Help with bump steer problem

I have a 07 toyota prerunner double cab 4.0 v6 with stock 20'' rims. Stock tires, size 265/50/20. I just bought the truck a few weeks ago. I've replaced front hubs. And bought new tires + an alignment . The truck had really bad bump steer before .Its better now but its still not right at all. The truck reads the road/ follows the crown. The slightest bump makes it steer one way or the other. I took the truck back and had it realignment.Still has the same problem but seems to move to the left more then it did before. It all depends on what side the bump is on and the crown of the road. Two separate shops has told me everything is tight on my front end. I cant make it 40 ft down the road without it pulling one way or the other. Also there is a clunk noise when I hit a hard transitions from one road to another or a hard bump form entering onto a bridge. on gravel roads the steering wheel is going crazy and there is a clunking feeling and slight noise as the wheel goes back and forth. I really need help on this. I'm at my wits end and no one seems to be able to figure out whats wrong. I also believe that the bump steer is killing my gas mileage. I'm only getting 13 mpg.Any help would be much appreciated. God Bless

 

Is the truck lifted? I don't believe Tacomas came stock with 20s on them.

 

Do you have the alignment numbers from when they aligned it? Bump steer shouldn't be an issue unless the truck height has been lifted or lowered.

 

Firstly, this is not causing your bad MPG. That's a seperate issue.

What did the alignment shop set the caster at? It sounds like its too low.

 

If everthing is good in the front end, what about the rear? Loose u-bolts or a broken leaf?

If good, I'm thinking low caster.

 

I stand corrected.I do not know if the truck has been lifted. I bought it from the first owner and he said hes never changed anything from stock. The standard tires are 16'' P245/75R16. The truck is (Toyota Sport Series Edition)
(Distributor installed options)And with that came 20'' chrome wheels and tire upgrade. So is it stock in a way.Just not all the standard equipment.

 

here are the alignment numbers. The 2nd numbers is after I took the truck back and complained that it was pulling right and still had bump steer.

 

OOPS SORRY ABOUT THE PICS

 

Why is one truck listed on the report a 2wd and the other a pre runner? The min and max caster setting are different on both the reports.

 

I'm a newbe. How do I check for loose u bolts

 

Damn I didnt even notice that. I see they also got my tire size wrong.Do you think that would make a difference. Like they're setting the alignment to the wrong truck specs

 

That and I think your caster is still too low.

I don't know about the tire size if it will or not.

 

Are the rims you have hub centric? Running rims that are lug centric can cause problems. Your rims should be hub centric.

I believe the issue here is with your caster though. But I'd check and make sure those rims are hub centric.

 

The first alignment was done to the specs for a five lug 2wd, but comparing the specs for the prerunner, it was a better alignment than the second one. The pulling to the left after the second alignment is thanks to the caster difference between sides.

For the rear ubolts, torqing the nuts to 75-80 ft-lbs is the best way, so long as they aren't terribly rusty and seized. Tapping the side of the ubolt with a small hammer works too, if tight, they will ring. If loose, you'll get a dull tap sound. One can look for signs of movement where the spring meets the axle too. That said, the thrust angle was consistant between both alignments, so its not likely shifting around.

What tire pressure are you running?

 

How do I check if the rims is hub or lug centric?

And I just want to thank everyone for their input and help.

 

Do you think since the dealership put 20' rims from 16' that they might of lifted the truck to do so?

 

OP, as was already posted, ask the alignment guy why he did not get the casters into the correct range? If it's lifted he will tell you that.

 

Caster at least 2.5 will help tremendously with the bump steer and wander...it sounds like the truck was lifted, if that is so, then you may need to replace the UCA's with aftermarket to achieve proper alignment...


And, you need to get an alignment tech that knows these trucks, not just someone that follows some general technical alignment specs for a stock suspension...

 

I'll take my truck back up there tomorrow and have them set my caster to 2.5 and ask the tech if the truck has been lifted.Thank you and God Bless

 

If Toyota supplied and installed them they should be hub centric. I thought they were aftermarket rims someone else installed.