Front Brakes

[leversole]

Tracking down why/how the front brakes are disconnected...

I have a B model air line diagram and have traced the lines (doesnt match 100%) and have a question or two...

On the limiting quick release valve(I think), it has supply (I assume) from the pedal valve, two lines out to front brakes,

and a small line that runs into the cab presumably to the limiting valve in the dash. It is loose and hanging in the cab.

Another line that presumably comes from the limiting valve runs to a T on the left brake line where it passes thru the frame.

My question is, does the limiting valve small line send air pressure to allow air to flow to the front brakes when in normal mode?

Also, when in slippery mode, does it limit, or shut off air to the front?

Should I replace with a std quick release, or try and hook up the dash valve switch?

Thanks

[Rob]

Tracking down why/how the front brakes are disconnected...

I have a B model air line diagram and have traced the lines (doesnt match 100%) and have a question or two...

On the limiting quick release valve(I think), it has supply (I assume) from the pedal valve, two lines out to front brakes,

and a small line that runs into the cab presumably to the limiting valve in the dash. It is loose and hanging in the cab.

Another line that presumably comes from the limiting valve runs to a T on the left brake line where it passes thru the frame.

My question is, does the limiting valve small line send air pressure to allow air to flow to the front brakes when in normal mode?

Also, when in slippery mode, does it limit, or shut off air to the front?

Should I replace with a std quick release, or try and hook up the dash valve switch?

Thanks

If I remember correctly the dash flip switch for selection of slippery, or dry conditions applies air pressure to the limiting quick release valve when in the slippery mode. This application of air pressure to the valve LQR valve allows this valve to apply about 60% brake application pressure to the front brakes therefore limiting the front brake shoe application pressure from the dry position, (or normal application pressure).

I like front brakes on a steer axle myself but I do not have a trailer to pull. One of my B61 trucks does not have front brakes and it's dangerous, (too me) to drive when wet outside. Probably quite a bit different with a trailer latched I'm certain.

Rob

[leversole]

If I remember correctly the dash flip switch for selection of slippery, or dry conditions applies air pressure to the limiting quick release valve when in the slippery mode. This application of air pressure to the valve LQR valve allows this valve to apply about 60% brake application pressure to the front brakes therefore limiting the front brake shoe application pressure from the dry position, (or normal application pressure).

I like front brakes on a steer axle myself but I do not have a trailer to pull. One of my B61 trucks does not have front brakes and it's dangerous, (too me) to drive when wet outside. Probably quite a bit different with a trailer latched I'm certain.

Rob

So, with the small "control" line from the dash switch disconnected, the front brakes should recieve full line pressure correct?

Maybe the limiting valve is bad 'cause I got nuthin' on the front! I think I will replace it with a new plain jane quick release valve

Thanks

[Rob]

So, with the small "control" line from the dash switch disconnected, the front brakes should recieve full line pressure correct?

Maybe the limiting valve is bad 'cause I got nuthin' on the front! I think I will replace it with a new plain jane quick release valve

Thanks

That is the theory. If you have no brakes on the steer axle, this would be the first thing I'd change if all else is working.

Did you know this truck had these many miscellaneous problems when you purchased, or are you finding "surprises"?

Rob

[41chevy]

Before you buy parts,check for a blockages in the front brake lines. I had a similar isue with an older truck. A couple of old timers told me that they would block off the lines from brake supply to the cans to eliminate the front brake. Tthey would put a screw or a ball bearing ball in the line. Their theroy was that the front brakes would cause jackknifes. Some of the pre '72 Freightliners and K.W.s came from the factory with no front brakes. I'd hate to see you go through the expense and labor to still have the problem. (like I did) Paul

[leversole]

Before you buy parts,check for a blockages in the front brake lines. I had a similar isue with an older truck. A couple of old timers told me that they would block off the lines from brake supply to the cans to eliminate the front brake. Tthey would put a screw or a ball bearing ball in the line. Their theroy was that the front brakes would cause jackknifes. Some of the pre '72 Freightliners and K.W.s came from the factory with no front brakes. I'd hate to see you go through the expense and labor to still have the problem. (like I did) Paul

Thanks! Will check the lines...

[leversole]

Got it! Truck stops much better with front brakes! It was the limiting quick release valve...will take it apart tomorrow and check it out...