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| 84-87 rear spindle - why not swap out for a newer GM FWD spindle w/ large brakes? (Page 2/6) |
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fieroguru
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MAY 23, 09:54 AM
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| quote | Originally posted by sourmash:
If you had a suitable substitute spindle, it's just a matter of swapping sides to make them front steer, right? That's what we did with some 1970s GM car. Maybe it was Nova to GTO. |
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Swapping right to left will get the connection points in the right general area, but until you verify what doing so does to bump steer and ackerman results might not be as expected.
That is the challenge with these conversions, anyone can take whatever upright they way, toss it under the car, modify the connection points to get acceptable camber and toe in the forward/stationary position and call it an upgrade. But if it has horrendous bump steer because the elevation and connection point of the steering arms to the tire rods are all wrong or it starts dragging/pushing one of the front wheels as you turn corners around town... the resulting performance is a downgrade from stock.
This is one of those areas where you need to go into it with eyes wide open and verify what you have stock and what you will have with the changes. There isn't a requirement to stay stock, especially if you plan to use the car in a non-stock manner, but you absolutely need to know if the changes you make will get you closer to your ideal performance or further away from it than stock.
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qwikgta
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MAY 23, 10:08 AM
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| quote | Originally posted by fieroguru:
Swapping right to left will get the connection points in the right general area, but until you verify what doing so does to bump steer and ackerman results might not be as expected.
That is the challenge with these conversions, anyone can take whatever upright they way, toss it under the car, modify the connection points to get acceptable camber and toe in the forward/stationary position and call it an upgrade. But if it has horrendous bump steer because the elevation and connection point of the steering arms to the tire rods are all wrong or it starts dragging/pushing one of the front wheels as you turn corners around town... the resulting performance is a downgrade from stock.
This is one of those areas where you need to go into it with eyes wide open and verify what you have stock and what you will have with the changes. There isn't a requirement to stay stock, especially if you plan to use the car in a non-stock manner, but you absolutely need to know if the changes you make will get you closer to your ideal performance or further away from it than stock. |
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Fully understand, but this is an itch i've wanted to scratch for the last 25 years. I can only figure that it can't be done and thats why it hasn't. there are too many 84-87 owners out there that could have done this, or maybe they have and it wont work. I have the time, and an 87 to play with.
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sourmash
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MAY 23, 10:11 AM
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Tangent: what could it possibly cost to have a spindle/knuckle newly cast (assuming the design was already complete) with or without drop geometry that would satisfy larger bearings?
Has anyone got a recent handle on the cost to have cast?
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fieroguru
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MAY 23, 10:15 AM
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| quote | Originally posted by qwikgta:
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Do the tierods mount on the top or bottom of the steering arms? Bottom would be better than top if the plan was to install in the rear of the 84-87. Generally speaking having the tirerod pivot as close to the same elevation as the lower balljoint will get you very, very close to zero bump steer.
The lower ball joint with the pinch bolt likely is larger diameter than the 84-87, so ball joint upgrade or some other work is likely needed.
The overall horizontal distance from the wheel rotor to the ball joint will need to be checked to see if installing this upright on the stock fiero a-arm will pull the wheels in, push them out, or leave them stock. Might need to rework the lower a-arm or might need to change axle lengths depending on what you are trying to accomplish.
The angle of the strut will likely limit wheel/tire clearance (probably 8" or less unless other modifications are done) and require moving the top strut mount outboard from stock. There is a limit to how far you can go as the spring (assume coilovers) will have to stay inside the upper frame rail as it is lower than the top of the strut tower. Just another thing that has to be verified either by a test fit or detailed drawings.
GM switched to a common wheel bearing mounting bolt pattern for most of the cars. So the W-body uprights I have been playing with have a 5x115mm pattern, but the C5 bearing with the 5x120 also bolts to it so having a wide range of available bolt patterns is pretty much a non-issue as long as you can find the right CV housing to work with your axles.
The cobalt SS upright is very similar to this one (I have several W-bodies, Solstice, C5 and others on the shelf, as well as an assortment of aluminum upper and lower a-arms).[This message has been edited by fieroguru (edited 05-23-2020).]
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fieroguru
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MAY 23, 10:52 AM
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| quote | Originally posted by qwikgta:
Fully understand, but this is an itch i've wanted to scratch for the last 25 years. I can only figure that it can't be done and thats why it hasn't. there are too many 84-87 owners out there that could have done this, or maybe they have and it wont work. I have the time, and an 87 to play with. |
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But it has been done, but never made it mainstream... there are probably 20+ examples where people went down this path and ended up with running/driving cars. The issue is effort involved to bring it to completion, overall cost to get there, overall performance once complete, and is it economical to bring to market.
The issue is that using off the shelf parts will only get you in the ball park, but not able to get you precisely where you want to go. This is why most vendors who went down this path, eventually migrated to building the custom spindles to get what they wanted. Now 20+ years have passed and there are a lot of other OEM options to look at, but you literally are looking for a needle in a haystack... finding a suspension component that is 20 to 30 years newer with complimentary suspension design to a 1980s chassis. There likely is a "workable" solution, but "workable" means having an OK fit, OK performance, and moderate fabrication effort to make it work. To find this holy grail of a part is a costly endeavor. I easily have over $2000 in aluminum suspension and upright bits on the shelf and I still am still working the solution to better optimize the goal and at this stage it requires a new custom cradle which.
