Instruments

Drive Joints

888Drive joints are used to correct inaccurate speedometer operation resulting from a change in a vehicle's axle ratio, and/or tyre size. Installing a drive joint of the proper ratio between the transmission and the flexible shaft alters the drive ratio to the speedometer to correspond to the vehicles alterations.

Method of Calculating Drive Joint Ratio
1. Remove old drive joint, if fitted, connecting the flexible shaft directly to the transmission.
2. Drive vehicle on a measured course of ~ 5 km. The longer the course, the more accurate the test.
3. Note distance measured on the odometer.
4. The Drive Joint Ratio can then be calculated as follows:

Actual Distance Travelled / Odometer Reading = Drive Joint Ratio

Speedometer reading too slow
Odo Reading
% Slow
Drive Joint Ratio
Odo Reading
% Slow
Drive Joint Ratio
3.0
40%
1.680
4.0
20%
1.250
3.1
38%
1.615
4.1
18%
1.213
3.2
36%
1.586
4.2
16%
1.202
3.3
34%
1.511
4.3
14%
1.166
3.4
32%
1.483
4.4
12%
1.136
3.5
30%
1.440
4.5
10%
1.111
3.6
28%
1.384
4.6
8%
1.088
3.7
26%
1.360
4.7
6%
1.071
3.8
24%
1.307
4.8
4%
1.041
3.9
22%
1.284
4.9
2%
1.018
Speedometer reading too fast
Odo Reading
%Fast
Drive Joint Ratio
Odo Reading
% Fast
Drive Joint Ratio
5.1
2%
0.982
6.1
22%
0.821
5.2
4%
0.961
6.2
24%
0.809
5.3
6%
0.944
6.3
26%
0.789
5.4
8%
0.933
6.4
28%
0.778
5.5
10%
0.912
6.5
30%
0.769
5.6
12%
0.897
6.6
32%
0.755
5.7
14%
0.879
6.7
34%
0.746
5.8
16%
0.862
6.8
36%
0.735
5.9
18%
0.850
6.9
38%
0.722
6.0
20%
0.831
7.0
40%
0.694

Calculating the Drive Joint ratio from known information

General Formula
 (Teeth in Driven Gear * 1000) / (Tire Rev's per Mile * Axle Ratio * Teeth in Drive Gear) = Drive Joint Ratio

Self assembly kits
 Includes all common parts.
Gears must be ordered to required ratio as per chart F525, available on request

Kit No.
31802AA117 Makes A777B Boxes
31802AB117 Makes A777F Boxes
31802AX117 Makes A777TF Boxes

Drive Joint fittings
 
No
End
Length
End
101451
0.152 dia.
1 1/8"
0.187 dia
101452
0.187 dia
1 3/16"
0.187 dia
101453
0.203 dia
1 3/16"
0.187 dia
 
101454
0.187 dia
1 1/4"
0.187 dia
888 Series

F.D.A. right angle Drive Joints are used -
To alter ratio and/or direction of rotation from the original drive unit.
To effect a take-off at right angles to the original connection

Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
7/8-18 Internal .104" Square
7/8-18 Internal .105" Sq Hole
1.000
Suit most American type Transmissions
31601AA167
Reverse
1.000
31601AB167
Constant
0.500
31601AA137
Constant
0.250
31601AB127
Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
5/8-18External .104" Square
7/8-18 External .105" Sq Hole
1.000
Suit most Adaptor plates and couplings
31601AC167
Reverse
1.000
31601AD167
Constant
0.500
31601AC137
Reverse
0.500
31601AD137
Reverse
0.250
31601AC127
Reverse
5/8-18 External .104" Square
5/8-18 External .104" Sq Hole
0.500
Extra Long Input Thread
2100329
Reverse
0.250
2100330
Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
5/8-18 External .105" Sq Hole
5/8-18 Internal .104" Square
1.000
Suit most American type Speedometers & Tachometers
31601AE167
Reverse
1.000
31601AF167
Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
7/8-18 External .104" Square
7/8-18 External .105" Sq Hole
1.000
Suit most American type Transmissions
31601AG167
Constant
0.500
31601AG137
Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
7/8-18 External 3/32 Drive Pin
7/8-18 External .105" Sq Hole
1.000
Suit Perkins 6/354
31601AJ167
Constant
1.00
31601AK167
Rotation
Input End
Output End
Output Ratio
Remarks
Part No.
Constant
7/8-18 External .105" Sq Hole

7/8-18 Internal .104" Square

7/8-18 External .105" Sq Hole
1.000
Allows two instruments to be driven froom the one system
31601BC167