Thought I'd post some pics and do some explanation of what I've been working on for the last couple of months. With much help from Brian (Luce), the original designer of this IRS, we have fabricated all of the parts and made a few changes from the original setup.
Here's the car on the lift ready to begin:
A shot of the soon to be retired 9" axle:
Axle and 4 links removed:
Here's the fabricated framework and control arms:
Had to modify the frame gussets to clear the IRS frame:
Test fitting and tacking in the IRS frame:
For some reason, I had to cut 3/4" off the front of the frame in order to have the wheel centers in the right position. My car is a 2001 kit, so there may have been some frame changes between then and now. The newer frames should not require this.
Modifying the beefier Wheel hubs to fit the cobra wheels:
Before and after shot. Note the pilot hub shoulder is machined off:
Test fitting the lower control arms and uprights:
Mounted the frame tabs for the upper control arm and coilover. Since I had to move the frame forward, I also had to remake some of the tabs to fit differently. Plasma tables are real handy here. There is a lot of cutting and grinding here to remove the original mounts.
In the IRS setup, the coilovers tilt inward at about a 45 degree angle. This reduces the vertical force of the springs by about half, so it's necessary to use heavier springs. I will be using the QA1 7-550 springs.
That's where I am at the moment. The pumpkin will be a ford 8.8 aluminum unit, with the Eaton True Track differential unit installed. 3.55 gears. I'll get that test fitted shortly and then I'll be able to measure the exact length I need for the half shafts. The pumpkin is actually offset toward the passenger side slightly so that the axle shafts can be made the same length and will be interchangeable. This has the added benefit of making sure that the driveshaft U joints are not concentric with the transmission tail.
I'll post more as I get more done...
RIck
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Here's an update on what I've been working on.
The differential frame is all aligned with the car frame to within 1/16". Got it all welded up with all brackets too.
Here is the IRS differential test fitted to the frame in order to measure the half shaft length. There are braces underneath the lower control arms to hold them level, where the suspension should be when the car's weight is on the springs.
I used some wood dowel pressed into the half shaft CV joints to measure the correct center shaft length. I'll send the center shafts off to a shop and have them shortened and re-splined.
Welded on the brackets for the Wilwood brake caliper and the wildwood spot caliper for the park brake. The position of these is critical, so you have to mount the rotor and caliper, then spot weld to get it in just the right spot.
I did the wheel bearing a little differently from the setup that Lone Star is currently making. You can see the custom machined bearing housing welded to the uprights. This allows me to use a beefier wheel bearing that presses into the housing. It also allows the use of standard half shafts that will be much less expensive.
Both uprights now ready for sandblasting and powder coat.
Here is the upright with the brackets on and test assembled with wheel bearings, wheel hub, rotor and calipers.
Next - sandblast and powdercoat all of the parts. Sand, clean and paint the frame under the car.
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A few new things to report.
All of the IRS components have been sandblasted and powder coated. Ready to install
The new IRS frame is fully welded, and all the new brackets are in place. I also decided to add some reinforcement for the rear cowl bar. I have my safety harnesses attached to that, and I wasn't too confident in the strength of it previously. It was originally bolted to the fiberglass with 1/4" bolts. Now bolted with 3/8" bolts to some 1/4" thick steel plate, which is welded to the frame.
Passenger side
Driver's side
The new differential is being worked on right now. Installing the Eaton True Track differential unit, as well as new bearings and seals. The half shafts are being re-machined and should be here in a week or so.
Next to install the new brake lines and remake some of the stainless fuel line to the surge tank. Should have everything ready to go when I get the other parts. Hope I'm not cutting it too close for San Marcos...
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OK, It's been a long weekend.
Got the brake lines and fuel lines reconnected. I was able to re-use the stainless fuel lines I had previously and just re-bend some parts straight again, and then bend new angles in the right place. This stainless is good stuff. This kind of thing is a serious pain with the body on.
The differential will be installed offset to the right a bit. This will make both half shafts the same length, as well as making sure the driveshaft clears the fuel lines.
Upper and lower control arms mounted, uprights mounted, coilovers mounted.
