air brake conversion

I have a wedge brake axle set up from a 939 series rear drive.
also have a front drive axle set up off same series.

the rear set up has central inflation.
the front does not.
the drums are different betwen the two set ups. any clue if the front backing plates will bolt up to an old style steer axle? (at first look they should)


was there more than one style of drums used?

I need to convert one of my trucks over to air brakes and thought this would be the easyest way.

I dont have other 939 trucks here to look at so I will be thankful for any help.

been a long time since ive worked with wedge system but I think it can be sorted out.

I also have been looking for plumbing diagrahms with out much luck.

If you were closer I would offer to let you take a look at my m936..

Derrickl112 said:

If you were closer I would offer to let you take a look at my m936..

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It may be worth the trip if I cant figure out how to plumb this mess.

does yours have ABS by chance?

another question I have is why is there air to both sides of the diaphram on the service brake canister? Is the back side fitting just a remote vent or some type of positive pull off?

I will put up a few pictures later tonight.

As an aside, is there any way to easily add ABS to a non ABS truck?

Yes it has ABS.

Drive down, swap systems, axles and all, pay a little cash and drive home... We do not have any with CTIS though.

Going to watch this thread as kind of like to do it to my tractor.

91w350 might have to talk to you about road trip in couple weeks if price ain't bad on something like that after taxes come home.

DaveP said:

another question I have is why is there air to both sides of the diaphram on the service brake canister? Is the back side fitting just a remote vent or some type of positive pull off?

I will put up a few pictures later tonight.

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If you mean the ones on the rear axles, then that is for the maxi brakes (parking brake).
By applying air to those, it releases the spring tension from the maxi (the second air can), and releases the brakes to work as normal.
If air pressure is lost, or you remove air pressure (pushing in the parking brake) then it allows the springs to apply and hold the brakes, fully locked up.

This is a very good opportunity to mention that the information associated with a CDL is very helpful for anyone working with air brakes. Whether or not you go through with the process of getting one, going through the preparatory learnings for a CDL will teach you the difference about Foundation Brakes, Service Brakes, Spring Brakes etc etc, and in doing so will help you learn an incredibly valuable skillset.

Subscibed

Hammer said:

If you mean the ones on the rear axles, then that is for the maxi brakes (parking brake).
By applying air to those, it releases the spring tension from the maxi (the second air can), and releases the brakes to work as normal.
If air pressure is lost, or you remove air pressure (pushing in the parking brake) then it allows the springs to apply and hold the brakes, fully locked up.

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the line I was talking about is on the back side of the service brake diaphram. these play no role in the maxi/parking brake.
turns out they are plumbed this way for a remote vent according to another member who owns a M939 truck. this makes sense to me. so one more question put to rest.

Now i need to sort out what dash valves will work with the axle relay valves. the bendix book only listed 2 that they say will work with this particular relay valve. not sure why yet but Im looking into it.

the good news is-- the relay valves do work even after sitting for a few years. and they are still available thru heavy truck parts suppliers for about $100 if needed.

No pics yet as i seem to have misplaced my patch cord for my camera.

I did however find a photo of an service brake can like im working with.
this is on a trailer axle but is the same type.

you can see the fittings with the blue plugs in them.

this going on your 820 tractor?

timothy1 said:

this going on your 820 tractor?

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Yes---on this pile of parts.

Ah, ok. I see now from your picture what you are talking about.
Probably for the potential for a fording kit maybe?

DaveP said:

Yes---on this pile of parts.

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that is one sweet truck...

Trango said:

This is a very good opportunity to mention that the information associated with a CDL is very helpful for anyone working with air brakes. Whether or not you go through with the process of getting one, going through the preparatory learnings for a CDL will teach you the difference about Foundation Brakes, Service Brakes, Spring Brakes etc etc, and in doing so will help you learn an incredibly valuable skillset.

Click to expand...

Would love to see pix of your next build.

Bolkbich said:

that is one sweet truck...

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Thanks

Bolkbich said:

that is one sweet truck...

Click to expand...

found the parts to load pictures.

easy to see the differences in the 2 drum types.
I dont know how many types of drum/shoes were used but heres two!

dont laugh to loud at me about my axle stand. it beats sitting my butt on the ground.