IRS vs SRA
06-02-2010, 03:43 PM
#1
6th Gear Member
Thread Starter
Join Date: Oct 2006
Location: Texas
Posts: 10,551
IRS vs SRA
A member on the board asked if a couple others or me could compile a fact sheet of sorts for Mustang rear ends. Ill do my best to describe everything as best I know, feel free to add on/correct any of the info. I’m going to try to explain this thread in layman’s terms, so I will not get into the super technical aspects of the rear ends themselves.
Here is probably the most complete suspension article for our cars: Jazzers Page
SRA Info:
Ok, so lets start with the basics. The SRA (solid rear axle) is in the V6, GT, Mach 1’s, 96-98 Cobras. The SRA is a very, very simple rear axle design, and is a decent platform for anyone who wants to do straight-line racing. All you need for serious power is a set of decent lower control arms, some upper control arms and a 31 spline set up and you can call it a day. However, this may shock some people, but not everyone finds racing in a straight line to be all that fun.
Open track racing and autocross really expose the weakness of the SRA. The 4 link set-up really is a **** poor design by many peoples standards, and needs a decent amount of parts to get a predictable feel from the axle. With the correct parts, a stick axle can be made to eat a road course for dinner.
The main issue with the SRA in the handling department is getting rid of the 4-link setup. Ideally you would want to do a Watts link setup/torque arm combo. This will take car of most every geometry issue the SRA has. But this comes at a price, comfort. Also, some will find that their watts link doesn’t allow them to run tailpipes (if this is a big deal to you, buy a panhard bar instead, just know a panhard bar does not help as much as a watts link).
Here are a few Stores that carry the parts to turn your SRA into one bad ****:
Maximum Motorsports
Griggs
Further SRA Info:
Torque Arm Recommendation Table
Watts Link Theory
Now don’t get me wrong, just because you do a TA/WL setup does not mean your going to have a super harsh ride. BUT, it is just a fact that you will have to run stiffer torque arm springs in the rear, which those alone will cause a harsh ride. Some may find this uncomfortable, but this setup on an SRA really does handle with the best of them.
IRS Info:
Now, for those of you out there who are more interested in a comfortable daily driver, that handles well the Independent Rear Suspension or IRS may be an option for you. This is a common swap for GT owners and Cobra owners who have opposite goals. Cobra owners who want to drag race, but don’t want to spend a fortune upgrading their IRS to handle their power level find the SRA to be the best option.
The Mustang IRS is the best option for comfort and handling that Ford offered from the factory. Unfortunate, It could be better. To make everything easy on themselves, Ford decided that they would design the IRS to be a direct mod to the existing chassis of the Mustang. This is good for people who want to swap, but it led to an IRS that could be better.
Many issues come along with the IRS; the main one is wheel hop. 99 Cobras have the weakest one. These assemblies are 28 spline setups and have the weakest halfshafts. 01 Cobras have 31 spline setups but also have weaker half shafts, but these assemblies are considerable stronger than the 99 assemblies. The 03/04 IRS assemblies are 31 spline setups with carbon clutch packs and stronger half shafts. These assemblies are the holy grail of IRS swaps, just because they are the strongest. Many parts exist to build up the IRS assemblies to handle power, but they are not cheap. Differential braces, bushings and halfshaft upgrades are a must for anyone going to a lot of power.
The IRS assemblies handle noticeable better than a stock or mildly modded (no watts/TA combo) and ride very smooth. This is why a lot of SRA Mustang owners like to swap with Cobra owners.
Here are some great stores for IRS parts:
Maximum Motorsports
Full Tilt Boogie Racing
Further IRS Information:
IRS Bushing Locations
More In-depth IRS Research
SVTP Postban Article
***My personal opinion is that while the 03/04 setups are the best, if your not going to abuse your car, any IRS assembly will suffice***
************************************************** **************************
What an SRA/IRS swap call for:
Having done one myself, the swap is bloody simple. Basically, 4 bolts is all it takes with a couple small steps in between. All parts will be a direct swap in New Edge cars. The actual list of parts that need to be swapped will vary depending on years of the cars used. The differential tail shaft bolt pattern(the piece that connects to the driveshaft) and transmission will determine if the driveshafts/tailshafts need to be swapped.