High pressure fuel pump mounted around the new frame tabs. I was able to use the same lines, and only had to change one AN fitting. Worked out well.
New differential mounted
Received the half shaft centers back from the machine shop. The are shortened and resplined.
I just stuck them and the other half shaft pieces in the powder coating oven. Next, I'll reassemble the half shafts and install them. Then, I need to measure the length for the new driveshaft and have that made. Hook up the new park brake cables and spot calipers. Install the brake calipers and bleed the system. Set the camber and toe on the rear wheels.
Rick
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Well, I got so busy trying to get this all done before San Marcos, that I didn't have time to post the rest. As most of you probably know, it worked out pretty well, but here's the rest of the assembly process.
Once I got the shortened center sections back from the shop (They were shortened to 18"), I reassembled them with synthetic grease. I recommend 2 or 3 whole rolls of paper towels and a whole box of latex gloves for this job, it's a messy job. You don't have to regrease everything like I did, I just wanted the synthetic grease. I used Redline CV-2 grease here.
When I went to install the half shafts, I ran into a problem. The shafts would not seat all the way to the seals in the differential. Looking through the bearing hole, you can see a perpendicular shaft which interferes with the half shafts. Turns out that this piece is intended as a stop for the axle shafts in an 8.8 live axle, but isn't needed for the IRS setup. The shop put it in there anyway for some reason.
I had to remove the whole differential, open it up, and remove the pin that was in the way. Put it all back together and the half shafts snapped right in.
Once the pumpkin was mounted, I measured the length from the transmission tail to the flange of the differential. Had Driveshaft King in Dallas shorten and balance the shaft for me. They did nice work. Be sure to make the whole thing an inch or two shorter than the measured length so it will clear the differential flange bolt during installation. With the new setup, the diff will not move, so you don't have to worry about the slip yoke moving in and out as it does with a live axle and 4-link.
You can see how the driveshaft is offset to the passenger side. The sides of the differential are centered in the frame, but the input shaft is offset. This makes it clear my fuel lines, and allows the half shafts to be the same length. It also makes sure that the driveshaft u-joints are never concentric.
BTW, I'm using the newer 2006 model of ford 8.8 differential here, which is different from Luce's original and Lone Star's current setup. These were easier to find for me with few miles. The only difference is the 2 mounting bosses rather than 1 on Luce's and Lone Star's.
With U-joints, it's important to set the pinion angle. With the IRS, the diff never moves, so the pinion angle is always the same. My transmission was at a 2.5 degree down angle, measured from the flat on the transmission rear bearing. Therefore, the flange on the front of the diff, needed to be at a 2.5 degree up angle. I plasma cut some round donuts out of 1/4" steel plate and stacked them up on the cross brace to achieve the 2.5 degree angle. There is another of these donuts at the top which acts as a stop for the rubber mounts in the diff housing. You can see the stacks in the above pic.
Here's something that's handy. I had one of these cheap level gauges from Harbor Freight. It has a button that will freeze the reading, so you can reach it in someplace and press the button without having to see the gauge. Then pull it out and read the angle. I used this to set the pinion angle.
Now that the half shafts are installed, I had to set the rear wheel camber angle. With this setup, it's done by moving the 2 heim joints of the upper control arms in and out. You have to remove and reinstall the mounting bolts each time you set it, but it only ever has to be done once. I used my handy dandy homade alignment stands to do this while being able to access everything. They allow the wheel hub to pivot in any direction. The rear wheel camber was set to -0.8 degrees.
Lastly, I had to set the rear wheel toe. I used a set of toe plates against each rear wheel, and 2 tape measures to set the wheels parallel to each other. Then put a laser level on each of the toe plates so that the laser shoots forward toward the front wheel hub. Measuring the laser line from the front wheel hub allows you to set the thrust angle. I adjusted the rear wheel toe adjusters equal turns so that they stay parallel, but move the thrust angle left or right. Once that was set, I just dialed in about 1/8" of toe-in. The whole thing worked great on the first try. On the first test drive, the steering wheel was straight, and the thrust angle was good.
