Volvo A35 Haul Truck Drop Box Speed Sensors

[gm@diezel]

Recently purchased a 1994 Volvo A35 haul truck and having some issues with the high and low range. Suspicious my problem may be with a sensor on the drop box somewhere. Unsure as to which sensors do what. Can somebody clue me in or have a diagram?

 

[mg2361]

Welcome to HEF gm! I'm sure the Volvo guys will want a serial number, a more specific description of your issue as well as any codes if you have them.

 

[sfrs4]

Hi gm@ as MG2361 says a little more information will help as there are 2 different drop box's dependent on serial number, machine serial number and what exactly is happening
As a rough idea the high low selection is controlled by the ECU and it uses a few inputs to decide what it's doing the first two are the actual high low sensors the third is the engine speed sensor.
SE54 Sensor for low range
gives the ECU information about which range is engaged in the dropbox (H/L). When low range is engaged, SE54 is closed and SE55 is open.
SE55 Sensor for high range
gives the ECU information about which range is engaged in the dropbox (H/L). When high range is engaged, SE54 is open and SE55 is closed.
SW69 Switch high–low range
is used for selecting high or low range in the dropbox. This selection can be made while operating but the actual shift occurs first when the machine is stationary and the engine speed is below 12.5 r/s (750 rpm)

it could be that SE54 and SE55 might need adjusting a little do you have the information panel in the cab so you can see them?
SE54 and SE55 are located on the very top of the dropbox right next to each other.
The engine speed sensor is on the oil pump between the torque and the transmission but if this was at fault i would of said you would transmission shifting issues as well

 

[gm@diezel]

The machine serial # A35V2400. It is a 1994 model. I replaced the SE55 sensor and also a cracked air line at the solenoid and now the machine seems to shift from high to low okay and drives. My tachometer on the dash doesn't work though and could that lead to a faulty engine speed sensor?

 

[sfrs4]

The machine serial # A35V2400. It is a 1994 model. I replaced the SE55 sensor and also a cracked air line at the solenoid and now the machine seems to shift from high to low okay and drives. My tachometer on the dash doesn't work though and could that lead to a faulty engine speed sensor?

Try SE43 in the middle of the front of the upper casing. that shouldn't effect the engine speed sensor as SE43 is just used for ground speed readings

 

[Adrian Cox]

Hi gm@ as MG2361 says a little more information will help as there are 2 different drop box's dependent on serial number, machine serial number and what exactly is happening
As a rough idea the high low selection is controlled by the ECU and it uses a few inputs to decide what it's doing the first two are the actual high low sensors the third is the engine speed sensor.
SE54 Sensor for low range
gives the ECU information about which range is engaged in the dropbox (H/L). When low range is engaged, SE54 is closed and SE55 is open.
SE55 Sensor for high range
gives the ECU information about which range is engaged in the dropbox (H/L). When high range is engaged, SE54 is open and SE55 is closed.
SW69 Switch high–low range
is used for selecting high or low range in the dropbox. This selection can be made while operating but the actual shift occurs first when the machine is stationary and the engine speed is below 12.5 r/s (750 rpm)

it could be that SE54 and SE55 might need adjusting a little do you have the information panel in the cab so you can see them?
SE54 and SE55 are located on the very top of the dropbox right next to each other.
The engine speed sensor is on the oil pump between the torque and the transmission but if this was at fault i would of said you would transmission shifting issues as well

How would one adjust the se 54 se 55 sensor

 

[sfrs4]

How would one adjust the se 54 se 55 sensor

the sensors have a lock nut on them, so slacken it then adjust in and out to suit. Then tighten the lock nut. they shouldn't really come out of setting while in use.

 

[Adrian Cox]

the sensors have a lock nut on them, so slacken it then adjust in and out to suit. Then tighten the lock nut. they shouldn't really come out of setting while in use.

Ok I did that still won’t go in gear unless in limp mode

 

[Adrian Cox]

so now I'm trying to locate the speed sensor But aren’t having any luck.

 

[sfrs4]

right completely different parts of the machine Se54 and se55 are on the dropbox, this has nothing to do with gear selection, just taking the driven power from the transmission to the front and back axles and giving you option of two speed ranges of the transmission.

 

[Adrian Cox]

But it does that have something to do with the high and low gear

 

[sfrs4]

when you say won't go into gear unless in limp mode? do you mean with the "get home" ecu plugged in?

 

[sfrs4]

in what way? are you getting the error code? in that case if the error is still there then either the wiring loom is damaged or you have an internal problem with the dropbox

 

[Adrian Cox]

I unplugged it from this and plugged it into this

 

[sfrs4]

looking back at what I put, the trans will withhold gears if it thinks there is no hi or low selected, so go back to the switches and give them a couple of go's at setting, maybe there is play internal so you think they set then try them again and see if they still are set correctly.
yes the smaller box is the "get home" trans ecu, the bigger one is the actual ecu

 

[Adrian Cox]

Ok I’ll try that and get back with you

 

[sfrs4]

try theses to help