MR688S

MC - Thanks for the info. I'll stay with Red Engines on my OTR Tractors. Meanwhile, I'm playing with two Mack MR688S COE tandem axle 80K Tractors with the Renault E-7 E-Tech Engine - 2006, 2007, just before the M-7 came out, well, a "special" US Postal Service Contract run of the COE's. At least they have DAVCO FuelFilter/Water Separators - easy to drain, swap filters, fill and GO! I'm still looking for E-Tech E-7 Manuals to show how to flash the ECU to get the governor turned up or off. All the Best!

Also, MC you mention Mercedes - as in Freightliner Cascadias with the "DD" 15??? It appears that once Mercedes was given Detroit Diesel, they just canned the Series 60 and put up the Mercedes engine and called it a DD whatever. I see lots of plastic and aluminum parts on those engines and they scare me. I saw a video of the top end aluminum cam/rocker holder blocks having their hold down bolts just strip out of the aluminum blocks with helicoils gone bad that are supposed to hold them in place. Why would they put aluminum on such an important part of the engine. When the bolts go, the engine becomes pretty useless. I would have a hard time trusting the repair on those blocks after that. Have you experienced this? Let me know what you think. All the Best!

Thanks MC. I'll see what the local Volvo/Mack people say about that and the price. I run mostly Cummins ISX15's in Internatiional Prostars and I'm happy with them as long as we keep the EGR/DPF Systems clean. These Macks are for a local haul contract that's fairly casual, so, they're not going to be running all the time and we can do maint. on them easily.

Hi, I bought a Mack Postal Service 2006 MR688S and a 2007 MR688P 6x4 and 4x2 COE Tractors and I'm looking for any manuals on them or spec sheets, build sheets, etc... They're running fine, but I like to have the info for maint., etc... I also want to change the E-7 Engine ECU Governor to allow a higher RPM than 1700. Got a response from a Postal Driver that the service raised the trucks he was driving to 2100 RPM. Any later model MR688 people out there with knowledge of the trucks - I'd love to pick your brain for a bit. THANKS! Tomm in Nevada

Hi, looking for an operators manual and a service manual for a 2006 Mack MR688S COE 4x6 Postal Tractor with the E-7 12 Litre Renault Engine and Allison 6 speed Auto Transmission. Real manuals or digital files/CD-ROM's, websites, whatever, as long as I can read them and get info from them. I'm happy to buy the info at reasonable prices. No rush. Here's a pic of what the truck looks like. Thanks!

If there are any MR owners out there who have specs and a service manual, it would be good to chat with you. I've got the truck running smooth and the cab tilting and able to get all the fluids changed and clean her up. The only thing remaining is driveline vibration under torque. If anyone knows of common MR problems in this area it would be good to hear. I'm changing all the U-Joints and the Carrier Bearing for starters and we'll see if things improve. Then, if it needs more attention, I'll get into pinion bearing adjustment and rear transmission yoke issues, etc... Thanks All!

Ah, I understand now - the custom MR is just a pic you found, not your truck. I'll stop bugging you about MR specs, etc... All the Best!

GHG - Good to know about the 2100 RPM on a 1996 MR. I found a manual for the Postal MR, so, I'll have more info soon. Thanks!

The only problem I see now is driveline vibration. She gets a vibration under torque in high gear going up hills or stronger acceleration. I let off to keep it from being too drastic. I'm putting in all new U-Joints and a Carrier Bearing and checking yoke positions. If that doesn't fix it, I'll look at pinion bearing adjustment and rear trans yoke for play. I had the rear axle locked out, so, I don't think it's the power divider. Please let me know if you've seen any of these problems. I think it's just the Postal Service letting one of their older units go out to pasture and not worth spending time for maint.

