For Service to Racing Car Transmissions.
HEWLAND Specialist.

Postal address - 43 Hawthorne Ave, Long Eaton,
Nottingham, ENGLAND. NG10 3NG
Workshop address - Unit 2, Wood Court, Clifton Avenue
Long Eaton, Nottingham, ENGLAND NG10 2GA
Telephone: +44 (0)115 946 1013 Answerphone & Autofax
Mobile: 07740 123119 (text message is good first point of contact)


CHANGING GEAR RATIOS on the OPEL/VAUXHALL/LOTUS with HEWLAND internals, with variations for STAFFS SILENT GEARS internals.

With practice all gear ratios may be changed within 30 minutes.
These instructions are given assuming some mechanical knowledge.
In the following instructions, the numbers in square brackets refer to illustration numbers in the Hewland MARK 8/9 MANUAL page 8, and also Hewland Engineering Web Site - navigate to 'Parts Locator' and 'Mk8/9 5 speed Geartrain Assembly'.

Equipment required
1¼"A/F socket (STAFFS 1 1/8"A/F)
120 lb.ft. torque wrench Soft mallet
1/2" Allen key Drain tray
7/16"A/F & 13mm (+1/2"A/F for Staffs) sockets and extensions Clean tray in which to strip gears
13mm open end spanner Gear oil, SAE 80/90, 4 pints/2¼ litre
Side cutters
Light sealer (e.g. Hylomar) 2 x 5/32" split pins (HEWLAND only)


1) Remove 7 x ¼"UNF nuts and washers[5,6] (STAFFS - 8 x 5/16"UNF) from rear cover. Remove cover[1].

2) Disconnect selector finger[20] from gear linkage (various fittings, according to car manufacturer). Remove finger (cannot remove finger on STAFFS).

3) Remove 2 split pins[39] from large castellated nuts (no split pins on STAFFS). There is no long screw[38] in the centre of the layshaft[58] (lower shaft).

4) Lock gearbox in two gears, 1st and 5th (upper and lower selector rods out)[21,23]. Turn shafts or roll car until engagement is complete. Slacken both large castellated nuts, lower[37] is right hand thread - leave on shaft, upper nut[34] left hand thread - remove completely. Return selector rods to neutral.

5) Remove 9 x 13mm nuts and washers[17,18] securing selector housing to main case, one is only accessible by open end spanner. Tap housing lightly to break seal and to clear the dowels. More force is not necessary and can damage the housing. Do not use levers. If in doubt, re-check previous items.

6) Carefully slide away the housing, complete with gears, supporting pinion shaft gears as they come away. If there is a shim between the pinion bearing and the front hub[42], this must be fitted on re-assembly.

7) Turn assembly on end and support (the end cover is useful for this). Remove layshaft nut previously loosened and remove layshaft[58], keeping gears and spacers in strict order.

8) Remove the following sub-assemblies from their forks and place on a clean surface - 1st/2nd/reverse hub/gear[41,42,43,44,45,46], 3rd/4th hub/gear/clutch ring[47,48,49,50,51,52], top gear hub/clutch ring assembly[53,54], top gear/inner track[40,55,56], top gear thrust 'top hat' (this part is slightly different to the HEWLAND drawing).

9) At this point, take the opportunity to examine all parts for excessive wear. Dogs are subjected to constant wear every time that gear is engaged, but once the dog edges on both gear and clutch ring are rounded one third down, that gear is unlikely to stay in engagement. Pay particular attention to the gear teeth for signs of scuffing which may indicate that replacement parts are required. If you notice any heavy loadings on the ends of gears and hubs or up and down movement of the pinion shaft, then seek specialist advice.

10) Change gear ratios strictly as a pair of gears (one gear from each shaft). Both gears in a pair are stamped with the number of teeth on both gears (e.g. 19/32 ratio consists of one 19 tooth gear stamped '19 32' and one 32 tooth gear stamped '19 32'). Any other stamped letter (e.g. M or S) must be on both gears or they are not a matched pair and will not normally run together. First (layshaft) gear is integral with the layshaft, as is reverse. Second (layshaft) gear has a built in spacer, 3rd, 4th and 5th are identical in fitting. Due to different internal dimensions, HEWLAND first and second gears are not inter-changeable with STAFFS.

11) Re-assemble pinion (upper) shaft parts in this order, lubricating as you progress - make sure top gear thrust 'top hat' is in place in the needle roller bearing in the selector housing: top gear[56], dogs uppermost: needle roller bearing[55]: inner track[40] (part of the hub[54] on STAFFS): clutch ring[53] in top gear fork[28]: top gear hub[54] (the short one) inside clutch ring: 4th gear[51], dogs down: needle roller bearing[52]: 3rd gear[49], dogs up: needle roller bearing[50]: clutch ring[47] in fork[27]: next largest hub[48], shank down: 1st/2nd/reverse hub/gear assembly[41,42,43,44,45,46], 2nd gear[45] with dogs down: needle roller bearing[46]: 1st gear[43] with dogs up: needle roller bearing[44]: reverse sliding gear[41] with groove above teeth and well located on its fork.

12) Re-assemble layshaft gears in this order - washer[66] next to ball bearing in housing: top gear[65] with a chamfered side towards the housing (later gears have chamfers both sides): one large spacer[64]: 4th gear[63], chamfer up: 3rd gear[62], chamfer down: 2nd gear[60] spacer part down: carefully slide the layshaft[58] through this assembly, into the layshaft bearing[35] and locate with the right hand thread large nut[37].

13) Now pack away any gears not being used, in pairs (check markings). This double checks that you have fitted true pairs.

14) Check your gear assembly. Pinion shaft gears should increase in size from 5th to 1st, layshaft gears should decrease. Each pinion shaft gear should line up with its mating layshaft gear. The dogs of pinion shaft gears should face clutch rings. Clutch rings and large reverse gear should be well located in their respective forks.

15) Clean housing faces and apply sealer. Only a small amount of light sealer is required, excess will eventually choke the bearings. Silicone rubber sealer is not necessary, and not particularly recommended due to the great effort needed to clean off the old sealer prior to re-application.

16) Supporting pinion shaft gears to prevent them falling away from the forks, offer up the assembly, turning shafts or rolling the car to line up the splines. If you are baulked at the last 1/2" or so, try selecting top gear (upper rod backwards) and roll the car again. Do not use the mallet until the housing reaches the dowels. If in trouble, start again from 13).

17) Fit the pinion nut and just 2 of the M8 nuts and washers[17,18], 'nip up' the pinion and layshaft nuts[34,37], then check that all gears engage correctly. If in any doubt, take apart and check again. When satisfied, fit the rest of the nuts and washers.

18) Lock in two gears as in 4). Tighten pinion shaft and layshaft nuts to 120 lb.ft. and 70 lb.ft. respectively before lining up to the next split pin hole. Slacken the long layshaft screw to line up its split pin hole. Fit split pin and bend the tails over in opposite directions. Remove any tail that is likely to foul the end cover (for STAFFS, 100 lb.ft on each nut, no split pins).

19) Return selector rods to neutral and refit the finger[20] (HEWLAND only), smearing its bore with grease. Connect selector finger to gear linkage.

20) Clean mating faces, apply sealant and fit end cover[1]. Check that all gears can be engaged from the gear lever, then refill with oil - 4 pints (2¼ litre) from dry, 2.5 pints (1.5 litre) from a ratio change.

© Tony Wilson. April 2009.