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obsolete
obsolete GRM+ Memberand HalfDork
2/26/22 12:28 p.m.

In reply to maschinenbau :

If you want to try doing the dynamic toe measurement with a laser, I just did it on the front end of my car, documentation starts here: https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/1988-chrysler-conquest-ecotec-swap/178574/page9/#post3424234. Hopefully some of that is useful to you.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/7/22 9:17 a.m.

Progress is being made. I assembled the front end just enough to align the backbone frame with the tube frame. Very carefully checked wheelbase vs diagonal measurements vs ride heights until everything was square and level. Then I added temporary jigs and removed the frame as a single piece, leaving the powertrain/subframe behind. The past couple weeks have been a tedious process of filling in the remaining tubes, which all have funky angles to cope, test fit, grind, fit, tack...etc. Luckily I can lift the frame by hand like a wheelbarrow to move it out of the way when I want to drive the El Camino. The hot rod has been trapped for months by the engine though. This is what building a 3rd car in your 2-car garage looks like.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/7/22 9:25 a.m.

Oh, I forgot about this part! Remember back when I was patching holes in the backbone frame? The inside floor of the backbone section was heavily rust pitted, like the surface of the moon, and I was worried about strength. Didn't want a floor jack punching a hole in the metal. So I cut 2 long strips of 16ga, bent them at work on the 4ft press brake, and plugged and stitched them in to overlap the original frame bottom. Added a few pounds but also some stiffness and peace of mind.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/13/22 7:13 p.m.

Roller!

This meant I could finally drive the hot rod again for the first time in months. Which reminds me that I still have a lot to do on that car...

But I also discovered a problem, potentially a really serious one. The rear sits like 3" lower than expected. Not sure if I mis-judged the coilover preload, or I have the wrong numbers for the spring rate, or what. But at ride height the lower flat part of the rocker arm should be parallel to the ground, and instead it's way rotated. Also if you bounce on the rear of the frame, it hits the ground. Not good. You can see how angled the UCA is due to the Carolina Squat I have going on.

The easy answer is just move the coilover mount closer to the rocker. So I hacked it all up, moved it 1.5" rearward (motion ratio is 1:2, so that's 3" ride height). 

...and now I've run out of travel to even install the coilover. I max out the upper ball joint at full droop, which is not enough droop to let the rocker rotate enough to fit the coilover. Basically I need like 1-2" more preload on the coilover spring, but it doesn't have it. I could try to find a longer spring of the same rate and put that on the coilover, but that just adds even more cost, and I don't have the right compressors for these. I could remove the UCA to allow more droop, but once you load the knuckle it gets all cattywampus and unstable. No matter how I re-design the rocker arm setup, the lack of droop travel means I will always have this problem, unless I can get more preload. Kinda feeling lost.

I might scrap the rocker arm system altogether. The whole thing is feeling kinda mickey mouse to me anyway, and too complicated for a Lotus. Total budget of the rocker suspension, with rockers, hardware, and coilovers, was $150 so far.  Options to replace:

  • Preload adding device on the coilover mount - like a shackle on a threaded rod that I can use to raise the car up after installing the rockers. Feels very mickey mouse.
  • Stock Lotus rear coilovers. Super rusty (worse than the fronts), Really low spring rate like 75 lbs, and very long therefore hard to package. But, free.
  • Simple coil spring with custom fabbed perches + normal shock, acting directly on the knuckle (motion ratio 1:1). Only problem is I need something really short, like 8-10" at ride height +-3" minimum of travel. And no larger than 4" OD to fit in the UCA. And 175-250 lbs/in for the spring.
  • DIY or used coilover. Could get pricey since I'm starting from scratch. Similar specs above.
  • Something else equally ridiculous. Quarter elliptical leaf spring?

Original suspension idea: those coilovers don't have enough travel, and rate is too high, hence this whole rocker arm suspension debacle.

