14mm IRS bolt question

[2001gunmetalgt]

Maximum Motorsports 03-04 Cobra 14mm IRS Subframe Mounting Bolt [M14-109Bolt] : Lethal Performance, Performance parts for Ford Mustangs


My Cobra is a 2004 later production 04. Anyone got a picture of where this bolt is located to see if Ford put the correct size in from the factory. I dont want to order this and come to find out I never needed it. Thanks. I guess I just check to see if a 14mm socket fits over the stocker and if not then its a 12mm and I need to order this.

 

[SVT32VDOHC]

Pull the lower IRS subframe bolt out and see if a 12mm or a 14mm open end wrench fits tightly around it.

I have a later production 04 as well. I'm gonna do this when the weather gets better to check mine. This in itself should get rid of some wheel hop.

 

[Cobra-21]

I'm pretty sure what you want to check is the FRONT IRS subframe mounting bolts, where the IRS cradle mounts to the back end of the factory frame just in front of the wheelwell. You will need to measure the shaft diameter, not the bolt head.

 

[TORQJNKY]

i'm pretty sure what you want to check is the front irs subframe mounting bolts, where the irs cradle mounts to the back end of the factory frame just in front of the wheelwell. You will need to measure the shaft diameter, not the bolt head.

^^+1^^.

 

[JamesHell]

I have a real late 04 and the front bolt was 12mm. The back one (the one you see when taking off the tire) is supposed to be 12mm.
To get to the front one you have to put the car on jack stands (not under the IRS subframe) then get a jack under the front of the IRS subframe. The spring puts a lot of pressure on the bolt. Relieve the weight of the spring and loosen the bolt and pull it out to measure the diameter of the actual bolt not the head. You probably could just pull the nut off and measure over the threads to give you a good idea what bolt it is. remember dont lower the jack without the bolt in.
Hope this helps,
James

 

[20psirabbit]

i'm pretty sure what you want to check is the front irs subframe mounting bolts, where the irs cradle mounts to the back end of the factory frame just in front of the wheelwell. You will need to measure the shaft diameter, not the bolt head.

+2

 

[Jomo1994z71]

Pics would be sweet...

 

[SVT32VDOHC]

It's the front one where the old lower control arms used to bolt up. Why in the hell would Ford have done that.

I bet that bolt cures a lot of the wheel hop??? Am I right?

 

[mu22stang]

It's cheaper/easier for Ford because the same bolts were used front and back. All Cobras have this and its a good idea to change them. I changed mine and it did little to alleviate wheel hop. ac427cobras kit or something similar is about as close as you can get to "eliminating" wheel hop. That, and careful tire choice.

 

[2001gunmetalgt]

So Should I get the MM 14mm bolts or is there some other type that bruce makes (9/16 or something). I guess both are virtually the same, don't exactly know.

 

[black 10th vert]

So Should I get the MM 14mm bolts or is there some other type that bruce makes (9/16 or something). I guess both are virtually the same, don't exactly know.

Just measure the length of the bolts that are there, and pick up some grade 8 9/16" bolts at your local Ace Hardware. From memory, I believe the length you need is 4 1/2". The length is from the underside of the head, to the end - not overall length!

 

[SonicTerminator]

Just measure the length of the bolts that are there, and pick up some grade 8 9/16" bolts at your local Ace Hardware. From memory, I believe the length you need is 4 1/2". The length is from the underside of the head, to the end - not overall length!

+1 kinda hard to find the low profile ones though. the MM bolts gotta be cheaply made, i rounded the allen head off taking them out. had to beat a torx bit into it to get it out. and no i dont have cheap allen sockets. jap. junk

 

[black 10th vert]

You are right about the low profile ones for the rear, but I assumed he was referring to the front bolts, since the rears have to stay the stock size due to the welded in nuts.

 

[GodStang]

Grade 8 9/16 is the way to go. I have been running 9/16 since 2003. The 14mm still has alot of play in it but the 9/16 has almost zero play. Got mine from Lowes.

And yes its the shaft not the head and its the front bolt not the top bolt.

