The Hydragas Register- Trade section
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Quick trim height calculator
Note that Austin/MG Metro (up to 1990, with A-series engine) must be measured front and rear as the suspension is not interconnected in the usual way.

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Checking procedure
  • Trim height is measured from the centre of the wheel straight up to the wheelarch.
  • Tyre pressures should be correct, and the vehicle should be parked on a level surface.
  • Put the steering straight ahead and the handbrake off.
  • Bounce the front of the car, allow it to settle, then measure the trim heights.
  • Road test the car, recheck and adjust if necessary

Thanks to MG PoloRover for providing the image on the right. This shows the suspension at the factory recommended trim height.
MGF Hydragas Suspension
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How much to charge for a Hydragas pump-up

The fluid costs about £20+VAT for five litres, and a pump-up takes about half an hour's labour. I've never actually measured the amount of fluid required for an adjustment but I'd have thought a litre or two would easily cover it. For replacing displacers, the process requires evacuating and refilling, so obviously a greater charge must be made both for labour and fluid. Bear in mind that you're unlikely to make any profit on parts as they will probably be sourced by the customer. Most garages I've spoken to (including our own) charge in the region of £25-£40+VAT as a fixed charge for an adjustment. Individuals often do it for just the cost of the fluid, as a way to meet other enthusiasts. I enquired about it at an ex-Rover dealer and they quoted me £90!

Bear in mind

You can't pump-up Hydragas on a two-post lift or anything else that takes the weight off the wheels. On the MGF and BMC 1100/1300, the pump-up points are under the bonnet so can easily be done on the floor. The Metro has pump up points under the back, a four post ramp is ideal although a pit would be fine- you can actually access the rear valves easily enough with the car on the floor, just ahead of the rear wheels. Also, if you get into replacing parts, you'll need a pump with vacuum facility to evacuate the air before pumping up with fluid.

Parts and data

Pick a car for technical data.

Morris Mini Austin Metro Rover Metro MGF

Other cars


If you have a garage and also work on modern cars, we also run a register for Hybrid and Electric vehicle repairers- see HEVRA. HEVRA Membership also includes unlimited technical support, tool hire and numerous other benefits.

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