From the Cobra you may or may not need (depending on year of Cobra):
Driveshaft
Rear brake lines/calipers
IRS assembly
You may need to swap tail shafts
IRS exhaust
ABS harness
Mounting brackets for lower IRS bolts
Front/rear springs (to avoid any retarded spring matchups)
If wide tires are going to be used (10" or bigger), Low profile rear subframe bolts are necessary as to not cut into the sidewall of a lower cars tires. They are cheap and an easy install. (Click here to buy)
You may or may not want to swap rear brake calipers. Since the GT/V6/Cobra use the same rear caliper, all that is needed to complete the swap is to swap brake pads. The Cobra has thinner vented 11.5'' rear rotors, so a different pad is needed than the GT/V6 pad.
Of course the Cobra owner will need the corresponding parts from the GT/V6 plus a few extras:
Pinion snubber
Exhaust hanger brackets
Quadshock brackets
In 99-04 cars, this swap is direct and you will not need to do anything special to the cars. In older year cars you may need to drill a few holes, nothing big.
***It is in my opinion that the swap should cost no party any money. ***
************************************************** *******
'99 Cobra IRS into '01 GT parts list:
Here is a list of EVERYTHING that came off the cobra and onto my '01 GT with a T-45 Tranny
From Cobra:
ABS Harness
Rear brake Pads
IRS Assembly
Lower IRS mounting point brackets(not sure of name)
IRS Catback
Front/Rear Springs
No driveshaft swap was needed because both the '99Cobra and my early '01 GT use the same tranny/differential tail shaft.
From My GT:
ABS Harness
Rear brake pads
SRA assembly
Quad shock brackets
Exhaust hangers
Front/Rear Springs
Catback
All the brake lines fit fine and non needed to be transfered. The brake line locations were perfect with no fexing or stress.
Here is a Weight Distribution Calculation set that shows the effect on the WD ratio with IRS swap.
Here is the write-up I used as a guide.
************************************************** ******************
IRS Torque Specs:
Subframe-to-body bolts 76 lb-ft
Subframe-to-rear bracket bolts 76 lb-ft
Subframe rear bracket-to-body bolts 59 lb-ft
Shock absorber-to-lower arm and bushing bolts 98 lb-ft
Shock absorber-to-body nuts 30 lb-ft
Upper arm and bushing-to-subframe nuts 66 lb-ft
Upper arm bushing-to-knuckle nut 66 lb-ft
Lower arm and bushing-to-subframe bolts 184 lb-ft
Lower arm and bushing-to-knuckle nut 85 lb-ft
Toe link-to-subframe nut 35 lb-ft
Toe link-to-knuckle nut 35 lb-ft
Stabilizer bar bracket bolt 41 lb-ft
Stabilizer bar link nuts 35 lb-ft
Rear axle diff rear insulator-to-axle housing bolts 76 lb-ft
Rear brake disc dust sheild-to-knuckle bolts 89 lb-in
Brake line-to-rear brake caliper bolt 30 lb-ft
Parking brake cable bracket-to-lower arm bushing bolt 11 lb-ft
ABS sensor bolt 17 lb-ft
Axle shaft-to-hub retainer 240 lb-ft
Wheel nuts 95 lb-ft
Here is probably the most complete suspension article for our cars: Jazzers Page
SRA Info:
Ok, so lets start with the basics. The SRA (solid rear axle) is in the V6, GT, Mach 1’s, 96-98 Cobras. The SRA is a very, very simple rear axle design, and is a decent platform for anyone who wants to do straight-line racing. All you need for serious power is a set of decent lower control arms, some upper control arms and a 31 spline set up and you can call it a day. However, this may shock some people, but not everyone finds racing in a straight line to be all that fun.
