Hewland NMT Guide de l'utilisateur

PAGE 1

SERVICING INSTRUCTIONS AND ILLUSTRATED

PARTS LIST FOR HEWLAND NMT GEARBOXES

HEWLAND ENGINEERING LTD

WALTHAM ROAD, WHITE WALTHAM,

Last Update 10th July 2012

MAIDENHEAD, BERKSHIRE,

SL6 3LR, ENGLAND

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CONTENTS :-

page page

Technical specification 4 Changing gear ratios 13

General notes 5 Powerflow differential 14

Differential bearing preload 6 Differential Options 15

Pinion shaft mounting 7 Illustrated Parts List 22

Pinion shaft bearing preload 8 Gearbox Tooling 35

Crownwheel backlash setting 9 General Technical Bulletins 36

Sequential barrel setting 10 Oil system layout 38

Gearbox assembly 11 Recommended Tightening 39

Torques

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ILLUSTRATIONS :-

page page

fig.1 Differential bearing preload 6 fig.12 Casings & Associated Parts 25

fig.2 Pinion shaft setting 7 fig.13 Layshaft Assembly 27

fig.3 Pinion shaft bearing preload 8 fig.14 Pinion Shaft Assembly 29

fig.4 Crownwheel setting 9 fig.15 Selector Assembly 31

fig.5 Sequential barrel setting 10 fig.16 NLT-218-Tripod Assembly 33

fig.6 Powerflow diff assembly 14 fig.17 Gearbox Tooling 35

fig.7-10 Differential Assemblies 15-21 fig.18 Oil system layout 38

fig.11 Differential Subsidiary Parts 23

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TECHNICAL SPECIFICATION

The NMT gearbox is a transaxle unit, designed for mid-engined, rear wheel drive cars. The unit is produced with six

forward gears, reverse, and a powerflow differential.

The gear selection mechanism is sequential, with a separate, mechanically interlocked reverse engagement mechanism.

The drive is taken from the engine via the clutch shaft, which turns input and pinion gears to drive the final transmission

assembly.

Gear changing is effected through non-synchronising face dogs. An extensive range of gear ratios provides a wide

range of gearing requirements. The gear ratios and differential assembly can easily be changed without removing the

gearbox from the vehicle.

Heat treated nickel chrome steel is used to manufacture all gears and shafts. The selector forks are also steel.

Lubrication is by splash or optional internal pump with distribution circuit, and the oil is retained by lipped oil seals.

In general configuration, the NMT-200 is a high tech racing transaxle unit which achieves the maximum effective use of

power, in conjunction with extremely stiff integral rear suspension mountings.

weight (AL) 128 lbs (58 Kg) 1st to 6th gear ratios from 3.31:1 to .89:1

oil type SAE 80 or 90 final drive ratio 11/31, 10/31, 9/31

oil quantity 7 pints (4 litres) clutch shaft made to customer's requirements

max. torque 320 lbs.ft (430 Nm) Pinion shaft nut tightening torque = 120 lbs.ft (163 Nm)

Crownwheelbolts=75lbs.ft(100Nm)

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GENERAL NOTES :-

a/ Read these instructions carefully and with reference to the illustrations.

b/ Before dismantling the gearbox, see that a clean tray is available, in which to place the parts.

c/ Thoroughly clean and inspect all parts before reassembly. Discard any worn or damaged components and replace with new

ones.

d/ Use only genuine Hewland parts as replacements. These are manufactured in our workshops to the fine tolerances necessary and

are rigorously inspected.

e/ Always ensure that locknuts, and oil seals are in good condition when reassembling.

f/ All studs and screws must be Loctited or wirelocked in position, unless stated otherwise

g/ Bearing Replacement :-

Bearings can only be removed or renewed if the casings have been warmed in an oven, or with a blowlamp. In the latter case,

keep the blowlamp moving while heating the casing.

Note: Do not overheat. Test with a spot of water which will bounce off at the correct temperature.

Once a casing is heated, all bearings should be pressed into their respective seatings without delay, thus eliminating the need to

reheat. At the correct temperature, fitting the bearings should present no difficulty.

During cooling, or when the casings have cooled, it is advisable to once more lightly press the bearings to ensure that they are

correctly seated.

h/ Oil:

Fill the gearbox through the plug hole on top of the maincase. The oil will find it's own level within the gearbox.

Note: Too much oil will not directly cause any harm, but is undesirable as it may induce power loss and overheating of internals.

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DIFFERENTIAL BEARING PRELOAD

Requires special tool No. SK-119-FGC

Assemble the differential case (57) and end cap (58),

and bolt the crownwheel (56) to it. Fit the differential

unit into the maincase (1) using dummy bearings SK-

119-FGC, and fit the sideplate (3). Adjust the shims

(103) if necessary, to achieve 4 – 6 lbs.ft of bearing

preload torque (to turn the diff assembly in it’s bearings

when oiled.).

The table below is to inform you of which sideplate

spacers should be used with which crownwheel when

mounted on a TPT differential. The reason that there are

two sets of spacers, is that the crownwheels have

different mounting distances.

