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Steering, Suspension And Brakes


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Hi guys

Been a member for a while and what a great forum this is - I've learned so much about the LS400 and how to keep it running economically.

I'm hoping someone will help with a couple of issues I'm experiencing with my 10yr old LS400 mk4...

My local garage (excellent service and reputation) replaced the front discs (Brembo) and pads (Mintex) due to the discs being warped (common problem). Now the car pulls slightly to the left on braking and I have to correct by right-steering. Also (and this happened before the disc change as well), when I brake steadily to a halt, foot still on brake and Drive engaged, I then engage neutral (foot still on brake) and the n/s front rises more than the o/s. With foot still on brake, I engage Drive again and the n/s dips down more than the o/s. That's before I start moving. Possibly dampers? Garage and MOT tester says they work fine but I suspect may be mis-matched due to wear.

Also, when driving, the steering wheel doesn't completely self-centre after a turn, I have to correct it slightly. And when I make a gentle turn, I can feel a pulsing as I rotate the steering slightly. It's as though the tyre tread isn't centred on the wheel, if you understand. It feels like a partially seized balljoint, each revolution of the wheels moving the steering a little bit more in the chosen direction.

Garage says balljoints ok, geometry ok, tyres and wheels ok, and as far as they can tell all bushes are ok. Car has done 110k miles and has been fully maintained since 9k miles. No advisories on recent MOTs.

It just doesn't feel as smooth as it used to, and it's a bit tiring to keep correcting the self-centreing (sp?) as I drive.

Any ideas, guys? I've tried to give as much info as possible in the hope that it aids diagnosis (I suspect some of the symptoms are related), but if you need more info please ask. I really appreciate your time.

Kind regards

Paul

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Hi guys

Been a member for a while and what a great forum this is - I've learned so much about the LS400 and how to keep it running economically.

I'm hoping someone will help with a couple of issues I'm experiencing with my 10yr old LS400 mk4...

My local garage (excellent service and reputation) replaced the front discs (Brembo) and pads (Mintex) due to the discs being warped (common problem). Now the car pulls slightly to the left on braking and I have to correct by right-steering. Also (and this happened before the disc change as well), when I brake steadily to a halt, foot still on brake and Drive engaged, I then engage neutral (foot still on brake) and the n/s front rises more than the o/s. With foot still on brake, I engage Drive again and the n/s dips down more than the o/s. That's before I start moving. Possibly dampers? Garage and MOT tester says they work fine but I suspect may be mis-matched due to wear.

Also, when driving, the steering wheel doesn't completely self-centre after a turn, I have to correct it slightly. And when I make a gentle turn, I can feel a pulsing as I rotate the steering slightly. It's as though the tyre tread isn't centred on the wheel, if you understand. It feels like a partially seized balljoint, each revolution of the wheels moving the steering a little bit more in the chosen direction.

Garage says balljoints ok, geometry ok, tyres and wheels ok, and as far as they can tell all bushes are ok. Car has done 110k miles and has been fully maintained since 9k miles. No advisories on recent MOTs.

It just doesn't feel as smooth as it used to, and it's a bit tiring to keep correcting the self-centreing (sp?) as I drive.

Any ideas, guys? I've tried to give as much info as possible in the hope that it aids diagnosis (I suspect some of the symptoms are related), but if you need more info please ask. I really appreciate your time.

Kind regards

Paul

Hi

With regard to not stopping in a straight line, take it back as you've paid for the brakes to work perfectly and they don't. If this is not an option, check the parking brake isn't binding as well as the pads. The parking brake shoes can brake down over time.

When you engage drive, the rear sinks rather than the front rising. The problem could easily be rear springs and/or shocks. Have a look to see if any of the springs/shocks have been replaced as it is possible that the opposite one is ready to go.

With regard to the steering issue. It almost certainly a geometry issue irrespective of what they say. Have they done a full computerised check? have they disturbed the rear suspension because this will have a dramatic effect on the streering. Are you using original wheels or aftermarket replacements? If the latter, this can cause the symtoms you describe even if the geometry (front and rear) is correct. Also an issue are tyres if they are not correctly matched and free of defects.

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Thanks, guys. Your suggestions were gratefully received. I've now got something to work on. First thing Monday I'll get the caliper pins checked, followed by a full geometry check - that seems like a good start. I'll let you know what happens...

Paul

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Still no progress.

Seems the seized caliper pin issue doesn't apply to a year 2000 Mk4 car because they're not the same caliper arrangement as older cars. (Is that correct?). Pistons are free, everything that requires greasing has been greased, yet the car still pulls to the left on braking (new discs and pads fitted last week - about 200 miles ago).