Open track racing and autocross really expose the weakness of the SRA. The 4 link set-up really is a **** poor design by many peoples standards, and needs a decent amount of parts to get a predictable feel from the axle. With the correct parts, a stick axle can be made to eat a road course for dinner.
The main issue with the SRA in the handling department is getting rid of the 4-link setup. Ideally you would want to do a Watts link setup/torque arm combo. This will take car of most every geometry issue the SRA has. But this comes at a price, comfort. Also, some will find that their watts link doesn’t allow them to run tailpipes (if this is a big deal to you, buy a panhard bar instead, just know a panhard bar does not help as much as a watts link).
Here are a few Stores that carry the parts to turn your SRA into one bad ****:
Maximum Motorsports
Griggs
Further SRA Info:
Torque Arm Recommendation Table
Watts Link Theory
Now don’t get me wrong, just because you do a TA/WL setup does not mean your going to have a super harsh ride. BUT, it is just a fact that you will have to run stiffer torque arm springs in the rear, which those alone will cause a harsh ride. Some may find this uncomfortable, but this setup on an SRA really does handle with the best of them.
IRS Info:
Now, for those of you out there who are more interested in a comfortable daily driver, that handles well the Independent Rear Suspension or IRS may be an option for you. This is a common swap for GT owners and Cobra owners who have opposite goals. Cobra owners who want to drag race, but don’t want to spend a fortune upgrading their IRS to handle their power level find the SRA to be the best option.
The Mustang IRS is the best option for comfort and handling that Ford offered from the factory. Unfortunate, It could be better. To make everything easy on themselves, Ford decided that they would design the IRS to be a direct mod to the existing chassis of the Mustang. This is good for people who want to swap, but it led to an IRS that could be better.
Many issues come along with the IRS; the main one is wheel hop. 99 Cobras have the weakest one. These assemblies are 28 spline setups and have the weakest halfshafts. 01 Cobras have 31 spline setups but also have weaker half shafts, but these assemblies are considerable stronger than the 99 assemblies. The 03/04 IRS assemblies are 31 spline setups with carbon clutch packs and stronger half shafts. These assemblies are the holy grail of IRS swaps, just because they are the strongest. Many parts exist to build up the IRS assemblies to handle power, but they are not cheap. Differential braces, bushings and halfshaft upgrades are a must for anyone going to a lot of power.
The IRS assemblies handle noticeable better than a stock or mildly modded (no watts/TA combo) and ride very smooth. This is why a lot of SRA Mustang owners like to swap with Cobra owners.
Here are some great stores for IRS parts:
Maximum Motorsports
Full Tilt Boogie Racing
Further IRS Information:
IRS Bushing Locations
More In-depth IRS Research
SVTP Postban Article
***My personal opinion is that while the 03/04 setups are the best, if your not going to abuse your car, any IRS assembly will suffice***
************************************************** **************************
What an SRA/IRS swap call for:
Having done one myself, the swap is bloody simple. Basically, 4 bolts is all it takes with a couple small steps in between. All parts will be a direct swap in New Edge cars. The actual list of parts that need to be swapped will vary depending on years of the cars used. The differential tail shaft bolt pattern(the piece that connects to the driveshaft) and transmission will determine if the driveshafts/tailshafts need to be swapped.
From the Cobra you may or may not need (depending on year of Cobra):
Driveshaft
Rear brake lines/calipers
IRS assembly
You may need to swap tail shafts
IRS exhaust
ABS harness
Mounting brackets for lower IRS bolts
Front/rear springs (to avoid any retarded spring matchups)
If wide tires are going to be used (10" or bigger), Low profile rear subframe bolts are necessary as to not cut into the sidewall of a lower cars tires. They are cheap and an easy install. (Click here to buy)
You may or may not want to swap rear brake calipers. Since the GT/V6/Cobra use the same rear caliper, all that is needed to complete the swap is to swap brake pads. The Cobra has thinner vented 11.5'' rear rotors, so a different pad is needed than the GT/V6 pad.
