Corvair DiagramCorvair Photo
Corvair Center
home forum corvairs calendar links Corvair Podcast
California Corvairs
Clarks Corvair



Chevy Corvair License Plate
Chevy Corvair Chrome Wheel
Corvair Center Forum :  Corvair Center Phorum The fastest message board... ever.
Corvair Center 
Current Page: 4 of 7
Re: Rack and pinion for Late model???
Posted by: teddbrown ()
Date: December 07, 2010 03:48AM

Bump

Whats the latest on the Miata R&P.
Did we rule out the Mustang II/Pinto R&P?
What is the true inner pivots (for junkyard cruising)

I think this would be a worthy project if made safe and not to crazy on modifications of the Corvair.

Pics are always good... even bad ones.

Ted Brown
Anderson, SC
68 Convert 110/PG/EFI/DIS
61 Loadside Automatic
130HP/PG/Honda Engine Project
**UPDATED** Corvair Fuel Injection and DIS Page

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Vairforce1 ()
Date: December 08, 2010 05:42AM

Here's some more info about the Miata steering rack to digest:

1990-1997 Miata specs (1999-2005 are very similar):
Front track: 55.5 in / 1410 mm
Manual rack: 3.3 turns lock-to-lock, 18:1 ratio
Power rack: 2.7 turns lock-to-lock, 15.3 ratio
Rack width (no tie rod ends): 48 3/16"
Tie rod length: 11.25" (approximate)

3.3 turns too slow? Then "de-power" a Miata power steering rack. There are a couple ways to go about it:
1) Simply remove the excess power steering fluid and loop the hoses (easy): [forum.specmiata.com] or [www.specmiata.com]
2) Or remove the internal seals (more involved): [flyinmiata.com]

Misc.
Steering rack polyurethane bushings: [www.flyinmiata.com]

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Jonathan Knapp ()
Date: December 08, 2010 07:29AM

Hi Everybody,

Craig, Richard, Eric, and Al have all gotten to the correct understanding of bump steer in my book. Richard's drawing and Craig's description have shed light on both why the problem occurs and what produces the solution. I do not agree however that obtaining correct Ackerman is simply a matter of adjusting the position of the rack fore or aft. I talked with you Craig, when you were here in Seattle at the Orphaned Car Show two years ago, about proper Ackerman for a front steering front suspension. Eric, you and I have spent time on this subject too. I don't know Richard and Al.

My careful graphing of all of the movements of the front suspension and steering of my autocross car shows that you can never get anything close to correct Ackerman on a front-steering Corvair front suspension with stock steering arms and the problem is way worse with quick arms whether they be GM or aftermarket.

The main reason my autocross car is so good at turn-in and fast through the slaloms as well as neutral all the way up to 1.2 g lateral acceleration is because the Ackerman is close to optimal. It is not perfect, and could not be made perfect with drum brakes. But it is pretty close. In the compromise between correct Ackerman and correct bump steer I sided as close as I could to Ackerman. My resulting bump steer actually helps turn-in because as the suspension compresses (loaded in a turn) my front wheels toe out slightly, giving the inside wheel the extra degrees of turn that it lacks from the not-quite-perfect Ackerman.

Correct Ackerman for a front-steer front suspension would be a straight line through the steering arm pivot (outer tie-rod end) through the lower ball joint that points directly at the center of the differential. That means the end of the steering arm has to be quite far outboard of the lower ball joint. This is very hard to do on a Corvair, especially if you want to minimize bump steer (as outlined above) for a street car.

The real solution is the one offered by the gentleman who talked about the Omni: a rear-steer front suspension. This way the line through the outer tie-rod end and the lower ball joint pointing at the center of the differential has the outer tie-rod end inboard far enough so that controling bump steer is attainable. Unfortunately a rear-steer front suspension creates big problems for the location of the rack itself as well as of the gas tank. There are also big challenges for the front suspension front strut (torque control) rod and perhaps for rear mounted calipers for disk brakes.

Unfortunately Tom, there is no easy near-bolt-on product that will work. Each of you will have to struggle with imaginative solution for your particular car. I will say that if you like to go fast in a Corvair around corners on pavement (not dirt, Eric!) at high turning angles (that means autocross, not road racing) the struggle is well worth it.

Jonathan Knapp
Seattle, WA
'66 Corsa Autocrosser

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Tom Z ()
Date: December 08, 2010 03:05PM

..I plan on removing the springs from my Mustang and Corvair front-ends,and comparing dimensions--hard to do on the Vair out-of-car,but I *DO* have the frame rails off the junked 65 coupe..

Tom Z,,Rochester NY


Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: 1bad67 ()
Date: December 08, 2010 05:04PM

I agree Johnathan, I haven't found perfect (or even acceptable) ackerman with the front steer setup. Rear steer is probably worth the trouble to do. The big problems are relocating the sway bar to the front side, and modifying the gas tank for room to mount the rack. Mounting the rack on the front still requires modifying the tank, so it really isn't that much more work.

