Steering goes loose when driving downhill

[nsa]

Driving on flat or uphill the steering is nicely weighted, but driving downhill the steering becomes very light and wanders off-centre. It's worse when I apply the brakes.

1997 Toyota 4Runner. IFS. new pattern part LCA and UCA and bushes, tyres OK, new power steering column (old one was leaking), alignment done (0 camber, 0 toe). The garage said they weren't able to do caster on their Hunter (seems odd), but I can see the camber bolts take the lower arms quite far forward. Wheel hub to wheel hub measurements on both sides are the same, so whatever caster is, it's consistent.

Toyota spec for caster is 2 degrees, but a lot of people run 4 deg. Is that likely to be my problem?

[GreenV8S]

The symptoms suggest you have a problem with suspension flex or play which is sensitive to driveline loads. You might need a hefty pry bar to apply enough load to find where it's deflecting.

[nsa]

Many thanks. Not looking forward to tracking that down.

[bigothunter]

nsa said:

Driving on flat or uphill the steering is nicely weighted, but driving downhill the steering becomes very light and wanders off-centre. It's worse when I apply the brakes.

1997 Toyota 4Runner. IFS. new pattern part LCA and UCA and bushes, tyres OK, new power steering column (old one was leaking), alignment done (0 camber, 0 toe). The garage said they weren't able to do caster on their Hunter (seems odd), but I can see the camber bolts take the lower arms quite far forward. Wheel hub to wheel hub measurements on both sides are the same, so whatever caster is, it's consistent.

Toyota spec for caster is 2 degrees, but a lot of people run 4 deg. Is that likely to be my problem?

So there's a known problem which owners fix by increasing caster beyond spec. Prompts a few questions:

- What problem are they solving?
- Is it loss of steering effort, same as you are experiencing?
- What are the caster measurements of your car?

Will be difficult to analyse and solve the problem without understanding these basics.

[nsa]

I took it to a garage that only does alignment. They said the wheels were toed in. The previous places used a Hunter machine, but either they weren't calibrated, or the operators didn't know what they were doing.

[bigothunter]

nsa said:

I took it to a garage that only does alignment. They said the wheels were toed in. The previous places used a Hunter machine, but either they weren't calibrated, or the operators didn't know what they were doing.

Has that solved the problem?

[PaulKemp]

Toe alignment is usually toe in so under braking or fierce acceleration the wheels don’t go toe out but flex to straight ahead at the most. I would suspect the your toe setting is wrong, it will be specified in a Haynes manual or similar so you can check when you have it aligned

[nsa]

bigothunter said:

Has that solved the problem?

It's better, but still not right. Still checking out whether there is any deflection in the suspension. The garage said they could only get 0.68 degrees of caster, when the spec is 2.25, and the printout they gave me says 3.00 each side.

TBH I just want rid of the thing now.

Edited by nsa on Friday 14th July 06:38

[nsa]

Update: Found out the gauge on the air compressor I use to inflate the tyres at home reads low. Recommended 32psi, I was running 25psi. Inflated the tyres to spec and it's made a big difference. The tyres are 275/70/16, so they have a lot of profile anyway - I can only imagine that the sidewalls squirmed enough so it felt like the wheel could move independently of the tyre.

Either way, it's much better now.

[nsa]

GreenV8S said:

The symptoms suggest you have a problem with suspension flex or play which is sensitive to driveline loads. You might need a hefty pry bar to apply enough load to find where it's deflecting.

You were exactly right.

All four lower control arm bushes were fked. I took the car to five different alignment places over the past year and none of them picked it up. The last two I specifically said "let me know if the bushes are no good and I'll replace the LCAs". Eventually I decided to get in there with a crowbar and it was obvious that things were flexing. Replaced LCAs, got a halfway-there alignment with a vertical laser doodat, and will try to get it sharpened up for free at the last shop I visited.