Rev 02 March 2014
– 25/30 Scuttle shake/shimmy
These notes have been compiled while:
The car concerned is a 1937 25/30 four door Touring Saloon, by Thrupp and Maberly.
¾ Front view of car Image: bulkhead-shake-01.jpg
Scuttle shake, which is a secondary effect, can be induced by one or more of several causes as well as from driving over uneven surfaces. The shimmy itself can be so violent as to require stopping the car. The following points need examination:
1. Perished or hardened rubber bushes in the bulkhead. ( Four sets)
2. Steering system faults
3. Crankshaft damper malfunction due to incorrect poundage of the slipper drive.
Other helpful suggestions have been offered relating to settling of the front springs and the axle control anchorage (A frame). These have not proved to be necessary on this car.
After over 70 years of service a 25/30, and its Bentley contemporaries, almost certainly require replacement of any original rubber parts. The factory fitted bushes and gaskets were the best available at the time but after more than 7 decades the rubber becomes brittle and hard thus negating the original reason for its use.
Note: These notes are based on excellent advice and guidance received from Tony James, the Spares Editor for the RREC Bulletin.
1.0 Introduction
1.01 Under the bonnet just below the top edge of the bulkhead there are four cheese headed ¼ inch bolts which clamp the bulkhead to the body cross member through rubber bushes to provide some flexibility which may by now have been reduced or lost altogether as the rubber perishes and hardens.
1.02 Inside, behind the dash, you will find that the bolts pass through another rubber bush retained by a ‘penny’ washer and two nuts. The inner nut is flat and sized for a 7/16 BSF spanner and the outer, a standard ¼ inch BSF, to act as a lock nut.
The shank of each bolt is isolated from the scuttle and bulkhead by passing through a rubber tube of ½ inch OD and ¼ inch bore.
1.2 Parts required to refurbish:
4 – engine stabiliser bushes for a Mk1 Mini. I received part numbers – KKF100390,
0.5 metre of fuel hose . I used hose of 6.3mm bore and approx 12mm OD.
Set of parts required for the task Image: bulkhead-shake-02.jpg
1.3 Procedure:
1.3.1 Remove the old parts, of which the tube may not readily extract. If not, remove it with a 12mm drill bit to provide a clean hole through the wooden cross member.
1.3.2 Deep freeze the bushes then slice them transversely with a new hacksaw blade. I cut them approx 1/3 and 2/3 with the thinner one having the flange.
1.3.3 Feed the tube through the bulkhead from the engine side, until it protrudes on the inside to hold the thicker bush and about 1mm below the outer face.
1.3.4 Slide the thinner bush over the tube so the flange side is flush against the bulkhead and mark the tube.
1.3.5 Again, cut the tube to be about 1mm within the outer face. This allows for the later compression of the bushes.
1.3.6 Now assemble the clamping bolt with the ‘penny’ washer under the head, then the thinner bush followed by the tube. I used the original nickel washer under the head followed by a larger diameter (25 mm) SS ‘penny’ washer to spread the force more evenly across the face of the bush.
1.3.7 Insert the assembly into the hole and tap through until snug.
Assembly ready for tapping into position Image: bulkhead-shake-03.jpg
1.3.8 On the inside (footwell side), slide the thicker bush over the protruding tube.
1.3.9Add the ‘penny’ washer and the flat nut followed by the ¼ locknut.
View from footwell side Image: bulkhead-shake-04.jpg
Do not tighten at this stage. Carry out the same procedure for all four fixings.
1.3.10 Remove the rubber strip, acting as a gasket, between the bulkhead and the scuttle. This too, has generally hardened to become ineffective.
1.3.11 Prepare a new strip about ¾ inch (say, 2cm) width and about 40inch ( 100cm) length.
Notes: The gap may vary according to the coachbuilder. In my case it is about 3/16 inch (5mm).
Vintage Complete, C.O.H. Baines or others can supply a proprietary strip. I cut my strips from a sheet of rubber matting of 5mm thickness and with corrugations on one side. Image: bulkhead-shake-05.jpg
1.3.12 The strips need to have cut outs to clear the clamping bolts and their rubber tubes and relief to allow bending around the two corners to the vertical.
1.3.13 Fix the strips in position. I used Evostick impact adhesive on the flat side to bond against the bulkhead face. Introducing strip into position Image: bulkhead-shake-06.jpg
1.3.14 Now tighten the four clamping bolts and secure with the Lock nuts
The Bulkhead and Scuttle should now be restored to their former happy relationship !
View of completed assy from engine side Image: bulkhead-shake-07.jpg
Note 1 : Vintage Supplies (01692 406510) can supply expanded EPDM sponge strip, skinned on all four sides. Suitable for the gap between bulkhead and scuttle.
SSSc – 6 x 19mm
SSSf – 10 x 16mm
SSSg – 13 x 25mm
Note 2 : Fiennes Restoration Ltd can also supply the various rubber components required for this project.
