Rolls Royce Silver Spirit - SZ Series

Problems I've fixed over the years and some requiring the help of an RR specialist

I first noticed petrol dripping from the float chamber drain valve when the car was up on a ramp having its MOT last year. Recently, whilst stationary with the engine running I noticed petrol dripping from beneath. Starting and stopping the engine seemed to clear the fault. My searches suggested that it could be any of the following:-

Problems with the HIF7 SU carburettors, float, needle valves and seats. Or the non- return valve mounted in the return fuel line sticking. Or the recirculation valve adjacent to “A” bank carburettor maybe blocked.

Using the TSD4400 manual I decided to examine the carburettors first. So removed floats seats and needles. The floats were OK. The needle valves had formed a groove around the Viton tips. To check I held the seat with needle above my head and sucked, air could be drawn in under certain positions. Ordered and fitted seats and valves from Burlen.  One float did require float chamber adjustment between 0.51mm-1.52mm. Whilst reassembling I did remove and check the recirculation valve, this was clean.  So far no more petrol leaks! Ashamed to say that it took me 5½ hours to complete the job!

Suspect Old and New float Valves

Sometime ago whilst driving I heard horrible noises when moving the steering wheel the oil cooler part of the radiator (air conditioning condenser ud23237 ) had a pin hole leak in one of the feed pipes This item is very expensive!  In consultation with my RR specialist this is the inexpensive solution  to the problem.

Power steering feed pipes on air conditioning condenser
New power steering feed pipes on air conditioning condenser
Wheel arch wax oil injection hole

Click an image to enlarge group photos

Many years ago I noticed a small blister of paint on one of the rear wheel arches. At the top of both arches and in about 5mm from the front face I drilled a small hole to accommodate the injecting tube from an aerosol just sufficient to get through the first layer of steel IMPORTANT!! only. To enable me to inject wax oil into this small void the aerosol tube was pushed a couple of inches into the hole on the left hand side of the arch and sprayed till the wax oil dripped from the bottom of the arch, this procedure was then repeated the on the right hand side of the arch. [See photo of wheel arches today- not too bad for a 36 year old car]

RR Near side wheel arch
RR Off side wheel arch
Loosened Bolt body creak

One of the front suspension struts failed. So both front struts were replaced with Harvey Bailey struts which gave the car better handling although a much firmer ride. However under certain conditions this made the car creak and could be heard through the dashboard. It took ages to find the source of the creak and remedied by slackening a bulkhead bolt.

Cruise control malfunction not working – this is a relatively easy fix; one or both solenoids become seized. Remove rubber bellows, spring and plate with toilet chain attached. Apply WD40 or something similar to the solenoids, with a small screwdriver check and free the rods as necessary. Note there is very little movement on one solenoid.

Cruise control solenoids WD40
Bellows unit testing

It’s worth checking

The photo on the left shows a vacuum test on the rubber bellows CD6410 to see if it can maintain a good seal. Compress the bellows unit shown on the right and then apply 12 volts. It should remain compressed if the solenoid pads are in good order. If the test fails and the bellows are still pliable ensure the solenoid plate and the chain pickup plate have the correct orientation then seal the edges with Evostick and fix tie wraps or something similar.

Bellows unit compress test
Bellows cruise control testing
Bellows cruise control testing activated

These photos show a basic test that can be carried out on the bellows unit. If the test fails the bellows could be cracked  - If it's still pliable, small cracks can be sealed with super glue. Also check the 4 solenoid pads sometimes they become unstuck. Carefully use an impact glue to re-fix them. If the alloy body is corroded and your tempted to clean around the pad areas by removing the solenoids, beware  it's very difficult to refit the phosphor bronze shims which hold the valves closed!

M8-5 speed control diagrams TSD4400
12V feed for bellows unit
12V relay feed for bellows unit
LED display attached to windscreen
Led test circuit
Solenoid LED connections
UD25279 Cruise Control PCB

The  LED circuit enables you to carry out electrical tests on the cruise control whilst driving. The yellow LED  which is connected across the coil of the speed control relay stays lit if car travelling less than 30MPH - this proves the 10A fuse [Item 2 Reverse Lamps, stop Lamps, Speed control] Gear change actuator switches and wiring are OK. If travelling greater than 30MPH Green LED remains lit when pressing set or resume - this proves +12v has been applied to one of the solenoids and that the speed relay and brake switches are functioning OK. When pressing set or resume the red LED will flicker and as you increase speed become dimmer. This shows the set and resume switches, wiring, relay 11 and ECU are functioning OK.

Inside the ECU Cruise Control PCB UD25279 module. If the green LED which monitors the +12V to the solenoid does not light, sometimes the ZTX550 transistor can fail, It feeds the brake switches and contacts of the speed relay.

Years ago the trailing arms rusted through the spring cups. My RR specialist informed me that these were very expensive to replace, parts alone at the time were £1500 each. The specialist carried out the repairs by fabricating and welding two new spring cups to both trailing arms at a much more economical price of £300.

Air conditioning not working - The fans were inoperative when selecting Low Auto and High

Using TSD4400 trouble shooting guide chapter C5 - 34 I established the fans would work when setting the ACU to defrost. I skipped the wiring tests and checked the delay fan thermostat by unplugging it - The fans worked!

C5- 34
Faulty Otter switch

The replacement otter switch in the thermostat housing UE39593 is very expensive £261.52 (Incl VAT) I searched for an alternative arrangement a KSD-9700 series bimetallic thermal protector. These are available in a number of operating Temperatures. As I have fitted the unit to the outside of the thermostat housing  I chose 40C NC [normally closed] One of the leads is connected to the metal case so ensure this lead is connected the the chassis side of the 2 pin socket.

KSD-9700-pins1 KSD-9700 fitted to thermostat housing

The KSD-9700 series bimetallic thermal protector works well. I paid £2.51 from Ebay

RR Silver Spirit Speedometer calibration

I noted when the car was traveling at 70 MPH my Garmin SatNav  said 62 MPH a nearly 13% error.

I wanted an accurate reading. The speedometer is electronic, it obtains pulses from the transducer UD24231 on the gearbox.

The difficult part was working out how many pulses per second for a given MPH. I researched the net - wheel size, final drive gear ratio, turns per mile but not knowing how many pulses come out of the transducer for one revolution I was stuck.

RR silver spirit SpeedometerEventually I deduced from the label on the rear of the speedo 8000 imp. that this represented  8000 pulses per mile an hour.Smiths Jaeger Speedo Label

These are my calculations

8000 ÷ 60 ÷ 60 x 30mph = 66.6Hz

8000 ÷ 60 ÷ 60 x 50mph = 111Hz

8000 ÷ 60 ÷ 60 x 60mph = 133.3Hz

8000 ÷ 60 ÷ 60 x 70mph = 155.5Hz

8000 ÷ 60 ÷ 60 x 80mph = 177.7Hz

To bench test the speedo you need a signal source. I used this Download the appropriate program and use the audio line output of your PC. In the program choose Generator icon, set to square wave and an RMS level dBFS of 0, enter the frequency in Hz. The signal needs to be boosted to drive the speedo. A single transistor amplifier diagram is shown on the right,  it produces a  good square wave to drive the speedo. To adjust the speedo there is a small hole covered by a label on the top, use an appropriate size insulated shaft screwdriver to adjust the preset.

After road testing, the speedo now shows the same MPH as the SatNav.

You may prefer to have your speedo read a few percent high, I suggest from the table above use 70mph 155.5Hz and set the speedometer MPH accordingly.

RR silver spirit Speedometer rear square wave drive
Speedo amplifier

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