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Rear Suspension

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Rear Suspension

Post by a2ndopinion on Sat Mar 23, 2013 1:42 pm

For those of you who have seen my "Front Suspension" thread http://vintagecorona.forumotion.com/t144-front-suspension , I'll now begin to compliment it with the other end.
As I linked in the front suspension thread, I have a whole bunch of info over on http://www.celica-gts.com/forums/index.php?topic=16360.0 if you want to look at some of what led up to this.

All the rear end has so far is two factory leafs removed and one Hilux overload leaf added up-side-down on both sides, and I put in the stiffest shocks I found laying around.

Here's what I have so far - this is the rear end info, quoted / paraphrased from celica-gts.com:

After some prodding by shonuff while I was in Seattle (well, just outside of Auburn actually), I went to work on the rear springs.

I wasted about an hour measuring the five leafs that were OE in the wagon and the overloads that shonuff gave me before I said "%#!& it" and just gave it the ol' college try! :wall:

The OE springs had a negative arch to them, and are mounted under the diff.



The easiest way to simply lower the back end would have been to add blocks. The problem is that the leaf springs are too soft, from both a performance/handling stand point, and for loading the wagon to haul stuff/people.
So how to stiffen the back and slightly lower it at the same time, with the overload springs that Ryan gave me?


It looked like the overload could basically replace the 3rd (center) leaf, but it is as thick as two OE springs.



After disassembling the right side, I took out the third and fourth leafs, and put in the overload.


It looked good, so I finished both sides, and also swapped in some gas charged cheapy Monroe shocks, and took it for a drive.

What a difference! That is definitely stiffer, but it is a hair higher than it was. Sad

Close inspection shows that the front of the springs need about 1/2" taken off, so that will drop it a very slight amount, but the springs now appear to have a slight positive arch. I had installed the overloads with a positive arch, but am going to try turning them over to give then a negative arch and see what that does!



Pic taken 05/02, after doing the fronts:


Pic taken 05/10, after first attempt at rear springs:


I'll post again when I get the rear springs cut 1/2" and turned over!



Alrighty then!
It took a while, but I got it!
I started shortly after 5PM and finished at 10PM, but I did a considerable amount of work there.

First, as you can see from the following pic, that even with the overload spring, there is negative arch to the springs. That is why I wasn't worried about having the overload up-side-down:


So I disassembled it (again):


This is how little of an arch the overload spring has - hard to see, but that's my straight edge on top:


It's easier to see here with the negative arch:


Here's the two I took out, and the one that has replaced them:


Look at the difference in thickness - twice as thick!


I took the overloads to the grinder so that they wouldn't run over the spring clip on the 2nd spring:


I also cleaned them all up so I could grease them!




And cleaned up the ends, so as not to damage the next spring:


All back together and greased, the right side looks good:


The left side may still settle out okay, but I forgot to mark it before I started, so I guessed - oops!



I'll get a pic in the morning to compare height, as it was too dark.

As for the ride (a short trip around the block), it is just a tad bit softer since the overload is not under hard compression, but bouncing the back end, it is still hard.
I think it is going to be just right, but I'll find out for sure when I get out and about on Tuesday - wow - that's today! I'm tired and going to bed.

The drive today was great! There is just enough softness that the normal bumps on the road, and dips on the freeway, especially I-84 heading out of Pdx towards the Gorge, are on the smoother side, but the bigger bumps are definitely firm. The handling is very nice - especially compared to what it was like.
At this point, if it turns out to be too soft, I can always turn the overloads right back over, but will then have to add blocks to drop it to a better height, which I still may do yet anyway.
I do have to wonder though, if the now greased springs would feel softer with the overloads turned over than they did before. Maybe I should try that, and add blocks too!

My concern with being on the stiffer side now is that I still have marginal shocks/struts, don't have urethane sway bar mount or link bushings yet, have 28 Y.O. rubber leaf spring bushings, and no rear sway bar or PHB/Watt's link. All of these pieces will firm it up some more, especially the shocks/struts and leaf spring bushings.

Anyway, the left side did settle past the clip that it was touching.


Here is the height as of today:


Day before yesterday:


And last week:


I think it needs to drop about 1" in the back and maybe 1/2" in the front.(?)

And one more piece of info...

I filled up with fuel in Beaverton before I headed to Adam's (yella'81) on Saturday, and filled up yesterday morning - 356 miles later - and it took 12.6 gallons for a new best of 28.25 MPG! I advanced the timing just a hair (RCH?) before leaving up there. I think it can advance just a bit more, so I'll get the dial back timing light out tomorrow and check it.

After driving it for a couple of days, and really liking the feeling of the back, I got a pic last night...

Loaded ride height – Groceries, ¼ tank of gas, daughters and wife, 05/14/09:

Can't you tell how much my daughters love me?

Hitting bumps with the load still felt good! I am very pleased - thank you shonuff!

Overload springs now “up side down” and empty, 5/12/09:


Overload springs “right side up” 05/10/09:


Only the front “done” 05/02/09:



So as you can tell, I haven't touched the rear suspension in almost 4 (four) years! It still wanders around behind the front end, but with the front end finally getting finished(?), I need to get my ass in gear (pun intended)!


