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10/16/2011 8:23 am  #1


IRS in my 67 shelby gt 350

on June 4, 2010, 11:54 pm, tyrellracing wrote:

I came across your irs site several months ago and have completed the same conversion since. About 7 years ago I worked for a automotive spring company here in Portland for over ten years. While employed there I worked on nearly every conceivable hot rod and muscle car to grace the streets of America. From real AC cobras to Hemi Cudas. All I did was suspension work and conversions so I am knowledgeable to a wide range of irs and live axle configurations. Oregon roads are typically in poor condition so trying to corner on these roads can be scary. With the unsprung weight of the nine inch rear with under ride traction bars, watts linkage and leaf springs in my Shelby, bumpy corners taken fast would cause a over steer condition due to the rear tires not staying in contact with the road surface. This is not a controlled slide like the car dose on smooth asphalt but sudden lateral shifts that are instantaneous and if my reactions are not razor sharp, its game over for my Shelby. I read your article, purchased a complete jag rear suspension with 2.88 gears on a open carrier and tapered roller bearings on the stub axles. The width was fine as is because I converted the front suspension to a tube steel performance suspension with coil over Afco shocks supporting the car by the LCA years ago. I also installed four wheel disk brakes with 13.7 inch front rotors that widened the front by two and a half inches. I also fabricated strut rods virtually identical to the ones you sell but I used 3/4 heims at the same time. Back to the rear end, I purchased a 19 spline power lock and 3.50:1 ring and pinion on E-bay and installed them in the Jag differential housing with a install kit I got locally. I fabed a cross member and installed the suspension. I fabed a plate to help prevent the LCA's from ripping their brackets off the diff. housing the same size as the 8 bolt pattern that the jag used for the same purpose. I then used two tubes with threaded inserts welded into the ends for heim joints to tie the a fore mentioned plate to the original front spring eye mounts. This sort of triangulates the bottom of the diff housing to the unit body to control torque loading. You referred to the Jag rear suspension as having caster. This is incorrect. Caster is the inclination of the spindle of a steer axle that allows the tread patch to follow the steering axis. The only application where the suspension travels at the same angle as the caster is on a MacPherson strut type lay out. This makes the tires lean when turned and pull back to the forward position after a turn. Since the tread patch follows the steering axis it behaves like a caster wheel on a shopping cart. This adds stability to the steering axle. Since the rear suspension does not turn, the angle the LCA's are mounted at cannot be called caster. The Jag suspension has anti-squat built in to the design. Anti-squat is critical for good acceleration. All vehicles with front engine/rear drive have some form of anti-squat in their design. This has always been easier to attain with a Hotchkiss drive or multi-link live axle configuration than it is with a IRS regardless of the configuration.On the Jag rear suspension, when the pinion angle is set at a complementary angle to the crank center line, the inner pivots of the LCA's will be at aprox. 6 degrees positive inclination. This causes the suspension to resist squatting under hard acceleration by allowing the tires to move at the same inclination down and forward in relation to the unit body when viewed from the side. The problem with this design is it is too torque sensitive. The under powered six of the 4000 lb. Jag did not cause the rear to hop. My Shelby has a 408 stroker Cleveland with Yates C3 heads and a solid roller cam that produces 575 lb/ft of torque and my first hard launch with the new suspension nearly ripped the drive shaft out of the car! That much angle on the LCA's is too much for the torque my engine makes. I am a machinist now and have the machine tools to make new brackets out of 4140 heat treated steel. Through trial and error and many attempts I found the angle that worked best with my vehicle weight and engine torque. On my second try I set this angle to zero, I could not get the rear tires to hook up. Dry asphalt gave the same traction as wet. When I put in two degree positive inclination brackets and tested traction, I found what I think is my best setting. It will exhibit small amounts of wheel hop but nothing like the first launch. This suspension cannot and will not launch like the nine did but for lateral g-force fun on average roads its far superior. Like I mentioned earlier, this design is very torque sensitive. The LCA angle is critical and must be set to the application the rear suspension is installed. One angle will not work for all apps. Now my car corners better than it ever did with the nine inch. Its not as noticeable on smooth roads but on rough roads, its ability to maintain grip is impressive. I have yet to have dry enough weather to test it on a 300ft. skid pad but I will soon! I am seriously thinking of building new hub carriers and brackets to convert this configuration to the Klaus Arning design. More on that later. I am still looking for better quality copies of the blue prints than the ones I found on line.