Here is an LS4 swap that started with a modified W-body cradle, kept the Aluminum upright, modified the toe link connection (I am not endorsing this method), and you can see the bolt hole mismatch between the upright and strut. This is nothing that some welding couldn't fix, but people willing to weld on a fully charged strut are probably in short supply. Purging the strut, doing the needed welding, and installing a strut cartridge as a solution is going to get spendy.
Here is a picture of a highly modified W-body upright being used in the front. The big thing to notice is the work to correct the location of the steering arm for his specific suspension design. Once you get into having to modify the part in 2-3 locations to make it work, you are not that far off from custom fabrication and able to better optimize the geometry.
Like I said, I am going down this path for the 88's because it is something I want for my personal car... but even at this stage, I can see that having something that could be brought to market at a reasonable price is well below 50/50 odds.
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cvxjet
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MAY 23, 12:20 PM
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The biggest mistake that was made in the Fiero was the length of the rear tie-rod; A MacPherson strut type suspension should have the tie-rod length based on a Triangle using the top of the strut, and the inner and outer mounting points of the A-arm...The Fiero A-arm is approx' 12 inches long, and anyone looking at the geometry of the Fiero suspension will KNOW that the tie-rod, being ABOVE the arm, should be SHORTER than the A-arm....Yet they made the arm 15 inches long!
I believe that the engineer who designed the setup did not know anything about strut suspensions, and thought, "I will make the Tie-rod arm LONG so it doesn't change length over the suspension travel!".......But the A-arm WILL change length, so that longer arm will cause a bunch of bump-steer!
The Tie-rod length should have been around 11 inches...most of the rear suspension bump-steer would have been eliminated.
Whatever you do, make sure the tie-rod arm is shorter than the lower A-arm, and that it runs parallel to that lower arm.
 [This message has been edited by cvxjet (edited 05-23-2020).]
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sourmash
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MAY 23, 03:33 PM
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He's drilled a 3rd hole instead of doing any welding, it appears. There's for certain a hole but no why there's no bolt yet is of question.
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Blacktree
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MAY 24, 11:02 AM
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| quote | | Originally posted by qwikgta: With an 88 you are stuck with the suspension geometry unless you get very creative and spend a lot of $$$$. |
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Interesting. That's basically what I think about the pre-88 rear suspension. IMO, the '88 rear suspension is pretty damn good, right out of the box. With a couple hundred bux, you can roll your own suspension links (rod ends and threaded tubes), and have lots of adjustability. The one downside is lack of camber gain, but Fieroguru sells a kit for that.
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qwikgta
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MAY 24, 05:38 PM
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| quote | Originally posted by Blacktree:
Interesting. That's basically what I think about the pre-88 rear suspension. IMO, the '88 rear suspension is pretty damn good, right out of the box. With a couple hundred bux, you can roll your own suspension links (rod ends and threaded tubes), and have lots of adjustability. The one downside is lack of camber gain, but Fieroguru sells a kit for that. |
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I have two 88's and I've got a set of AMS lateral links on one of them, they have heim joints on the ends and have been working great for about 10 years. The second one has a set of WCF trailing arms w/ poly. Spindles are stock and both have 13" brakes on them. I don't have any issues with the 88 suspension.
My issues in this thread are for the 84-87 suspension. I haven't owned a pre-88 since 1995 and back then I just drove them, I didn't modify them. Walking around the junkyard all the time I see a TON of GM front ends with 12-13" brakes, aluminum spindles and wonder if they would work for the Gen I cars. Since I haven't owned one in 20+ years I now have a reason to see if any of those GM spindles/brakes will work. I have access to so many newer GM cars I just want to see if any will work.
As Guru has written, and i'm sure i will find out, while they may be close, I doubt i'll find anything that just "bolts on", I may not find anything even close, but I have wanted to research this for so long. I'm interested in seeing whats involved, not b/c I plan to make a kit or sell anything, just b/c I want to help the community with a chance for newer parts w/ multiple hub/bolt patterns.
Rob
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qwikgta
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MAY 24, 05:48 PM
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| quote | Originally posted by cvxjet:
The biggest mistake that was made in the Fiero was the length of the rear tie-rod; A MacPherson strut type suspension should have the tie-rod length based on a Triangle using the top of the strut, and the inner and outer mounting points of the A-arm...The Fiero A-arm is approx' 12 inches long, and anyone looking at the geometry of the Fiero suspension will KNOW that the tie-rod, being ABOVE the arm, should be SHORTER than the A-arm....Yet they made the arm 15 inches long!
I believe that the engineer who designed the setup did not know anything about strut suspensions, and thought, "I will make the Tie-rod arm LONG so it doesn't change length over the suspension travel!".......But the A-arm WILL change length, so that longer arm will cause a bunch of bump-steer!
The Tie-rod length should have been around 11 inches...most of the rear suspension bump-steer would have been eliminated.
Whatever you do, make sure the tie-rod arm is shorter than the lower A-arm, and that it runs parallel to that lower arm.
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But in the Gen I cars, isn't the rear end just a transplanted X body front end? And if so, isn't the suspension tie-rod just the steering outer tie-rod that is hard mounted to the cradle, in about the same location and height as the original steering rack? If so, and if the steering rack was kept in place, would there still be a lot of bump-steer. in other words, is there a lot of bump steer associated with the X body cars. I was not aware that the steering rack had a significant impact on the suspension geometry.
Rob
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