You can also see in the above pic. the spot calipers that were used as park brakes instead of the wildwood drum setup. I never could get the drums to hold very well, even with the lengthened levers on them. The spot calipers work great though. As a secondary park brake and theft prevention measure, I also installed a rear hydraulic brake valve under the dash. It locks pressure on the rear calipers.
When I first test drove the car after the installation, I had a lot of tire rubbing on the wheel wells. I had to take the wheels off again and cut out the fiberglass in a football shape, just above the 45 degree angle in the frame. Since the IRS has camber gain under wheel compression, the wheels turn inward and rubbing is more of an issue than with a live axle. I put some ABS plastic over the cutout, heated it with a heat gun, and shaped it to fit around the wheel. Later on, I'll glass it up right. The modification didn't interfere with the seats.
I was in such a rush to get to San Marcos, I didn't take another pic when it was all reassembled. I need to put it back up on the lift for a couple of tweaks, so I'll shoot some finished pics.
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OK, Time to wrap up this thread.
The IRS worked beautifully. Drove her around all over the place in San Marcos without a hitch. I did have a little bit of banging during shifts, which is being caused by the lack of a rubber stop at the top of the front differential mounts. I'll fix that shortly.
Here is the whole thing finished up.
Left wheel:
Right wheel:
I do think I'm going to add some rear sway bar. The feel of the suspension is completely different than with the live axle. Ideally, you want the suspension to be as soft as possible, without bottoming out so that the tires don't unload and lose traction. Right now, I feel like the front is stiffer than the rear in a quick turn, and I'd like to get front and rear about equal, so the front and rear have equal body roll. I may have to try a few different spring rates to accomplish that.
Here's a shot of the wheel, showing the park brake and rear brake caliper mounted. This setup eliminates the wildwood drums, and just uses the rotor. The spot caliper at the front is also wildwood. It works better than the drum setup, which I never could get to hold reliably, even after lengthening the lever arm on the drum end. I also installed a valve on the rear brake lines as a backup and security measure, so I have 2 park brakes.
Note that the brake spot caliper and main caliper are pretty close to the inside of the wheel. This setup won't work with wheels smaller than 17". Can't really find decent tires for anything smaller anyway.
Rick
Here's the car on the lift ready to begin:
A shot of the soon to be retired 9" axle:
Axle and 4 links removed:
Here's the fabricated framework and control arms:
Had to modify the frame gussets to clear the IRS frame:
Test fitting and tacking in the IRS frame:
For some reason, I had to cut 3/4" off the front of the frame in order to have the wheel centers in the right position. My car is a 2001 kit, so there may have been some frame changes between then and now. The newer frames should not require this.
Modifying the beefier Wheel hubs to fit the cobra wheels:
Before and after shot. Note the pilot hub shoulder is machined off:
Test fitting the lower control arms and uprights:
Mounted the frame tabs for the upper control arm and coilover. Since I had to move the frame forward, I also had to remake some of the tabs to fit differently. Plasma tables are real handy here. There is a lot of cutting and grinding here to remove the original mounts.
In the IRS setup, the coilovers tilt inward at about a 45 degree angle. This reduces the vertical force of the springs by about half, so it's necessary to use heavier springs. I will be using the QA1 7-550 springs.
That's where I am at the moment. The pumpkin will be a ford 8.8 aluminum unit, with the Eaton True Track differential unit installed. 3.55 gears. I'll get that test fitted shortly and then I'll be able to measure the exact length I need for the half shafts. The pumpkin is actually offset toward the passenger side slightly so that the axle shafts can be made the same length and will be interchangeable. This has the added benefit of making sure that the driveshaft U joints are not concentric with the transmission tail.
I'll post more as I get more done...
RIck
Quote
Edit
Share
Pin Topic
Here's an update on what I've been working on.
The differential frame is all aligned with the car frame to within 1/16". Got it all welded up with all brackets too.
Here is the IRS differential test fitted to the frame in order to measure the half shaft length. There are braces underneath the lower control arms to hold them level, where the suspension should be when the car's weight is on the springs.
I used some wood dowel pressed into the half shaft CV joints to measure the correct center shaft length. I'll send the center shafts off to a shop and have them shortened and re-splined.