Dusterbd13-michael
Dusterbd13-michael MegaDork
3/13/22 7:43 p.m.

Why not shim the motorcycle coilovers? Essentially add a 1-2 inch coil spring spacer in it, thereby giving back your preload adjustability? 

Alternatively, i have some 400lb coilover springs up here that can be had super challenge budget friendly. 

Mr_Asa
Mr_Asa GRM+ Memberand PowerDork
3/13/22 8:03 p.m.

When in doubt, test it out.

Should be able to build a test rig that will let you figure out how much weight it takes to compress the spring an inch.  Do that, do the math, figure out where you went wrong.  Might give you a better option for the rockers?

nocones
nocones GRM+ Memberand UberDork
3/13/22 8:22 p.m.

So If I understand it correctly your wheel rate is to low with the current Belcrank ratio.  

Can the suspension sit with no shocks on blocks where you want ride height to be?  

The MC shock should have sufficient spring rate to get to as much as a ~550-600lb wheel rate.  They will only give 2-2.3" of travel at that Wheel rate.  

Before you scrap it all put a set of holes in the pushrod side of the Belcrank that is halfway along the Belcrank.  That should stiffen the suspension quite a bit.  

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/13/22 9:19 p.m.

To be honest I'm not sure I understand the problem either now that I've cooled off. If it was a spring problem, it would be bottoming out the shock, but it has plenty of travel left. Going to take another look at it tomorrow. 

Nocones, you're using Hyabusa shocks right? Those are like 700 lbs compared to my GSXR600 which are between 400 to 530 depending on year (and I don't know what mine are). 530 puts me at 1.4 Hz with this rocker. 

nocones
nocones GRM+ Memberand UberDork
3/13/22 9:31 p.m.

In reply to maschinenbau :

I'm using R1 shocks at all 4 corners.  

 

Take a quick video of jacking the car up and setting it down.  

What happens when you bounce on it?  

It also looks a bit like at ride height you have a very falling rate.  This is from a computer screen miles away though.  It looks like the angle between the Belcrank and the shock is increasing at ride height.  That's not be best because the Belcrank effective length gets shorter which lowers the spring rate quickly.  

A longer pushrod should be able to recover the ride height at a minimum.    

TurnerX19
TurnerX19 UltraDork
3/13/22 10:10 p.m.

I think Duster is on to it. You may very well need higher rate springs, but the spacer will get you to static height, and put the rocker back into the correct part of its travel arc. Also they are cheap to make from tube or scrap coil over perches.

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) GRM+ Memberand MegaDork
3/13/22 10:51 p.m.

I'm with nocones on trying a longer pushrod to get the ride height back, and I agree with his assessment that you've got a lot of falling rate built in there. Looks like your bellcrank pivot should be a couple inches further forward.

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
3/13/22 11:07 p.m.

You still have Camry struts?

I mean, listen to nocones and angry first. But as a backup at least you know the Camry stuff is strong enough for a car...

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
3/13/22 11:08 p.m.

Ooooooooooorrrrrrrrrrr 

Are the belcranks on backward?

 

 

 

Mr_Asa
Mr_Asa GRM+ Memberand PowerDork
3/13/22 11:42 p.m.
Robbie (Forum Supporter) said:

Ooooooooooorrrrrrrrrrr 

Are the belcranks on backward?

 

 

 

I've done that before.  Thankfully only in a class, but that oversight on the project dripped my group a letter grade.

My bad Ben and Mike.

TVR Scott
TVR Scott GRM+ Memberand SuperDork
3/14/22 4:46 p.m.

Seems like you could remake the bell-cranks without too much headache.  Assuming the shock travel and rate are basically workable.

Brotus7
Brotus7 Dork
3/14/22 7:13 p.m.

Is it as simple as your pushrods too short?

Happens even to the best of us.

TurnerX19
TurnerX19 UltraDork
3/14/22 7:32 p.m.

