raindog

Hey folks: I had a similar experience as Mild Thunder did (see recent post 1998 E7 wont start). After a couple days of head scratchin and speaking to some knowledgeable folks, I found out that my ECM is bad. Was pretty much sure it was bad when I went over it with a multi-meter and the wiring diagram (I have a copy for a 1994 RD 688S if anyone ever needs one). Found out today that the ECM is bad for 100% sure, because the truck fired up instantly on a "test" ECM a very helpful service tech loaned me. Ok, so the old ECM is bad, I understand that I will need to get a new (used) ECM and have it "cloned" at a Mack Dealer. I've been told that there are places that remanufacture these (and do the programming too) and offer a lifetime warranty (apparently they use heavy duty components, etc). Can anyone recommend an outfit that will ship you a good ECM if you ship in your old one (assuming they can read the codes off the bad one?) Thanks in advance,

just realized I hadn't read this thread all the way thru page two. Can someone help out with the nomenclature-- What does TDC stand for? What does TEM stand for? I have a wiring diagram for my E7--it shows an Engine Shutdown Relay. Is this the same as what is being called a fuel shutoff solenoid, and does this have anything to do with the problem that mild thunder was having? Think I've got the same problem.

Mild thunder-- Did you get truck fixed? If so, what was it? I've got an E7, 1995 in an RD 688. Seems to be an electronic issue--fuel every where, except coming out of the pump. Noticed at least a dozen or so difficult starts in the previous year where it didn't appear to be getting fuel, but eventually did. Feel certain its a fuel shutoff switch gone from sorta bad to all bad, would be curious to know what you found out. Could you by any chance post a pic of the problem part? Thanks,

41chevy, I think you're right. I'll give the hinge a shot of silicon spray every week to get as much out of these hinges as possible. Also, my local Mack parts guy says he'll contact the hinge vendor to see if the spacers can be purchased separately. If anyone is ever around Princeton, WV, the Worldwide Equipment Mack folks there will go out of their way to help.

Got the steerable drop axle installed (back in May actually), and after running it for about 3-4 months it seems to be doing great. I put low profile tires on it, but it still drags some when I go across a dip. Haven't gotten hung up yet, but I imagine someday I'll hang the truck up in a creek crossing or something. The wheels so far back actually help keep my knuckleboom outriggers from dragging through the dirt. I was able to add several feet to my overall length, and have 11 feet on the back axle group, so I can haul a decent load of logs now without being overweight (at least in Virginia). Costs: $300 for the used front axle and the ridewell kit $125 for wrong brackets $125 for the right brackets $600 for new low profile tires $225 for the shocks to make it steerable $240 for the controls (it picks up automatically when I put it in reverse) $1200 or so to a friend of mine to install it. plus I just bought some new air bags to keep it lifted up for about $220 today Approx $3000 in all. Better to pay these folks than the motor carrier safety division!!

Recently, the driver side door hinges on my RD 688 log truck sprung to the point where the door was rubbing against the body panel and would barely close. There was an "event" that caused this--I was using the rear mounted knuckleboom with the door open (which I never do, but the latch had just busted), and that can shake the cab around pretty good, so the door was probably flopping around pretty bad.. So insult to injury I have to replace the door latch and the hinges. I did try shimming the hinges, fiddling with the position of the hinge bolts, but when that didn't work I replaced the hinges. Everything's in good order now. No more running the knuckleboom with the door open. The new hinges (and the hinges on the passenger door) have little spacers made out of some kind of high density plastic that slide against the inside of the hinge. After a while, I imagine these things wear out. Can they be replaced to keep the hinge tight and running smoothly? Or when they go does the whole hinge have to be replaced?

Below is a picture of the offending double check valve. It is mounted on a crossmember, driver's side in the vicinity of the quick release valve. The replacement part recommended is the DC4 double check valve, which looks a little different from the original part (below) but it functions the same and is probably a bit sturdier than the old one. Hope this will help someone who may have a similar trouble down the road...

