

 

[MFE92]

"Bind" is a misunderstood condition. In this case it refers to wheel rate (spring rate, as seen at the wheel) that is added by different suspension and bushing configurations. Most people don't care about bind until they hit a bump in the middle of their favorite on-ramp going balls-out and wonder why they're suddenly going backwards. Bind causes snap oversteer.

Here, from a long-ago post on another forum...with actual tech, showing how much wheel rate is added from various rear end setups.

While bind is only one of many parameters determining the handling characteristics of a suspension system, it is useful information, and has been a subject of great debate on these message boards. As part of the research we did in developing our rear suspension system, MM has actually done quite a bit of roll-bind testing. I can offer some hard numbers for everyone to consider. I will define ‘bind’ to be any resistance to wheel movement in a roll situation that is not from the spring or sway bar.

Let me say that this information is not intended to be negative toward any particular system, but should be used to gain understanding of the way cars with different setups feel/handle. This information can help everyone to optimize whatever setup they may have.

Of the tests we have done, following are the tests relating to the rear suspension systems most often discussed. All tests are with the sway bar disconnected, cycling one wheel through 3” bump/droop as if in a roll situation. The results are organized in order from least bind to the most bind.

1) 4 Link - LCA with spherical bearings or rod ends at both ends / Stock UCA’s

6lb/in Linear

This shows the stock upper arms introduce 6 lb/in of wheel rate.

2) 4 Link – MM LCA 3 piece poly, spherical bearing / Stock UCAs

9lb/in Linear

This shows an additional 3 lb/in resistance from our 3 piece urethane compared to a rod end.

3) MMTA/PB – LCA with spherical bearings or rod ends at both ends

10lb/in Linear

Here we removed the 6lb/in from the UCAs, but added 10lb/in due to lateral deflection of the TA during roll.

4) 4 Link – Stock LCA / Stock UCAs

11lb/in Linear

This shows that the stock LCA adds 5 lb/in of wheel rate, which is actually more than our LCA of case 2.

5) MMTA/PB – MM LCA 3 piece poly, spherical bearing

13lb/in Linear

Again illustrating an additional 3lb/in additional resistance of our 3 piece urethane compared to the rod ends in case 3.

6) 4 Link – LCA with 3 Piece Urethane at both ends / Stock UCAs

26lb/in Linear

Case 6 shows that the 3 piece poly (or any LCA) works best with a spherical bearing at one end. 17lb/in is added over case 2. Note that the effect of adding a 3 piece urethane at only one end adds 3lb/in. Add it at BOTH ends and the increase is 17lb/in… NOT 6 lb/in as one might expect.

7) 4 Link - LCA with delrin, spherical bearing / Stock UCAs

30lb/in Linear

This shows that delrin does not allow necessary angular deflection resulting in an additional 21lb/in over case 2.

8) 4 Link With PB - Stock LCA / Stock UCA

In the first 1” travel 47lb/in
Between 2-3” of travel 30lb/in Decreasing Rate

In case 8 & 9 the Panhard bar defining a new lower roll center is forcing control arms to travel a new path of higher resistance.

9) 4 Link With PB – MM LCA / Stock UCA

In the first 1” travel 50lb/in
Between 2-3” of travel 30lb/in Decreasing Rate

10) 4 Link – Stock LCA / UCA with rod end at chassis, stock rubber at axle

In the first 1” travel 63lb/in
Between 1-2” travel 39lb/in
Between 2-3” travel 20lb/in Decreasing Rate
Case 10 represents trying to locate the axle with a stiffer bushing configuration on the upper control arms. Since the upper arms need to have an effective length change, the rod end in this case actually creates MORE bind.

11) 4 Link – LCA with urethane at both ends / Stock UCA’s

67lb/in Linear

Case 11 is similar to case 6, but shows that a standard poly/poly control arm does not allow much angular change.

Keep in mind that the above information is with no cornering force on the axle. Therefore, there is a huge gap in this information if you are trying to correlate this data to how these systems would feel in use. I would say that the Torque-arm in case 3 & 5 outperforms any other case shown, although it does not have the least amount of bind in this test. We have begun to build a fixture that loads the axle laterally, as if in a corner, to THEN see how the bind behaves. Any system with a Panhard bar should have no significant increase in bind over what is already shown here. This predictability that a PB provides is why we recommend it on a 4 link (with the correct control arms) for people on a budget, or Solo II Street Prepared cars (not allowed to remove uppers). True, you are inducing bind in this situation, but that bind should not significantly change as you load the suspension laterally. When driving the car, the effective added spring rate (from bind) balances well with the new lower RC, and the improved stability and predictability. YES this is a compromise, but I feel it beats trying to locate the axle laterally with stiffer bushings. Obviously, if the pocket book or rulebook permits, the best thing to do is add a Torque-arm and remove the upper control arms. All this binding is also why you are able to add at least 50lb/in wheel rate to the rear when you add a Torque-Arm and remove the UCAs.

Ehren VanSchmus
MM Design Engineer

 

[tunedin302]

MFE - great info! Thanks

 

[1987stangman]

Well guys, here is what I did. I went poly except spherical bushings on the axle-side bushing of the uppers and kept the stock control arms for now. At this point I have most of it back together, I have to re-install all the drum brake crap as I pulled the whole rear out to clean it. Hopefully I will have the car back on the road next day or 2 and can report back on how it rides.

Next is gonna be a full five lug swap and rear disc brakes as soon as I find a nice set of wheels.

BTW: I did some internet and forums search and did not find any real info (thanks for the above bind post, it was very helpfull) or real world complaints on people that have experianced bind even with full poly. Also, not that they are going to but the instructions that came with the Prothane kit does not warn against bind or mention it.