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on August 28, 2010, 6:38 pm Daze wrote:
If the forum administrator didn't require a family atmosphere I would have a few choice words to say about an issue that has come up on my install
Ok enough rambling here is how it all began. Last night I was laying in bed building the project in my head as I often do and was thinking about the upper watts link. I had decided that I wanted to pursue that upper mount and was thinking about the clearance needed to have the large pivot clear the frame. As I was pondering weather or not it would clear my side bar supports I suddenly realized that the optional upper watts mount was the least of my worries... was there enough clearance for my hub the clear?? Because the side mounts bolt in to the stock leaf spring locations they actually wider than the original Mustang frame by 2" on each side.
If you look at the picture the side frame is under the bump stop housing rather than under the frame rail and does not begin to lide under the frame rail until the back corner where the mount begins to angle down.
This began to bother me so I got up and went out to the garage, grabbed a tape measure and measure the total length of my cross bars, 45" then I measured the empty Jaguar cage I have in my garage which was only 43" from outside to outside. To make matters worse I narrowed up my rear end 2.125" inches per side so that meant that unless the original Jaguar hub had at least 3.125" clearance between the hub and the cage, I was not going to have enough clearance between my wider frame and hub. Unfortunately it was late and I did not have a chance to investigate it further.
This morning I was able to go out and mock up the setup on the bench and sure enough the side bar is directly over the hub.
With the wishbone level there is only 1.25" between the top of the hub and the bottom of the side bar which is obviously not enough suspension travel. Crud!!!! So here are the option I have come up with so far.
1. Ditch the bolt in sidebars and weld tabs directly to the Mustang frame after reinforcing it. The outside edge of the Mustang frame is lined up with the inside edge of my side bar, so there would be enough clearance there. I still like the original leaf spring mount bolt in option so a big part of me does not want to do that however it would be the easiest solution.
2. Cut the 1/2" tab off of the top of the hub and then notch the side frame to clear the hub. If I do that the middle of the side bar would be 1.5" X 1" … not sure if that would be strong enough
3. Redo the half shafts and wishbones 1" longer on each side and then cut the tabs off of the hubs. Of course this is probably the worst idea, as it will cost a lot of $$ and then I will have tire fitment issues so I really don’t want to do this.
4. Snake the side frame under the Mustang frame. It will be harder to do and get the sidepieces mirror images of each other. Doable but I really don’t want to do that either.
Truth is I don’t like any of these options so what would you do?? Which option do you like best, or is there another idea that I have not thought of??
Last edited by Daze (10/27/2011 7:49 pm)
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Daze I was looking at your pics and comparing them to Irstang's and it also looks like you have a height problem. If you look at his left side pic it appears his third member is higher also which puts your shock mounts to low. It looks as though Irstang beefed up his unibody and used the same area for the Jag IRS.
Ralphy
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Maybe, maybe not. I love a good debate To make that statement that my height is off you must assume three things, his set up produces the “correct" rear end position (not saying his is wrong, its just one of the assumptions), we both want the same ride height, and we both plan on having the LCAs at the same angle when the suspension is at resting ride height. weather these assumptions are true or not still remains to be seen, but it is a good point and needs further review.
It looks like the top of his diff, is right in line with the bottom of the frame rail, so with the assumptions in place my set up would have the car sit abut 2" taller than his because my differential sits about 2" lower than his however lots of things could change that and I doubt we have the exact same things in mind. I like a little bit of rake to my car so I intentionally added about ½" of extra height to my initial calculations. Also I came up with my ride height based on two things. I first took every conceivable measurement of the original live axle so that mounting brackets could be built in such a way that the new suspension would be in the same relative position as the live axle. Also I took a good look at Mustsed’s install and the top of his differential sits about 1.5" below the frame rails based on measurements I took off of his pictures. Thirdly I want the wishbones to be as close to 0º incline at resting ride height which requires it to sill a little lower.
All that said, I really appreciate the heads up. Since I have my original support structure ready to mock up in the car, even though there is a clearance issue with the hub, I fully intend to mock up what I have to check the ride height. It just makes sense to see exactly where it is at that way I can make any other adjustments as I redesign my system. Your thoughts on the matter are welcome!! I know this post seams like I am simply trying to defend my position and say way "I'm right" but really all I am doing is explaining my full thought process that got me where I am , right or wrong.
Last edited by Daze (10/27/2011 7:52 pm)
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Guessing Game Here Well it's a little hard to judge height from a few pics. IRStang's wheel-well looks pretty close to good. However pics are not as good a measuring tool as a ruler.
Then in my case I plan to build a frame which can be adjusted accordingly for the height. To do this I know my starting point has to be a little low. Because it sure will be easier to raise the rear then lower it.
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I never cared much for the idea of those heavy tubes running parallel to the frame. At what point does it make since to go through all the hassle of making the shock mount adjustable rather than adjustable threaded shocks. All of the posted web sites showing IRS's in cobras and so on have in every application including my own chose to go with adjustable coil overs and after market springs. I think there is a pattern there somewhere. May be that got over thought too. All in good humor LOL
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OK, so you were going by the hub location in relation... to the wheel well. yes in that case they do look fairly centered, but if you look at his other picture:
to get that center placement, his wishbones are angled down and I want mine to be closer to parallel with the road.
Besides the measurements I took of the original rear end location, these pictures were a huge deciding factor.
