Less clunk with 14mm bolts(pics)

[hotcobra03]

qoute on pinks

I'm looking at the MM Low Profile IRS bolts on Lethal right now but it doesn't say if they're 14MM, anyone know? I'd hate to get them here only to find out they're still a 12MM

cant stop laughing ,,(20 cars) my buddy was a ricer,,took me 5yrs to get him to switch,,he now drives a 01Lightning,,

hes now a full blown adult:beer:

 

[TERMIN8TR]

ive read that you can check bolts with a wrench on threads...but if its only on some cobras,what was the reason?

wrong bolts first?

ran out of bolts,than used 12mm?

the assembly line operators were having a very hard time inserting the 14mm bolts and the engineers ok's the use of the 12mm bolts from what i understand.

 

[Juruense]

In hindsight clearly the wrong decision!

 

[Steve2050]

This is en easy and inexpensive fix. I'm glad to help out any SVTP members as I've learned tons here about these cars.:beer:

 

[dezracer]

yea, ,my clunk is pretty much gone after installing the 14 ml bolts.

 

[JustaGT]

I put mine in and it helped for sure kind of a pain in the ass to get them and line up though.

 

[COBRA_ESQ]

Can you tell which one you have by the size of the socket that fits the head?

 

[BigBeez03]

I put the 14mm bolts in my car, but did sub frame connectors and MM IRS Grip Box all at the same time so I'm not sure how much the bolts helped. I still have "clunk" when starting off in 1st gear from a stop however I don't get the "pop" I used to have when turning slowly onto an incline (i.e. my driveway).

 

[GodStang]

Guys 14mm is still too small. The correct size to use is 9/16". Been running them for 6 years in many different IRS cars. I have a complete write up on it in the suspension section.

 

[hotcobra03]

bolts

Guys 14mm is still too small. The correct size to use is 9/16". Been running them for 6 years in many different IRS cars. I have a complete write up on it in the suspension section.

question? on the 9/16 bolt is the shoulder longer than the pics of his 14mm bolt?

also i havent looked at mine..but question on the sleeve in bushing,,,ford like to put bumps in the tube to pick up the slack...which didnt work that well after awile:beer:

i worked with the trucks and twin ibeam pivot bushings had them..as did the shocks/trac bar on the superduty,,and many other parts that had bushings in it:beer:

 

[WS6JJP]

Hey Steve, im glad these worked for you!

Anyone else that needs a set PM me.

 

[WS6JJP]

if you cant rid of the clunk forget everything else and do what i did oke:

 

[DaveMan]

Just did this today. WOW! What a difference!

 

[GodStang]

question? on the 9/16 bolt is the shoulder longer than the pics of his 14mm bolt?

also i havent looked at mine..but question on the sleeve in bushing,,,ford like to put bumps in the tube to pick up the slack...which didnt work that well after awile:beer:

i worked with the trucks and twin ibeam pivot bushings had them..as did the shocks/trac bar on the superduty,,and many other parts that had bushings in it:beer:

Like I said I have been running them for 6 years on different cars and love the 9/16"

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]

I made a thread about this last week. I agree....I installed mine and the rear seemed tighter. I didn't have a clunk, but I felt shifting. It's great now.

Between the 275 Nitto Drags and the 14mm front subframe bolt....I have no wheel hop. Teh poly diff bushings I ordered won't even be used. What a waste of 50 bucks. lol

The 9/16" bolt is the best fit, but it would be harder to get started to get in the bushings sleeve. I had a slightly hard time getting the 14mm started since my subframe moved a little. I had it on a hoist and supported, but a friend to help you would be a huge benefit. I was by myself. I used a come-a-long to pull the IRS frame forward....then hit the bolt with a smaller hammer to get it started, then it tapped right in.

 

[hotcobra03]

how about on stock bushings? the 9/16 will fit? How come you dont use a steel lock nut? Im not to crazy about the elastic lock nuts..

than how is the ride feel? What im feelin now is rear end twist...like the rear is steering the car left to right when on than off gas...

kinda seems to me ply bushings are like a bound up rubber bushing...

Bound Up

An overstressed isolation (rubber) mount that transmits vibration/noise instead of absorbing it.

ive used them on the front of differential ..clunk was gone but have a ruffer ride feel...

but it sounds like most are happy after changing to them

 

[SVT32VDOHC]

With the new 14mm bolts/nuts, my 04 seemed to take off straighter and just overall rode better over bumps. I went from F1's and 12mm bolts to Nitto's and 14mm bolts the same day. In the mid 50's....I had no wheel hop. None. The car hooks decent too....once it warms up it will hook 100% with a 275-40R17 Nitto and almost 600RWHP.

 

[WS6JJP]

ive also heard that some people have problems getting the 9/16" bolt in there too. The nice thing about Ford 14mm bolts is they have a flange style head so there is no need for a washer. You'll get more clamping area with a bigger head on the bolt. Also, the nuts are also slightly "ovaled" on one end so they are a locking design, they also have a flange built in too.

 

[hotcobra03]

bolts/bushings

cool...looks like im gonna try just front bolts....


thanks for everyone time:beer:

 

[COBRA_ESQ]

Can you tell which one you have by the size of the socket that fits the head?

Anybody???