In reply to Brotus7 :

Look close at the photos. It is the spring that is too short. The shock is very compressed, and the spring perch is wound all the way up by my view. Spring spacer on the chassis end of the spring will bring the rocker back to better geometry as well as raise the car, A longer push rod will raise the car, but it also causes decending rate.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/18/22 10:17 a.m.

Big long post warning - very technical. I took some measurements, did some math, and I have a few paths forward.

First some pictures. This is full droop, limited by upper ball joint angle. If not for that, the rocker would hit the UCA.

Then target ride height, with favorable rising rate rocker geometry as designed.

Then current ride height, roughly 1.75" lower than target. This is just past the transition from rising rate to falling rate. 

I found out I don't need a compressor to remove the spring. It's only 8.375" long, and there's enough adjustment on the sleeve to fully relieve compression. Based on this searchable site (racetech.com), it should be a 2001-2005 GSXR 600 or 750, which is anywhere from 403 lb/in to 448 lb/in. I'm assuming 410 lbs for now. Very standard 2.5" ID coilover spring, which means I could replace them with something else. Anything longer will require compression to assemble though.

Speaking of spring rates, here's what I could find so far. YMMV, check my math, etc...

I plotted everything out. I also took some extremely rough corner weight measurements using the bathroom scale and lumber lever method. Approximately 450 lbs sprung weight, 100-120 lbs unsprung, 570 total corner. Also keep in mind the body will add some rear weight, so I'm using a higher corner weight in my calculations.

The reason my ride height did not end up where I thought it would is because I assumed the wrong spring lengths and preload. If I change nothing else, and just add about .75" to 1" of preload, I should have correct ride height. 

Two problems with adding preload:

  • Spring will now require compression to be assembled. Probably a hydraulic press and custom tooling. It's a very small lip around the outside for tooling, and about 600 lbs of load. Not a fan of doing this, especially with spacer rings that won't perfectly center the spring.
  • Preload adds cost to an already costly and complicated suspension. I can get custom spacers cut and shipped for about $40. I can't fab these without turning from a huge 3.5" diameter chunk of lathe stock. Might be able to turn from a large piece of 3" steel SCH40 pipe, if I can find it cheap enough. I can buy longer springs for probably about that or more. Cost comparisons opens up the can of worms of "if I remove the GSXR coilovers from budget...what else can I do instead?"

So, what else can I do instead?:

  • Replace GSXR 600 coilovers with higher rate coilovers from Hyabusa GSXR 1300. 730 lb/in vs 410 lb/in. This increases ride frequency from 1.3 Hz to 1.7 Hz, greatly mis-matching the front which will be around 1 Hz with the stock springs. Also I don't know if my rockers will mount to these without re-drilling. They are also more expensive, adding about $50 to the budget on top of all the rocker arm parts and pieces.
  • Replace with newer 06+ GSXR 600 coilovers, with 530 lb/in, and still require a decent spacer. Increases ride frequency to 1.5 Hz. Same cost as the current coilovers.
  • Replace EVERYTHING with MacPherson strut + ebay coilover sleeves. If I can't reuse the Avalon struts, I bet I can cut down the housing and add an old-school strut insert (like OEM MR2 or VW Rabbit)...this paves the path for aftermarket upgrades later, like Koni single or double adjustable inserts. Camber curve is not as good (at best, constant with bump), but travel and droop will greatly increase for better road manners. It's also very in tune with "simplify and add lightness". Basically following this instruction, but for a Toyota Avalon and hoping the strut tube is the right size. Something like this:

Current rear suspension is about $190 in the budget right now. If I can keep the Toyota strut valving without buying an insert, I will come out ahead.

Some ride freq calculations:

I'm open to advice, but mostly just posting to let you know where my head's at with this. This weekend I'm going to cut up some Toyota Avalon struts to see if that's even a path forward at all. I am leaning towards that solution if possible. It just seems easier, cheaper, and less sketchy to get tuned right. Fewer moving parts, fewer custom fabricated parts to go wrong. And 1.5" of droop seems pretty awful for the road. Yes this is a $2000 race car, but I will be driving it on the street to car shows and autocrosses. I don't want a one-trick pony.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/20/22 4:07 p.m.

