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  #61  
Old 07-05-2019, 08:08 PM
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There might be some joy in locating at in a rear steer setup. Here is a C3 with steering box and associated steering arms.


You can note the position the rack "might" fit into, but then need to swap sides of the uprights and configure the tie rods. Also not having the motor mounts (motro plates) makes some space available too. But, I've re-tapered the arms (on the uprights) for the ball joint to mount from above. Could conduct some major surgery and fix that I suppose.

The Roadster shop has a pretty cool setup that would be helpful - front steer low, c5 etc for a C3 But that is a whole frame solution...

I think I'd want to move a bit of weight forward - just aft of 50/50 now, and fuel etc will move further aft.

Ahhh, ain't hot roddin' fun!?

Cheers - Jim
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  #62  
Old 07-05-2019, 09:22 PM
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Jim,

Swapping spindles designed for front steer that have fixed steering arms has its own set of problems. For anywhere near correct Ackermann, the front steer uprights have the steering arms angled outboard so a line drawn from the outer tie rod end through the upper ball-joint-to-lower ball-joint line points in the general direction of the center of the rear end. Uprights designed for rear steer have the steering arms angled inboard to point in the same direction (toward the center of the rear end). Using the C7 spindles with their fixed steering arms on a rear steer set-up will give you some really wonky Ackermann. There are spindles, like the SpeedTech ATS spindles, that are made for late Corvette bearings and brakes that have removable steering arms. I built the steering arms out of 7075 aluminum to achieve the steering ratio and Ackermann I wanted. I think you are better off sticking with front steer with the C7 spindles.

Pappy

Edit: It occurs to me that if you opt to go rear steer with the C7 uprights, the tie rod extenders you built actually pull the pivot points for the outboard end of the tie rods into about the correct position.

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Last edited by mfain; 07-05-2019 at 11:42 PM..
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  #63  
Old 07-06-2019, 01:04 AM
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Originally Posted by phantomjock View Post
There might be some joy in locating at in a rear steer setup. Here is a C3 with steering box and associated steering arms.


You can note the position the rack "might" fit into, but then need to swap sides of the uprights and configure the tie rods. Also not having the motor mounts (motro plates) makes some space available too. But, I've re-tapered the arms (on the uprights) for the ball joint to mount from above. Could conduct some major surgery and fix that I suppose.

The Roadster shop has a pretty cool setup that would be helpful - front steer low, c5 etc for a C3 But that is a whole frame solution...

I think I'd want to move a bit of weight forward - just aft of 50/50 now, and fuel etc will move further aft.

Ahhh, ain't hot roddin' fun!?

Cheers - Jim
Respectfully, I'm not following why you would want to purposely move weight forward given the present f/r ratio you have.
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  #64  
Old 07-06-2019, 01:08 AM
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Originally Posted by mfain View Post
Jim,

Swapping spindles designed for front steer that have fixed steering arms has its own set of problems. For anywhere near correct Ackermann, the front steer uprights have the steering arms angled outboard so a line drawn from the outer tie rod end through the upper ball-joint-to-lower ball-joint line points in the general direction of the center of the rear end. Uprights designed for rear steer have the steering arms angled inboard to point in the same direction (toward the center of the rear end). Using the C7 spindles with their fixed steering arms on a rear steer set-up will give you some really wonky Ackermann. There are spindles, like the SpeedTech ATS spindles, that are made for late Corvette bearings and brakes that have removable steering arms. I built the steering arms out of 7075 aluminum to achieve the steering ratio and Ackermann I wanted. I think you are better off sticking with front steer with the C7 spindles.

Pappy

Edit: It occurs to me that if you opt to go rear steer with the C7 uprights, the tie rod extenders you built actually pull the pivot points for the outboard end of the tie rods into about the correct position.

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I'm not familiar with C7 knuckles. Do they have "centered" spindles, or are the spindles offset rearward like C4 knuckles?
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  #65  
Old 07-06-2019, 11:49 AM
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The C7 is very similar to the C5/6 - except for the casting:


Here is the C7. The steering is 'forward'


For today, I'm planning on keeping the front steer setup, and opting to use the steering gear reverse box. It is on order and should be in next week. A bit of complication to locate it, but all do-able.

Regarding CG. My "Guestimator Spreadsheet" was off a bit, and the scales showed the truth, such as it is. The old 50/50 is a nice bench-racing tale, and closer to 40/60 often seen as the better choice. Then there is always the balance of Center of Rotation vs CG, which you can futz with a bit. I've been reviewing a bit of these details and am planning on using the square setup and aero to get more or less grip at either end. The R&P is a heavy piece of gear for sure, but other bits I've yet to attach at the rear are too;, Setrab oil cooler/radiator etc for transaxle, fuel pumps, filters, blah, blah. If I need to add some grip aft, then its bigger tires (wider) and staggered, etc.

Its bloody hot outside today - Heat Stress Warning. I may get a few minutes on the brakes today. Will post as it goes.


Cheers - Jim
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  #66  
Old 07-08-2019, 11:04 PM
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My concern with the grand am rack is the CTO... When I had one configured for rear steer, the bracket that I made to position the tie rods in the correct location/length had some deflection about the center two mounting bolts. That was with street tires and only ~5* of castor. With sticky, wide tires and (assuming) 6+* of castor I wonder if that rack might be prone to fail earlier under the abuse I hope youre going to put it the car through.

Excellent to see some progress!
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  #67  
Old 07-09-2019, 02:46 PM
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Chris -

Did the bracket fail or the rack? Yeah, I plan on it seeing some ause, and the 1/4" steel bar stock is just there to position bits and make sure I can steer to push/roll on/off the trailer.

Here is one that is well sized, but if the rack is the failure prone item, this wouldn't matter:


Threat of tropical depression this weekend - so clean up the garage and push the car into the clean spot.

Back to it.

Cheers - Jim
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  #68  
Old 07-09-2019, 03:10 PM
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Quote:
Originally Posted by vette427sbc View Post
My concern with the grand am rack is the CTO... When I had one configured for rear steer, the bracket that I made to position the tie rods in the correct location/length had some deflection about the center two mounting bolts. That was with street tires and only ~5* of castor. With sticky, wide tires and (assuming) 6+* of castor I wonder if that rack might be prone to fail earlier under the abuse I hope youre going to put it the car through.

Excellent to see some progress!
I was concerned with the torque on that bracket and the two mount bolts when I did my Grand Am setup. The tie rods attach to those bolts in the Grand Am so there is basically no torque on that center mount.

When I was laying this out, I found that the rack input shaft was usually rotated up about 45 degrees. That causes two problems. It makes it impossible to use 2 U joint couplers with the same angle an one of those angles is greater than 15 degrees. Also I found that rotating the input shaft down (to 30 degrees) moved the CTO mount bolts towards the tie rod ends. That reduced the offset and therefore the torque on that mount.

I also machined these mount holes and they are zero clearance with the bolts.

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  #69  
Old 07-09-2019, 05:48 PM
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BBShark -

Once again a great hint! Thanks, I got the C4 bit and its a perfect fit on the rack. I will make it into a short stub and add a u-joint to the DD shaft. Easy-peasy.

Also, the steering gear reversing box arrived from Coleman just now too. Much faster than if I setup to make my own. It will let me keep the front steer. Now to copy the mount for the CTO as you built!

With the car in the garage, and a break in the heat, I might get the front end done (soon). Brakes, etc.

Cheers - Jim
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