Review: The complete IRS Delrin/UHMW/Aluminum bushing package

[Snake Eyes]

Below is my full review of Bruce aka ac427cobra's IRS Delrin/UHMW/Aluminum bushing package.

Initial Impressions:
As I opened the kit the first thing I noticed was that each set of bushings were packed separately with labels text side out in clear zip lock bags. The parts are top quality. In my opinion these bushings are of the same quality as Maximum Motorsports or Griggs Racing's parts. Everything is exactly as pictured in Bruce's pictures and no corners were cut.

Install:
Having done lots of automotive work including nearly every mod done to my cobra, these bushings are not easy to install but that isn't to say that is a negative on them, it just isn't an easy job. But if you compare how difficult these bushings are compared to some others I have encountered I would say they are as install friendly as you can get. Bruce has paid very close attention to detail once again and made many refinements to make things as easy as possible but don't attempt the install unless you have the proper tools, a lot of time, and a load of patients.

Driving Impressions:
The first thing you will notice is the planted dependable feeling the rear end gives you after install. The rear end is now planted and the first test is straight line acceleration.... YES no hop! The car either grips and goes or spins the rears depending on the available traction. I personally spun all the way through first gear and in to second with out a hint of hop. Turning under acceleration no longer feels uneasy. The car feels like you are driving on rails when on smooth roads. Bumps and road irregularities no longer agitate the car, the suspension now absorbs those without transmitting them to the car and the cars manners while on poor roads is that of a true modern sports car. While this may seem counterintuitive to what you would think with solid bushings installed but the bushings allow the suspension to do what it was originally designed to do before the NVH engineers lowered the bushing durometer to that of a marshmallow. While there is a small increase in road noise transmitted to the car, it is not even noticeable when a loud exhaust is present or the stereo is on. The largest increase in noise is from the differential because of the solid mounting but a little gear whine is tolerable. It is akin to the amount of noise increase going from the stock shifter to an aftermarket unit without the use of sound deadening materials. I have been flogging this suspension for weeks now and have yet to find a single flaw. In my opinion this is a must mod for any IRS equipped mustang owner who is serious about their vehicle's performance. If you are willing to put money in to the motor, or the appearance, put a little in to the handling of your vehicle you wont be disappointed.

IRS vs. Solid Axle:
For the last time I wish to say it, though I'm certain I will have to many more times. The ONLY time I believe anyone should swap their independent rear for a solid axle is if drag racing has become more important than any other use of the car and you are willing to make sacrifices in handling and road manners. In my opinion the IRS is the superior suspension system and Chuck Schwynoch, CEO of Maximum Motorsports agrees (link).

Final Thoughts:
I could not be more pleased with this kit. I have been advocating the system approach for years and it is nice to see someone address the bushings and differential bushings with such attention to detail while keeping costs to a minimum. I see absolutely no reason to purchase these parts from any other vendor. These are the best parts and the best deal. To top it off, Bruce is a great guy to deal with and stands behind his parts and is willing to answer any questions you may have, honestly I might add. Your mileage may very but I recommend these parts with no hesitation. I would be glad to answer anyone's questions with regards to my experience with these parts, other questions about the IRS, Mustang suspensions, or any other topic.

Additional Links:
My Technical Write-up on the 1999-2004 Mustang Cobra Independent Rear Suspension
The IRS Tech Article

Full Details on my Car
My Cobra

The Bushing Kit Reviewed Above
The complete IRS Delrin/UHMW/Aluminum bushing package

[Quadcammer]

nice write up. I agree that the IRS can be modified to be an acceptable suspension package.

However, while the bushings make it work the way it should, for people with more power than stock, things like the diff brace and some upgraded half shafts are a must.

Further, I've found that the IRS hops the most on the cusp of wheel spin. When you bake them, its fine, but when you are right on the edge of spinning and gripping, thats when the hop is the worst.

I guess what im saying is that both the SRA and the IRS can be made to work well. For my power level and driving requirements, I've found that a simple, well sorted SRA setup works very well at a MUCH lower price.
This is purely for me though, and I cannot speak for others.

I think that you will enjoy your new suspension setup.

thanks again for the writeup.

[01 Venom]

very nice write up, thanks for sharing. For my purposes the IRS is great. A few more things go on this friday

[01cobravortech]

I enjoyed the writeup and know exactly what you're saying since I had all the MM IRS bushings in my old 01 Cobra. Its a very different feel to the car and even I can tell the difference in the way my 03 drives in relation to the way my 01 did with all the bushing upgrades.

[Snake Eyes]

Actually I have had a built IRS for quite some time now. Bruce asked if I would be interested in reviewing the kit and I thought it would be best to remove the mishmash of parts I had and replace them all with a single manufacturer's kit. Plus I feel a bit of an obligation to the Mustang community to continue to provide unbiased and objective advise and suggestions. And with Postban gone I get a lot of questions regarding the IRS and I cant fully recommend a part unless I have used it.