2.0 Cross steering tube
References: T.D.S. 2066 Service Instruction Leaflet RR/N2 (1963)
Bentley Service Instruction Leaflet BM/L1 ( Sept 1953)
Special Tools: A joint puller will be needed for this and for section 3.0
A Sykes No 818 has been recommended as suitable.
Section drawing of cross tube end Image: bulkhead-shake-08.jpg
Note: I am much indebted to RREC member Allen Crisp who shared his own experiences in overhauling this assembly on a 20/25 and for his advice and for copying me with the documents which were necessary for reference.
2.1 General
The cross steering tube should be tightly held by the ball joints at either end. To test while in situ, clamp a 10in (25cm) lever in the centre of the tube and apply a spring balance. A force of 8 to 9 lbs (3.6 to 4.0 kg) should be required to turn it, ideally the resistance should be equal at each end. If it falls below this then remove the tube assembly. End of Cross-steering tube in situ without boot Image: bulkhead-shake-09.jpg
2.2 Procedure
2.2.1 Remove the leather ‘boot’ covers.
2.2.2 Mark the tube with Tipex, or similar, Offside and Nearside to avoid later confusion when reassembling.
2.2.3 Remove the split pins from the castellated nuts below each end.
2.2.4 Loosen each castellated nut with a 7/16 BSF spanner. Do not remove it and its locating washer yet
2.2.5If a joint puller is not available, then the taper may be separated as follows:
Two people are required. The first to position a bar beneath the cross tube pivoted so that a substantial upward force can be applied to the tube. The second person can then apply sharp blows simultaneously with a pair of hammers ( say 2lb) on each side of the housing for the ball pin shaft to spring the taper apart.
2.2.6 Undo the nuts and their locating washers
2.2.6Lift the cross tube from the steering arms.
Steering arm without cross tube Image: bulkhead-shake-10.jpg
Cross-steering tube end, ready for reinstallation Image: bulkhead-shake-11.jpg
Notes: 1. Both the above Service Leaflets have excellent annotated section views of the ends of the tube and the leaflet RR/N2, although it relates to the fitting of a new cross tube, gives instructions regarding setting up the correct clearances and a method for making a small change to the toe-in of the front wheels, if required.
NB 1. When reinstalling the Cross Tube it is essential that the ball pins are correctly orientated to ensure the chassis lubrication system operates efficiently. The lubrication is directly fed i.e. not through drip plugs. This means that if they are incorrectly fitted, oil may escape and lower the pressure for feeding the rest of the system. To orient the pins the washers above the castellated nuts have tabs on their outer rim and flats on the inner. The tabs locate in the steering arms and the internal flats must mate with flats on the pins.
To do this the pins may have to be rotated. A steel pin through the split pin hole can be used to gain leverage against the preload of the pins in their spring loaded housings.
Cross tube ready for reinstallation Image: bulkhead-shake-11.jpg
2. Avoid over enthusiastic depression of the Bijur foot pedal unless you have isolated the feed to the clutch withdrawal mechanism.
3.0 Side Steering Tube
References: RREC Technical Manual 1972 pp 92 and 93
RREC Technical Manual 1984 pp 39 and 40, an update by Will Fiennes
Sectioned drawing of tube end Image: bulkhead-shake-12.jpg
The joint at the rear of the Side steering tube provides some degree of shock elimination in the steering linkage and also a degree of damping by the preload non the ball. It has been suggested that the amount of preload should err on the higher side.
The constant shuttling of the pistons, if not adequately lubricated, can cause significant wear in the comparatively thin walled tube. The ball can also show evidence of wear where abutting the pistons.
Side steering tube end, without leather boot Image: bulkhead-shake-13.jpg
While the ‘banjo’ of the central lubrication system to the bottom of the drop arm is disconnected, test the flow of oil by depressing the foot pedal. If there is inadequate flow then check the drip plug with reference to the notes below.
Notes:
1. Lubrication:
The pin at the bottom of the drop arm which locates at the rear of the side steering tube is lubricated via a Bijur drip plug (size ZE.1) located on the side of the steering box within the engine compartment.
2. Drip Plug overhaul: Stephen Boddice gives very clear details of the device and its maintenance in www.boddice.co.uk .Scroll down to Maintenance Procedures and click on Drip plug overhaul .
3. Leather ‘boot’ covers: New ones can be sourced from Fiennes Restoration but if the old ones are reuseable it is suggested that the laces are replaced by new shoelaces.
4. Bijur-Luvax lubrication pump: Matt Pickles describes the pump, its components and overhaul procedure in a feature published by the RREC Northern Newsletter of March 2011.
He cautions against excessive testing of the system by frequent depressing of the foot pedal, since this may send an excess of oil to the clutch linkage and then some may leak onto the linings,
Acknowledgements
Tony James, Allen Crisp, Will Fiennes and Tom Clarke for their valuable advice and for generously sharing their own experiences.
Stephen Wragg, John Hibbert and Matt Pickles for their practical advice, help and assistance without which the projects may not have been implemented.
These notes have been compiled by Bryan McGee. They carry no official endorsement by the Club and are offered for reference by members to use at their own risk.
