power steering bump steer - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gab50 · 07-13-2010, 02:40 PM

I have just got back on the road after a power steering install on my 50 1\2 ton which used the steering box from a late 70's pickup and the steering arm and drag link from CPP. First impression is it steers good on smooth road with hands off no wander. It has a little bump steer on bumps. I think this is due to a bunch of things, some being the setup has a very short drag link, presently has very little caster ( 1 degree ) and wide tires on the front (265 ). I have a 4" dropped axle from Sids enroute so will not address caster until that install but plan on 6 degree caster shim at that time as truck should sit with a 1.5 degree nose down rake so the effective should be 4.5 degrees of caster and front tires will be reduced to 205's or 215's as turning will be a problem with fender contact after lowering. At this time the drag link is parallel and will be after the axle install. Anyone else with this setup have any opinions or things you have done to make it better.

dwcsr · 07-13-2010, 05:40 PM

I don't have that setup but bump steering will continue to be an issue with a straight axle. What your doing with help greatly but it will never go away completely. Wide tires magnifies the problem.

T Hilde · 07-13-2010, 06:30 PM

Is your drag link (tie rod from steering box to spindle) level or close to it?

gab50 · 07-14-2010, 04:45 PM

yes the drag link is level

raycow · 07-14-2010, 07:34 PM

How about crossover steering like on 4WD?

Ray

gab50 · 07-27-2010, 04:57 PM

Ray

I did some calculator work and that would sure cut the bump steer to 25-35% of what it is. Also looked at available pitman arms and sprint car steering arms and it looks doable. Next step is to measure for clearance between springs and frame. Final measure will have to wait until the dropped axle is in.

RootBeer 6117 · 07-27-2010, 11:04 PM

I have had to use steering stabilizer shocks to cure similar problems on straight axles trucks, I remember one scared the crap out of me it started wobbling so bad when I hit a bump.

**robnolimit** · 07-29-2010, 08:22 PM

That style of Gm p/s kit will always bumpsteer, it always has, as the draglink is way too short, and the box is on the wrong side of the spindle. Sorry to tell you that the drop axle will probably make it worse. Does it turn more one way than the other, and try to lift the frame on a right turn? A cross steer set up may be your best bet, but remember to stiffen up the frame, or the p/s box will crack it.

gab50 · 07-30-2010, 09:11 PM

I think I will do the cross steer as using a draglink that short is kind of like trying to make honey out of you know what but with the solid axle there isn't a lot of choices for power steering. I have several pitman arms and some say too much time so I decided to do some experiments. I had it installed so the back of the draglink was about 3\8" up. It had some bumpsteer but not too bad. I changed around and had it so that the back was 1" down and it drove like crap. I then set it so the back was 1 1\4" up ( which I thought it would be bad ) and it drove really well. It is such that a person could live with it. From all I had heard and from physics it should have been worse. Go figger.

07-13-2010, 02:40 PM	#1
gab50 Registered User Join Date: Jul 2009 Location: Bellingham, WA Posts: 40	power steering bump steer I have just got back on the road after a power steering install on my 50 1\2 ton which used the steering box from a late 70's pickup and the steering arm and drag link from CPP. First impression is it steers good on smooth road with hands off no wander. It has a little bump steer on bumps. I think this is due to a bunch of things, some being the setup has a very short drag link, presently has very little caster ( 1 degree ) and wide tires on the front (265 ). I have a 4" dropped axle from Sids enroute so will not address caster until that install but plan on 6 degree caster shim at that time as truck should sit with a 1.5 degree nose down rake so the effective should be 4.5 degrees of caster and front tires will be reduced to 205's or 215's as turning will be a problem with fender contact after lowering. At this time the drag link is parallel and will be after the axle install. Anyone else with this setup have any opinions or things you have done to make it better.

07-13-2010, 05:40 PM	#2
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,134	Re: power steering bump steer I don't have that setup but bump steering will continue to be an issue with a straight axle. What your doing with help greatly but it will never go away completely. Wide tires magnifies the problem.

07-13-2010, 06:30 PM	#3
T Hilde Registered User Join Date: Apr 2009 Location: Faribault, MN Posts: 385	Re: power steering bump steer Is your drag link (tie rod from steering box to spindle) level or close to it? Last edited by T Hilde; 07-13-2010 at 06:30 PM.

07-14-2010, 04:45 PM	#4
gab50 Registered User Join Date: Jul 2009 Location: Bellingham, WA Posts: 40	Re: power steering bump steer yes the drag link is level

07-14-2010, 07:34 PM	#5
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: power steering bump steer How about crossover steering like on 4WD? Ray

07-27-2010, 04:57 PM	#6
gab50 Registered User Join Date: Jul 2009 Location: Bellingham, WA Posts: 40	Re: power steering bump steer Ray I did some calculator work and that would sure cut the bump steer to 25-35% of what it is. Also looked at available pitman arms and sprint car steering arms and it looks doable. Next step is to measure for clearance between springs and frame. Final measure will have to wait until the dropped axle is in.

07-27-2010, 11:04 PM	#7
RootBeer 6117 Registered User Join Date: Jul 2010 Location: Columbia Mo Posts: 395	Re: power steering bump steer I have had to use steering stabilizer shocks to cure similar problems on straight axles trucks, I remember one scared the crap out of me it started wobbling so bad when I hit a bump.

07-29-2010, 08:22 PM	#8
robnolimit Senior Member Join Date: Jul 2010 Location: Dandridge, Tn. USA Posts: 2,226	Re: power steering bump steer That style of Gm p/s kit will always bumpsteer, it always has, as the draglink is way too short, and the box is on the wrong side of the spindle. Sorry to tell you that the drop axle will probably make it worse. Does it turn more one way than the other, and try to lift the frame on a right turn? A cross steer set up may be your best bet, but remember to stiffen up the frame, or the p/s box will crack it.

07-30-2010, 09:11 PM	#9
gab50 Registered User Join Date: Jul 2009 Location: Bellingham, WA Posts: 40	Re: power steering bump steer I think I will do the cross steer as using a draglink that short is kind of like trying to make honey out of you know what but with the solid axle there isn't a lot of choices for power steering. I have several pitman arms and some say too much time so I decided to do some experiments. I had it installed so the back of the draglink was about 3\8" up. It had some bumpsteer but not too bad. I changed around and had it so that the back was 1" down and it drove like crap. I then set it so the back was 1 1\4" up ( which I thought it would be bad ) and it drove really well. It is such that a person could live with it. From all I had heard and from physics it should have been worse. Go figger.



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