FIGURE 1

PART No. RATIO MOUNTING

DIST

ITEM (90) ITEM (91)

NMT-221-AW 11/31 2.316” FGC-206-2A NMT-205-2

NMT-221-BW 10/31 2.316” FGC-206-2A NMT-205-2

NLT-221-CW 9/35 2.200” FGC-205-2A NMT-205-2A

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FIGURE 2

PINION SETTING

Requires special tool No.SK-1470-A & SK-1913

Press the pinion head bearing inner (37) onto the

pinion shaft (4). Fit the bearing housing (37) and

shims (40) into the maincase. Assemble the pinion

shaft into the maincase (1) and fit the bearing carrier

(2). Tighten the pinion shaft nut (111) onto the

pinion shaft until the pinion shaft requires 20-25

lbs.ins to turn it in it's bearings (equivalent to a

tangential force of 16-20 lbs at the outside diameter

of tool SK-1913)

Fit tool SK-1470-A into the maincase diff bearing

bore, and use feeler gauges to measure the gap

between the tool and the pinion front face. This

clearance should comply with the dimension

indicated on the pinion shaft label (also stamped on

the front face of the pinion shaft), and can be

adjusted by adding or removing shims (40) from

behind the pinion head bearing housing (37).

Alternatively, the pinion mounting distance can be

measured with a height gauge, and set to the

dimension on the pinion shaft label.

Note: It is not correct practice to replace a pinion

shaft without measuring the setting distance, even if

the old and new shafts have the same calibration.

SK-1913

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PINION BEARING PRELOAD

Requires special tool No.SK-1913

Having installed the correct pinion shaft

bearing shims, remove the bearing carrier

(2). Add the spacer (14) and hubs (20,33) to

the pinion shaft, and replace the bearing

carrier. The thickness of the spacer (14)

should be adjusted, by grinding, to give a

bearing preload torque of 20-25 lbs.ins with

oiled bearings (measure torque as when

setting pinion shaft, using tool SK-1913).

FIGURE 3

It is essential that the pinion bearing preload

is checked and adjusted if any of the pinion

shaft components are replaced, with the ex-

ception of the locknut and locking ring.

Fitting a longer six gear spacer (14) will de-

crease the pinion bearing

preload, whereas shortening the six gear

spacer (14) will increase the pinion bearing

preload.

SK-1913

PAGE 9

CROWNWHEEL & PINION BACKLASH SETTING

Requires special tool No. SK-1913

With the pinion shaft correctly fitted, and the correct diff

bearing shims ascertained, the actual backlash can be

measured by means of a dial test indicator against the

notch in the outside diameter of tool SK-1913. Be sure to

take at least 6 backlash readings, turning the crownwheel

30-45 degrees between each reading (this is to ensure

that any variation due to manufacturing tolerances are

taken account of.

The correct backlash figure should be taken from the

card supplied with the gears. If the measured backlash is

incorrect, rectify it by removing some shims (103) from

behind one diff bearing, and inserting them behind the

other, thus moving the diff across in the maincase. Do

not add or discard any shims at this stage, as to do so

would affect the diff bearing preload.

Once the correct backlash has been achieved, replace the

dummy bearings with bearings (83) and confirm that the

backlash is correct.

Note: Dummy are used so that it is easy to change the shims

during the setting procedures. Before fitting the actual diff

bearings, it is important compare thier width with that of the

dummy bearings and compensate the shims accordingly for any

difference.

FIGURE 4

PAGE 10

FIGURE 5

SEQUENTIAL BARREL SETTING - Requires special tool No.SK-1451

a/ Assemble the barrel (15), spacer (26), bearing retaining plate (25),

bearing (27), and nut (29). Heat the bearing carrier (2), slide the barrel

assembly into the bearing carrier, and secure using screws (12).

b/ Place the roller (24) onto the detent plunger (21), and insert them into

the bearing carrier (2). Add the detent spring (22), bonded seal (115),

and detent plug (23).

c/ Slide the selector forks (17) over the barrel (15), and secure using

selector pins (18). For final assembly, Loctite the pins (18) into the forks

(17).

d/ Stack the pinion gears (16), hubs (19,20), clutch rings (19) and spacer

(14) in place in the bearing carrier, and slide the whole thing onto the

dummy shaft of fixture SK-1451.

e/ Tighten the pinion shaft nut (111) onto the end of the dummy shaft,

ensuring that the disc spring on the fixture preloads the bearings.

f/ Rotate the barrel to engage first gear. Measure and record the gap

between the dogfaces of third through sixth gears. Engage third gear and

repeat the measurement for first and second dogfaces. It is important

that these dimensions are not taken when the barrel is in the neutral

position.

First, third and fifth gear dog gap measurements will be similar (as will

second, fourth and sixth). Any difference between the odd & even gear

measurements must be corrected by replacing the barrel spacer (26) with

one of the correct thickness.

Note: It is not possible (or necessary) to individually adjust each fork.

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