Of course the Cobra owner will need the corresponding parts from the GT/V6 plus a few extras:
Pinion snubber
Exhaust hanger brackets
Quadshock brackets
In 99-04 cars, this swap is direct and you will not need to do anything special to the cars. In older year cars you may need to drill a few holes, nothing big.
***It is in my opinion that the swap should cost no party any money. ***
************************************************** *******
'99 Cobra IRS into '01 GT parts list:
Here is a list of EVERYTHING that came off the cobra and onto my '01 GT with a T-45 Tranny
From Cobra:
ABS Harness
Rear brake Pads
IRS Assembly
Lower IRS mounting point brackets(not sure of name)
IRS Catback
Front/Rear Springs
No driveshaft swap was needed because both the '99Cobra and my early '01 GT use the same tranny/differential tail shaft.
From My GT:
ABS Harness
Rear brake pads
SRA assembly
Quad shock brackets
Exhaust hangers
Front/Rear Springs
Catback
All the brake lines fit fine and non needed to be transfered. The brake line locations were perfect with no fexing or stress.
Here is a Weight Distribution Calculation set that shows the effect on the WD ratio with IRS swap.
Here is the write-up I used as a guide.
************************************************** ******************
IRS Torque Specs:
Subframe-to-body bolts 76 lb-ft
Subframe-to-rear bracket bolts 76 lb-ft
Subframe rear bracket-to-body bolts 59 lb-ft
Shock absorber-to-lower arm and bushing bolts 98 lb-ft
Shock absorber-to-body nuts 30 lb-ft
Upper arm and bushing-to-subframe nuts 66 lb-ft
Upper arm bushing-to-knuckle nut 66 lb-ft
Lower arm and bushing-to-subframe bolts 184 lb-ft
Lower arm and bushing-to-knuckle nut 85 lb-ft
Toe link-to-subframe nut 35 lb-ft
Toe link-to-knuckle nut 35 lb-ft
Stabilizer bar bracket bolt 41 lb-ft
Stabilizer bar link nuts 35 lb-ft
Rear axle diff rear insulator-to-axle housing bolts 76 lb-ft
Rear brake disc dust sheild-to-knuckle bolts 89 lb-in
Brake line-to-rear brake caliper bolt 30 lb-ft
Parking brake cable bracket-to-lower arm bushing bolt 11 lb-ft
ABS sensor bolt 17 lb-ft
Axle shaft-to-hub retainer 240 lb-ft
Wheel nuts 95 lb-ft
Last edited by H0SS302; 07-16-2010 at 10:51 AM.
06-02-2010, 03:58 PM
#4
6th Gear Member
Thread Starter
Join Date: Oct 2006
Location: Texas
Posts: 10,551
06-02-2010, 09:19 PM
#6
6th Gear Member
Thread Starter
Join Date: Oct 2006
Location: Texas
Posts: 10,551
06-02-2010, 09:19 PM
#7
6th Gear Member
Join Date: May 2007
Location: Columbia, MO
Posts: 6,347
overall i think you did a good job!
06-02-2010, 09:27 PM
#9
6th Gear Member
Thread Starter
Join Date: Oct 2006
Location: Texas
Posts: 10,551
Added '99 Cobra/ '01 Early GT transfer list.
And 94, to adress your comment, I guess I should have said it different. What I mean is, the Cobra owner is planning on pushing a ton of power(most likely a whipple/KB swap), so they are looking for a stronger, cheaper rear to build. Most GT owners are looking to do the swap for autox/open track or comfort. So I dont think most ppl do the IRS swap then mod the IRS more than maybe the bushings and a brace.
And 94, to adress your comment, I guess I should have said it different. What I mean is, the Cobra owner is planning on pushing a ton of power(most likely a whipple/KB swap), so they are looking for a stronger, cheaper rear to build. Most GT owners are looking to do the swap for autox/open track or comfort. So I dont think most ppl do the IRS swap then mod the IRS more than maybe the bushings and a brace.
Last edited by H0SS302; 06-02-2010 at 09:30 PM.
