93 RR classic LWB vibration at high speed

[rezdiver]

hello,
Wow, I never knew this board existed or there was a club in BC. this is great.
I need some help please.
I have a 93 range rover LWB with a 4.2 and air suspension.
I have had this problem develope and now it is at a point that i am almost scared to drive it and even the mechanic shops cant figure it out.
Going down the road at sppeds of over 80km/hr if i hit an offset bump or pothole i get this huge vibration in my steering, like a bumpsteer but at a rapid rate. it is uncontrollable. at one point when it was happening i looked out the window to see my tires just shaking side to side. I have to slam on the brake and reduce the speed to around 50 to make it stop and everything is fine after, except for the big rig that had to slam on his brakes behind me.
To try and fix this, all tierod ends are perfect. new shocks(bilstein), new steering dampner( oldmanemu), new steering shaft to the steering box, steering box tightened, air suspension reset, all new poly bushings front and back, tires ballanced and rotated. all this was done after the vibrations started to try and fix the problem.
I still have the same problem but it is worse now because the poly bushes send the vibration right through the chassis.
help please. :?:

cheers,
Reza

[Roverworks]

Your driving complaint is due to front end wear...In particular, the swivel pins, bearings and bushings that allow the swivel housing to turn. I see you are in Victoria, there are some good mechanics there which will confirm the diagnosis. Others will be able to recommend a suitable shop.

Of course, there could be other problems...Fixing LR's over the Internet is not yet an exact science.

Alan Simpson, IP mechanic
Rover Works B.C. Ltd
Spences Bridge B.C.
250-458-2447

[Rob]

I would agree with Alan... hee is some info from rangerovers.net on this subject...

Steering Vibration / Shudder
The 4.0/4.6 has a much better steering box and system than the Classic. However it is of the same basic design, and some owners have reported the steering judders upon going over bumps at speed that are so notorious and common in Classic models. If you have checked out all the ball joints and tie rod ends, the most likely cause is the steering box needing adjustment. Like the Classic, the 4.0/4.6 steering box has an adjuster on top -- this one has a screw with an internal hex and locknut. Jack up the front wheels and screw in the adjuster until there is minimal play in the steering at dead center. Then turn the wheels lock to lock to make sure there are no tight spots. The other thing to check is the swivel pin bearings, which need to be kept adjusted as per the shop manual, oor replaced. Ian Dugdale had this problem and after trying the usual remedies (suspension bushings, steering damper, etc) he replaced the swivel pin and steering joints and that made a huge difference. Also (and this needs to be done very carefully) he tightened the steering box slightly (about 1/8 turn). Overall that made a major improvement in the driveability of the vehicle. A member of the Range Rover forum, Rundeep_32, found 90% of his steering shudder went away when he replaced his shocks (he used Woodhead units sourced from DAP which appeared to have strong rebound damping and relatively mild comression damping).

source: http://www.rangerovers.net/newrremedies.htm#steering

hope it helps!

Regards, Rob

[HeadDamage]

Yep... Like Allen said. My old 110 used to do this untill I adjusted the shims on the upper swivel pins to take up the slack and it drove great after that.

[rezdiver]

thanks for the replies,
well still no fix, i have even reshimmed and sorted out the ball joints and its still a scary drive... , so we have everything done from the list above and the balljoints and still no good......

Some one mentioned to me that it could be a diff or transfer case issue where by hitting the bump causes the diff to lock or transfer to lock and screws up the front to back rotation, this seems strange to me but has anyone heard of that??
any other ideas.

Reza

[Bill E.]

Hi Reza,
I'm the one you were talking to at the ABFM. What my friend was trying to explain to you is that if the viscous coupling in your T-case is shot you will get natural wind-up between the front and rear axle. Going over tracks or a pothole can unleash the wind-up producing the vibration you are describing. My friend also recommended getting an alignment by someone who knows Range Rovers, not just your corner garage. There are special considerations when aligning wheels on these vehicles that seem counter intuitive to the average alignment shop. Of course these suggestions were made based on all of the other items mentioned by Alan and the rest being checked first. Poly bushings and other aftermarket fixes can sometimes exagerate symptoms. Type, condition and pressure of tire on Range Rovers is critical. Make sure all of these basics are in order.
Bill

[rezdiver]

OK i tried the simple test for the viscous coupling by putting the T case in neutral and jacking up each front side one at a time and trying to rotate the tires. i can rotate the tires and i get lots of resistance while doing it, but they do rotate and i can see the front shaft rotate. from these results i am taking a guess that the VC is OK..... guessing

also after changing the transfer oil i noticed the front output bearing out of the transfer case had some up and down slop to it when i grabbed the unijoint to check it. could this cause my symptoms, maybe affecting the VC from too much slop.

or could my VC be ok in a stationary position for testing and heating up and locking when i am driving away.

maybe to try and expalin the symptom a bit better its as if power load is being transmitted back and forth between the front wheels at an uncontrollable rate causing vibrations/wobbles/shimmy or whatever you want to call it. it seems more prominent when there is no load on the drivetrain from the engine braking at high speed coasting and hitting the bump.

Reza