If it isn't broken..... modify it anyway!!!!
 

10/16/2011 8:26 am  #2


Re: IRS in my 67 shelby gt 350

on June 5, 2010, 4:49 pm, Daze wrote:

Pictures pictures pictures !!!!! I would love to see some Pix of your installThanks for correcting me on my terminology. When I started calling the tilting back of the suspension travel, caster it was because I didn't have a better term for it. I new it wasn't caster, but I figured that would get the idea across. Thanks for setting me straight  Interesting how changing that angle effected how the car launches. I plan on running my car with total vertical travel, so the wishbones will be set at 0º but I don't do any hard launches. Welcome to the forum and I look forward to seeing lots of pictures of your setup... PLEASE!!!


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10/16/2011 8:28 am  #3


Re: IRS in my 67 shelby gt 350

on June 6, 2010, 9:38 am, tyrellracing wrote:

No prob. I have a few of them. I kind of gave the readers digest version with am economy of words due to my slow typing. I dont have many pix of the time the car was on my platform. I use a leveled steel plate 1.5 inch thick that is 12x18 ft. I have weld on jack screws with pads to support my car similar to jack stands. The main difference is when needed I weld the pads to the bottom of my frame. this allows me to level the vehicle very accurately. Not only level but apply negative pressure to the unit body to repair twisted and damaged body's. This gave me a stable platform to accurately measure all angles from the trans center line to the pinion center line. This I regret having not taken pictures of this because it seems to be a point of difficulty. The engine has been lowered 2 inches and set back 3 and now my trans angle is at two degrees. The car is lowered so the measurement from the bottom of the rocker panel to my plate at normal ride height is 4.5 inches so my frame rails have 3.That forced the diff to be tucked as high as I could possibly could get it and still get the two degrees reqd. There is very little room between the rear u-joint and the trans tunnel. bottom line, the engine and the pinion are at two degrees with a 3 inch off set to provide the required movement for the needle bearings. My first cross member came out looking like swiss cheese. Getting the ride height I wanted took several attempts. Mounting the shocks as close to vertical as the frame rails allowed produced the firmness I wanted but too much height. With the springs tilted further inward gave the desired ride height but made the spring rate appear too low. (too soft) My solution was to drill a 3/4 inch hole through the cross member then weld a tube with a 3/4 od and a 1/2id in it. The tubes were placed as close to the floor and as close to the frame rail as possible while following the inclination of the LCA's to prevent binding of the shock bolts during their installation. I discovered that one of my brake calipers has a bad seal so I have to drop the suspension to repair it. I made my own rotors and neglected to put access holes in them so caliper removal in the car is near impossible. This will give me another opportunity to provide pictures and measurements. I used a section of 3x2x1/4 wall tube for the cross member. this provided enough steel that I could mill the center where the diff mounts at the necessary angle and not get thinner than 3/32 inch. the rest was milled down to 1/8 inch to reduce weight. I used 1/4 plate to attach the cross member to the bump stop mounting pads that protrude from the frame rail near center on both sides. I say near because after measuring I discovered that the left side bump stop was 7/8 inch further forward than the right. there fore it can be seen when viewed from the top that I had to off set the mounts accordingly. I used four 5/16 grade 8 bolts in each bump stop pad and two 3/8 bolts through the inner flange of the mustangs frame accessed through the trunk. This places the fasteners on two separate planes to help resist torque twist. I drilled and tapped the holes in the cross member then welded nuts inside the tube before welding in the end caps. This made tightening the 3/8 bolts possible. It late so more later. I will take more pix and down load asap.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:29 am  #4


Re: IRS in my 67 shelby gt 350

on June 6, 2010, 5:40 pm, Daze wrote:

You are a welcome addition to the forum, however I find it interesting that most... of you on this forum are stuffing these under a 67. Sounds like you have put a lot of time and effort into this install. I know exactly what you are talking about in relation to ride height and spring/shock angle. I did a bunch of calculations before I began the fab work to get the ride height close and then I plan on making the upper shock mounts adjustable. I should be able to get a good compromise between ride height and suspension stiffness. so you said you work in a machine shop?? I would love to access to a really good lathe and mill. I have a harbor freight all in one machine that works fore some things, but I need to get a bigger lathe for sure.