The four-wheel alignment check at a reputable service place revealed that the front wheels toed out very slightly. This was adjusted (leaving the steering wheel slightly at an angle...). All other settings were deemed correct other than rear thrust line 1mm out but adjusters seized so unable to correct that. I have all the results if it helps any of the guys here to know them. No visible broken springs, and all shocks work.

At higher speeds it follows any slight imperfection or ridge in the road, needing constant minor correction, and the steering feels too light. Over 60 it feels like it's on a thin layer of snow. There's also steering wobble despite dynamic wheel balance. It's on Dunlop D8Z's by the way (free of defects), and has been since new. The wheels are the original ones, as are all springs and shocks.

It doesn't completely self-centre after a gentle turn, so constant correction needed there too, and when correcting it, the action feels lumpy. Could that be a PAS issue?

Frankly the car just feels wrong and I don't trust it as much as I used to. I've owned it for 9yrs and I know how it should be.

Any ideas please, guys? Clutching at straws now...

Kind regards

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Still no progress.

Seems the seized caliper pin issue doesn't apply to a year 2000 Mk4 car because they're not the same caliper arrangement as older cars. (Is that correct?). Pistons are free, everything that requires greasing has been greased, yet the car still pulls to the left on braking (new discs and pads fitted last week - about 200 miles ago).

The four-wheel alignment check at a reputable service place revealed that the front wheels toed out very slightly. This was adjusted (leaving the steering wheel slightly at an angle...). All other settings were deemed correct other than rear thrust line 1mm out but adjusters seized so unable to correct that. I have all the results if it helps any of the guys here to know them. No visible broken springs, and all shocks work.

At higher speeds it follows any slight imperfection or ridge in the road, needing constant minor correction, and the steering feels too light. Over 60 it feels like it's on a thin layer of snow. There's also steering wobble despite dynamic wheel balance. It's on Dunlop D8Z's by the way (free of defects), and has been since new. The wheels are the original ones, as are all springs and shocks.

It doesn't completely self-centre after a gentle turn, so constant correction needed there too, and when correcting it, the action feels lumpy. Could that be a PAS issue?

Frankly the car just feels wrong and I don't trust it as much as I used to. I've owned it for 9yrs and I know how it should be.

Any ideas please, guys? Clutching at straws now...

Kind regards

Hi again

Having owned it for such a long time tells its own story; you obviously do know how it should feel.

Did you check out the parking brake issue I mentioned before? It would be beneficial to check the parking brake operation and particularly the release/cable/shoes before any other braking aspect.

The steering could be the PAS pump or the rotary valve. The relief valve in the pump may have seized meaning that the high pressure needed when turning at low speeds is still operating at high speed/revs. This would give the light feeling you described.

The rotary valve senses the force on the steering wheel. When the steering wheel is not being turned, both hydraulic lines provide the same amount of pressure to the steering gear. But if the spool valve is turned one way or the other, ports open up to provide high-pressure fluid to the appropriate line. It follows that if there is a fault, high pressure fluid could be leaking through causing the wheel to turn away from dead ahead.

If you are satisfied that the steering geometry is perfect then it will be worth while looking at the PAS.

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Still no progress.

Seems the seized caliper pin issue doesn't apply to a year 2000 Mk4 car because they're not the same caliper arrangement as older cars. (Is that correct?). Pistons are free, everything that requires greasing has been greased, yet the car still pulls to the left on braking (new discs and pads fitted last week - about 200 miles ago).

The four-wheel alignment check at a reputable service place revealed that the front wheels toed out very slightly. This was adjusted (leaving the steering wheel slightly at an angle...). All other settings were deemed correct other than rear thrust line 1mm out but adjusters seized so unable to correct that. I have all the results if it helps any of the guys here to know them. No visible broken springs, and all shocks work.

At higher speeds it follows any slight imperfection or ridge in the road, needing constant minor correction, and the steering feels too light. Over 60 it feels like it's on a thin layer of snow. There's also steering wobble despite dynamic wheel balance. It's on Dunlop D8Z's by the way (free of defects), and has been since new. The wheels are the original ones, as are all springs and shocks.

It doesn't completely self-centre after a gentle turn, so constant correction needed there too, and when correcting it, the action feels lumpy. Could that be a PAS issue?

Frankly the car just feels wrong and I don't trust it as much as I used to. I've owned it for 9yrs and I know how it should be.