Welded on the brackets for the Wilwood brake caliper and the wildwood spot caliper for the park brake. The position of these is critical, so you have to mount the rotor and caliper, then spot weld to get it in just the right spot.
I did the wheel bearing a little differently from the setup that Lone Star is currently making. You can see the custom machined bearing housing welded to the uprights. This allows me to use a beefier wheel bearing that presses into the housing. It also allows the use of standard half shafts that will be much less expensive.
Both uprights now ready for sandblasting and powder coat.
Here is the upright with the brackets on and test assembled with wheel bearings, wheel hub, rotor and calipers.
Next - sandblast and powdercoat all of the parts. Sand, clean and paint the frame under the car.
Quote
Edit
Share
A few new things to report.
All of the IRS components have been sandblasted and powder coated. Ready to install
The new IRS frame is fully welded, and all the new brackets are in place. I also decided to add some reinforcement for the rear cowl bar. I have my safety harnesses attached to that, and I wasn't too confident in the strength of it previously. It was originally bolted to the fiberglass with 1/4" bolts. Now bolted with 3/8" bolts to some 1/4" thick steel plate, which is welded to the frame.
Passenger side
Driver's side
The new differential is being worked on right now. Installing the Eaton True Track differential unit, as well as new bearings and seals. The half shafts are being re-machined and should be here in a week or so.
Next to install the new brake lines and remake some of the stainless fuel line to the surge tank. Should have everything ready to go when I get the other parts. Hope I'm not cutting it too close for San Marcos...
Quote
Edit
Share
OK, It's been a long weekend.
Got the brake lines and fuel lines reconnected. I was able to re-use the stainless fuel lines I had previously and just re-bend some parts straight again, and then bend new angles in the right place. This stainless is good stuff. This kind of thing is a serious pain with the body on.
The differential will be installed offset to the right a bit. This will make both half shafts the same length, as well as making sure the driveshaft clears the fuel lines.
Upper and lower control arms mounted, uprights mounted, coilovers mounted.
High pressure fuel pump mounted around the new frame tabs. I was able to use the same lines, and only had to change one AN fitting. Worked out well.
New differential mounted
Received the half shaft centers back from the machine shop. The are shortened and resplined.
I just stuck them and the other half shaft pieces in the powder coating oven. Next, I'll reassemble the half shafts and install them. Then, I need to measure the length for the new driveshaft and have that made. Hook up the new park brake cables and spot calipers. Install the brake calipers and bleed the system. Set the camber and toe on the rear wheels.
Rick
Quote
Edit
Share
Well, I got so busy trying to get this all done before San Marcos, that I didn't have time to post the rest. As most of you probably know, it worked out pretty well, but here's the rest of the assembly process.
Once I got the shortened center sections back from the shop (They were shortened to 18"), I reassembled them with synthetic grease. I recommend 2 or 3 whole rolls of paper towels and a whole box of latex gloves for this job, it's a messy job. You don't have to regrease everything like I did, I just wanted the synthetic grease. I used Redline CV-2 grease here.
When I went to install the half shafts, I ran into a problem. The shafts would not seat all the way to the seals in the differential. Looking through the bearing hole, you can see a perpendicular shaft which interferes with the half shafts. Turns out that this piece is intended as a stop for the axle shafts in an 8.8 live axle, but isn't needed for the IRS setup. The shop put it in there anyway for some reason.
I had to remove the whole differential, open it up, and remove the pin that was in the way. Put it all back together and the half shafts snapped right in.
Once the pumpkin was mounted, I measured the length from the transmission tail to the flange of the differential. Had Driveshaft King in Dallas shorten and balance the shaft for me. They did nice work. Be sure to make the whole thing an inch or two shorter than the measured length so it will clear the differential flange bolt during installation. With the new setup, the diff will not move, so you don't have to worry about the slip yoke moving in and out as it does with a live axle and 4-link.
You can see how the driveshaft is offset to the passenger side. The sides of the differential are centered in the frame, but the input shaft is offset. This makes it clear my fuel lines, and allows the half shafts to be the same length. It also makes sure that the driveshaft u-joints are never concentric.