Is yours an Automatic? Mine is and it's governed at 60 mph/1700rpm. Have you or anyone you know removed the governor/ECU Flash, etc...? I'd like to get it to at least 63 mph in the 1800 rpm area. I understand the Renault E-7 engine doesn't like to go over 1800 rpm. I don't know until I get a proper manual on this truck. Meanwhile, I'll definitely respect that. Thanks! I started another thread this week on troubleshooting engine issues at the pickup site. After cleaning the DAVCO Fuel Filter/Water Separator, draining the main fuel tank of any water and gunk, and replacing the DAVCO fuel filter, she came back to life and within 10 min was running on all cylinders. I put some Howles Fuel Conditioner in the main tank with the first fill-up and she's purring now. (I learned the hard way that the two filters on the bottom of the engine on the left/USA Driver's side were OIL Filters after reading everywhere that they were fuel filters... I really have to get a shop manual for this rig! All Good! I learned in 103 degree dust devils in the desert and I won't forget what I found.) The cab lift hand pump worked in the raise position - it just took about 20 pumps to get her primed back up and now she lifts fine and I can drop the safety lock arm, etc... The undercarriage was a total MESS! The truck has the auto-greasing system and it's 2 liter reservoir is currently empty, so, it looks like they never cleaned any of the excess grease on the undercarriage and that is covered with a half-inch of dirt. I'll be steam cleaning the undercarriage this weekend and then doing a low pressure degrease on the engine to see the basic parts and look for any leaks, broken wires, etc... How was yours when you got it?

Oh yeah, I forgot to mention that all the diagrams online for the Mack E-7 engine show and say that the two filters under the left/USA driver's side of the engine are Fuel Filters. They even give a fuel filter part number for them. I reality, they're OIL FILTERS on that tandem manifold. Looks like all the fuel is filtered through the DAVCO Unit and that's it. If anyone knows of other placements of secondary fuel flters on the E-7 Renault engine, please let me know. I haven't been looking real hard after removing the two oil filters and getting them back on the engine and getting the DAVCO unit working properly with a new filter and cleaning. It will be nice to know that I've hit every filter that's in that system and there are no other variables. Thanks!

Miami Cossack - Thanks for the reply. I rebuild wrecks and work on engines all the time. OJT Mack school was cool. I learned that the Postal guys don't do much maint beyond oil, filters, belts, etc... the truck was never cleaned, caked with dirt and grease on the suspension, engine, etc... I'm not for pressure washing engines, but some degreaser and a bit of water from the garden hose goes a long way. I'm steam pressure washing the undercarriage and detailing the engine this weekend. I spent time on the Davco Filter/Separator and found some gunk in the ball check valve that was letting the reservoir drain around the filter. She's staying full now. This unit is governed at 60 mph/1700 rpm with the Allison Automatic 6 speed. (I'd tell you the model number, but it's so covered with dusty oil gunk, that I've decided to clean it before I start looking for the label and all those details. It's probably an HT4060, but we'll see when we see. It's definitely electronically controlled. Anybody ever shut off the governor on one of these units? I understand the E7 doesn't like to go over 1800 rpm, but I'd like to get in that neighborhood for a 63mph cruise at least. I predict it's an ECU re-program. If you've done one, please let me know. The only other large item to deal with is driveline vibration. This truck has 458,000 miles and it appears that the U-joints may never have been changed, and possibly not greased very much. The truck has a large auto greasing system, but the grease reservoir is basically empty. Looks like it takes about 2 liters of grease. I'm sure the carrier bearing is not a happy camper either. The vibration comes under torque, usually uphill in high gear when I put a bit more power to her. I'm going to just start swapping the u-joints and carrier bearing and checking the driveshaft yoke positions, then look at pinion bearing adjustment and transmission yoke play, etc... somewhere in there things are pretty loose. I lost a driveshaft due to u-joint death in my old 58 Chevy Suburban when I was dumb and in college and this vibration sounds the same, just tandem axle bigger. If there are any common Mack MR688 problems related to any of this stuff, everyone, please feel free to jump in with your suggestions. Thanks to everyone for reading and responding to this project!

41 Chey - thanks for the reply. I put myself through Mack school that day and that filter water separator was a complete locked up mess the bottom of the unit was black we cleaned it all out with brake cleaner and got it I got a new filter in truck started right up it’s been running great ever since it’s got a little air leak in the in the Davco fuel filter separator it drops down about an inch every man every two hours so we’re gonna work on that and see where the leak is it’s not a not an external leaks but other than that the trucks running great now

Throttle response. I just got this MR688S out of the Postal delivery yard this morning and it limped out missing on one or two cylinders. I took it for a test drive on a back road about a mile and it got progressively worse and now just idles with very little throttle response. Trans was good. Air cleaner clean. Now, looking at clogged fuel filter/s on the drivers side of the engine. The unit also has a DAVCO clear external filter - I don’t know what it does beyond being the first filter, then fuel goes over to the engine filters. Any thoughts? Thanks!

