ComplianceWashers

Fitting Compliance Washers to the Rear Tie-Bar

The suspension of the factory standard MGF is by comparison quite soft, and whilst this offers a comfortable ride, it does reduce the stability and response, especially on cornering and high motorway speeds. Various modifications are available to stiffen up the suspension, mostly involving replacing the existing rubber suspension bushes with polyurethane bushes. Some of the bushes are quite simple to change, others not so easy.

There is another modification that can be done quite easily, should only take about 1½ hours from start to finish and will make a significant difference. This is to add what are called Compliance Washers to the rear suspension tie-bars. Simply put, the standard design has a rubber bush (actually two separate half sections) held captive by large dished metal washers, but the design allows too much flexing of the rubber mounting, leading to suspension geometry changes affecting under- and over-steer.

The Compliance Washers, fitted between the rubber bushes and metal washers, literally reduce the space to zero, stopping the excessive movement, thereby making the geometry during cornering, acceleration and deceleration comply more with what is desirable.

If you want to understand more about suspension geometry and the changes that occur during driving, go to Rob Bell's website page. or The Family Car website page, or on the MGF BBS.

Before you start, you will need two specific tools, namely a 18mm "deep" socket for the rear nut, a 13mm "deep-offset" ring spanner, and axle stands, as well as your jack.

While the rear wheels are still on the ground, slightly undo the wheel nuts, only about half a turn but just enough so that it becomes easier to remove them fully once the car is off the ground.

Jack the car up and support on axle stands. If you put the axle stands under the rear side jacking points rather than under the sub-frame, you will have more space for working.

Remove the road wheels.

Apply some releasing oil to the 18mm nut and thread on the end of the tie-bar. This should greatly reduce the effort to remove the nut and also reduce the flexing of the bar in it's forward rubber mounting.

Using the 18mm deep socket, undo the rear nut. If the nut is very stiff, you will need to stop the tie-bar from rotating by using a tool such as a stillsen pipe wrench. Grip the tie bar half way along with the stillsens and pull it in the opposite direction whilst undo the 18mm nut.

Remove the nut and washer, noting the dished shape of the washer and which way round it is fitted.

Reaching through the wheel arch, undo the forward bolt that holds the tie-bar to the sub-frame. The bolt head is on the outer side of the sub-frame mounting and screws into a threaded hole in the bracket itself.

Remove the bolt completely.

Pull the forward end of the tie-bar downwards out of it's mounting slot, and rotate it through 180 degrees inwards towards the centre of the car, until the head of the bar is clear of the underside of the car.

You can now pull it forward out of the lower suspension arm.

Clean any road dirt and/or rust off the existing dished metal washers and rubber suspension bushes.

Coat both sides of one on the compliance washers with plenty of lithium based grease, and with the original forward dished metal washer on the tie-bar, slide the compliance washer onto the tie-bar.

Re-fit the tie-bar through the lower suspension arm, coat both sides of another compliance washers with grease, and slide this onto the rear threaded end of the tie-bar. Now fit the remaining metal washer and nut, but do not tighten the nut up completely.

Fit the forward end of the tie-bar into the subframe bracket, slide the bolt in and re-tighten. You may need to wiggle or even lever the tie-bar in order to get the bolt to line up with the thread. If you have to resort to leverage, use a stout piece of wood rather than metal to avoid damaging the paintwork. This bolt is required to be torqued up to 45Nm, but because of it's position you will probably find it impossible to get a torque wrench on it ( unless of course you have something special, in which case, please e-mail me! ). Using a standard length ring spanner, such as the one illustrated, assuming that you are average strength, and considering the awkwardness of the position, tightening the bolt as much as you can is not going too be far off 45Nm.

Now tighten up the rear 18mm nut. This too presents a problem as regarding torqueing it up to the required 80Nm, unless of course you have access to a car pit or lift. The torquing is supposed to be done with the car level on all it's 4 wheels, but in that position there is not enough room to use a torque wrench. If you can get the car over a pit or up on a ramp, you will find it a lot easier. The other option is that since the tracking will have to be reset, get the garage to undo and then torque up the nuts before they set the tracking.

Refit the road wheels, drop the vehicle off the axle stands and re-torque the wheel nuts to xx Nm

Now arrange to get the tracking reset, but note that one or more of the setting values needs to be changed.

Standard Rover tracking data MGF 1.8i

Ride height: 368mm (+/- 10mm)
Front wheel alignment: Toe-out 0°10' (+/- 6' each wheel)
Front wheel camber: Negative 0°30' (+/- 30')
Front wheel castor: Positive 5°0' (+/- 55')
Steering angle of inner wheel to outer wheel: Outer Wheel: 29°12'
Steering angle of inner wheel to outer wheel: Inner wheel: 34°42'
Rear wheel alignment: Toe-in 0°10' (+/- 6')
Rear wheel camber: Negative 1°0' (+/- 30')

Recommended setup

Whilst there are recommendations for tracking settings following specific suspension modifications, there are also different points of view as to which values are the most appropriate. I recommend that you read the various documents and then make up your own mind.

DO NOT alter the rear tracking if no compliance bush washers or replacement poly bushes are fitted- do so could be rather too exciting for road use- and *may* be dangerous.

For the record, without the rear suspension mods, the BBS recommendations are:
      Front toe-IN 0 degrees 5 minutes
      Rear toe-IN 0 degrees 10 minutes

If the rear suspension mod has been performed then use:
      Front toe-IN 0 degrees 5 minutes
      Rear toe-IN 0 degrees 5 minutes.

Standard MG-Rover figures are:
      Front toe-OUT 0 degrees 10 minutes
      Rear toe-IN 0 degrees 10 minutes.

All measures +/- 3 minutes.

For another source of information regarding the fitting of Compliance Washers, go to Dieter's web page