Sensitive steering

t-vicky · November 27, 2012, 08:08:45 PM

My 40 Chevy with Mustang II front RP has always been touchy on the steering. It is SBC with the old style power steering pump. A few months ago I seen Borgesons ad for a shim kit to reduce the pressure. Bought it, installed it, loved it. Worked good.
A few weeks ago I changed tires & wheels. Went from 15"X 5" with 165/R1586T to 15"X 7" Chevy rally wheels with 195/60 R15 tires. Cant hardly keep this thing on the street. It is twice as touchy. Had these same tires on it on different rims before with no trouble.
Anyone got any ideas?

unklian · November 27, 2012, 08:46:10 PM

Caster ?

enjenjo · November 27, 2012, 09:01:50 PM

Quote from: "unklian"Caster ?

Could also be toe in too. In my experience, with radial tires a Mustang front end works best with 0 to 1/16" toe in, and 4 to 6 degrees caster.

Arnold · November 27, 2012, 11:04:34 PM

Rim offset changed?

unklian · November 27, 2012, 11:40:19 PM

Quote from: "enjenjo"
Quote from: "unklian"Caster ?

Could also be toe in too. In my experience, with radial tires a Mustang front end works best with 0 to 1/16" toe in, and 4 to 6 degrees caster.

Yes.

chimp koose · November 28, 2012, 06:48:42 PM

different offset with the wider wheel could change scrub radius . If the scrub radius increases the wheels will want to toe outmore at speed causing it to feel 'twitchy'.

t-vicky · November 30, 2012, 12:08:03 PM

Well, I guess I will make an appointment at the front end shop>

wayne petty · December 01, 2012, 01:30:06 AM

a few things to read...

http://www.anewtoronto.com/wheel%20alignment.html

this one includes some info on the scrub radius...

http://www.carparts.com/alignment.htm

i ran across a better one the other day. this is 66 pages... and well written ..

http://priertiresupply.biz/pdf/hofmannbrochures/fundamentals%20of%20alignment.pdf

t-vicky · February 03, 2013, 11:39:28 PM

OK Took it to the alignment shop about 2 weeks ago & everything is set just where it should be. The guy told me that everything was good and tight and set right. 3 days ago momas Nissan breaks down & I have to drive her around. (No way she is driving the Chevy) Yesterday she gets her car back & I take the Chevy around to the garage. Its cold out there so I get out the hood side panels & put them on. Today this weird car drives fine! What the hell does side panels have to do with steering? This car is going to drive me nuts. I think I will put a manual RP on it.

wayne petty · February 04, 2013, 08:25:38 AM

the mods to the pump ... you added a shim kit to the pressure control piston.. under the nut..

did you swap the fitting to one with a reduced size to limit the flow... so it does not become OVER POWERED when the pressure is TOO HIGH?

?

this is what makes them twitchy.. too much flow ..

since the system with the wheel straight ahead is flowing normally... when you turn the wheel the torsion bar allows the valves to open or close. diverting fluid to one side of the piston or the other.. excessive flow causes excessive reaction to driver or wheel inputs..

just as touchy as if you had 300 psi running to your air impact.. the slightest touch of the trigger and it is going to twist off any wheel stud... back the pressure/flow off to 90 psi.. it will work as designed..

the GM pumps were with a steering box designed for more flow as the piston with GM steering boxes is HUGE.. the piston with a ford rack and pinion is tiny ..

there are actually 3 or 4 different volume GM pumps.. different displacements for different apps.. but they all still require the tiny opening to restrict the flow for your MII rack.

restrict your flow... find a 78 to 80 chrysler TC3 and grab its 1" nut outlet fitting.. not the pump.. the fitting.. there are several aftermarket fittings also..

perhaps some of the other forum members have some idea of the drill size to check that its the proper fitting...

sorry if i am repeating my self.. i am not quite awake yet..

wayne petty · February 04, 2013, 05:21:21 PM

This

http://www.speedwaymotors.com/Mustang-II-Power-Steering-Flow-Valve-for-GM-Pump-2-GPM,5852.html

t-vicky · February 04, 2013, 06:42:46 PM

Thanks Wayne, I will order that & see what happens.

t-vicky · February 08, 2013, 07:36:53 PM

Ok, Ordered that part & got it installed today. That must have been the problem. It works good now. Feels like a mustang RP but not near as touchy as it was.

wayne petty · February 08, 2013, 07:58:41 PM

so glad it worked...

the ford racks have a thru put flow that needs the 2 GPM ...

with the saginaw pump that can put out MUCH more.. the restriction of flow in the rack outlet builds internal pressure and causes twitch as its hyper pressurized...

lowering the pressure does not reduce the flow rates.. only the tiny opening in the fitting you purchased will fix it..