I have been having some issues with Motor6D’s so i decided to change all of the motor6D’s to hingeconstraints but now i have another issue.
I cant get the hingeconstraints to stay in place without glitching out.
Is there a way to prevent the hingeconstraints from moving on the client?
Hmm. 
Well, I’m pretty sure this is a Roblox issue, but I think you can use ActuatorTypes. You can check out their wiki page here or if you want to see everything else you can do with a hingeConstraint you can do so here.
Hope this helps. 
The mass of the retracting part of the landing gear is too low compared to the plane, and due to ROBLOX physics it starts jittering.
To fix this you need to increase the mass of either the wheel or the grey strut.
Could massless also fix the issue? or do i really have to increase the mass
You’ll still have to increase the mass. Massless will only make it jitter more.
Is mass the Density of a part?
Density increases mass, yeah
Could you use welds and set the wheel friction to 0?
I cant use welds because there is no way to enable welds on the client without having any issue.
I tried disabling a weldconstraint on the client and it doesnt update the server so it stays welded on the server but not on your client.
And by enabling or disabling the weldconstraint on the server it teleports the attached pieces all over the map if they are moving.
Couldn’t you just set the HingeConstraint ActuatorType to Servo, set ServoMaxTorque to inf (math.huge), set the angular speed to something like 5 and then change the TargetAngle so that it keeps the wheels in their fully extended position
If the MaxTorque is too high the constraint is more likely to glitch out
Why is that so? The constraint seems to work fine with a high max torque with just a single hinge between two parts. It makes it so the mass is irrelevant as torque increases with mass but if you have an extremely large torque, the code which accelerates the (current) angular speed up to the AngularSpeed (property) is not limited by mass.
Edit: I think it also needs a high torque so that it generates more resisting force on the wheels in response to whenever the wheels hit the ground. The entire mass of the vehicle probably creates a large impulse force whenever the wheels hit the ground. Also, the wheels have to bear the weight force of the entire plane which means high torque is required (to prevent them from swinging up to a retracted position) I believe.
Last time i checked it was always glitching out if the maxtorque was above 300000 but now it works fine somehow.
I think this is because i removed all of the customphysicalproperties from every single part.