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Richard Treacy (
Posted on Tuesday, 19 March, 2002 - 22:05:   Edit PostDelete PostView Post/Check IP

Courtesy of Richard Vaughan in th USA (RROC Inc) , I have implemented a thouroughly worthwhile modification on my Turbo R, SCBZSOTO9HCH20037, which has dramatically improved the performance of the window lifts from being mediocre and unacceptable to outstanding. This is so successful that I am posting this publically.

The basis of this modification was developed by R-R themselves, but I have taken it slightly further, particularly due to the presence of a diode suppressor in the relays of later cars.

The total cost of components is only about AUD$120 for the complete job on three windows.

Wow. Thundering windows alright !! This modification is a MUST. I have never been so pleased with such an easy modification. It took about 15 minutes to prepare each of five modules, and 20 minutes to fit each to the car.

The reason for all this is that, in order to save weight, R-R used very thin wire on the window circuits, in my opinion only thick enough to power the clock. From memory, R-R toyed with the idea of using a ring main on these cars, but backed off and simply used thinner wires than on the Silver Shadows. The windows on our '72 T-Series are just superb, but the Turbo R's were just embarrassingly slow.

Originally, both window motor suppliy leads are normally live leaving no electrical potential between them. When its window switch is activated, one supply wire is grounded to produce the voltage across the motor to lift or lower the window glass. Given that the circuits are metres long and supplied by mere microswitches, the voltage drop in the circuit is excessive, especially as the cars age. Particularly, when the microswitch grounds its wire, the voltage at the motor lead can be as high as five volts instead of zero. Time for a local relay to remedy this. My driver's door was OK, but the other three left somewhat to be desired of this fine beasty of a car.

To fix the three wanton window lifts, you will need to make up 5 modules, each made from:

* One changeover relay identical to those already on your car. My car uses Bosch 0 332 204 122-850 changeover relays (R-R 26632); earlier cars use UD22452 - Lucas ?? - take a sample to your local autoelectrician and he will have them in stock. Your car already has about 50 such relays, and they are used on many other brands of car.
* socket to suit. (pairs may be tandemed for the rear door by sliding their slots together)
* 6 spade receptors to suit the above
* two pairs of spade plug and socket (standard automotive type)
* 25 cm black, 30 cm red: 2.5 auromotive power cable
* 60 cm automotive low power cable, white, 0.7 sq. mm
* cable ties
* 1 diode, type 1N4001 or equivalent.
* earthing lug (bolt it too the door frame together with the relay socket)

One issue adressed here using the original R-R equipment Bosch type of relay: you must insert a diode before each relay coil as there is potential to reverse bias the coil slightly on the de-energised relay when the power supply (cigar lighter) is on load, enough to blow the diode supressor inside if an external diode is not fitted. Incidentally, this extra diode even simplifies installation as all five modules are identical. By the way, I implemented this with a configuration such that the motor is normally at zero volts, not live as original. I have an aversion to leaving electrical devices permanently live. To do this job, I opened up a rear door to see the arrangement, designed the simple layout, made two in the workshop and then installed them.

Previously, I measured typically 4 volts across the rear door motor supply leads when activated; now it's at least 11 volts and the windows are fast as lightning.

The slowest window is now the driver's !!! The solution on the passenger side works amazingly well, and the windows are now as fast as any new car. The rear doors each have a high current supply for the cigar lighters available, but the front ones do not, so a half solution improving the grounding on the passenger's door is the only easy one, but it gives a 100% result anyhow. My LH rear window was inoperative from the driver's door because of the poor conductivity, but now zips up and down like a new one. It had 4 volts across the motor terminals when operated locally, and 2 volts when operated from the driver's door. I used 2.5 power automotive cable for the power side of the mod.

The front passenger's door uses one module, the rear doors two each. The modules are fitted adjacent to the window motors on each door.

I reused the original motor plug connector unaltered, so the motor and its supply plug and lead are strictly original in case of replacement. To the existing socket fitted to the car side, I fitted new spade receptors. To do this, cut the existing motor supply wires at the socket and remove the old receptors. Use a pair of identical spades and sockets to connect the existing pair of wires to your new relay set, so that if the motor direction ends up incorrect you may simply reverse them.

Along with the modification, it is advisable to replace the 20A cigar lighter fuse with a 30A one, in line with the original window fuse rating. I raised all four windows at once and the fuse did not blow.

I strongly recommend this mod to all SZ car owners ! Anyone who wants a schematic and layout may E-Mail me on with a fax number or I can e-mail them as jpeg files.


Richard Treacy.