Here is a write up I did long ago on one of my swaps:


I have gotten a lot of questions on this so I decided to get some info together and will keep adding as I get more. Most if not all 99-04 Cobras with IRS come with a 12mm 10.9 (grade 8 equivalent) in the front of their irs were it connects to the frame. A common upgrade is to get 14mm bolts and replace the 12mm. I was getting ready to upgrade to MM subframe bushings. We were in the store with the front bushing sleeve seeing how well the 14mm fit. It fit a whole lot better than the 12mm. Well as we started to leave my dad grabbed a 9/16" (14.2875mm) bolt and slid it in and it fit perfect. No slop. Well some people asked what is the difference besides less movement of the irs to help get rid of the clunk. So I ran some calculations. Hope this helps.

Tensile Strength of a Grade 8 bolt (10.9 Metric) is 150,000 lbs per square inch.

12mm: 0.1753007in^2 X 150,000 lbs/in^2 = 26295.105lbs

14mm: 0.2386044in^2 X 150,000 lbs/in^2 = 35790.66lbs

9/16in: 0.2485042in^2 X 150,000 lbs/in^2 = 37275.63lbs

So for tensile strength 14mm has 9495.555lbs more than the 12mm and the 9/16" has 1484.97lbs more than the 14mm and 10980.525lbs more than the stock 12mm.

In our application we are more interested in Shear strength then in Tensile strength. Shear strength of a Grade 8 bolt (10.9 Metric) is around 60% of the tensile strength. We are going to use 91,000 lbs per square inch since that is what a lot of people were using.

12mm: 0.1753007in^2 X 91,000 lbs/in^2 = 15952.3637lbs

14mm: 0.2386044in^2 X 91,000 lbs/in^2 = 21713.0004lbs

9/16in: 0.2485042in^2 X 91,000 lbs/in^2 = 22613.8822lbs


So for Shear strength 14mm has 5760.6367lbs more than the 12mm and the 9/16" has 900.8818lbs more than the 14mm and 6661.5185lbs more than the stock 12mm.

I know some people have mentioned NAS bolts. I have looked every where for these bolts and the best I can find is $250 a piece online so I will not be using these on my car. I feel that the 9/16" grade 8 is more than adequate in strength and in size to minimize clunk and help improve the IRS.

Now I am also doing research for a better bolt to go in the top of the IRS so that I will not have to file down head to fit 10.5 rims. Alot of people are complaining about the MM low profile head not being able to be torqued well. Right now the best I can find is $159 for 1 bolt.

Please feel free to ask questions and add info.

Here some pics of the bolts and bushings:

These are the MM bushings with the sleeves notice how two sleeves are narrower then the other two. The narrow two go up top and are 12mm.

Here is the stock 12mm neck to the new 9/16"

Here is the 9/16" and nut

Proof of grade 8

 

[SVT32VDOHC]

^ That is an excellent post above!! So....9/16" bolts are the trick!

 

[Cobra-21]

Grade 8 9/16 is the way to go. ... grabbed a 9/16" (14.2875mm) bolt and slid it in the MM bushing and it fit perfect. No slop.

You said it fits in the MM bushing sleeve...how well did it fit in the actual framerail holes? Any need to ream out those frame holes or not? Im thinking that's where reducing any play would really help reduce a clunk.

 

[GodStang]

You said it fits in the MM bushing sleeve...how well did it fit in the actual framerail holes? Any need to ream out those frame holes or not? Im thinking that's where reducing any play would really help reduce a clunk.

I have had some cars that it slide right in and I have had others that you had to open the whole ever so slightly. Like less then a half a milimeter.

 

[SVT32VDOHC]

A file will open them up. I installed all the 14mm LCA's and bolts on a fox body. I used a 2001 set up and I just filed them out on that car no problem. It won't take much.

 

[spp114]

Just measure the length of the bolts that are there, and pick up some grade 8 9/16" bolts at your local Ace Hardware. From memory, I believe the length you need is 4 1/2". The length is from the underside of the head, to the end - not overall length!

Can someone confirm the 4 1/2" length? I like to pickup a set without having to remove the current bolts?

Also, will I need a washer or lock washer to go with the nut - won't it be difficult to find a nut / lockwasher combo like the stock setup?

 

[Cobra-21]

The length of the stocker is close to 4-1/2" due to the tapered end, but the threaded portion is only 4" as shown in the pics above. I asked at a fastener specialty store about a similar bolt and they didn't have a source for it. I just got the bolts from Lowe's, but they didn't have the locknuts. I got them from the fastener store. They said locknuts don't have the same grading system as bolts, so instead of grade 8, get grade "C".