Tyre Skip/Juddering

[daveenty]

Not sure if this should be in here or the American section but, as it's really trye related, went for here.

I'm hoping that someone could offer advice on a steering issue I am experiencing? It's fine in a straight line, OK around left hand bends but tends to judder a lot on right handers. It's like tyre skip really, noticeable at low speeds while manoeuvring but also happens on the road though not as pronounced.

The motor in question is a 1970 Ford Ranchero which is the Torino based pickup. It's fitted with 235/60/15 Cooper Cobra Radial G/T on 7.5" Centerline Drag Rims. According to my research it originally came with several combinations of wheel and tyre, starting at ~7.00 x 14 on a 5Jx14 up to a 205/70/15 on a 6Jx15. My thoughts are that the fronts are just too wide for it to cope with. I was thinking of reducing the size to 205/50/15 which would not only reduce the contact area but also lower the ride height a bit, which is also needed and would save me messing with springs.

All steering joints are either new or sound, many having been replaced less than 1,000 miles ago, wheel bearings are also sound with no real play. There is a little play in the drag link ends but not enough to justify immediate replacement.

Any suggestions/recommendations would be appreciated.

[daveenty]

Rotary Potato said:

You don't explicitly state it ... but all your troubleshooting seems to be focused on the front axle, so I'm assuming you believe it's coming from there?

I take it there's no chance it's coming from the rear and is actually diff related? If it's noticeable at low speeds, maybe get someone to film from the outside, to confirm exactly which axle it is that's skipping. It'd be a real face palm moment if you spent ages buggering about with the front, only to realise that it was the back axle all along!

I only mention it as the only time I've experienced something like that was many years ago (when I was young and silly) and I had a welded diff in my daily driver, and maneuvering around a car park would have it hopping and skipping away.

Edited by Rotary Potato on Wednesday 10th July 11:50

I appreciate the thought though can assure you that it's definitely from the front, the diff is a 9" Locker and in good condition. You can actually feel the jerkiness through the steering wheel, especially around the 30mph mark on a sharpish right hand bend. It's like the tyre's trying let go but just managing to grip to get me around the curve. Understeer to the extreme if you will. I appreciate the tyres aren't the best of brands, hence another reason for wanting to change.

Incidentally, tracking was checked and adjusted on a Hunter machine after I fitted the new ball joints, along with camber and caster.

[daveenty]

E-bmw said:

As above, you only seem to be talking about fronts, but don't forget if you change the front tyre/wheel combination it will mess with ABS/ESC unless you do all 4.

Nothing technical like that, it's a 1970 US commercial vehicle so has never seen a computer, let alone had one fitted to it.

Rears are 10" x 15" rims fitted with 295/50/15 so certainly not original but they're staying.

[daveenty]

Olivera said:

Is the 9" diff permanently locked? If so a lot of scrub when turning sounds like exactly what I'd expect.

No, locker's just the name they're known by. It's standard LSD