I've got a 94 RD 688S log truck. Something's wrong with the air system. Air pressure builds to 120 in both primary and secondary tanks, but parking brake control button won't push in/release. Air horn and shifter splitter also not getting air. When I drain the air pressure in the secondary tank to less than 30 psi whatever blockage and/or malfunctioning valve "fixes" itself and parking brake controls, air horn, and shifter splitter all commence working. Once secondary pressure builds back up 90psi or so, setting the parking brake just once causes the blockage and/or malfunctioning valve to quit working. No more air horn, no more releasing parking brakes, no splitter shifter, etc... After a day and a half of head scratching, I think I've found a valve on the driver's side (in the vicinity of the quick release valve) that has both secondary and primary air connected to it, with a diaphram held in place with a ring-clip sort of thing. Can anybody tell me what this valve is called? Can anybody suggest whether this might be the answer to my troubles? Any other suggestions? My theory is that it has been cold. I left the truck parked facing uphill (a pretty good hill) for about a week or so in cold weather. The slope caused condensation to run down the line and build up behind the diaphram and then when it froze it pushed that ring-clip out causing the valve to malfunction. But I can come up with a theory for just about anything, except maybe why I would quit a perfectly good job to go into logging

Local heavy truck parts supplier can sell a shock/spring kit for this...Also can sell me an add-on and/or replacement controls that will wire in to my reverse so that the axle will raise automatically when in reverse. Only thing I needed to make sure of is that the kingpins aren't welded fast (they're not, just need a little bit of grease) so the front axle will steer. It will be several more weeks, heck maybe months before I get this put together, but I'll post a photo or two... Thanks again to all of you for your help!

Thanks dirtymilkman and gearhead204. I'll try to post some pics once I get it figured out, and will also report on how/whether it handles any differently, too.

I've been hunting for a steerable lift axle to use as a tag axle on my RD 688S log truck. Want it configured as a tag because I have a heavy knuckleboom loader mounted at the very tail end of the frame, and I can't haul very much payload without being overweight on the axles. Want it steerable because I've been told a non-steerable tag axle will make it impossible to steer on the many curves on our Appalachian mountain roads. Want it cheap b/c, well, there's not much money in logging these days... So I found a used steerable lift axle from a local paving company, with a large fleet of dump trucks. This one was taken off an R-model dump truck before it was sent to the quarry... Best I can tell it looks like someone took a front axle and a lift axle and put the parts together. I'm pretty sure I can't run it like that or it will wobble all over the place... Is there a way to cut the tie rods and attach them to some stiff shocks and/or springs to stiffen the steering up but still allow the axle to steer? Any help would be greatly appreciated..

Hey thanks. Glad I asked before I pulled it apart any further. Only thing I've lost is the time spent pulling up the floor panel.

I've got a 94 Mack RD688 log truck that I purchased this spring. Since the weather got cold, the splitter selector won't work when it's cold. By won't work, I mean it won't put the transmission into underdrive when the splitter button is in the down position. All that happens is I hear air escaping out of what I presume is an air relief hose... Once I've run a few miles (10 minutes or so) with the splitter in normal drive (over drive?) and I presume things are all warmed up, when I split a gear, I hear no sound of air escaping, and the transmission splits just fine. On a hunch, I pulled up the floor and put a space heater on what I presume to be a control valve unit on the top of the transmission (this has 2 small air lines coming from the splitter selector and 2 large air lines going to what I presume is the actual splitter unit on the rear of the transmission). After about an hour, it warmed up and splitter seemed to worked ok again. My question is--does this sound like something as simple as water from the compressor system in the air line and freezing? or does this sound like something wrong with the control valve unit? I'm running air brake antifreeze in my air system...is there a way to ensure this antifreeze gets to the control valve unit to keep this from freezing up? Any help would be greatly appreciated...