I have been wanting to upgrade my front suspension and I had an idea the other day. I want to gain the ability to easily adjust/change the front suspension dampers and springs. A coil over conversion is obviously the most logical option. However, I dont like the idea of having to remove the wheels every time I want to make a change to the suspension settings. This got me looking into race care style pushrod suspensions. This allows the coil over unit to be remote mounted and therefor can be placed in a more accessible location. I started thinking about if there could be a simple way to adapt this to a fiero. The idea I had would be to start with one of the Arraut(held) Motorsports "sport suspension kit" which is a coil over conversion using tubular a-arms and factory spindles. Then replace the top coil over mounting bracket with a custom rocker pivot, then mount a heim joint pushrod between the lower a-arm mount and the rocker pivot. The rocker would then attach to a transverse mounted coil over in the front trunk area. The inboard side of the coil over would attach to a cross-brace running between the two front frame rails. The end result would look very similar to the Aventador front suspension.
For reference here is a different custom front suspension to show roughly where the rocker pivot would be mounted, and come through the inner fender. You can see the top of this coil over would be roughly where the pivot point would be.
My only problem I can see this far is the clearence under the brake master/booster for the coil over unit to pass under. If there is enough room I think this would be pretty straight forward to build. Your thoughts?
Just a thought: how about angling the coilover assemblies forward, so they don't interfere with the brake / clutch master cylinders? IMO, it would be REALLY cool if you could lay them on top of the frame rails.
Yes, I think that might be the way to go. After looking more closely at the clearance around the brake booster, I think mounting the units longitudinally would be the only feasible way. Similar to this. This would add less weight as well, not having to put a cross brace in.
It's a great idea for several of the reasons you mentioned, but most importantly it reduces the unsprung weight of the front suspension, allowing it to react faster to road irregularities. For what it's worth though, I don't believe this photo is the Aventador's front suspension:
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Originally posted by Bridgetown: The end result would look very similar to the Aventador front suspension.
If it were, there would be no means to steer the wheels since the pushrod is attached directly to the knuckle. I suspect this is a rear wheel.
I think the biggest challenge to what you're proposing is going to be designing the bell crank mounts. They're easier if you run the coil-overs transversely across the car since the pivot axis of the bell crank lends itself well to mounts welded to the frame rail.
Running the coil-overs longitudinally becomes more complicated since:
a. the bell crank must be installed at approximately the same angle as the pushrod to avoid complex loads and exceeding the misalignment specs of the typical spherical bearings used on both the pushrod and the shock; b. it forces the placement of the bell crank and mounts to the outside of the frame rail to avoid interference between the pushrod and the frame, and between the spring and the frame through the range of suspension travel; c. the cantilevered mounts will experience complex bending and torsional loads requiring well thought out mounts; d. running the coil-over backwards under the brake master cylinder will be tough because even if there is enough clearance, it will be very difficult to access the frame rail to weld the mounts for the fixed end of the coil-over; and e. if you decide to run the shocks forward to avoid the brake hardware, you should double check the available room lengthwise for a bell crank and a coil-over so it doesn't impact the light pods.
If you haven't visited my build thread, you might find some interesting tidbits of info that I've learned while designing and fabricating a 5 link pushrod coil-over for the rear of an '88 Fiero here: www.fiero.nl/forum/Forum3/HTML/000116-20.html
Thanks Blooze those are some good points. Taking some very rough measurements has yielded the following limitations: Based on the location of where the pushrod would pass through the wheel well, the only option is to run the coil over lengthwise towards the front of the car. From the pushrod to the front bulkhead behind the headlight assemblies there is just over 12" of length for a coil over to reside. Taking a look at the shocks available from QA1 they offer a double adjustable damper with a compressed length on 8.625". http://www.qa1.net/qa1_moto...uble-adjustable.html It looks possible that this unit would fit well in the space. The front bulkhead could be strengthened to accommodate the mounting bracket for the coil over. This setup avoids the brake booster and hydro distribution block all together.
Does anyone know how these pushrod systems control compression limits, in other words what do they use for a bumpstop?
It appears they use a rubber bushing around the shock shaft itself rather than a rubber bumper hard mounted to the frame. Pretty much the same way a strut does it.
[This message has been edited by Khw (edited 01-07-2014).]
It appears they use a rubber bushing around the shock shaft itself rather than a rubber bumper hard mounted to the frame. Pretty much the same way a strut does it.
Yup... you can see it in one of the pics previously posted...
Yep, you can just put a rubber bumper on the shock absorber shaft.
As for the packaging of the bellcrank and stuff... if using one pivot doesn't work, you could try using two. The first pivot (on top of the pushrod) would be a simple lever, like a see-saw. The second pivot would be a bellcrank at a right angle to the first pivot, and positioned just below it. The second pivot would rotate forward (pushing on the coilover spring / shock assembly) when the suspension is compressed.
