Bedford mj air brake problem

[bedford trucker]

HELLO

 

am having trouble with my bedford mj, its not getting up to air pressure only reaching 3.5bar on both gauges and takes around 10-15 mins to get to that and drains in around 10 mins to 0. checked around the system and cant find any obvious leaks with soapy water anywhere. i can hear air escaping from the reservior internally but cant find where the air is going. any ideas or things to check for

thanks

paul

[N.O.S.]

One possibility is the non-return valve between compressor and condensing reservoir (the one on left hand side at front).

 

It is on the 2nd frame crossmember nearer to left hand chassis rail. If you build up air and then undo pipe on compressor side of non-return valve that will indicate if it is leaking.

[bedford trucker]

ok will check that today, is there anyway to pressure up the system using a compressor so i dont have to run the engine i was thinking of connecting it to the tyre inflater but dont want to cause any damage

thanks paul

[N.O.S.]

Would not advise that - there is a pressure regulating valve before the tyre inflator.

 

No obvious point to attach external compressor that I can see from schematic. If the non return valve is not at fault you could make up an adapter pipe to attach on compressor side of valve for external compressor.

[Richard Farrant]

Would not advise that - there is a pressure regulating valve before the tyre inflator. No obvious point to attach external compressor that I can see from schematic. If the non return valve is not at fault you could make up an adapter pipe to attach on compressor side of valve for external compressor.

 

When we have had leaks on lorries that are difficult to trace and not allowing the tank pressure to build, the simplest way was to remove the tank drain tap and with suitable fittings, use an airline from a compressor to charge up to operating pressure. If a self sealing coupling is used, the compressor can be turned off allowing you to trace the leak by sound as well as feel. As the questioner says he can hear air escaping from the tank, then it seems like a suitable test.

 

Also check if there is any air escape from trailer couplings, they can be forgotten sometimes, but will indicate a fault within the system.

[N.O.S.]

I think this is the right schematic for your truck - says MOP in the civilian manual but pretty certain this is the army MJP. I don't think the Army had any MJR?

 

[Richard Farrant]

I think this is the right schematic for your truck - says MOP in the civilian manual but pretty certain this is the army MJP. I don't think the Army had any MJR?

 

 

hi Tony,

The only difference that I can see, is the load sensing valve, I cannot recollect them fitted on army MJ, certainly not on the MK. It has been a few years since I have crawled around under them so may be mistaken.

[bedford trucker]

thanks everyone, had a good look over the thing today and found it was the dual relay valve was leaking after a quick chat to a friend. hopefully i should be able to clean it out inside and try again. it does have a load sensing valve fitted.

 

thanks paul

[Richard Farrant]

it does have a load sensing valve fitted.

 

 

 

Hi Paul,

good that you have found the fault. Sixteen years since I was involved in MK/MJ and I could not recollect that load sensing valve, can remember a lot of other things though!

[Glenn Swaby]

Hello I have just got a mj  haha  noticed the two belts  on the alternator are slack  do the belts run the compressor for the brakes ??  Also we’re can I get service parts . Thank you Glenn