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Old December 5th, 2015, 09:19 AM   #1
ID I
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Default IRS drop questions

I have a 69 IRS that I am trying to drop while maintaining a decent ride quality. I have read several different ways on going about it but I am unsure on what to do given my application.

I have 3" adjustable drop plates installed and re-indexed 4 degrees (set it at 16 degrees from the stock 20). Sorry not sure how many splines. Just figured that should give me about another inch of drop from the charts.

I am trying to go for a 5" ride height with a 32" tire in the rear.

In the pic I still need to flip my trailing arms.
I know I can shave the metal down to gain more travel. The problem I can see is that the arm is still going to slap the upper shock mount.



I planned on running air shocks.

If I have to cut and relocate the shock mounts where would I move them?

Last edited by ID I; December 5th, 2015 at 10:11 AM.
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Old December 5th, 2015, 01:05 PM   #2
V8Transporter
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Default Re: IRS drop questions

By shaving metal, I take it you mean cut from below the unused upper hole in an upward rearward arc just to above the upper of the three bolts? I don't know what it looks like when it is flipped, but I'm guessing about the same. My last experience with this sort of thing was back in the mid-seventies when I ran a full Corvair IRS powertrain in a '72 bug. I managed to save the stock towers.
I'd be amazed if someone here doesn't know exactly what to do.
Looks like a neat project.
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Old December 5th, 2015, 01:42 PM   #3
d3ghia
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Default Re: IRS drop questions

There are a few different ways to achieve your desired ride height (as you mentioned). It may just come down to how do you want to do it?

Question for you. Will a 32" tire clear the torsion bar housing? I ask because in running bajas - a 31" tire is REALLY damn close (that is what I run on my Baja). Granted, you could use spacers and move it out - use early torsion bars that are shorter so that the endcap doesn't stick out 5" - but it is another thing to look at.

There are a couple builds on here running a pretty large tire - I can't remember what they were doing - but flipping the trailing arms is a good start - as well as having the drop plates.

You could also channel the body - look up Alteisen and the way that Ray Dean achieved a lower body while maintaining the suspension characteristics.
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Old December 5th, 2015, 01:50 PM   #4
ID I
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Default Re: IRS drop questions

The red area is normally done and I know I need to at least do that.

The green area I have seen done and its basically taking the "lip" off to allow the plate to travel.

If I do the green area I will still slap following the yellow arrow unless I cut the top shock mount out to allow more travel. I might have to go even further back.



I have a couple problems:

1. I don't know exactly how much to adjust the plate on a naked chassis. I threw the trans in there and that's just enough to see that it's not totally resting on the stop.

2. I don't have a tire and rim to give me my exact adjustment to get to my desired heights. The tire I have now is a little over 26".
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Old December 5th, 2015, 02:03 PM   #5
ID I
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Default Re: IRS drop questions

@d3ighia

Yeah the torsion bars are going to be an issue and I will have to use spacers on an offset rim. In retro spec I should of went with shorter bars but I have the new plates now and that's what I have to run with.

Channeling is not an option. I'm not doing the body work and my budget is for the roof chop only.

I have read a ton of builds but most are on swing axles dropping this low/tire set up. It is also why I am consider going the lower profile wide street tire look. The difference atm is cost. Street tire I would be looking at purchasing fairly new rims as opposed to finding a common truck rim at the pick and pull.

Oh and my here is my insparation for the tires. It is the Section 8 build.


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Old December 6th, 2015, 07:49 AM   #6
ID I
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Default Re: IRS drop questions

Not opposed to raising the trans and plan on raising it to take some stress off the cv's. Raising the torsion tubes I'm not comfortable with. I would rather cut the support out and refab something that works.

Just want to make sure I don't have other options be for I get to that point.
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Old December 6th, 2015, 10:29 AM   #7
V8Transporter
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Default Re: IRS drop questions

If you removed the upper portion of existing shock mounts as in the red/green marked photos, you could fab a new mount from 1/4" plate to mimic the original. This would have a radius to provide a large weld surface where it would attach at the torsion bar housing just inboard of the original mount. A second diagonal brace from up near the shock mounting point back down to a spot a couple of inches inboard of the new piece would be a good idea. Basically these would be two long triangles. Use cardboard for templates.
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Old December 26th, 2015, 08:26 AM   #8
ID I
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Default Re: IRS drop questions

Don't know what the hell I thinking. Whozawhat was right on with the torsion housing raise. Finally had time to go back and reread some builds. I had somehow merged trans raise and torsion raise in my mind. This became real apparent when I took my wife's spare truck tire and use it for a mock up.

Now that I'm pointed in the right direction again the next issue will be those damn long torsion bars. Feeling real stupid about buying those spring plates already.

Anyone know if rear disk brake conversions offset the rear wheels any? I really think I don't want to run 4"+ wheel spacers with a heavy rim.
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Old December 29th, 2015, 06:50 AM   #9
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Default Re: IRS drop questions

OR, sell the current springplates and buy/swap what you need. You never have to stick with a part just because you already have it.
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Old January 5th, 2016, 12:35 AM   #10
metalmaster1766
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Default Re: IRS drop questions

I made some drop plates for my IRS suspension, the only problem I ran into was I needed shorter shocks, the shocks I used weren't short enough because I broke the top or the bottom mounting hole off the shocks, relocating the shock mounts was an idea, but I never did it yet
I have an IRS torsion housing resting on my bench, I just haven't found the time, mainly the money to do it right, someday I'll get around to it, I just don't know when, but it will rest on my bench until I get to it, I have a bunch of spring plates to work with, making new ones can't be all the tough either
I'll try to promise to get around to it someday soon, but soon to me could be 2 years, by that time I'm sure somebody else will come up with an easier way, if not, just wait, I may get around to it before the end of this year, just please don't hold your breath unless you plan to stop by & help me do it
I have way more going on than most of you know, then again every 90 days I can get put on light duty work for 2 to 3 weeks & that just deflates everything I wanna do


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