Any ideas please, guys? Clutching at straws now...

Kind regards

Re your steering as Steve says above.

The sliding pin arrangment,on the brake calipers is shown on the parts diagram to be only on the rear for yr.2000 models.

Try swapping the wheels around to see if it will run straight after that.

After a run feel if any wheel/hub feels noticeably hotter than the others.[bEWARE DO NOT BURN YOURSELF!]

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Still no progress.

Seems the seized caliper pin issue doesn't apply to a year 2000 Mk4 car because they're not the same caliper arrangement as older cars. (Is that correct?). Pistons are free, everything that requires greasing has been greased, yet the car still pulls to the left on braking (new discs and pads fitted last week - about 200 miles ago).

The four-wheel alignment check at a reputable service place revealed that the front wheels toed out very slightly. This was adjusted (leaving the steering wheel slightly at an angle...). All other settings were deemed correct other than rear thrust line 1mm out but adjusters seized so unable to correct that. I have all the results if it helps any of the guys here to know them. No visible broken springs, and all shocks work.

At higher speeds it follows any slight imperfection or ridge in the road, needing constant minor correction, and the steering feels too light. Over 60 it feels like it's on a thin layer of snow. There's also steering wobble despite dynamic wheel balance. It's on Dunlop D8Z's by the way (free of defects), and has been since new. The wheels are the original ones, as are all springs and shocks.

It doesn't completely self-centre after a gentle turn, so constant correction needed there too, and when correcting it, the action feels lumpy. Could that be a PAS issue?

Frankly the car just feels wrong and I don't trust it as much as I used to. I've owned it for 9yrs and I know how it should be.

Any ideas please, guys? Clutching at straws now...

Kind regards

Re your steering as Steve says above.

The sliding pin arrangment,on the brake calipers is shown on the parts diagram to be only on the rear for yr.2000 models.

Try swapping the wheels around to see if it will run straight after that.

After a run feel if any wheel/hub feels noticeably hotter than the others.[bEWARE DO NOT BURN YOURSELF!]

Thanks, ROYT and Steve for the brakes pointers, will investigate the parking brake this week.

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Still no progress.

Seems the seized caliper pin issue doesn't apply to a year 2000 Mk4 car because they're not the same caliper arrangement as older cars. (Is that correct?). Pistons are free, everything that requires greasing has been greased, yet the car still pulls to the left on braking (new discs and pads fitted last week - about 200 miles ago).

The four-wheel alignment check at a reputable service place revealed that the front wheels toed out very slightly. This was adjusted (leaving the steering wheel slightly at an angle...). All other settings were deemed correct other than rear thrust line 1mm out but adjusters seized so unable to correct that. I have all the results if it helps any of the guys here to know them. No visible broken springs, and all shocks work.

At higher speeds it follows any slight imperfection or ridge in the road, needing constant minor correction, and the steering feels too light. Over 60 it feels like it's on a thin layer of snow. There's also steering wobble despite dynamic wheel balance. It's on Dunlop D8Z's by the way (free of defects), and has been since new. The wheels are the original ones, as are all springs and shocks.

It doesn't completely self-centre after a gentle turn, so constant correction needed there too, and when correcting it, the action feels lumpy. Could that be a PAS issue?

Frankly the car just feels wrong and I don't trust it as much as I used to. I've owned it for 9yrs and I know how it should be.

Any ideas please, guys? Clutching at straws now...

Kind regards

Hi again

Having owned it for such a long time tells its own story; you obviously do know how it should feel.

Did you check out the parking brake issue I mentioned before? It would be beneficial to check the parking brake operation and particularly the release/cable/shoes before any other braking aspect.

The steering could be the PAS pump or the rotary valve. The relief valve in the pump may have seized meaning that the high pressure needed when turning at low speeds is still operating at high speed/revs. This would give the light feeling you described.

The rotary valve senses the force on the steering wheel. When the steering wheel is not being turned, both hydraulic lines provide the same amount of pressure to the steering gear. But if the spool valve is turned one way or the other, ports open up to provide high-pressure fluid to the appropriate line. It follows that if there is a fault, high pressure fluid could be leaking through causing the wheel to turn away from dead ahead.

If you are satisfied that the steering geometry is perfect then it will be worth while looking at the PAS.

Your explanation of how the PAS system works might just be of help, Steve. It certainly fits the effect I'm getting from the car. Is the PAS unit serviceable, or is it a complete replacement?

I'm determined to get to the bottom of this because I love the car! (although it makes no financial sense...)

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