Last edited by a2ndopinion on Mon Mar 25, 2013 10:40 am; edited 4 times in total

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DD -'81 Corona wagon - 22R hybrid P&P, Crane stage 3, Si valves, Erson springs/retainers, Weber, Cannon, MSD, Thorley, Borla, 3rd gen Celica front suspension, Cressi Big Brakes, coilovers, Camber plates, RCAs, AGXs, Addco, all urethane bushings, Hilux leafs...
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Re: Rear Suspension

Post by a2ndopinion on Sat Mar 23, 2013 2:02 pm

What is left for the rear end is a Mk I Supra disc brake, 3.90 geared LSD, Camaro (shorter) AGX shocks, a "wishbone" or "A frame" rear diff locator, leaf spring sliders and installing the urethane bushings. The diff has the four-link mounts cut off, but needs to be cleaned up and then have the leaf spring perches welded on.
The sliders have been ordered:


to replace the shackles:


here's why:

The angle of the shackle can stiffen or soften a spring's normal rate. You can determine the effective angle of a shackle by drawing a line through the middle of both spring eyes and a line through the shackle pivots. Then measure the angle formed by the two lines (measure ahead of the shackle - see illus. 3). You can increase the effective rate of a leaf spring by decreasing the shackle angle. An increase in shackle angle will produce a decrease in the effective leaf spring rate of a leaf spring.


A good starting point for shackle angle is 90 degrees. In this position the shackle has no effect on spring rate. Keep in mind that the shackle angle changes (and consequently the spring's effective rate changes) whenever the suspension moves. Also, the shackle's angle will change whenever you change the chassis' ride height, the arch of the leaf, the load on the leaf, or the length of the shackle. Since the shackle direction changes when the leaf is deflected past a flat condition, you should avoid deflecting the right rear leaf to an extremely negative arch condition. This could cause a very large shackle angle at high loads and consequently a very soft spring rate. Excessive body roll and poor handling could result. You can correct this problem by decreasing the shackle angle, increasing the arch, of the spring by increasing the rate of the right rear leaf spring.

Shackle length is another factor affecting the rate of a leaf spring. A short shackle will change its angle (and the effective rate of the leaf spring) quicker than a long shackle upon deflection of the leaf. There is a second shackle effect on the stiffness of the rear suspension that counteracts and sometimes exceeds the shackle's effect on spring rate. This second effect occurs whenever the shackle swings in its arc and moves the rear spring eye vertically.


The vertical movement of the rear spring eye causes a jacking effect. If the shackle movement forces the rear spring eye downward, the leaf will deflect and exert an upward force on the chassis that will add stiffness to the rear suspension. Conversely, the shackle will reduce suspension stiffness if t causes the rear spring eye to move upward during suspension travel.

The stiffening effect occurs during suspension deflection whenever the rear spring eye is ahead of the upper shackle pivot and the shackle is moving rearward (see illus. 4, example B). In this position, however, the shackle also produces a softening effect by reducing the effective rate of the leaf spring (due to the large shackle angle). The overall effect to the stiffness of the rear suspension is determined by the greater of the two shackle effects. Under opposite conditions, you can expect a reversal to the above effects. If the rear spring eye is located behind the shackle pivot (illus. 4 example A) the shackle effect will tend to reduce suspension stiffness whenever the shackle moves rearward. However, the small shackle angle will tend to stiffen the spring's rate. The overall effect to the suspension's stiffness is determined by the more dominant of the two shackle effects. Keep in mind that the movement of the rear spring eye (from its static position) is mostly forward under racing conditions.

If a leaf goes into negative arch the travel direction of the shackle changes and the shackle effects change. Handling is not consistent under these conditions.

The second effect of the shackle can be enhanced by increasing the length of the shackle. Generally, the second shackle effect (jacking)is dominant.

Leaf spring sliders can eliminate the up and down movement of the rear spring eye caused by shackles moving through their arcs during suspension travel. Consequently, the rear suspension's loading points displace less during suspension movement. Sliders, depending on their installed angle, generally reduce the shackle effectæ and provide more consistent spring rates than shackles. There is no shackle effect to the rate of the spring when the slider is mounted to point directly at the front spring eye center(this is the preferred mounting position). Since sliders are usually more rigid than shackles, they have less tendency to bind laterally during cornering. In general, sliders improve the handling consistency and predictability of leaf spring equipped race cars.


And the wishbone axle locator - this one is only for the idea. Mine will be mounted underneath, directly paralleling the leaf springs. It stops side to side movement like a Panhard Bar, Watt's link, etc, but in my case, will also act like traction bars, preventing spring wrap up.


I believe that with the rear end mounted this way, I will not need a rear sway bar. Only time will tell...
Oh, and the sliders will lower the rear end about half the height of the shackle, so I guess I'll need to flip the overload leaf back over to hopefully bring it back to about where is was.


Last edited by a2ndopinion on Mon Mar 25, 2013 10:52 am; edited 1 time in total

_________________

ASE certified: Master Auto, Truck, Machinist & Collision Repair/Refinish Tech/Damage Estimator, Undercar & Parts Specialist, Service Advisor; Oregon Certified Vehicle Appraiser
DD -'81 Corona wagon - 22R hybrid P&P, Crane stage 3, Si valves, Erson springs/retainers, Weber, Cannon, MSD, Thorley, Borla, 3rd gen Celica front suspension, Cressi Big Brakes, coilovers, Camber plates, RCAs, AGXs, Addco, all urethane bushings, Hilux leafs...
20/22R/RE & Celica Guru, 2nd & 3rd gens - GT-Ss - 'vert, coupes & liftback... & Chevy fanatic
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Re: Rear Suspension

Post by mandalore on Sun Mar 24, 2013 4:04 pm

This is a gold mine for rear leaf spring lowering advice! Thank you

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Re: Rear Suspension

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