BTW, I'm using the newer 2006 model of ford 8.8 differential here, which is different from Luce's original and Lone Star's current setup. These were easier to find for me with few miles. The only difference is the 2 mounting bosses rather than 1 on Luce's and Lone Star's.
With U-joints, it's important to set the pinion angle. With the IRS, the diff never moves, so the pinion angle is always the same. My transmission was at a 2.5 degree down angle, measured from the flat on the transmission rear bearing. Therefore, the flange on the front of the diff, needed to be at a 2.5 degree up angle. I plasma cut some round donuts out of 1/4" steel plate and stacked them up on the cross brace to achieve the 2.5 degree angle. There is another of these donuts at the top which acts as a stop for the rubber mounts in the diff housing. You can see the stacks in the above pic.
Here's something that's handy. I had one of these cheap level gauges from Harbor Freight. It has a button that will freeze the reading, so you can reach it in someplace and press the button without having to see the gauge. Then pull it out and read the angle. I used this to set the pinion angle.
Now that the half shafts are installed, I had to set the rear wheel camber angle. With this setup, it's done by moving the 2 heim joints of the upper control arms in and out. You have to remove and reinstall the mounting bolts each time you set it, but it only ever has to be done once. I used my handy dandy homade alignment stands to do this while being able to access everything. They allow the wheel hub to pivot in any direction. The rear wheel camber was set to -0.8 degrees.
Lastly, I had to set the rear wheel toe. I used a set of toe plates against each rear wheel, and 2 tape measures to set the wheels parallel to each other. Then put a laser level on each of the toe plates so that the laser shoots forward toward the front wheel hub. Measuring the laser line from the front wheel hub allows you to set the thrust angle. I adjusted the rear wheel toe adjusters equal turns so that they stay parallel, but move the thrust angle left or right. Once that was set, I just dialed in about 1/8" of toe-in. The whole thing worked great on the first try. On the first test drive, the steering wheel was straight, and the thrust angle was good.
You can also see in the above pic. the spot calipers that were used as park brakes instead of the wildwood drum setup. I never could get the drums to hold very well, even with the lengthened levers on them. The spot calipers work great though. As a secondary park brake and theft prevention measure, I also installed a rear hydraulic brake valve under the dash. It locks pressure on the rear calipers.
When I first test drove the car after the installation, I had a lot of tire rubbing on the wheel wells. I had to take the wheels off again and cut out the fiberglass in a football shape, just above the 45 degree angle in the frame. Since the IRS has camber gain under wheel compression, the wheels turn inward and rubbing is more of an issue than with a live axle. I put some ABS plastic over the cutout, heated it with a heat gun, and shaped it to fit around the wheel. Later on, I'll glass it up right. The modification didn't interfere with the seats.
I was in such a rush to get to San Marcos, I didn't take another pic when it was all reassembled. I need to put it back up on the lift for a couple of tweaks, so I'll shoot some finished pics.
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Share
OK, Time to wrap up this thread.
The IRS worked beautifully. Drove her around all over the place in San Marcos without a hitch. I did have a little bit of banging during shifts, which is being caused by the lack of a rubber stop at the top of the front differential mounts. I'll fix that shortly.
Here is the whole thing finished up.
Left wheel:
Right wheel:
I do think I'm going to add some rear sway bar. The feel of the suspension is completely different than with the live axle. Ideally, you want the suspension to be as soft as possible, without bottoming out so that the tires don't unload and lose traction. Right now, I feel like the front is stiffer than the rear in a quick turn, and I'd like to get front and rear about equal, so the front and rear have equal body roll. I may have to try a few different spring rates to accomplish that.
Here's a shot of the wheel, showing the park brake and rear brake caliper mounted. This setup eliminates the wildwood drums, and just uses the rotor. The spot caliper at the front is also wildwood. It works better than the drum setup, which I never could get to hold reliably, even after lengthening the lever arm on the drum end. I also installed a valve on the rear brake lines as a backup and security measure, so I have 2 park brakes.
Note that the brake spot caliper and main caliper are pretty close to the inside of the wheel. This setup won't work with wheels smaller than 17". Can't really find decent tires for anything smaller anyway.
Rick