I agree that the original bump stop mounts are a good place to support the weight. I plan on cutting the rubber so that it is just a hair longer than the space between my side frames and the frame so that the bump stops will distribute part of the load of the car on to the frame.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:31 am  #5


Re: IRS in my 67 shelby gt 350

on June 8, 2010, 3:03 am, tyrellracing wrote:

When I worked at Oregon auto spring I had access to a lathe and a knee mill for making and rebuilding suspension parts. this was where the interest in machine tools began in earnest. Then I worked for a company rebuilding machine tools and my collection began. I bought a used 22x72 Monarch engine lathe and completely refurbished it to like new condition. Then I purchased two Bridgeport knee mills and refurbished both of them. I kept the better of the two and made enough on the other to pay for both. Now my collection includes a Swiss made 12x36 Hardenge tool room lathe, a Cinncinnatti rise and fall production mill, an Induma horizontal knee mill with a universal head and indexer for cutting gears and splines. (very handy machine),a Sparton horizontal boring mill and a Brown and Sharp surface grinder. I was self employed in my own shop for a few years but work was spotty so my wife insisted I get a real job. (her words) So now I am a journey man machinist for Central Machine of Portland Or. Sadly enough when I started there, they had 27 full time machinists. Now every one has been laid off except me and the shop foreman. It pays to be good at what you do. At any rate in my shop I make all kinds of neat things like a Honda Pilot sand rail with long travel suspension, sho engine with a SC blower mounted mid engine configuration to a wrx six speed trans axle with 15x16 paddle tires. The engine produces 320 hp. and the vehicle weighs 1250lbs. with me in it. It moves like a raped ape so when my GT350 is down it is my adrenalin fix. Last winter I built a CBR900rr powered quad. Like you I use a T5 trans in my stang. However they don't last long behind my 408 Cleveland. Since there cheap in the wrecking yards I keep four or five rebuilt ones on hand. Now I am in the process of making a twin counter shaft T5. This more than doubles the strength of the gear trane of the T5. The most common failure of world class T5's is third gear. This is because third is closest to the break between the input shaft and the main shaft. Under severe load gears tend to separate due to shaft deflection and case distortion. On a twin counter shaft configuration the shafts are all side by side, three wide. This gives the break in the main shaft nowhere to go plus there are always two sets of teeth engaged for all forward gears except fifth. This is how most semi and some high end specialty clutchless drag race transmissions are laid out. As of this evening I have the steel case nearly complete and the stock T5 top plate with its shift forks and rails mounted. The tail shaft housing and reverse linkage are all that remain to be finished. In theory, This set up should support over 650 lb/ft torque in first through fourth. Since fifth gear synchro is on the counter shaft only one can be used because it would be impossible to shift two fifth gear synchros absolutely simultaneously. Ignoring that one modification I used only stock world class T5 internals! The only draw backs are the width at the bell housing is 12.25 inch and the bolt pattern is now unique. The original upper two bolt holes are now buried by counter shaft head gears and had to be moved inward 2.125 and up .875 inch per side. I have not taken any photos yet but will. I have misplaced the cord to my camera that I need to down load the images I already have.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:33 am  #6


Re: IRS in my 67 shelby gt 350

on June 11, 2010, 7:26 pm, tyrellracing wrote:

In one of your responses you said that you were planning on trimming the bump stop rubbers and sandwiching the remaining segment between the factory bump stop pad and the cross member flange. If I understood you correctly, I am not sure that would be the best approach to rubber isolation of the cross member. That method will lead to imprecise locating of the cross member. Something similar to the Jags cage mounts with a higher durrometer would do a far better job. If the cross member were to shift under load with the bump stop method it would be inclined to stay in that position where a mount consisting of two flat plates with rubber vulcanized between them would be far better suited for this task. This set up would give the flex to absorb the road noise you are looking for but would always return to the correct position when the heavy load subsides. I have noticed some road noise coming from the solid mounted rear but its less than the old 9 inch with bronze front spring eye bushings. I am surprised the jag's cage worked as well as it did being mounted with pretty soft rubber mounts. The cage mounts must have deflected real bad on v 12 applications. I think the vehicles weight played an important role in keeping the cage attached to the car.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:36 am  #7


Re: IRS in my 67 shelby gt 350

on June 9, 2010, 2:54 pm, Daze wrote:

By setting the pinion at 2º how did you deal with the difference... between the transmission angle and the differential angle??

