Maruha motors

Maruha LSD Vol.1



MARUHA Custom LSD for NA6 2way
LSD for NA6CE 2WAY(2023年11月〜)
code:mar04052148 For NA6CE


MARUHA Custom LSD for NA8/NB 2way (not for Turbo)
LSD for NA8 /NB (除くNB-ターボ) 2WAY(2023年11月〜)
code:mar04052149 For NA8 NB(除くターボ)

To install Maruha LSD for NA6CE(B6)/90-93model, the special output shafts are required. 
If your Miata is an open differential type (not viscus LSD), you can use stock parts again for our LSD. 
Please check the following.

The different length type on L and R : you have to change stock parts for our LSD
The same length type on L and R : you can use stock parts for our LSD

On the later model since '94(NA8C / NB6 NB8) with larger differential, stock output shafts don't have to be changed. (Available reusing for Maruha LSD) 

We recommend you to use new parts of side bearings and side oil seals to avoid troubles.

(LSD lecture)

Mechanical LSD and standard LSD by Mazda (Viscous and Torque sensitive) are completely different in mechanism, features and performance.

The mechanical LSD drives the general differential (usually called as open diff) out of tuning market in performance. (stable drive, climbing, cornering, acceleration etc) 

For more enjoyable driving we recommend Maruha LSD, which is not only for circuit attack but also drifting and winding roads. 

You hear chattering from the LSD. In the case of mechanical LSD, it cannot be avoided. 
With low initial setup and additional treatment, Maruha's LSD is designed so that there is not too much chattering. 

2.Open differential


The following parts are for open differential as components.

Side gear (x 2) -------------- to drive shafts (L/R)
Pinion gear (x2)------------ mesh with side gears
Pinion cross shaft (x 1)---axis of rotation for pinion gears

(Going straight)


The difference in turning speed between left and right drive shafts does not happen, and left and right side gear rotate together. 
So pinion gears do not rotate.

Example :
Input rotation to the differential (Finial pinion gear) 100rpm
Left drive shaft : 100rpm
Right drive shaft : 100rpm



The case of turning to the right

The right drive shaft is inside (slow rotation), the left drive shaft is outside (fast rotation).
Cornering is smooth.

he right side gear rotates slower than the differential case.
The pinion gears rotate, and give the rotation speed of the spinning opposite way to the left side gear.
The left side gear rotates faster than the diff case. 

Slow rotation of the right drive shaft and fast rotation of the left. 
This balance is transmitted through a differential.
The difference of rotation speed between right and left drive shafts is adjusted to keep the balance automatically based on the large load wheel. 

Example :
Input rotation to the differential (Finial pinion gear) 100rpm
Left drive shaft : 70rpm
Right drive shaft : 130rpm

Demerits of an open differential

Can not escape from a muddy place. 


When the one wheel to drive slips in a muddy place, the load of that wheel is zero(0), the opposite side wheel receives all traction. 

The grounded wheel does not rotate.
The slipping wheel rotates with two times more speed.

After all, a vehicle can not move at all. 

It is impossible to transmit traction during hard cornering.

The inside wheel is rifted in hard cornering by centrifugal force.
In this case, the inside wheel loses the traction at the moment and the speed lessens.

On usual driving on street, the torque of drive shafts changes constantly by affection from road situation and tires and keep balance through the differential. 

To cove this demerit of open differential type which is " traction concentrates on the low load shaft, LSD is required. 

LSD is the device to get the high driving force as much as you can. 

3.Maruha mechanical LSD


This kit consists of 25 parts.


Side gear (x 2)・・・Connecting to drive shafts (L/R)
Pinion gear(x4)・・・Coupling to side gears
Pressure ring (x2)・・・kept in a differential case, and can slide by cam mechanism.
Pinion cross shaft (x1) ・・・axis of rotation for pinion gears
Clutch plates (drive x4)・・・friction plates rotating with a diff case
Clutch plates (driven x4)・・ friction plates rotating with side gears
Spring plate(x2) ・・・pushing clutch plates at all times
Washer(x2) ・・・ receiving trust from side gears and prevent from blowout 

Pinion gear rotates based on pinion cross shaft, side gears mesh to pinion gears.
Pressure rings can slide and have a ditch like the letter V to set the pinion cross shaft.

The pinion cross shaft floats between the pressure ring (left and right) and doesn't connect to the diff case. 

The pinion cross shaft is installed directly to the diff case on open differential.

Each clutch plate (drive and driven) is set mutually between a pressure ring and a diff case.

(LSD motive power)

When the accelerator is on the motive power is input to LSD and pressure rings and a diff case start rotating together.
Drive shafts will keep the speed by inertia.
These both powers (accelerator on / drive shafts) bump at V ditch between pressure rings and pinion cross shaft. 

Thus the gap comes out between the pressure rings and pinion cross shaft (V ditch), the pinion cross shaft pushes the pressure rings to open, and the clutch discs are locked firmly by sliding of the pressure rings.

Side gears of the left and right connect to the clutch plates. The lock ratio of the side gears is changeable by V ditch movement as " cam function".
This cam function is by traction (acceleration on/off) and inertia (drive shafts rotation) to keep a balance.
Therefore it is called " torque response type" . 
The mechanical LSD is not 100% lock type. 

We can change the feature of the cam function. 

l In the case of a wider angle of V ditch.
The force of the Pressure ring opening is stronger. The LSD effect is firm.  

l In the case of more narrow angle of V ditch.
The force of the pressure ring opening is weaker. The LSD effect is infirm.

There are three types of cam functions of the V ditch.

1 V ditch with left and right symmetry----" 2way type "
The LSD is effective in both cases - when the accelerator is ON/ OFF

2 V ditch with left and right is not symmetric----" 1.5way type"
The LSD effect is infirm when the accelerator is OFF. 

3 The V ditch with vertical angle on one side-----" 1 way type "
LSD effect is zero when the accelerator is OFF. 

(Initial torque)


The spring plate(x2) puts pressure on the clutch plates all the time.
The friction of clutch plates by this pressure is the " Initial torque".

The initial torque has two roles.

  1. Controlling cam function at some degree → Preventing hunting by a little bit of torque changing.
  2. Assisting cam function when the wheel slips→Improvement in pick up.

If the initial torque is set harder, the LSD becomes effective all the time (Not torque response type), 
it would cause lower performance at cornering.

To adjust these conflict roles, you should consider your usage first and then decide a spec.

Example :
Race, circuit, drifting ------High initial torque →The priority of LSD effectiveness.
Street-------Low initial torque→The priority of torque response

Contact us here


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