Ackerman is also more important than bump steer in my opinion as well. Especially for autocross, and daily driving. I can't pull into a parking spot in the rain without the front tires skidding.

It really made no sense for the factory to optimize ackerman or the front suspension anyhow. The goal being to design a car that would understeer at the limit of traction to make it easier to control.

Eric
Portland Oregon



Pics of my '65 Corvair
Pics of the Convertible

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: gnvair ()
Date: December 08, 2010 08:25PM

Why not just graft a C4 or C5 Corvette onto the front end? I believe Jimish successfully installed a C5 Vette front end onto his car.

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: carango ()
Date: December 08, 2010 08:52PM

check out the front suspension do it youself parts at: www.welderseries.com/hardcopy/weldercat.pdf

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: MattNall ()
Date: December 08, 2010 08:53PM

So did Charlie Friends





MODERATOR
Somewhere between Sea Mountain and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
.............................PG...................................Turbo

Attachments:
Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Vairforce1 ()
Date: December 26, 2010 05:24AM

Check out this thread on the HAMB of a dude adapting a Corvair front suspension to his old school project: [www.jalopyjournal.com] He starts out talking about using a Mustang II rack but I think he settled on one from a Chevette (as an aside, see this thread about the difference between Chevette and Fiero racks: [www.fiero.nl]).

This thread has elicited a lot of comments for and against adapting the Corvair IFS, with some occasional useful info and humor thrown in. One thing I found to be of interest was that a number of the old school HAMBers have had good luck adapting racks from an MGB. And if there is any promise in MGB racks, there are modern repros made for a reasonable price: [www.mossmotors.com]

Dave

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: teddbrown ()
Date: April 27, 2011 12:14PM

BUMP

Wondering if anyone has any success or failure to report on the R&P for the LM? I see where the Chevette R&P is also a canidate along with the Miata R&P.

Too many project and too little knowledge for me to try now.

Ted



Edited 1 time(s). Last edit at 04/27/2011 12:15PM by teddbrown.

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: afterdarkgames ()
Date: April 27, 2011 02:25PM

91 MR2 rack also measures up nicely...and if you look around you may be able to find an electric powersteering setup from one... believe they were on the turbo models. System is esentially standalone and requires no inputs other than steering wheel angle to keep the pump from running all the time

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: 66cv8 ()
Date: April 27, 2011 02:50PM

Ted, I can report a degree of sucess. I have put a couple hundred miles on CV-8 with only my garage alignment and its fairly close but not rack perfect especialy caster. Car tracks straight and is not darty. My car is more of a race car than a street car and rides as such. There are only a few rubber bushings left in the car the anti roll springs' and thats it. You feel everything on the road.

The things I would change is the original gas tank location by using a fuel cell then I would use a different ratio box mine is 16:1 too fast for my taste. I would center the rack mount and make it adjustable up/down, in/out to tweak for ackerman and bump steer.

I will consider this a future project since finances and effort went towards my 69 Vert. For now I will have it aligned (when I find a competent shop that can get my Very LOW car on the rack) and just drive her.

Allways learning and thinking for ways to optimize.

Joe

66 500 Crown 350/4 on road
66 Corsa Convertible 140/4 rough
69 Monza Convertible 140/4 in progress (original 95/3)
Nu Joisey

" A LITTLE KNOWLEDGE IS A DANGEROUS THING"

"STUPID is the NEW SMART"

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Jim ()
Date: April 27, 2011 03:08PM

If you have tons of cash? this bolts in.

Attachments:
Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Tom Z ()
Date: April 27, 2011 03:09PM

..weird,I started back into this last week;the 65-500 out back, (mid-4.3 car/project) that NEEDS the R/P is up on blocks under the center of the x-member so to start from 'stock' setup,it'll be supported under the LCA's..can't seem to find the '66' short-shaft box tho,the longshaft 65 box is missing the pitman arm..I really want to use the new Must-II dropped spindles,but the arm for the upper BJ extends 'inward' more than the Corvair,and I'm not sure how to re-do the upper control arm and how that change will affect steering/susp travel..I could move the inner (upper) pivot shaft inboard,but that will change the "H" lines to locate the rack..BTW, all the racks shown above don't look like Must-II,more like the Fairmont/Granada rack,,a few 'Must/Pinto racks I have use a U-clamp around the tube to mount..

Tom Z,,Rochester NY


Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: 66vairman ()
Date: April 28, 2011 02:38AM

I'm no fan of the old "worm" gear boxes, but I have to admit in a car like the Vair, with the light front end, the steering feel is just fine. If you need a "faster" box, then I've been told by others the flaming river unit works great (if the other front suspension bits are in good order - of course)

Doubtful a rack and pinion would offer much improvement, especially considering the cost to "get it correct".

Now when you get into heavy front engine cars that need power assist, the rack and pinion set up is usually much more precise. Still I've driven a few FWD cars with rack and pinion that were numb and vague. So rack and pinion is not a cure all.

