JoeH

A thread chaser might be handy for the end of the trunnion bar. Ours was pretty worn away, but we managed to chase some threads clean enough for the clamp to thread back on.... Remember, the bar hangs from the spring. So put cribbing under the bar before cutting u bolts.

Sorry I was basing it off this conversation from several years ago.

Looks like they start on 44k setups?... Don't know if they make 38k versions. Also I havent seen any weight ratings listed on any of the quick research I just did. So I wouldn't trust it as far as I could throw it. 38k is a bit light weight for off-road dump truck work, but we have a 1979 volumetric concrete mixer truck we have had since 1986. Same 38k rears, the suspension has held up very well. It just got new rear springs a couple years ago, one side was sagging, other side finally broke a leaf. Now that you know what breaks to look for I'd say run it. Also, the trunnion bars do break sometimes. We had one break on our 58k setup between the saddle and the stand.

Top bar and bottom bar on 2003 MR688S. I'd figure it takes any twist out of the frame by creating a "box" support structure. Battery box on one side, fuel on the other, and it's about 2 feet forward of where the splay starts in the frame to go around engine/trans. I think I heard a few years ago that at one point Mack had frames cracking oddly, so they tweaked cab mount design and probably added these frame stiffeners.

My top bar isn't any heavier than the lower bar.

Mildest winter we've had in PA in a long time. Gonna be 85 for the rest of the week here near Philly.

I always figured they help with frame stress where the frame splays out around the engine and trans. My MR688 has 2 of those bars, one below, bolted to a bracket on the rear spring hangers, and a second one that goes across the top above the trans, right behind the engine.

They are rubber/nylon bushing saddles, you can see the tube/bolt sticking out. Look for broken U bolt on the inside of the spring pack, down IN! the saddle holes. Our broken U bolt had rusted thin down inside the hole and thus the break was in there, where you can't see it unless you know to look for it.

The U bolts keep them from fanning out. I suppose you could have a broken U bolt, we did have one of those a couple years ago. But we also had broken springs develop on that same truck. The U bolts keep the springs sandwiched with thousands of pounds of force. The only way the springs could slop around is broken leaves, or stretched/broken U bolts.

I'll let your imagination figure out what happens when all 3 bottom leaves break and the one axle disconnects from the spring pack. Remember the springs "hang" from the axles, so that side will hit the ground.

I'd be jacking that truck up and cutting the u bolts to inspect leaves. After I ordered a new spring pack. And you'll want to do both spring packs at the same time, otherwise one side of the truck will ride higher than the other.

Those leaves probably are broken, the breaks are likely hiding behind the u bolts.

Stock that engine should make 30+ psi of boost. If you were making less than that then I'd suspect boost leak. Our 95 E7-350 had dropped down below 25 psi, so we checked for leaks and found a nice long crack down the weld on the charge-air-cooler.

Did you lube the fuel filter O-rings before putting them on?

What's the history of this truck? Have you owned it long? Did you buy it with this problem? Did the problem start after having the brakes replaced? Joey may be on to something with that frame twist. Looking at it, it would appear the frame is twisted in such a way to apply the least weight to the passenger rear wheels. Typically trucks have ABS on the steer and the front drive axles, not on the rear drive axle. So your ABS would of course do nothing in this situation.

Any chance of swiping the oil pickup off the truck you're getting the pan from? I doubt the pickups are different depending on pan. Only differences I could foresee would be based on sump positioning. The pan and oil pump assembly can be flipped end for end depending on front axle to engine positioning, but I don't recall if there was a "center sump" oil pan.

My first though was compression ring, but that'd have a hard time getting out and dropping down. Looks like it's a bimetal piece, 2 separate colored metals appear to make up the piece.

I wouldn't mess with the filters. Leave it as is.

ESI (extended service interval) package is a 2 filter set up, 36qt oil change I believe. 32 qt pan, 2 qts per filter. ESI+ is the 3 filter setup. 6qts total in the filters, and about 50qts in the oil pan. 56 qt oil change, every oil change is more expensive, but you can go something like 25k miles between oil changes. It was an option for cross country tractors to increase uptime. For local/off-road I'd go with the smaller pan, better ground clearance on rough terrain and cheaper oil changes. Especially if you're not putting 50k+ miles on the truck per year.

Oil "level" is the same, so suction elevation should be the same. The deeper high capacity oil pan allows you to go further between oil changes, and is accompanied by a third oil filter, giving you extra filtration capacity for that extended oil change interval.

I'd bet a few bolts walked out, and the remaining bolt that stayed in finally had enough and snapped. Again, these bolts are supposed to have locktite, and the mechanic probably reused the bolts without putting any on. Certain bolts come from Mack with locktite already on them.

Having trouble seeing exactly what's going on with the bolts... One sheared off and the other walked out?... They're supposed to have locktite on them I think, so they can't walk loose.... if they walk loose they're subject to all sorts of fatigue as the engine/trans flex under power. It's not "normal wear and tear", I'd suspect it wasn't put together properly when the trans was replaced. We're getting ready to retire our 1979 mack, it has a trans bracket that keeps coming loose on the aluminum bell housing. 1 bolt hole is stripped out and the other 3 keep walking out.

Google Street View of the intersection doesn't show any low ground clearance signage, I'd be harping after the municipality and CSX that they should have had signs up with minimum ground clearance requirement signs. I've never driven a low boy, but I have seen ground clearance signs for exactly this type of thing...

The gal in the car summed it up about right: "oooohhh noooo....."

He probably has big brakes. Our 1980 dm686sx has 18"? Brakes instead of the standard 16"? Brakes. Truck always had great stopping power. I wish more trucks had them.