Shift Servo Help

[MSM546]

I have recently started constructing my Scania R470 and have finished everything but the cab. I decided to do a test run before I finished the whole truck and have noticed that when i change to 1st gear the whole servo actually 'twists' which stops the servo from moving the shift rod into 1st. Just wanted to know if other people have come across this problem before and what solutions there are for this. I was thinking of wedging something in front of it to stop it from moving

Also just a quick question. How loud are the 3 speed gearboxes supposed to be because i don't know whether or not the gearbox is supposed to sound the way mine does as it is louder than i expected, even though I have greased it up a lot. I looked at some videos on youtube and they seam quite loud aswell without the MFU

Thanks

Ryan

[MadInventor]

I've had a quick look at the isntructions and the servo mount seems reasonably sturdy. The servo should not need to apply a lot of torque to move the shift rod. Have you got your neutral point for the servo and the length of the servo 'horn' correct ?. bear in mind that if the gearbox is not rotating it is possible that the gears may not be lined up correctly in the dog clutches inside the gearbox, preventing the shift rod from moving. Try putting the truck on blocks, running the motor, and see if the problem still looks the same when the gearbox is turning. Hope this helps, let us know how you get on.

[roots]

Hey Ryan, I just built a Scania 470 too. Though mine was second hand so I can always blame the previous owner if something goes wrong. From my recent experience I will mention two things.

My transmission was very noisy too and it turned out that the pinion gear was too close to the spur gear. By backing it off a little the noise was greatly reduced. But given your problem with the servo it sounds like something else is wrong inside. With the servo detached can you change gears freely with your hand? If not open her up and from there look for what MadInventor was talking about.

Hope this helps.

Steve

[MSM546]

I've detached the shift servo from the actual gearbox and the gearbox seems fine, the shift rod can change gear easily. I re-checked assembly of the gearbox again and all is ok, nothing wrong there

I took off the casing of the gearbox and was running the motor, and what seems to be the problem is that the shift servo is not pulling the shift rod far enough to engage 1st gear, and what is stopping it from engaging 1st gear is the fact that the shift servo moves around

Ill get some pics up shortly to show you what I think the problem is

Another problem i have noticed whilst driving around is that when you use full throtle, the gearbox sounds like the gears are grinding slightly and there is no movement of the truck, so i can only start off slowly and gradually increase speed. Is this something that is normal or can't the gearbox handle full throtle starts???

Thanks

(p.s.: will be shortly making a build thread)

[MadInventor]

I've detached the shift servo from the actual gearbox and the gearbox seems fine, the shift rod can change gear easily. I re-checked assembly of the gearbox again and all is ok, nothing wrong there

I took off the casing of the gearbox and was running the motor, and what seems to be the problem is that the shift servo is not pulling the shift rod far enough to engage 1st gear, and what is stopping it from engaging 1st gear is the fact that the shift servo moves around

Ill get some pics up shortly to show you what I think the problem is

Another problem i have noticed whilst driving around is that when you use full throtle, the gearbox sounds like the gears are grinding slightly and there is no movement of the truck, so i can only start off slowly and gradually increase speed. Is this something that is normal or can't the gearbox handle full throtle starts???

Thanks

(p.s.: will be shortly making a build thread)

This sound could be the gearbox jumping in and out of gear, especially if your shift servo is loose. I.e. the dog clutch gear is riding in and out of the drive gear it's supposed to slot into. When I had my king hauler I put a larger pinion on the motor to get more speed out of it, but it kept jumping out of gear in 3rd. I ended up having to fit a high torque servo to hold the gearbox shift lever in 3rd and this cured the problem. You could try disconnecting the servo and rigidly fixing the gearbox in 3rd (collar on the shift rod possibly, or careful use of a cable tie) and then giving full throttle and see what happens.

Hope this helps,

Madinventor

[MSM546]

PROBLEM SOLVED!!!

Firstly the problem with the servo was fixed by reinforcing the shift servo with another 2 screws. It can now easily shift from 1st all the way too third

But to find the answer to the grinding problem it required me to take the gearbox out and carry out further inspection. What I found to be the problem was that the pinion gear could not be tightened to the flat of the motor shaft properly meaning that the motor shaft was just spinning and not moving the pinion gear. This meant that there was no grinding of the gears, it was just the sound of the motor spinning at high speed

This is what the pinion gear look like after I took it out:

Closer up:

If you can see the thread in the gear has split meaning that the grub screw could not be tightened up properly

Thanks for your help guys