Finally - Narrowed trailing arms for IRS

284D9E91-4EEE-4C19-8279-54D1F55D0620Hey All,

Kevin @Coolrydes presented me with my 1.5” Narrowed arms for my JPS Coupe. They moved the bearing housing and capped the end and it all looks like it came from the factory. He even had it media blasted and ready for coating.  He has made other sets while he had the jig set-up. Give them a call! I will be coating these with KBS Rust Seal. I have been told that you will need two Type 3 Automatic left axles to make it all work. They are available from most supply houses. It will be nice not having the tires squeaking against the body at all the bumps. 

Brian

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Good to see someone set up for this modification again! A 7" Fuchs alloy (with a 205 or 215) fits nicely against the stock spring plate (the sidewall will hit the block on an adjustable spring plate) with beetle drums. If you're going for the wheels/tires being tucked in as far as possible you'll probably have to replace 1 spring plate bolt with a lower clearance allen head bolt (to clear the tire sidewall) and you may have to cut back the bump stop near the top of the shock.

Kevin's work looks very similar to the way my friend Bruce (here in the Vancouver area) did it in the late '80's/early '90's. Check out the June '94 Hot VW's for an in-depth look at how it's done. Al

Gordon,

Mango smoothie (Paul) gave me the original info and Kevin confirmed. Just need the left axle for a Type 3 Automatic IRS. They are shorter than the Type I. Buy two of them! I believe Moore parts over here in SoCal has them and a general search will give a dog selection. Kevin was quoting $500 plus your cores.

Brian

 

My friend Bruce said that's what the stud length was sticking out of the hubs on a car with Fuchs he measured. Too long and the studs hit the ends of the lug nuts. Too short and there's not enough thread engagement.  And when you press the studs in make sure that the non threaded part that goes into the hub doesn't protrude and hit the threads on the nuts.

Hey Wolfie,

1.5” per side. I haven’t found anyone with a Coupe who has done this. Mango Smoothie has always been my reference point. Gonna look similar I hope. Yes, I plan on taking many pics. I wanted to let the SOC group know that there are sets sitting on the shelf waiting for new owners. My wait was a good 8 months due to production runs going on at Coolrydes with their other products. I will have a good set of stock IRS arms and axles available afterwards. 

Brian

i remember this step VERY well as i had the suspension in/out/re-welded many times to get the caster just where i wanted it.

my only other $0.02 is to undo the body/pan bolts and many sure it's dead in the middle when you are talking mm's clearance. (undo - loosen, measure via back spacing, rinse / repeat until the chassis and body are perfectly centered)

Gordon - as with pretty much my whole build... internet.  i was looking through an empi spec book for drive shafts (in my free time LOL) and saw the different lengths.  i saw the trailing arm design concept (same pic above - same i did too) and the rest is history.  i did cut my bearing carrier completely off so i could factor in how low i was going to run.

Brian - don't sell yourself short.  I'm just a regular guy who is passionate about this kind of stuff.

 

Gordon Nichols posted:

How the hell did you ever remember that??

He must not have his brain filled with all that old now useless computer stuff like the Hollerith Code, JCL and Assembler language. I sure wish I could do a selective brain reformat and gain back a few gig.  I'm not even asking for a terabyte.

Ah, the golden days of programming.  A smart guys with good problem solving skills could take the simple (crude) tools and do just about anything.  Now you have to get specialized training in about 4 million different complex tools to do anything, and it has more to do with a voluminous memory than creativity.  Yeah, computers do a thousand times more, but they need a thousand times faster processors and a million times more resources to do it.  Kids coming out of school now with computer science degrees are clueless about managing resource utilization and being efficient.

You kids get off my lawn!!!

EDIT: And by the way, I like assembly language!

I got my first computer in 1978.  The manufacturer went out of business 6 months later.

So, I had to learn how to program it and repair it.  I even figured out how to make modifications to the motherboard.