Hi Terry T and other Mack E7 experts: I got delivery of the 2006 Postal MR688S and she runs but has a misfire and I drove it about a mile and it’s losing power and very little throttle response. I’m thinking fuel delivery issue - clogged fuel filter, etc... I checked the air filter and it’s clean, Donaldson can is clean. Any thoughts? I’m getting the cab to tilt open and then I’ll have a look around the engine room. Thanks!

In the pics of the MR, it looks like mine has an electric pump lifting the cab and a manual pump for emergencies. The batteries were dead from sitting and they jumped it. I wonder if they just didn't try the lift pump with the engine on. I'll get into it when I get there - probably something stupid simple. Bringing a couple gallons of Delvac to get her back to the shop, if needed. Then, we'll change out all the fluids and go from there. I'm a driveline first guy, then, we make it pretty. Here's a pic of my little '97 International 4700 LP. Just basic stuff, DT466, Allison 3060. It was T-Boned and pushed into a ditch by a big rig. I brought it back to a normal working truck and put the sleeper on it so I can stop when I want to. Been driving it for 5 years. More later.

Gone Postal!!! Amazing looking COE! Roof Air Conditioning? Where do you get the full rear fenders? I've seen a bunch of vintage trucks going into Reno last year for the historic truck meet and they were amazing! I found another 60's conventional Mack with the Flat Front Grill and I may restore that, too. What is the normal horsepower/torque for the Postal E7? Have you done anything to the engine? Nice chrome and silver work. I've been considering where to put the Bulldog and your placement looks good! How many gallons is the single side tank - stock? Yours looks a bit bigger... Thanks for the pic! I'd love to stay in touch and pick your brain. Oh yeah, my truck's cab lift pump appears to be out of fluid in the reservoir, does it take ATF? Hydro Fluid? Brake Fluid? Any easy way to bleed it, or will it work itself out? All the Best!

Terry T - yes exactly. Runs and drives, 8k hours on it. E7 12L Allison Automatic, probably a 4060 or larger for the tandem axle rigs. I'll see it the first time on Monday. Getting the rescue kit together. We'll get the cab tilted, check the engine compartment out and do a full walk around and fix whatever needs fixing, then take a test run to see if she stays cool, has proper power, etc... if good, we'll take her a couple hours away to the shop. More details later. I have another post looking for a manual that shows more pics, etc...

kscarbel2 - Thank you!

Hi All, I have a new to me MR688S Postal 4x6 COE Tractor 2006/7 that they can't get the cab up to tilt, etc... I'm looking for instructions and or a design diagram or how the system works, like, is it a manual pump or electric/hydraulic, spring lift, is there a lock switch/lever hidden somewhere, etc...? Also, any troubleshooting info, any common problems with this system, etc... I'm picking up the truck on Monday and I'd like to be armed with info to get the cab tilted and be able to check the oil, coolant, belts, etc... basic walk around inspection, etc... I'm a good mechanic and rebuild trucks, cars, and motorcycles from wrecks, etc... so, I'll understand the system once I see how it's put together. Thank you so much!

The first thing I want is a Bulldog in the center of the nose or up on the roof.

There were only two of them in tandem axle and the other was a non-runner. There may be more, but I only needed one. If you have any E-7 engine info beyond specs, I'm interested in finding a service manual, maint. interval chart, etc... I'll get a line card from the local dealer soon. Thanks for the reply!

Hi All, I bought an '06 MACK MR688S COE Tandem Axle Road Tractor with 8800 hrs. on it to do general short haul runs with a 53' dry van hauling lightweight/high cube material. It has the E7 engine and an Allison 6 speed auto trans., class 8, air brakes, etc... It's a former US Postal Vehicle, so, not sure how good the maint. and daily treatment was and I'm going to go through it and do all maint. and checks. It runs well right now, but I'm a preventative maint. nut because I don't like to breakdown on the road. If any of you can let me know your experiences with the E-7 12 liter engine or direct me to online specs, common issues reports, etc... that would be great! Thanks!