Since the "see-saw" link is pushing straight down on the second pivot, that allows you to position the second pivot however you want in the horizontal plane, without affecting the transfer of force through the system. So, for example, if your coilover spring / shock assembly were too long to lay on top of the frame rail, you could angle it inward to gain some clearance. And since your "see-saw" link is basically just a straight rod that pivots in the middle, you won't have to do much cutting to the wheel well to make room for it.
Sorry, but I suck at digital artistry. I hope you were able to understand what I was trying to describe there.
One drawback I see to this idea is that the more links you add in series, the more slop you add as well. The slack of each link in the series adds up. You'd have to be careful to make sure all the attachment points are tight, and use wear-resistant materials.
I'm also not sure if you'll have enough vertical space in that area to do the dual pivot setup. But IMO it's worth looking into.
Originally posted by Bloozberry: It's a great idea for several of the reasons you mentioned, but most importantly it reduces the unsprung weight of the front suspension, allowing it to react faster to road irregularities.
Is this true? The pushrod, rocker, and outer portion of the shock still move with the suspension as it moves through its range of motion, so aren't they technically unsprung weight? If so, would you actually be increasing upsprung weight with the addition of the pushrod and rocker arm?
I did some searching online to find the answer and have found as many sources that say it doesn't reduce unsprung weight as ones that say it does.
[This message has been edited by Silicoan86 (edited 01-07-2014).]
The weight of the bell crank and coil-over are reacted only by mounts that are directly attached to the chassis so they must be sprung weight.
The reduction in unsprung weight is equivalent to the difference between the weight of the coil-over (shock and spring) and the weight of the pushrod since one effectively replaces the other. It may be several pounds considering the spring is usually pretty heavy, which helps counteract some of the additional unsprung weight that gets added by using larger diameter and wider wheels and tires.
But the mass of those components (bell crank and a portion of the coil-over assembly) still must move with the rest of the suspension so wouldn't it still attribute to the overall inertia?
[This message has been edited by Silicoan86 (edited 01-07-2014).]
Everything attached to the control arm adds inertia to it. That includes the inertia of the pushrod, bellcrank, etc. That inertia will need to be controlled by the spring and damper. So for all intents and purposes, it's unsprung weight.
The inboard parts of the setup are also sprung weight, since they will be resting on the chassis.
Everything attached to the control arm adds inertia to it. That includes the inertia of the pushrod, bellcrank, etc. That inertia will need to be controlled by the spring and damper. So for all intents and purposes, it's unsprung weight.
The inboard parts of the setup are also sprung weight, since they will be resting on the chassis.
The way I understand unsprung weight is that it is essentially the weight of everything the springs are supporting. Unsprung weight matters because if you hit a bump at say 50 mph, the wheel is going to accelerate upwards. This acceleration upwards will not change with a change in unsprung weight, so the more weight actually being accelerated upwards at the same acceleration results in a larger upwards force which unsettles the car more. So with a pushrod suspension the shock and spring are still being accelerated and then that force is translated to the wheel, so I feel as though it would not help with unsprung weight unless you used the bellcrank to change the ratio at which the shock travelled. So if only half the travel was required due to the geometry of the bellcrank then the acceleration of the shock would be half as large and would reduce unsprung weight.
This is just my current understanding. But maybe because the direction of the shocks inertia is not in the same direction as the rest of the suspension so it does not count as unsprung weight? But at the same time the resulting force that continues to allow the wheel to travel upwards due to the shock/springs inertia is still there... so it half reduces it?
since this thread started with a picture of my cars front suspension when it was first installed , i will throw my 2 cents worth in and talk about the drawbacks of the kit as it is delivered : 1- the travel is not adequate for proper ride height adjustment .it will bottom out . 2-the 8 " spring can be made to work , but only if you opt for a 400+ spring rate . 3-the only shock that can be used with it (stock length arms kit) is the small body carrera that does not have much adjustability.the pic of the kit shows this shock with the 2"ID 8" length springs .while i ran the kit in stock form i used a 10" 300 spring and that prevented the bottom out problem .later on i modded the spring perch and the upper control arms to be able to use a QA-1 big body 12 way adjustable coilover with the 2 1/2 ID spring : this is my final version note that i also added a street dreams by ross 1 1/2" drop spindle along the way .as you can see i have mounted the coilover upside down .i can adjust the shock setting just by turning the wheel full lock in either direction and reaching in the wheelwell .i can adjust height with the wheel on but i have to jack the car up to do it .that part is still awkward .but i am really happy with this setup, i have finally got it exactly the way i want it .but the inboard shock idea is really intriguing , but for now i will be trying to get my rear suspension the way i want it .hopefully some one will try this on a stock chassis soon.
[This message has been edited by wftb (edited 01-09-2014).]
