Front brakes and the LQ-2

[RocketScott]

'89 Pete 379, Cummins 444xt...

After getting my front brakes back together I fired the truck up to move it back to it's usual spot. When I applied the brakes I started losing a ton of air. The valve that splits the air at the front was just dumping air out of the exhaust port. Took it apart and it's toast, the seals are all hardened and cracked

After some poking around the web I figured out that it's an LQ-2 valve. The description says that they were used on 'pre FMVSS-121' vehicles. I've got a switch on the dash that says "slippery/dry" that cuts the front brake application by 50% when the roads are slippery. My front brakes haven't worked since owning the truck so I have no idea how well this system actually functions. I do know that they don't set trucks up like this anymore...

So my question is: Do I just replace the valve with the same or should I upgrade the front braking system to something closer to current standards (but without installing a full ABS system)?

Not sure if there's a better way to proportion the braking between front and back without going full ABS

[Rawze]

(07-19-2020 )RocketScott Wrote:  '89 Pete 379, Cummins 444xt...

After getting my front brakes back together I fired the truck up to move it back to it's usual spot. When I applied the brakes I started losing a ton of air. The valve that splits the air at the front was just dumping air out of the exhaust port. Took it apart and it's toast, the seals are all hardened and cracked

After some poking around the web I figured out that it's an LQ-2 valve. The description says that they were used on 'pre FMVSS-121' vehicles. I've got a switch on the dash that says "slippery/dry" that cuts the front brake application by 50% when the roads are slippery. My front brakes haven't worked since owning the truck so I have no idea how well this system actually functions. I do know that they don't set trucks up like this anymore...

So my question is: Do I just replace the valve with the same or should I upgrade the front braking system to something closer to current standards (but without installing a full ABS system)?

Not sure if there's a better way to proportion the braking between front and back without going full ABS

Because it is a safety=-related issue...
maybe ask what the truck maker recommends. That way there is no personal liability if something does not work out, or some moron pulls out in front of you one day and it becomes part of some 'legal' issue .. you never know what the future holds.

If there is an update or TSB related to it, and you do not have it done,.. it would become your personal responsibility if something bad were to ever happen otherwise.

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And then there is the more obvious issue there too... It is safe to say that if you found one valve with rotted out guts in the brake system... ehemm.. you'de be best to replace ALL the safety-sensitive valves with rubber guts + all rubber hoses related to the braking system while you are at it. This is to protect yourself, the motoring public at large, and to prevent chasing gremlins.

[RocketScott]

Ordered a replacement valve this morning. You're totally right about the liability aspect. I should have considered that

Also right about the rest of the valves, actually the rest of the truck really. I went through the back axles last year and replaced a lot of stuff. Just getting to the front now

[Brewster64]

Front brake limiting valves have been around a long time, they just changed a bit in 1975 with 121 brakes. Gone are the days of your dash switch shutting off the front brakes. They are gone now with the advent of ABS. In a nutshell, your 89 Pete with a dry/ slippery road switch will cut brake pressure to front brakes by 50 percent but only up to about 30 psi, by a 60 psi application the ratio will be up to 100 percent application to front brakes as this is deemed an emergency application. Alot of trucks actually had an automatic limiting valve that was basically always in slippery mode. To look at it, you would think it's a T with a QR in the bottom, but it actually had a function. These were in place to keep trucks from skidding steer tires mostly in town, going around tight corners, into driveways, etc to maintain steering control. Your original valve was was probably just stuck so your front brakes never worked at all, good thing the QR finally started to leak. Don't bother even thinking about ABS on that ol truck. Way less hassles without it.

[RocketScott]

I ended up cleaning up the old unit and rebuilding it. The inside was still in good shape once I cleaned out all the rubber and plastic bits. Blasted and painted the outside too

[Brewster64]

Atta boy! But you'd lose your "Technician " job at a Stealership if ya pulled that shi#t there, lol. Probably cost ya $5. Always amazes me. Have a leaky MVE2 or 3 in your dash at Safety time, shops want about $250 for the valve plus 4 hours. The rebuild kit is $12 and you can do it right in the dash. First one I did took me an hour. Mostly spent taking a Century dash apart. Half the failed air valves can be taken apart , clean the gunk out and put back together, good for another few years. Get to know an OEM mechanic , they can get most of the kits they won't sell retail.

[RocketScott]

The rebuilt kit was ~$20. Was a little hard to find, guessing there's not as much demand for the old stuff

One lesson I learned is to be very careful buying off ebay. Before deciding to rebuild it I bought a reman LQ-2 that turned out to be NOS. It was so old that the seals were cracked just from sitting around. I could see them through the top and bottom ports as soon as I took it out of the box