Bump steer?

[Klef72K5]

I just bought this 72 Blazer and it has a 6 in. lift with 33's under it. When I drive down back roads and hit a bump it chases it. Is this what they call bump steer? How can I improve it? Would double shocks help? I did notice that my bearing on the gear box (the one that the drop pitman is attached to) has a little play in it, could that be the problem?
Thanks in advance all!

<P ID="edit"><FONT SIZE=-1>Edited by Klef72K5 on 05/06/01 09:39 AM (server time).</FONT></P>

 

[JST12]

Klef72,
Double shocks probably won't help too much. A steering stabilizer will help a bunch with bump steer. Some argue that a steering stabilizer is only a band-aid for other suspension or steering issues, but I know it "feels" better when you're driving. If the truck is wandering, a stabilzer won't help too much, but for sudden bumps where the wheel jerks in your hands, the stabilizer is the way to go. JT

 

[Steve_Chin]

A bad sector shaft bearing might cause some steering play, but bump steer itself is related to changes in the geometry of the front suspension as it moves through its range of travel. Check the older posts here for some information on reducing the amount of bump steer...

 

[JST12]

Steve has a good point, and I know a good way to check steering geometry throughout range of travel. Find a road where there is a large dip or crest which will hit both front wheels at the same time and cause compression or extension of your front suspension. Drive fast over these and if the wheel pulls to the right or left , you have a geometry issue such as the wrong pitman arm / steering arm for your 6" lift. I did this on my other truck and after a couple different dropped pitman arms, found the perfect set-up. If the wheel stays straight when you do this , but only jerks when one wheel hits a pot-hole or rock, then the stabilizer should help. JT

 

[Donovan]

Sorry to tell you this but you just might never get rid of this. I had a 71 Blazer and it wandered all over the place. I thought it was just the tires and old worn out bushings. So I put a 4" lift on it with all new bushings. This didn't help. Next I change all the ball joints. This didn't help. Set the caster to 6 degrees that didn't help. I got pissed off and sold it. Now I am really kicking myself for it but oh well. Does it wander or does it just dart side to side after you hit a bump? My blazer just plain wondered all over. Maybe your is not like mine but there is a couple things to do yet that I didn't do. If I had it now I would have done it. Check the frame at the steering box to make sure it is not cracked if not then build a bolt in steering box brace. Like the ones for the later models. Next is to do a crossover steering. I am pretty sure this will take care of the bump steer that you have and the wondering if in fact it does wonder. Also you might try to add the wheel spacers to the rear so that the axle are the same width. This helps the tires from hunting in and out of grooves. If it is set right you should not need a steering stabilizer shock. This might not help you out at all but maybe it should help someone. BTW My parents bought this Blazer brand new in 71 and it never drove straight. GM even had a recall on the frontend to replace the balljoints but it didn't help. They sold it to a family friend in 73 when they bought a new 73. The 73 drove 100% better the the 71. I hope this help but probably not.



Donovan
<A target="_blank" HREF=http://www.rustbucket.coloradok5.com>http://www.rustbucket.coloradok5.com</A>
Bigger is Better

 

[Steve_Chin]

Wandering on a smooth surface has other causes. When I first bought my '72, it had new ball joints, new tie rod ends, new drag link ends, etc. (basically, the entire steering system was new except for the pitman arm and the steering box). It wandered all over the highway and was a horrible white-knuckle ride. Setting the tire pressures to the correct values corrected the problem completely.

 

[gokartergo]

You also could have radial wear. Try swaping the to front tires and see if that helps. I used to have cheap BFG A/T on it and it woundered all over the place untill I swapped the tires Dan

 

[Burt4x4]

I had tearable wander at hwy sppeds and added an aftermarket sway bar. I think ADDCO made it but can't remember I put it on back in 94-95. here is a pic

72K5

Led Zeppelin

Rock ON!

<A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>

 

[JST12]

One thing that most automakers have adopted on newer vehicles is the track bar which connects the frame on one side to a point on the axle on the opposite side. This of course keeps the axle from moving side to side. I am sure this would correct some of the wandering people are experiencing. My 71 wandered all over the place also. I took everything apart because of the resto I'm doing. I replaced the entire front axle with a '79 3/4 ton, and the steering box with an AGR. If this sucker still wanders when I'm done, I'm first going to brace the frame at the box. If that doesn't help, then it's time to add a track bar. If there is one thing that bugs me, it's having to correct the steering wheel every second to keep the truck going straight. I'll keep everyone posted. JT

 

[JST12]

Burt,
I see you have a frame brace bar in there. Was this added at the same time as the sway bar? If not, did your brace noticeably help the steering? Jt

 

[gassman]

My 71 wandered also after I put a 4" lift under it. Thought It was steering also but found out that tires are most of the time the problem. In my case it was the tires. Now I have new running gear and SSR tires and I can now let go of the steering wheel when I hit a bump and she stays straight as an arrow. Don't give up on her.

 

[Burt4x4]

That square stock that I painted black was added by the previous owner. I have reciently rewelded it in place and yes it keeps the steering box/frame from flexing.
Do any of you all have a stock cross member up front?&gt;???
I have no idea if GM put one up there or not????

72K5

Led Zeppelin

Rock ON!

<A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>

 

[JST12]

Ohhhh yeah, that's what's missing in your pic. The stock cross member is normally a tad behind where yours is mounted. It is a formed peice of sheet metal. I have plenty of pics of the stock one if you want to see it. Can we upload a pic to this site inside a thread, or do you have to reference a pic on another site to be able to see it like you did above? JT

 

[Burt4x4]

Oh ok I guess mine was remove and in it's place the squarestock was put in it's place.

I have some pics out on Zing.com
http://www.burt4x4.coloradok5.com

 

[Steve_Chin]

Re: Track Bar

Track bars, aka Panhard Bars reduce the lateral movement of an axle that is suspended by trailing arms. They introduce lateral movement into the rear suspension as it travels vertically and induce some weight jacking effects. They will bind up a leaf sprung system a bit because the leaves want to compress/extend in a vertical direction and the panhard bar will try to force the axle to the side as it moves vertically. A Watts Link will work MUCH better with a leaf sprung system (actually, they work better with trailing arm suspensions as well, but they are more complicated and expensive than panhard rods). Panahard Bars are a cheap solution to a design problem that should have been fixed by angulating the upper control arms...

 

[JST12]

Re: Track Bar

Steve,
My F350 4x4 has a track bar and leaf springs in the front. It works good as long as the drag link runs parallel with the track bar so the axle moves in the same arc as the spindles. Otherwise the wheel pulls left or right depending on whether the drag link or trackbar mounting point is higher. Anyway, it's tough to say what would happen on a Chevy with the steering arm set up. The axle would move laterally in an arc with a trackbar, but the front to back movement is what would pull the steering arm and thus the steering wheel. With a trackbar, the steering arm would rotate side to side on the ball joint but probably not pull it too much. Hmmm. JT