JoeH

Welcome to the MR688 club! I bought a 2003 MR688S with the AI350 almost 3 years ago and I love it! Except for the ride. It is rough on your back on highways. Tires likely aren't rated for more than 60mph, I had one come apart when I was doing 68 mph on my way back to PA from Iowa after getting a new volumetric concrete mixer body put on it. Personally I'd get the truck towed home, I wouldn't drive it. Fuses are all in the center console, there *should* be a decal in there telling which fuse is where, but I'm sure it's missing. Worth it's weight in gold is a flashdrive, Mack part number 23-021. It's available through the Mack eMedia website. I got it through my local Mack Dealer but I had to talk him into the EMedia site so he could see what I was talking about about. Listed as a DVD, it's a program with wiring diagram for every Mack chassis model from like 2001 to 2021. You can use Killem, but that doesn't dissolve the algae. You have some work to do to get clean fuel. You could also have a piece of trash floating around in the tank, getting sucked into the pickup tube occasionally. Active engine codes can be pulled out on the fly by holding the set/decel cruise control switch down for a second while the main on/off cruise rocker is off. It'll blink out a 2 digit code telling you what the fault is. I hope you got the truck for a steal, trash trucks of this vintage are mostly falling apart. We got lucky finding ours with good frame rails at 24,000+ hours and 414,000 miles. We pulled the frame out of ours and separated/sand blasted/painted them to clear up the rust jacking.

I've recently heard of the setups you mentioned being operated by leaving the truck off in reverse and using a remote starter button to back the truck up to the draw bar. But this system I'm asking about the truck is running so you can operate the mixer while moving the truck around the jobsite just from that joystick on the back.

What's it cost, how's it integrate? How does it hook up to the drive line to move the truck? How's it hook up to the steering?

A couple times now I've come across references to "remote chassis control" and seen pictures with this box mounted on the back of the truck. It appears to be a control box to crawl/steer the truck along while operating the concrete mixer on the back of the truck. Does anyone have any knowledge of a system like this and how it integrated into the chassis?

They could take notes, they couldn't have premade notes.

The 1975 is going to have a 2valve ENDT675 or 676 engine. Virtually the same block, but there are some differences. Mostly I think there were bottom end reinforcing changes over time, and the head bolt quantity changed at some point. It'll bolt right in, but it'll be a weaker engine. 675 is a 237 HP engine, 676 is 283 HP.

Are there any parts differences? My 2003 MR688S is a bit of a dog. The 1480 ft lbs with 60% torque rise sounds nicer than I forget what the 350's torque with like 30% torque rise. Would be nice if all I have to do is get the dealer to reprogram the EECU. It's paired to an Allison HD4560, which according to the Allison sheet I looked up seems to be rated for 500hp/1680 ft lbs. Not sure if the spec sheet is for a newer generation 4500 series or if it covers mine.

https://macktrucks.vg-emedia.com/ProductDetail.aspx?ProductId=6302 You can also buy this through your local Mack Dealer, though I had to talk my parts guy through the EMedia website so he could find it to order it. It's a flashdrive, not a DVD. Worth it's weight in gold, has every chassis model from 2000ish to about 2021.

Go to the Mack EMedia website and search for book 8-211, click View File. Everything you need should be in it.

Could you imagine being shot wearing that? You're basically guaranteeing further injury by having one of your own bullets exploding against you, lol.

Congratulations on the baby and the truck too! We have a 79 R686ST, fantastic truck, but ours has reached the end of it's hard working days. We just had our 5th 4 months ago.

If you need weight capacity/more surface contact to the ground you can run 315 dualies on 9"x22.5" rims. Tires rated usually from 8600 lbs to 10,000 lbs. 9"x22.5" rims are rated for 10,000 lbs, 8.25" rims are rated for 7500 lbs. I have a former trash truck now Volumetric Concrete Mixer that has 315's on the drives and lift, and I put 425's on the steering axle (rated around 12,000 lbs).

Short of finding a good 5 speed that matches, staying with a manual trans of some variation makes the most sense.

Have you put a test light to the wires on the headlight plugs? It is possible both highbeam filaments have failed. Just trying to think simplest/cheapest.

It is possible someone wired everything onto the one switch on the right, but the switch isn't rated for that much electricity to go through it. Unless they wired it to control a relay instead. I know headlight switches melting is a common problem on older pickups, so they sell aftermarket relay kits where the headlight switch controls the relays instead.

If you pick up that book I mentioned earlier it should largely have everything you need diagram-wise.

You're missing your clearance lamp switch to the left of the dimmer. The switch to the right of the dimmer is park lamps down and park/headlights up. Middle is off. The Signal switch up top to left of steering wheel is forward flashes headlights, backward flashes taillights. Center dimmer switch controls the dash gauge brightness.

Gear ratios should be stamped into the differentials. You can reach out to the Mack Museum in Macungie to get info on what tires the truck was originally built with.

Headlight hi/lo beam switch should be a button on the floor, for your left foot to push. Is this the dimmer switch you're referring to or are you talking about the dash mounted interior lights dimmer?... Just want to make sure we're talking about the right switches here.

What year are truck/engine is it?

I like closed shoulder/open center for my tire treads. Closed shoulder really helps each pair of tires to wear evenly. Open center gives that occasionally needed off-road grip. We replace tires one pair at a time. New pair goes on, old pair goes out to get capped, then it'll replace the next pair to get thin or blow a tire.

Is the software/EECU the same? Id expect some minor brand software differences.

Pictures don't show you much other than a plethora of wires. Double check, but I don't think there's any TCM. Just data sensors for the engine ECU. Trans temp, neutral safety switch, VSS, etc. You can see the PTO plate on top. Your best bet on donor will be a trash truck or an Oshkosh front discharge concrete truck. I have a 2000 MR688 cutoff with the HT740 cable shift, my 2003 MR688 has an HD4560 which has all sorts of electronics onboard. Pictures not posting, I'll try and get them up....

Any codes? Long cranks before start sometimes means your either your cam or crank position sensor isn't reading.

Vmac I, ii or III is which generation of electronics the truck has.