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Discussion Starter · #1 · (Edited)
I was reluctant to change my IRS bushings because they look like such a pia to do, and because my car has a slight 80 mph vibe. i was worried that the stiffer bushings may make it worse.

While I was watching Shaun work on the center section I finally say how the pumkin mounts into the IRS subframe. The front mounts with two rubber bushings that are not hard to change.

Both steeda and Kenny brown sell bushing kits:
http://cart.kennybrown.com/ProductCart/pc/viewPrd.asp?idcategory=121&idproduct=486

I can't figure how to link directly to Steeda's.

Anybody try these/ Any thoughts on Kenny Brown or Steeda?

I'm thinking about trying a set. If it makes the vibe worse or more noticable, I can easily switch back, unlike the 4 bushings that mount the IRS subframe to the body.

Also, per the two vibe websites (and the TSB) Shaun put the driveshaft back 180 degrees from where it was to see if the vive would get better or worse. It seems to be a little worse. I want to continue with the vibe elimination procedure.

http://home.hiwaay.net/~ctfrench/Driveline Vibration.htm
http://www.lx.net/jlynch/fieldbalance_r1.html
I wonder if it matters if I do it before or after I change the differntial bushings?

For reference as to what bushings are what, in the photo, the IRS bushings are in the read and green ovals, the differential bushings are in the purple ovals.

This pic found online at this site, it is not an '03 IRS, the brace is different, but the bushings are basically in the same spot:
http://www.mouthbreather.net/IRSSWAP.HTML

with me adding the purple ovals:
 

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JT,

Steeda and Kenny Brown get them from the same supplier (according to KB). My opinion on these FWIW is this: If you drag your car more than OT or autocross, skip this mod. The reason I say this is because my car chewed through two sets of these. Here's what I think is happening:

1. I believe that they are graphite impregnated poly and they can't handle the violent compression that takes place when the IRS pumpkin rotates under the onset of serious torque. Personally, I'd like to see these made from solid polyurethane.....I'd deal with the squeaking.

2. I believe that if a rear poly mount was added to replace the stock soft rubber one, in addition to the front mounts, the rotation of the housing would be further minimized and the bushings might survive better.

3. *** The differential housing is different then earlier years. It has been beefed up and as a result, the reliefs that are milled into the cast housing to accomodate the front bushings are not full circles. As a result, the new bushings do not rest completely flat on the surface. Instead a section of the bushing rides up on a ridge leading to abrasion and eventually premature failure.

My $.02

MJ

P.S. Fvckin' Kenny Brown customer service blamed the first bad set on me. Despite me telling them specifically that I used the proper grease they kept saying that I must've used a "lithium-based grease" on the bushings. I didn't so I ended up buying my second set from another vendor and this time didn't grease them at all. Guess what.....they still failed in the same way. KB:hammer
 

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Discussion Starter · #3 ·
MJ,
Thanks for the insight. After looking at how much the pumkin can roatate with hose bushings, I was a little alarmed. I wonder if all three where available, would it be harder on the diff, or not. The diff roataing can not be good for the driveshaft, plus the rotation probaly puts the rear support and the back cover in a bind rather then tension.
 

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mjchip said:
JT,

As a result, the new bushings do not rest completely flat on the surface. Instead a section of the bushing rides up on a ridge leading to abrasion and eventually premature failure.
This is true and I would not recommend installing them this way. I took a file and notched the edges to fit the ridge so that the bushings would sit flat. I have over 100 1/4 launches with these bushings. No problems. For me these bushings alone fixed extremely bad wheel hop. If you don't notch the bushings the crush sleeve will also not completely seat against the outside washers. Provided these areas are remedied I would not think you'll have a problem.
 

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kwladyka said:
This is true and I would not recommend installing them this way. I took a file and notched the edges to fit the ridge so that the bushings would sit flat. I have over 100 1/4 launches with these bushings. No problems. For me these bushings alone fixed extremely bad wheel hop. If you don't notch the bushings the crush sleeve will also not completely seat against the outside washers. Provided these areas are remedied I would not think you'll have a problem.
The second set, I did exactly what you did. I took down the sharp ridge on the housing with a die grinder. I also beveled the edge of the bushing so that it wasn't being pinched. The failure mode on the second set of bushings was slightly different. Only one donut on the second set split and started to squeeze out (top passenger side). This was maybe after about 50 runs of which most 60's were in the 1.7-1.8 range.

The night before FFW Epping I spent 3 hours putting the Ford rubber bushings back in. Still no wheel hop with my BFG 315 DRs.

MJ
 

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Here is the link to Steeda.
Steeda Differential Bushings


I have both, IRS assembly and differential, done and would expect the vibration issue to become more apparent after replacing the differential bushing. The main thing I noticed after installing them is the driveline clunk is more noticeable which should be expected as you are removing the rubber bushings which act as shock absorbers. I haven't had any problem with my bushings, but I would like to see aluminum bushings offered by a vender in replace of the polyurethane ones. I am going to replace my IRS assembly bushings with SHM aluminum version soon.

btw, I made this a while ago to show where each bushing went.
The red circles are the IRS assembly bushings. Sold by MM and SHM
The green circles are the crossmember #4 pinion differential bushings. Sold by Steeda and Kenny-Brown
The blue circles are the LCA bushings. Sold by Griggs Racing
 

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I have installed both bushings, IRS and Diff. I notched the diff some to accomodate the bushings. They did ride on the edge before notching it some. The bushings helped with ride handling and wheel hop. I still have some wheel hop, but it is greatly reduced. Haven't had an issue with the diff bushings coming apart yet. I have about 30 passes after installing the bushings, and about 60-70 before the install. I love the way the car feels after the bushings, except for the increase in driveline clunk.
 

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