If you look at the mounting location under the car the bottom of the support is lined up with the bottom of the frame rail. Then I was able to take the picture of the unit out of the car, take several measurements from it of actual Jag components that I could measure in my own garage and then use those number to determine the scale. From there I measured how far down the diff and shock mounts were from the bottom of the support and came up with 1.5" which Mustsed confirmed.
Either way all this is about to become irrelevant as I am hoping to actually mock the system up in the car and verify the ride height with the weight of the car on the springs. I need that info before I can decide exactly how I want to change my mount.
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Check this out. The guys at Snow White have done Jag IRS installs in many different street rods. Check out their instructions and recommendations on pinion, LCA and half-shaft angles.
I am designing this Mustang to sit lower than a Shelby. The straps you have seen in the pictures to date are not representative of ride height. I'll get some numbers and pictures of ride height as soon as possible.
I checked my numbers, today. Coilover extended length is 13.4. At 10 inches the hubs better be on the bump stops. 60% of the delta equals 2.04. So I'm sticking with 12 inches as my target ride height shock eye to shock eye. Pictures of my install you have seen to date all have shipping straps set at 12.5 inches. Too, much. My tires, however are centered in the wheel wells at this height. At 11 inches my half-shafts are just about parallel to the ground and my tires are well up in the wheel well. I am anxious to see what 12 inches will look like. We both know how much a half inch of spring compression can effect ride height.
All my calculations are based on two convertibles. One of them was mine and the other is a complete car. The center of the solid rear axles were 8 inches below the center of the frame rail directly above the axle. Tires looked centered in the wells on both cars. Curt Hamiltons cage positions the differential just under 7 inches below the top tubes. He sets up his cage with XKE geometry. According to Curt and some other source I read, the half-shafts should have a bit of a downward angle at ride height. Something around 2 degrees. I plan on setting up the car with the stock springs, first. I anticipate custom springs once I can get some corner weights on the finished car and determine exactly how it will sit. I want my Mustang to sit lower than stock in the back. It is way down in the front with the RC Motorsports MII conversion. So if I'm right with all this, the car will end up on a bit of a rake. I know we are in disagreement on the angle of the lower control arms at ride height, but that's alright. I think the Jag IRS will forgive us both.
My day was filled with my project. I will ponder your half-shaft to sub-frame interference problem.
Last edited by Daze (10/27/2011 8:00 pm)
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That right there is why I came up with the "assumptions"... early on in this thread. The biggest difference I see between your install and my own is ride height, I like it a little higher and you like it a little lower, and that would explain why our differentials are located in two different places relative to the bottom of the car.
Curt Hamiltons cage positions the differential just under 7 inches below the top tubes. He sets up his cage with XKE geometry. According to Curt and some other source I read, the half-shafts should have a bit of a downward angle at ride height. Something around 2 degrees.
I wonder if that is specific to the XKE... I am almost positive that the XJ6/12 was set at 0º To align a Jag you are supposed to set the wish bones at 0º prior to adding any shims, that would result in a little bit of positive caster given a slightly downward tilting wishbone. My plan is, as I said before to shoot for 0º however if I increase the angle of the shocks by using one of the three or four upper mount options I may end up with a slight angle on the wishbones which I am OK with
As far as my clearance issue between the sub frame and the hub, I think I have that fixed... at least in theory because I have not done any actual metal work to fix it. I am going to weld a piece of rectangular tubing to the inside of the sub frame and then gusset it. Once I do that I will be able to cut away 3 sides of the original sub frame tubing and get the clearance I need. It should easily clear at that point however IF the clearance is not quite enough or close than I will cut the 1/2" nub off of the back of the hubs to get the extra clearance.
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Curt corrected me on my use of the term XKE geometry. My tubular cage is set up to use XKE coilovers. With the halfshafts at a slight downward angle the springs will be at their proper compression. He recommends using adjustable coilovers to vary the ride height. They,also allow you to level the car side to side.
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I took a good look at wishbone angle today and after taking a bunch of measurements...
I think 4º os about max, I wouldn't want to do more than that. 2 would probably be about perfect.
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Hmmmmm, looks like I've problem too because I did ......
the same side supports as Daze.
Daze can you tell me the distance between the top inner edges of the hubs. The edges that would touch the supports according to the pic.
Thanks,
Mustsed
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I think you will be OK... or close seams to me the distance between between the frame rales is the same for a 65 and a 67 BUT the 67 is 2" wider and all I needed per side was about 1" if I cut the tab off of the hubs. Also when I narrowed my rear end I made it 1/2" narrower than the live axle so I am thinking you may be OK or only need minimal mods. What length are you half shafts center to center?? I will get that hub measurement for you tomorrow.
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Daze, I did the shorting WITH the 1" spacers....... in mind because I use the outboard brake hubs!
I shortened my halfshafts and LCA with the added 1" for the spacers in mind. Will take the distance tomorrow at work and let you know.
I finally got all parts on the bench and will start to put everything together. Will use the Monroe Sensatrac shocks with stock Jaguar coils that came with the IRS I bought. Next week is scheduled to install it onto the Mustang (hopefully).
Mustsed
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42" from the hub top to the hub top you could gain 1" by shaving the hub tops, also, I think I have a solution to the issue and still use the side bars. I will let you know once I have a chance to mock up the fix.
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I think I solved the problem... at least in my head.. I am going to weld a piece of rectangular tubing to the inside of the sub frame and then gusset it. Once I do that I will be able to cut away 3 sides of the original side frame tubing and get the clearance I need. It should easily clear at that point however IF the clearance is not quite enough or close than I will cut the 1/2" nub off of the back of the hubs to get the extra clearance.
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