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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 4997
Experience:  Owner at DJ Wilson
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The retarder is not working, MTB647 1990, I was looking for

Customer Question

the retarder is not working
JA: What is the model/year of your transmissions?
Customer: MTB647 1990
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I was looking for a wiring diagram. There is a cable disconnected from a cylindrical device on the bottom of the radiator. I need to find out what the device is and how it is connected.
JA: Have you checked the vehicle's manual?
Customer: I havent got one
JA: Anything else you want the mechanic to know before I connect you?
Customer: I think that should do
Submitted: 5 months ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 5 months ago.

My name is ***** ***** I will assist you with your question today.

I'm an independent contractor and I don't get paid until a rating has been made.

We can go back and forth as needed to help resolve the issue you are having. Follow ups are free after ratings, so rate in confidence!

what is the year, make, model of the vehicle you are working on?

Can you provide a picture of the device in question?


You want a 5 star service and I want to provide a 5 star service. Please consider that I don't know your skill level as well as I can't see, touch, smell, hear the vehicle/machine in question. Please provide as much detail as possible and I will provide as much back.

Once an answer is provided, you should see a rating screen. Please rate my personal service to you. The ratings are my personal feedback, they are not the site feedback.

Thank you for allowing me to assist you through Just Answer!


Customer: replied 5 months ago.
Hi Jeremy
This is a 1990 Scania 93M. It was a fire truck originally. The transmission is an MTB647I have had a good look over things and the wiring is a mess. I have attached photos of the SN and model plate, a switch at the bottom and what looks like an air activated switch at the top.There is a cable running from the switch on the dash for activating the retarder to the bottom switch, then to the air switch and then to a disconnected cable near the diff. It appears the cable at the switch should be introducing the 24v to the circuit. The switched side of the switch goes to a relay, which then runs back in the chassis a couple of feet behind the transmission and is cut off.I can't work out how the retarder is activated. From some literature I have downloaded about the MTB647, it appears it may apply 50% with no throttle and 100% when braking. How is the retarder activated? That would help me work out where some of the wires should be connected. I haven't found anything yet that is in circuit that will switch for no throttle or when the brake is applied.There is also an exhaust brake that is not working, which I suspect could be related to this problem.A wiring diagram would be helpful.Hope to hear from you soon.Graham
Expert:  Jeremy replied 5 months ago.

I don't work on Scania so I will opt out since I am not the right expert for you. I don't want to lead you on the wrong path.

Good day!

Expert:  Daniel Wilson replied 5 months ago.

Hi my name is***** will be glad to try to help. Let me see what I have for information to help in my archives.

Expert:  Daniel Wilson replied 5 months ago.

Click on this link for some initial information. i will see what I can gather for diagrams, etc. Also what is the make and model engine from the ID tag?

Troubleshooting 1

Expert:  Daniel Wilson replied 5 months ago.

Click on this link for some information i uploaded for you. Let me know if you have trouble accessing it.

Troubleshooting 2

Please remember to take a moment and rate my service as that is how the site credits the experts for their time helping on the site.

Customer: replied 5 months ago.
Hi DanielI had already downloaded the Mechanics tips. The troubleshooting manual is for an electronic control system. I am sure that there is no electronics in the MTB647 I have. Selection is via a mechanical cable to a lever as shown in 5.7 on page 37 of the Mechanics Tips, not a lever with hall effect magnetic switches as shown on 1-8 of the troubleshooting manual.It appears that the retarder is activated by air pressure. Is this correct? If so, it could be by the pipe shown in my photo top air switch. Is this a pressure switch that activates when the pressure is applied, or is it a solenoid that allows the pressure to be applied to the retarder to make it activate?What is the bottom switch that is in series with the air switch or solenoid in my photo "bottom switch"?Do you have an exploded diagram or wiring diagram for a retarder of 1990 vintage?
Expert:  Daniel Wilson replied 5 months ago.

thanks for the update. click on this link for some information I have

Troubleshooting 1

Expert:  Daniel Wilson replied 5 months ago.

Click here as well

Troubleshooting 2

Customer: replied 5 months ago.
Hi DanielIt isn't a Scania Retarder. It is a Scania.Perhaps Jeremy was better to deal with this.I have worked most of it our for now by just pulling things apart and working out what they might do.Do you really think you can help me?
Expert:  Daniel Wilson replied 5 months ago.

I have a lot of information in my archives. This is a 27 year old vehicle you are working on. I most likely have some information to help but at this point I am going to move on and opt out. I do not have the time to go through all my Scania manuals. It makes it tougher when something is almost 30 years old.

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