It had 64k of memory which was an astounding amount at the time. A lot of people had 4k to 16k. 

I worked in languages like Basic, Fortran, and Pascal.  I even did a little work with assembly language when speed was important.

This is when I learned about hexadecimal numbers.

WOLFGANG posted:
Gordon Nichols posted:

How the hell did you ever remember that??

He must not have his brain filled with all that old now useless computer stuff like the Hollerith Code, JCL and Assembler language. I sure wish I could do a selective brain reformat and gain back a few gig.  I'm not even asking for a terabyte.

Hey, One brain cell can be made to grow into a Supercomputer  

In 1984 I bought an MAI basic4 mini computer, from Tustin California.  20 meg HD I forgot if it had 16 mb of ram... $40K C$, a few years later $20K for 20megs more.   Interpretative basic, it was my start with a bit of basic coding.  Those were simpler days for sure.

DannyP posted:
Lane Anderson posted:

EDIT: And by the way, I like assembly language!

I KNEW there was something about you I didn't like.

You are truly the ONLY one in the universe that likes it.

I wouldn’t want to do it exclusively, but it’s fun because it really requires imagination.  Most of the time I prefer C or C++. I like to keep the layers of unknown stuff between me and the machine at s minimum.

IaM-Ray posted:

" Check out the June '94 Hot VW's for an in-depth look at how it's done. Al"

@ALB can you yodal a link to get a copy to read that article...  

I think I already have it scanned into my computer, Ray; in a previous discussion about narrowing rear suspensions (2? 3? years ago???) I seem to remember sending it to someone. I'll just have to spend a little time looking for it. If I haven't posted it by the end of the weekend feel free to remind me. Al

@IaM-Ray- here you go-

With Bruce's method the bearing housing is cut free and moved inward; probably a little more work than Paul's trailing arms (although I'm sure Paul will dispute that!), but (for those who care) you have to look a little closer to tell what's been done as the arms themselves don't look modified (at first glance). Both achieve the same end and I doubt if there' any strength difference.

My apologies for the upside pages- it was the first time I'd used the scanner. I think you'll be able to spin the pages- 

Note- Just noticed I cut the bottom off of page 2- it should read-

Left- cut out a "D" shaped piece of 3 mm thick steel and weld it to the trailing arm between the bearing housing and the spring plate mounting tab. This provides clearance for the backing plates or brake rotors.

I'll check pages 3 and 4...

Page 3 top- Right- another angle of the modified trailing arm shows how the bearing housing has been moved in. An additional gusset has been welded on the inside of the trailing arm to the bearing housing. You can see this one on the right side of the trailing arm.

Page 4 is good.

Paul's method- narrow tr. arms mango 2narrow tr. arms mango 4

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Thanks for posting it, I got a copy.  Is it being done by anyone outside of the few?  I often wondered why this was not being done to allow more tire size on the rear.  We had special rims widened "inward" on my last IM.  It seems you could do to have this done or produced by some manuf.... they do shortened beams... 

I don't know why it's not done more often; I guess because it's quite involved. With an irs it is the way to get the most tire under the rear, though, and if you look at the steady progression of wider tires under the rear of 911's through the years there is a benefit. A few different shops have done them over the years but I guess there's just not enough demand to keep shortened irs arms in stock.

ALB posted:

I don't know why it's not done more often; I guess because it's quite involved. With an irs it is the way to get the most tire under the rear, though, and if you look at the steady progression of wider tires under the rear of 911's through the years there is a benefit. A few different shops have done them over the years but I guess there's just not enough demand to keep shortened irs arms in stock.

my guess is the rear wheel alignment.  i found even the first small tack weld put the geometry out a few degrees.  IIRC, i had to set the rear caster where i wanted it, the grand off another 1-2 degrees (pivot from the first tack weld)... then do the first tack weld.  dont know if that made any sense, but even with cooling (outside) checked, i had to factor warping.  not hard, but LOTS of measuring.

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