Help! MR688S COE Cab Lift Instructions/Diagram

[MR688S]

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!  

[kscarbel2]

The cab hydraulic lift cylinder is atop the right front fender, under the muffler. Flip the lever direction and pump.

[MR688S]

kscarbel2 -  Thank you!

[kscarbel2]

23 minutes ago, MR688S said:

kscarbel2 -  Thank you!

No worries......we aim to please.

Nice truck !

[Terry T]

Looks to be ex-postal service unit.

[MR688S]

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...

[Terry T]

This is also ex-USPS

[MR688S]

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]

Not mine, just one that I've seen on websites and the net. Very well done and "rodding" an MR... It's just not done so to me it's very cool!  Thinking outside the box is something that I appreciate very much.

[MR688S]

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.

[MR688S]

On 8/21/2020 at 8:31 AM, Terry T said:

Looks to be ex-postal service unit.

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!

[MR688S]

On 8/21/2020 at 9:06 AM, Terry T said:

Not mine, just one that I've seen on websites and the net. Very well done and "rodding" an MR... It's just not done so to me it's very cool!  Thinking outside the box is something that I appreciate very much.

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?

[MR688S]

On 8/21/2020 at 9:06 AM, Terry T said:

Not mine, just one that I've seen on websites and the net. Very well done and "rodding" an MR... It's just not done so to me it's very cool!  Thinking outside the box is something that I appreciate very much.

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. 

[MR688S]

16 minutes ago, GHG said:

I drove a 1996 Postal MR like that, they were a custom build so a lot of stuff is in different places that where the manual shows. Mack made up a custom manual for these trucks, keep your eyes out for one. I'm not sure about the later engines, but when they raised the speed limits above 55 all our MRs got the governors reprogrammed from 1800 to 2100 RPM. Best of luck with your MR!

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!

[MR688S]

On 8/21/2020 at 9:06 AM, Terry T said:

Not mine, just one that I've seen on websites and the net. Very well done and "rodding" an MR... It's just not done so to me it's very cool!  Thinking outside the box is something that I appreciate very much.

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!

[MR688S]

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!