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View Full Version : irs rear bolts 12mm or 14 mm ??


mystic04
02-18-2004, 02:18 PM
ok got my 04 mystic have heard a lot fo talk about the rear irs botls that are 12m that are supposed to be 14mm bolts?/ has anyoen here heard for fact that they are to be 14mm bolts .i called SVt they said 12mm my dealer says 12mm . lots of guys eem to be changing over to the 14mm bolts from MM sports wiht the new bushing upgrade i understand that the 04 have a newer typ bushing and maybe they don't have to be changed but the bolts do . due to thread wear and being smaller than thye are suppsoed to be hearign that the holes drilled were for 14mm bolts and ford put in 12mm bolts so anyobdy knwo for sure on this matter. thansk anhead of time for any answer.

Firme
02-18-2004, 03:47 PM
I don't remember the specifics on what Ford stance is, but some IRS's came with 12 and some with 14. I do know that the Urethane bushing upgrade from the aftermarket call for 14 MM bolts in the front as it is stronger.

For a reference, refer to http://www.maximummotorsports.com/instructions/MMIRSU-1r1.pdf

Corner-Carver
02-19-2004, 09:02 AM
Ford goofed and put 12mm bolts in a 14mm sleeve.

The MM bushing kit comes with 14mm sleeves AND 12mm sleeves to match the factory bolts. I've had the bushings sitting on the shelf for 4 months... it's not a job I look forward to. I fugure when I do coilovers, I'll do the bushings at the same time so I won't have to fight the springs pushing the IRS around.

Firme
02-19-2004, 10:11 AM
Originally posted by Corner-Carver
Ford goofed and put 12mm bolts in a 14mm sleeve.

The MM bushing kit comes with 14mm sleeves AND 12mm sleeves to match the factory bolts. I've had the bushings sitting on the shelf for 4 months... it's not a job I look forward to. I fugure when I do coilovers, I'll do the bushings at the same time so I won't have to fight the springs pushing the IRS around.

I've had mine since Christmas...:D

This weekend, If i can get 6 jackstands, I will start the project.. I'm putting in the Upper and Lower Control arm urethanes also

mystic04
02-19-2004, 01:50 PM
Originally posted by Corner-Carver
Ford goofed and put 12mm bolts in a 14mm sleeve.

The MM bushing kit comes with 14mm sleeves AND 12mm sleeves to match the factory bolts. I've had the bushings sitting on the shelf for 4 months... it's not a job I look forward to. I fugure when I do coilovers, I'll do the bushings at the same time so I won't have to fight the springs pushing the IRS around.
All i want to do is change the bolts not put new bushing in i understand the 04 has better bushings already instaled. from what others have said. so is it just 2 bolts that need to be changed or 4 ??

pdogkilr
02-21-2004, 09:20 PM
Dugan Racing is installing a complete set of IRS bushings Monday on my '03.

I ordered the 14mm bolts and nuts with the bushing kit from MM. I don't care what came in the mustang, 14mm is going in with the bushings. I read MM's web site info and just to be on the "safe" side, I think the 14s are the way to go, if you are doing anything where the bolts come out.

Other than that, if it ain't broke .........

I would not change the bolts just to be changing them, unless you are having some vibrations that you can directly link to the IRS bushings, or control arms.

Just my .02c

Firme
02-22-2004, 01:39 AM
I just realized you asked about the rear....I was confusing myself, but now that I am looking at it, the 14mm goes in the front and the 12mm goes in the back. I don't think you can swap a 14mm in the back because the nut is welded on and is a 12.... I will verify though..

mystic04
02-22-2004, 10:41 AM
hey thanks for the answer will be waiting to hear more.

Racer_726
02-22-2004, 09:51 PM
Originally posted by Corner-Carver
Ford goofed and put 12mm bolts in a 14mm sleeve.


That's also what MM sais about some of the 03 cobras, but I really don't subscribe to this theory. I have installed 2 1999 IRS's in live axle cars, and both have had the 12mm bolts up front. The chassis holes are big enough for 14mm, and the bushings are big enough for 14mm, so why the 12mm bolts then, some may wonder? Must be a mistake by Ford! I'm not so convinced.

First of all, the bolt's function is to squeeze a sleeve, which is what holds the subframe up in the frame. This sleeve is serrated on the OEM bushings, and once the bolt is torqued, there is no play back there... the sleeve will not move, even though there's a 2mm gap between it and the bolt.

Second, the smaller bolts allow the rear subframe to be more accurately positioned in the frame, which is subject to wider manufacturing tolerances. The 2mm helps in alignment and makes it easyer to install on the assemble line. The parts books all call for 12mm bolts back there as well.

For the urethane subframe bushings, it's a good idea to use the 14mm bolts, even though MM's bushings are way ovesized. There are no serrations on the crush sleeves, and the 14mm bolts will reduce the likelyhood that there's any movement between the frame and the crush sleeve. The exception would be if the 14mm bolt is difficult to install due to misalignment, then a 12mm bolt may be retained. Just what i think about the matter, not like it does matter I guess.

Dave