More research. To recap on the wishbone-rocker setup, a 9" long 400-500 lb spring would make that system work, probably. Unfortunately cheap used 2.5" coilover springs only seem to come in 10" and 12" lengths. 

I looked into the strut conversion. It looks promising. Obviously stock Toyota struts are too tall, hence the whole reason I design a rocker setup. But can I make it shorter?

I just recently learned about strut inserts, the old-school predecessor to fully sealed struts. I learned about the classic grassroots hack of cutting apart a strut housing to use a shorter insert with coilover sleeves. KYB and Bilstein still support these applications, so I can always upgrade later. And I like how the Toyota stuts have the correct mounting brackets for the knuckle, brake lines and sway bar. It all sounds nice. But can you convert a modern sealed strut to use inserts? So I took them apart to find out. 

Here's the Toyota Avalon strut alongside the GSXR coilovers, the Holy Bracket, and a random GM shock.

First I removed the spring perch. This is where the adjustable sleeves and 2.5" springs will go once they arrive.

Then I removed the oil just by drilling a tiny hole. Oops, it's under pressure.

To get the rod out, I used a pipe cutter to slice the last 1/4" or so off the housing.

What do you know, the ID is just under 1.75" (44ish mm). The aftermarket Konis and most OEM ones are 43.5". This...could work.

To maximize clearance up top, I can add about a 1" cup to the bottom and still have clearance to the axle boot. Lots to grind here.

Now the trick is find the shortest strut inserts possible, so I can clear the Lotus body. I searched all over and I'm not the first to have this problem. Everyone from MR2 to Datsun to Volvo folks have tried to lower their cars, build coilover-struts, and use shorter inserts. The concensus seems to be Koni 8610 or 8611 (single or double adjustable). They come in a size with an 11.5" body. The shortest OEM seems to be 13.5", particularly the MR2 SW20 front strut. That's a good option, plus there are KYB adjustable versions available. But in my research I also found one for Daewoo Lanos, with an ulta-short collapsed length of 13.5" (which I don't know if that includes the rod stud or not). Also the same P/N for the 88-92 Pontiac Lemans? For only 6 freakin bucks each, it's worth a try. If it works dimensionally, I can always upgrade to MR2 KYB's which are probably valved more aggressively than these, or of course Konis.

Or if I run out of budget I will have a Lotus on frickin Daewoo struts inside modified Avalon housings.

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) GRM+ Memberand MegaDork
3/20/22 9:45 p.m.

Did you know that every 10" and 12" spring comes with a free 9" spring inside?

TurnerX19
TurnerX19 UltraDork
3/20/22 9:52 p.m.

In reply to AngryCorvair (Forum Supporter) :

With a much higher rate too!

TurnerX19
TurnerX19 UltraDork
3/20/22 9:54 p.m.

In reply to maschinenbau :

Daewoo Lanos and Pontiac Le Mans in those years came from the same factory.

maschinenbau
maschinenbau GRM+ Memberand UltraDork
3/21/22 8:50 a.m.

In reply to AngryCorvair (Forum Supporter) :

Normally I'd be the first to suggest cutting springs, in fact I did so on the Roll-ovalon and Datsaniti Challenge cars. But not with these coilovers that need ground squared ends. A tiny circlip holds it all together and I don't want that thing loaded unevenly after jamming in a longer spring.

Dusterbd13-michael
Dusterbd13-michael MegaDork
3/21/22 9:00 a.m.

I have 9 inch long 12kg springs sitting here. 2.5 coilover springs. 

MrJoshua
MrJoshua UltimaDork
3/21/22 9:11 a.m.

Are you sure those motorcycle springs are 2.5"? My memory had them at a problematic 2.25".

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