instdg

TONY WILSON

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)
e-mail:
tonywilson43@gmail.com

 

CHANGING GEAR RATIOS on the HEWLAND DG 300 TRANSAXLE

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 DG300 MANUAL page 4 (part numbers are on page 6), downloadable from Hewland's Web Site www.hewland.com.

Equipment required
1.5/8"A/F socket 14mm Allen key Side cutters
120 lb.ft. torque wrench 2 x 5/32" split pins Soft mallet
1/2" Allen key Drain tray Gear oil, SAE 80/90
1/2"A/F sockets and extensions Clean tray in which to strip gears 1/2"A/F open end/ring spanner
Light sealer (e.g. Hylomar)

Oil Capacity. For standard DG 300 transaxle, 3.5 pints/2 litres from dry. More oil is required where oil cooler is fitted.

Instructions

1) Drain the oil by removing the 14mm Allen key plug[29 on page 8] low down on the left hand side. Behind it, there is a gauze filter[28] to clean. Remove rear cover[3] - 8 x 5/16"UNF nuts[1] and washers[2].

2) Disconnect selector finger[38] from gear linkage.

3) Remove 2 split pins[8] from large castellated nuts[7,32].

4) Lock gearbox in two gears, 1st and 5th (lower[45] & upper[47] rods out) - do not lever against reverse plunger[16], you will bend it. Turn shafts or roll car until engagement is complete. Slacken both large castellated nuts, lower[7] is right hand thread - leave on shaft, upper nut[32] left hand thread - remove completely. Return selector rods to neutral.

5) Remove 10 x 5/16"UNF nuts and washers securing bearing carrier[12]/finger housing[5] assembly to main case (there is no need to split these two housings). 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.

7) Turn assembly on end, remove layshaft nut[7] and remove layshaft[21], keeping gears, spacer[20] and thrust washer[19] in strict order.

8) Remove the following items from the pinion shaft and place in order, on a clean surface - front hub[23], 1st & reverse sliding gear[22], 1st gear and 2nd gear with their bearings[24], centre hub[26], clutch ring[25], 3rd and 4th gear and their bearings[24], rear hub[27], clutch ring[25], top gear and its bearing[24], inner track[28], thrust washer[29]. Later DG300 has 'rotating thrust washer' DGB 229 and collar DG 229T (not pictured).

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 will indicate excess wear. Grasp the pinion shaft[11 page 8], if there is up and down movement, or if you notice any heavy loadings on the ends of gears and hubs, 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. 19/37 ratio consists of one 19 tooth gear stamped '19 37' and one 37 tooth gear stamped '19 37'. Any other stamped letter or number must be on both gears or they are not a matched pair and will not normally run together. First and reverse (layshaft) gears are part of the layshaft. Second (layshaft) gear has a built-in spacer. 3rd, 4th and 5th are identical in fitting and are called 'Standard gears'.

11) Re-assemble pinion (upper) shaft parts in this order, lubricating as you progress - make sure the thrust washer[29] is located in its groove, then fit top gear, dogs uppermost with its bearing[24], inner track[28] (the later 'rotating thrust washer' is fitted first, then top gear, dogs uppermost, bearing and collar): clutch ring[25] in top gear fork[51]: rear hub (smallest hub)[27] (short one) inside clutch ring: 4th gear, dogs down: needle roller bearing[24]: 3rd gear, dogs up: needle roller bearing[24]: clutch ring[27] in fork[50]: centre hub[26] (next largest), shank down: 2nd gear with dogs down: needle roller bearing[24]: 1st gear with dogs up: needle roller bearing[24]: first and reverse sliding gear[22] with dogs down and the groove above teeth and locate on its fork[49].

12) Re-assemble layshaft in this order - thrust washer[19] next to ball bearing[9] in housing: top gear with a chamfered side towards the housing (later gears have chamfers both sides): spacer[20]: 4th gear, chamfer up: 3rd gear, chamfer down: 2nd gear, boss down: carefully slide the layshaft[21] through this assembly, into the ball bearing[9] and locate with the right hand thread large nut[7].

13) Now pack away any gears not being used, in pairs (check markings). This is a double check 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. If 5th gear is fully floating, it easily falls out of line, so you may need to line it up through the upper bearing, until located on the pinion shaft. Selecting 5th gear (upper rod[47] out) might help. If you are baulked at the last ½" or so, try selecting 4th gear (upper rod[47] in) and roll the car again. Do not use the mallet until the housing reaches the dowels. If in trouble, go back to 13).

17) Fit the pinion nut[32] and just 2 x 5/16"UNF nuts[1] and washers[2], 'nip up' the pinion and layshaft castellated nuts[32 & 7], then check that all gears engage correctly. If in any doubt, take apart and check again. When satisfied, fit the rest of the 10 x 5/16"UNF nuts and washers.

18) Lock in two gears as in 4). Tighten pinion shaft and layshaft nuts to 115 lb.ft. and 80 lb.ft. respectively before lining up the next split pin hole. Fit split pins and bend the tails over in opposite directions. Remove any tail that is likely to foul the housings.

19) Return selector rods to neutral and connect selector finger[38] to gear linkage. Make sure that all gears engage correctly from the gear lever.

20) Clean mating faces, fit gasket[4] and rear cover[3]. Check that all gears can be engaged fully (turn shafts or roll car), clean gauze filter and refit, then refill with oil (see above).

Gear ratio options -

1st 16/53 to 16/40, 2nd 15/40 to 21/33, Standard (3rd, 4th, 5th) 16/38 to 30/24
© Tony Wilson. July 2002.
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