Popular Post eddeere Posted December 14, 2019 Popular Post Share Posted December 14, 2019 Started cleaning up the truck today. Found a lot of items that I am not sure about. Wires going thru the backing plate. One on all four rear drums. Any know what these are for ? Items in the cab instructions for lowing the floating axle, one air pressure gauge, and air pressure gauge with a switch & knob. I do not think I have the floating axle and sure never got the missile. Going to put the fifth wheel back on and cutting 30" off the frame extension with the pintle hitch. Any thoughts on this ? 3 Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/ Share on other sites More sharing options...
Quickfarms Posted December 14, 2019 Share Posted December 14, 2019 Page did make a spring retracted air suspension lift axleThe air switch below the lift axle psi tag looks like to is for a sliding fifth wheel Did you request the package from the Mack museum Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438005 Share on other sites More sharing options...
JoeH Posted December 14, 2019 Share Posted December 14, 2019 Wire to the drums looks like ABS. My 1980 dm686sx had a spring retracted lift axle. Trucks been retired and sitting as parts inventory. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438007 Share on other sites More sharing options...
JoeH Posted December 14, 2019 Share Posted December 14, 2019 The Page box looks like that's your lift axle control. Knob is the regulator to adjust pressure to the lift axle bags. Gauge on top of the dash could be for brake application pressure. See if it rises when you hit the brakes. Kind of a useless gauge, I've seen Pete's with brake gauges. Either you have enough pressure to stop or you don't and you need to push the pedal harder. Don't need a gauge to tell you that! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438008 Share on other sites More sharing options...
eddeere Posted December 14, 2019 Author Share Posted December 14, 2019 Thanks all. I got almost 80 pages of build sheets from the Mack Museum. Hendrickson RT 440 suspension Eaton 44 RTC two speed tandem axles with no mention of a lift axle. Someone must have added a lift axle. Maybe the military. I thought it would have been ordered that way. There is a switch in the cab for a Holland fifth wheel. I think JoheH is correct on the air gauge for the brakes. The wires going to thru the backing plates is still a question. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438014 Share on other sites More sharing options...
Vladislav Posted December 14, 2019 Share Posted December 14, 2019 Seems like someone just removed the missile at the last moment you provided the purchase. Hope you'll be able to manage all those gauges and other stuff sucessfully enough without that sure expensive option. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438018 Share on other sites More sharing options...
Rob Posted December 14, 2019 Share Posted December 14, 2019 FMVSS 121 ordered the installation of ABS in the mid 1970's. It was allowed to be disconnected as it was SO troublesome. That is what your wires are for to connect to a hall effect pickup reading a "tone ring" which spins with wheel rotation. The tone ring could be called a "reluctor", (same thing different name). Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438019 Share on other sites More sharing options...
Quickfarms Posted December 14, 2019 Share Posted December 14, 2019 The face of the air gauge says turner quick lift.Turner and page merged at some point so that gauge may be related to the lift axle.I do agree that the wires going to the brakes are probably for an early abs system. It seem to remember that the early abs was a POS and commonly disabled or removed.I think there is the remains of an ABS system on the military dolly in my storage yardThe wire goes into the flange the holds the brake spider to the axle housing The sheet metal covers, held on by the small bolts, are really just dust covers.We remove the dust covers and leave them off so that junk does not get trapped in there and you can easily tell if an axle seal is leaking Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438022 Share on other sites More sharing options...
JoeH Posted December 14, 2019 Share Posted December 14, 2019 What body was on the frame, and what trailer would be hauled by this truck? If this was a military truck, the Amazon is about the only place I can imagine that green being camouflage... Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438031 Share on other sites More sharing options...
JoeH Posted December 14, 2019 Share Posted December 14, 2019 I've heard missile mentioned a few times. If this was a missile truck then the only way to resto this truck right is fab a missile launcher with a paper mache? missile strapped on! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438033 Share on other sites More sharing options...
eddeere Posted December 14, 2019 Author Share Posted December 14, 2019 The early ABS makes sense. Four were made at the same time for ATAC . After the military sold the truck a fire department bought it and took the fifth wheel off and used it as a water tanker. Not sure about the missile launcher idea. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438042 Share on other sites More sharing options...
JoeH Posted December 15, 2019 Share Posted December 15, 2019 I'm wondering if the lift axle switch is for a trailer lift axle. But that's unusual to have the switch in the cab. It's an extra hose requiring hookup. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438058 Share on other sites More sharing options...
Quickfarms Posted December 15, 2019 Share Posted December 15, 2019 I'm wondering if the lift axle switch is for a trailer lift axle. But that's unusual to have the switch in the cab. It's an extra hose requiring hookup.You could look to see if there are any extra air lines in the frame ahead of or behind the tandems Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438059 Share on other sites More sharing options...
Rob Posted December 15, 2019 Share Posted December 15, 2019 My water wagon has much the same setup for the Neway "tag" axle. It is air down, spring up, with a regulator and gauge to set applied pressure on this axle: I don't have a photo of the dash indicator readily available but have found about 65psi, (indicated) when the truck is loaded is about even weight on all three axles when it is down. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438078 Share on other sites More sharing options...
davehummell Posted December 15, 2019 Share Posted December 15, 2019 The Brockway I drove had air down and spring up and when I was fully loaded I ran 60 lbs. I also had 10-22 tires on the front. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438082 Share on other sites More sharing options...
eddeere Posted December 15, 2019 Author Share Posted December 15, 2019 Two lines in front of the tandems. The one with the cap has no air with cap removed. The other has air with the switch in the cab. Both gauges read the same. The holes in the frame must have been for mounting the lift axle . Now I know more than I did. Have been working to get the cab to lift . The latches open but the cab only goes about an inch. Thanks for the help. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438095 Share on other sites More sharing options...
Quickfarms Posted December 15, 2019 Share Posted December 15, 2019 Did you try flipping the fifthwheel slider switch to see if you have air out of the second line? Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438125 Share on other sites More sharing options...
eddeere Posted December 15, 2019 Author Share Posted December 15, 2019 There is a third line in the picture with blue tape on it that has air from the fifth wheel switch. Quote Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438129 Share on other sites More sharing options...
ws721 Posted December 16, 2019 Share Posted December 16, 2019 I was able to buy new lift pistons from Mack. But if you try Power Packer in Indiana they are very helpful. The service tech man is great to deal with. They built lift cylinders for me. In fact they have refered a few COE people to me to answer questions. If the latches are opening then its down to the pump or lift clyinders not being up to par 1 Quote Remember if it's got a hood it's no good! Link to comment https://www.bigmacktrucks.com/topic/60180-f-797-st/#findComment-438150 Share on other sites More sharing options...
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