As for the IRS vs. SRA debate, I state my opinion and don't want this thread to turn in to another debate on the topic but if you actually compare a build IRS (minus level 5 half shafts) vs. a torque arm panhard bar SRA the built SRA costs more, period. If you leave it in it's original 4 link configuration then yes the SRA is cheaper but it is in no way in the same class as a built IRS. In an apples to apples comparison a stock for stock the IRS is a superior suspension and in a built vs. built comparison the IRS comes out on top again. People associate high cost with the IRS because of the DSS half shafts but they really are NOT needed unless you are making serious serious power. When you eliminate wheel hop you eliminate huge stresses on the shafts and can use stock 03 shafts or a set of Raxles for almost anything except high horsepower dragstrip runs on slicks or DRs. So unless every tenth matters in the quarter I recommend a modified IRS as detailed in my IRS Tech Article.

[ReallyRedCobra]

Good write up. I'm considering getting this kit since I've been bitten by the autocross bug, and my car is going to be out of commission for the winter anyways.

[ac427cobra]

Kyle:

I'm glad you like the results of the kit! The transformation the IRS goes through is really hard to describe. But you did a great job of it.

Enjoy the new feel of your car!

Originally Posted by quadcammer

However, while the bushings make it work the way it should, for people with more power than stock, things like the diff brace and some upgraded half shafts are a must.

quad:

I am of the opinion that possibly 80% of the people that upgrade to Level 5 halfshafts don't need them.

I agree with you that the 1999 28 spline halfshafts are not very stout. But the '01-'04 31 spline halfshafts should be sufficient for 90-95% of the people's needs. It's only the guys putting down more than 500 hp and pounding out holeshot after holeshot at the drag strip on slicks or DR's that need them. It is also my opinion that 90% of the broken halfshafts are NOT broken from sheer power. They are broken due to IRS assemblies and differentials gyrating and wheel hopping out of control because of all of the rubber mounts. Plain and simple.

FWIW

[Posi Performance]

Bruce you know I'll be getting the kit when the funds(WIFE) allow me to do the purchase!

[wikedcobra312]

nice write up

[BreBar21]

I was ruined my by the old Brand N delrin. I absolutely loved how the car handled. It felt much more solid everywhere. That was fun for about 3 months and then the bushings started squeaking over every little bump. It was LOUD. It drove me insane, so I took them out and put stockers back in.

How are these are far as squeaking is concerned??

[Snake Eyes]

I haven't had these bushings installed that long but I installed grease fittings in the LCA arms so if the bushings start to squeak, I just grab the grease gun and add grease until it squirts out and you are golden again. You will notice that the LCA bushings are a two piece design so if you inject grease between the two bushings you will have a large quantity of grease to keep the bushings quiet and if they get loud adding grease in the middle forces it out toward the ends. Simple but effective. The UCAs too far up in to the car to make a grease fitting useful but Bruce has machined a grove in the middle of the bushing to hold additional grease to keep them from making noise. The UCAs do not experience the loads that the LCAs do so I doubt they will squeak at any time. That is my experience so far.

[E. Green Cobra]

Can't wait for the cooler months to tackle my install!

[poneypower]

I've made over 10 runs at the strip this year with Bruce's kit installed. I still get a tiny bit of hop, but I think that is more due to the tires I am running than anything else. The hop is no where near where it was last year without the kit It did totally transform the feel of the car right out of the gate.

oh and snake, none of those links work....you get put to a page saying:

On to the new server.
This time for good

I hope ! Click here: http://69.13.120.175/forums/index.php


btw....can anyone tell me where the search button went?

[ccbdesign]

TO save a bunch of typing, after installing this, I agree 100% with Snake Eyes on the outcome of this project...

Quote:
Driving Impressions:
The first thing you will notice is the planted dependable feeling the rear end gives you after install. The rear end is now planted and the first test is straight line acceleration.... YES no hop! The car either grips and goes or spins the rears depending on the available traction. I personally spun all the way through first gear and in to second with out a hint of hop. Turning under acceleration no longer feels uneasy. The car feels like you are driving on rails when on smooth roads. Bumps and road irregularities no longer agitate the car, the suspension now absorbs those without transmitting them to the car and the cars manners while on poor roads is that of a true modern sports car. While this may seem counterintuitive to what you would think with solid bushings installed but the bushings allow the suspension to do what it was originally designed to do before the NVH engineers lowered the bushing durometer to that of a marshmallow. While there is a small increase in road noise transmitted to the car, it is not even noticeable when a loud exhaust is present or the stereo is on. The largest increase in noise is from the differential because of the solid mounting but a little gear whine is tolerable. It is akin to the amount of noise increase going from the stock shifter to an aftermarket unit without the use of sound deadening materials. I have been flogging this suspension for weeks now and have yet to find a single flaw. In my opinion this is a must mod for any IRS equipped mustang owner who is serious about their vehicle's performance. If you are willing to put money in to the motor, or the appearance, put a little in to the handling of your vehicle you wont be disappointed.


It is a costly project with a lot of work to install. Bruce's tools really make the job much easier and can't image trying to do the job with out them. My car really does handle better and with brand new Goodyear's F1 295zr18, when they break loose now, they just spin. Before they would be hopping all over the road..... I want to thank Bruce for the great job on providing the parts, tools, labeling, packaging, and instructions. They are excellent as well as the quality of material he is supplying. I am very impressed with his expertize on this. Anybody wanting to really make a difference in the rear end on their IRS, this upgrade is a must....
thanks again Bruce....

[SID297]

very nice write up