Also as far as building the "original Mustang" design, I would love to see that!!! I would think you could buy the hubs as the claus arning design, I believe used corvair hubs.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:37 am  #8


Re: IRS in my 67 shelby gt 350

on June 10, 2010, 4:54 am, tyrellracing wrote:

That was fairly simple. first of all the vehicle was on jack screw pads 16 inches off the fab plate and level within 1/16 inch. I built the cross member with a thick pad on center with the four holes lightly counter sunk for the factory bolts and correct location of the center section. Then I bolted the cross member to the frame with out the differential. I have a digital angle finder but a pointer type will work fine to measure the actual pad angle when installed. As I recall the companion flange is not at a right angle to the top mount pad in fact when the flange is at 2 degrees from vertical the top had a 3 degree angle remaining. So with the diff tilted down in the front 3 deg. and my cross member tilted up 4 degrees at the front, the combined angle came to 7 degrees. I then removed the cross member and dialed it in on my Bridgeport to the 7 degrees and then with a three inch shell mill removed the least amount of steel that still gave me the full pad for the diff. This amount of angle threw the bolt spacing off a little and now my counter sunk holes were off by 7 degrees. I was conservative on my counter sink depth knowing some alterations would be required. I flipped the cross member over,dialed it back in with parallels under my fresh cut pad. I have a digital readout on my mill and I used it to re-counter sunk all four holes and put them back on location and exactly perpendicular to the mounting pad with in .001 inch. Tapered counter sinks are forgiving to small changes and with a mill its possible to move the hole center a small amount with out much effort. From here I began to set up the shocks for the ride height I wanted. The real problem here Is I had no idea what the spring rate is on a stock Jag coil spring. Not knowing this I made a educated guess and tack welded segments of tube under the cross member for the shocks to be bolted to. I then bolted it all together and set it down on its tires for my first check.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:39 am  #9


Re: IRS in my 67 shelby gt 350

on June 10, 2010, 1:19 pm, Daze wrote:

Sorry, I was totally unclear as to what I was askingmy question was more along the lines of " does the difference in pinion and trans angles cause any problems with driveline vibration? I went back and read my post and it was about as clear as mud.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:40 am  #10


Re: IRS in my 67 shelby gt 350

on June 10, 2010, 5:36 pm, tyrellracing wrote:

No prob I understand what you are after now. The way the drive train came together looked rather unorthodox with the differential higher than the trans and with both tilted down to wards the rear. The way this works flawless is that they are at complimentary angles to one another. Both the trans and the pinion are exactly parallel to the thrust line or center line of the vehicle. Then They have exactly the same inclination front to rear at 2 degrees so the two u-joints cancel one another s vibrations out entirely. My original drive shaft was 50 inches center to center. The companion flange I made and the longer snout of the Salisbury rear end required a 48 inch shaft. So... I put mine in my lathe and carefully trimmed off the weld, shortened the tube, indexed, pressed it back together and welded it. I can do amazing things with my tools however I cannot balance the finished shaft. Knowing that it is nearly impossible to assemble a seamed tube drive shaft and have it turn out balanced. I took it to Six States and had them balance it for me for 24 bucks while I waited. The tech. there is an old friend of mine. With that task complete, the drive is smooth as silk!


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:41 am  #11


Re: IRS in my 67 shelby gt 350

on June 10, 2010, 5:55 pm, tyrellracing wrote:

When I set up drive trains I always shoot for exact angles in the drive and driven components. If I error a little it tends to still be with in the 3 degree limit of dis-similar angles. However I NEVER allow the components to stray away from being parallel to the center line of the vehicle. This is where 95% of the mystery vibrations are spawn. I have worked on hundreds of fire trucks that were brand new and vibrated so bad at 55 mph it blurred the drivers vision! Every one had the water pump that is used as a carrier bearing when not pumping water and said pump would be off parallel to the center line no more than 2 degrees. That is all it took with that heavy of drive shaft.


If it isn't broken..... modify it anyway!!!!
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10/16/2011 8:43 am  #12


Re: IRS in my 67 shelby gt 350

on June 10, 2010, 7:25 am, tyrellracing wrote:

The Arning design used early sixty's Corvette bearings and stub axles. The hub carrier I believe is unique to his design. The Corvair used a trailing arm set up similar to the old Datsun 510. I plan on using the Jag bearing and stub axles by either tig welding the necessary brackets to the Jag hub carrier or make a duplicate out of steel. In either case I will be leaving the brakes inboard. Shelbys already have scoops for brake cooling so I just found some stainless steel flex tube 3 inch dia and routed it accordingly.


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