Started to feel a shimmy in the steering wheel from irregular road surfaces. PS system pissing fluid at hose to rack fittings and elsewhere. Swapped in a clean used ZF rack and bled. But it’s still shimmying over uneven road. Not on the brakes, so it’s not the rotors. Front suspension is fresh rebuilt, so it’s not the bushings or balljoints. After warming up, there is a loud high pitched screech from the front of engine. Alternator is fresh and good. AIR pump belt removed, A/C compressor belt removed. Water pump has been replaced. Wondering if the power steering pump could be losing pressure or pulsing to cause the feedback to the steering wheel. Do failing PS pumps ever scream? Car is factory NON SLS, so no hydraulic circuit for that. Thoughts?
Harmonic balancer screeching/slipping.
One of your tires may be hooped/buggered/fd etc.
I agree with Larry regarding the HB.
We have just had to change out 2 rear tyres on our MG6 due to delaminating, the date stamp was 2019 so not that old. That could be the problem with the shimmy, with our car the effect was more pronounced at different speeds, sometimes not very much and at others really pronounced.
If you’ve check your belts for proper tension then It certainly sounds like your harmonic damper is failing and causing the noise. Paint or chalk a line front to back on the damper and pulley. When you hear the squeal again check the line. If it’s not still lined up your damper is toast and needs to be rebuilt or replaced. Just had the same problem so I had my damper rebuilt and it’s being shipped back to me as we speak.
I would discount your power steering rack as the problem since you’re experiencing similar problems with both racks. A failing rack tends to just leak but still operates normally, also a ZF unit is (in my opinion) far superior to Adwest.
So while it is possible that your failing damper is slipping and momentarily stops turning the pump that pressurizes the rack, I think wheel alignment and tire problems are more likely the culprits.
Kudos to Team JL on the harmonic balancer diagnosis. I’m hereby renaming it the “alternator activated - water pump clutch assy”. Due to the screaming noise getting louder from no beam to low beams to high beams, which was totally misdirecting my troubleshooting.
The good news is I’ve been racing David Langsathers balancers since he started decades ago and he’s just an hour up the road and he’ll have me taken care of this week. Huzzah!
As for the team’s shimmy diagnosis, I shall not, due to reasons of pride (or lack thereof) reveal the date stamp on those tires. Even my eyebrows climbed up my forhead. Off to Ebay to search for 235 60 15s seeing as there are no other 15s made anymore.
And perhaps on the delaminating tyres