Rack & Pinion Question

Rack & Pinion Question

I'm changing the steering system on my 1948 Desoto Suburban (9
passenger, 4800
pound vehicle) from the original pitman arm steering to rack and
pinion steering.

I purchased a rebuilt back-steer rack and pinion (45" long) that was
for a
1995-2005 Chevy Cavalier or Pontiac Sunfire. I built the mounting
housing, new
steering shaft, new power hoses from the pump, and new tie rod ends.
I still
have to cut one side of the motor mount (1" x 2") off to make room for
the
double D U-joint coupler so the rack can turn (not done yet).

I found the travel on the rack is only 2.5" on each side. This does
not give
me enough turning angles on the wheels (I need at least 4").

A couple of solutions I thought of are:

* To get a rack from some other vehicle (maybe a truck) that would
have more
then 4" travel on each side. Trouble is - I don't know which trucks
would have
this type of rack.

or

* To make a shorter steering arm for the existing Desoto but I would
have to
find a shop that could do this and I don't know if this would
compromise safety
as the tie rod ends and the rack will carry more stress when
turning.

Would anyone have suggestions on other ways to (safely) resolve this?
I can
email pictures of the steering configuration.

Re: Rack & Pinion Question

Hi

It's not as easy as swapping in a rnp as there are several steering
geometries that need to be taken into account. If one of them is not right,
you will have severe bumpsteer. Bumpsteer is exactly as it sounds, when you
go over a bump or hit a pothole, the steering wheel and the car will
violently turn in one direction.

Here's the things to consider:

1. Height of rnp in relationship to steering arm tie rod end.
2. Fore and aft position of rnp in relation to the steering arm tie rod end.
3. Relationship between the rnp rod ends and the front control arms. The
rack tie rod ends must follow the same arc as the front control arms.
4. As you found out, the rnp must travel relatively the same distanct. Not
really important as it just means you have a larger turning radius at slow
speeds.

The biggest problem is that you are working in a 3D space and trying to find
the sweet spot. I just went through that 5 years and don't recommend trying
it.

Here's my website that discusses more than you ever want to know about doing
this on a 54 Pontiac.

http :// www .cadvision,com /blanchas/54pontiac/rnp.html


Cindy wrote:

> I'm changing the steering system on my 1948 Desoto Suburban (9
> passenger, 4800
> pound vehicle) from the original pitman arm steering to rack and
> pinion steering.
>
> I purchased a rebuilt back-steer rack and pinion (45" long) that was
> for a
> 1995-2005 Chevy Cavalier or Pontiac Sunfire. I built the mounting
> housing, new
> steering shaft, new power hoses from the pump, and new tie rod ends.
> I still
> have to cut one side of the motor mount (1" x 2") off to make room for
> the
> double D U-joint coupler so the rack can turn (not done yet).
>
> I found the travel on the rack is only 2.5" on each side. This does
> not give
> me enough turning angles on the wheels (I need at least 4").
>
> A couple of solutions I thought of are:
>
> * To get a rack from some other vehicle (maybe a truck) that would
> have more
> then 4" travel on each side. Trouble is - I don't know which trucks
> would have
> this type of rack.
>
> or
>
> * To make a shorter steering arm for the existing Desoto but I would
> have to
> find a shop that could do this and I don't know if this would
> compromise safety
> as the tie rod ends and the rack will carry more stress when
> turning.
>
> Would anyone have suggestions on other ways to (safely) resolve this?
> I can
> email pictures of the steering configuration.

--
Eugene Blanchard
Visit my website Hot Rod Kustoms at
http :// www .cadvision,com /blanchas

Re: Rack & Pinion Question

Here's some options that sound more difficult but in the long run will save
you mucho time and grief:

http :// www .cadvision,com /blanchas/54pontiac/suspension.html

Eugene wrote:

> Hi
>
> It's not as easy as swapping in a rnp as there are several steering
> geometries that need to be taken into account. If one of them is not
> right, you will have severe bumpsteer. Bumpsteer is exactly as it sounds,
> when you go over a bump or hit a pothole, the steering wheel and the car
> will violently turn in one direction.
>
> Here's the things to consider:
>
> 1. Height of rnp in relationship to steering arm tie rod end.
> 2. Fore and aft position of rnp in relation to the steering arm tie rod
> end. 3. Relationship between the rnp rod ends and the front control arms.
> The rack tie rod ends must follow the same arc as the front control arms.
> 4. As you found out, the rnp must travel relatively the same distanct. Not
> really important as it just means you have a larger turning radius at slow
> speeds.
>
> The biggest problem is that you are working in a 3D space and trying to
> find the sweet spot. I just went through that 5 years and don't recommend
> trying it.
>
> Here's my website that discusses more than you ever want to know about
> doing this on a 54 Pontiac.
>
> http :// www .cadvision,com /blanchas/54pontiac/rnp.html
>
>
> Cindy wrote:
>
>> I'm changing the steering system on my 1948 Desoto Suburban (9
>> passenger, 4800
>> pound vehicle) from the original pitman arm steering to rack and
>> pinion steering.
>>
>> I purchased a rebuilt back-steer rack and pinion (45" long) that was
>> for a
>> 1995-2005 Chevy Cavalier or Pontiac Sunfire. I built the mounting
>> housing, new
>> steering shaft, new power hoses from the pump, and new tie rod ends.
>> I still
>> have to cut one side of the motor mount (1" x 2") off to make room for
>> the
>> double D U-joint coupler so the rack can turn (not done yet).
>>
>> I found the travel on the rack is only 2.5" on each side. This does
>> not give
>> me enough turning angles on the wheels (I need at least 4").
>>
>> A couple of solutions I thought of are:
>>
>> * To get a rack from some other vehicle (maybe a truck) that would
>> have more
>> then 4" travel on each side. Trouble is - I don't know which trucks
>> would have
>> this type of rack.
>>
>> or
>>
>> * To make a shorter steering arm for the existing Desoto but I would
>> have to
>> find a shop that could do this and I don't know if this would
>> compromise safety
>> as the tie rod ends and the rack will carry more stress when
>> turning.
>>
>> Would anyone have suggestions on other ways to (safely) resolve this?
>> I can
>> email pictures of the steering configuration.
>

--
Eugene Blanchard
Visit my website Hot Rod Kustoms at
http :// www .cadvision,com /blanchas

Re: Rack & Pinion Question

something sounds amiss...the cars you took the parts from probably had
respectable agility. transferring those parts shouldn't change that
characteristic unless you have a significant discrepancy in width
between front wheels. if yes, then definitely, ditch that system.

steering geometry is hard to get right if you're doing more than a
sandbuggy, and not seasoned as an engineer in the area. probably
fewer than 20% of the pro engine swappers are even qualified to do
what you trying. your best bet is to try to search past magazine
articles for a rack-and-pinion conversion on your car (or dodges/
chryslers if they have identical specs in that regard).

don't forget too, some companies offer complete weld in "systems".
these are costly, but often come with coil-overs that are
adjustable...if you're also doing a non-oem engine swap, you'll
probably have a justified need to for that anyway. if you buy a
system like that, talk to them about your application first. probably
the first thing they'll ask is your front track (width between front
wheels).