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: teddbrown ()
Date: April 28, 2011 01:15PM

I'm no front-end man, so excuse my ignorance........but if someone could explain with bumpsteer and ackerman being such a big deal, how does the standard Corvair front-end measure up?

With the Steering box Arm and Idler arm swinging in an arc during turns, this moves the draglink towards the front during turns, does that affect steering or has it been compensated for? If it has, please clue me in... ie: how they do that.

If a R&P was found, would they have to compensate for the front to back movement of the pivot points or is that the way steering boxes work and they just ignore the slight difference it makes.

Ted Brown
Anderson, SC
68 Convert 110/PG/EFI/DIS
61 Loadside Automatic
130HP/PG/Honda Engine Project
**UPDATED** Corvair Fuel Injection and DIS Page

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: 1bad67 ()
Date: April 28, 2011 01:56PM

Bumpsteer is when the front wheels turn just because they moved up or down. Makes the car darty on a bumpy road. The Corvair is pretty good in stock form.

Ackerman has to do with the inside wheels drive a smaller circle when going around a corner than the outside wheels. The Corvair is fair at best in this regard. In all fairness it doesn't really effect highway driving, or high speed road racing. It makes the biggest difference in pulling into a parking space, or Autocrossing. The tighter the turn, and the slower the car is going, the more it affects traction. Try turning around on a dirt road, and you can hear the front tires scrub quite a bit. The Corair pretty much sucks as it is, and the quick steering arms (especially the aftermarket ones) make it worse.

Hopefully I attached a picture that shows the ideal steering arm configuration for 'perfect' Ackerman. The Corvair though is a front steer, so the steering arms point to the front of the car, and should therfore point out from the center of the car. The problem being they want to be right where the wheel is.

Hope this helps.

Eric
Portland Oregon



Pics of my '65 Corvair
Pics of the Convertible

Attachments:
Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: cnicol ()
Date: April 28, 2011 02:05PM

Bump steer and to a lesser extent Ackerman angle are critical to handling.

BUMP STEER: Undesirable change in toe-in as the suspension moves up and down.

Here's how it happens: Viewed from the front, the suspension arms move up and down in an arc. From a neutral point, the entire wheel and knuckle move toward the middle of the car as the suspension is moved up or down.

From a neutral position, the tie rod also gets shorter as it is lifted or lowered by the suspension as it moves up and down.

If the tie rod is just the right length and the inner pivot is in just the right place, and the rod is parallel to the lower suspension arm (usually) the wheel will stay pointed straight as the suspension moves up and down.

There is only one length, inner pivot location, and relative angle that works. (OK there are two but the second one is weird and never used). If any of these three variables is wrong, the car will steer itself (dart) with every bump.

If the rack is the wrong width or mounted high or low you will have bump steer. I put a rack kit in a 62 Corvette and a 1" manufacturing error (vertical position) resulted in 2.5" of toe change as the suspension moved! (goal is .25" max)

Stock Corvairs are designed acceptably in regard to bump steer.

ACKERMAN ANGLE
Ackerman angle errors are less critical than bump steer errors.
Ackerman is the guy who's credited with recognizing the need for different turning angles on the front wheels in moderate to sharp turns.

In a turn, the inside wheel rolls around a smaller circle than the outside wheel so the front wheels need different turning angles. This difference is the Ackerman angle. The tighter the turn, the larger the difference. An incorrect Ackerman setup won't corner as well because one of the tires is skidding through the turn.

Stock Corvairs have an acceptable Ackerman angle compensation however Jonathan Knapp has studied the stock design and has found that there's a lot of room for improvement. His record winning autocross car (1.2G turning capability) is proof of the pudding.

Corvairs with aftermarket quick steering arms have poor Ackerman correction and this can be easily felt and heard (squealing tire) when making U-turns in parking garages and gas stations.

As Paul Harvey often said, "Now you know the rest of the Story"winking smiley

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
66 Red Monza 2dr 140/4 EFI 60k
61 Seamist Jade Rampside 140 PG
65 Cypress Green Monza 140/4 4dr
65 White 4-dr 110/AC/PG (parts)



19 Tons of parts in boxes




Edited 1 time(s). Last edit at 04/28/2011 02:06PM by cnicol.

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: teddbrown ()
Date: April 28, 2011 07:40PM

Excellent explaination as always Craig.... Even I could understand it. Your knowledge is valued.

Ted

Options: ReplyQuote
Re: Rack and pinion for Late model???
Posted by: Am-Iron ()
Date: April 29, 2011 01:27PM

I agree Ted. In my automotive school they called it steering axis inclination. The explanation was very similar and easy to understand. I build some hot rods too, and this one guy I was building a 40 Ford for kept calling it the acronym!

Options: ReplyQuote
Current Page: 4 of 7


Sorry, only registered users may post in this forum.
This forum powered by Phorum.