JoeH

Usually takes us a day or two to get it out, and another 3 days of rocking the transmission back and forth and up and down to finally get the input shaft into the pilot bearing. 😱

When we pulled the allison transmission out of our MR688 2 years ago we had the whole thing out and back in in one day! That MR is the easiest thing to work on. Our 1980 DM is about the hardest thing to work on. Don't recall how hard the clutch was on our DM, but it might not be too bad.

Our R models we usually stick a heavy wall pipe through the windows and hang the pipe from the roof with a rope going back and forth a bunch of times.  Gives us a beam crane for our chain hoist inside the cab to hang the transmission from.

I'm really itching to flag a manager down at home Depot when I'm in self checkout to tell them I expect an employee discount if I'm gonna be doing their job for them.

We usually take a fuel tank off the truck so we can get the transmission out from underneath, but if all you're doing is a clutch then you may not need to.

The Mack triple shaft transmissions sit like a V , it will want to fall over on a trans jack, so a cradle is a must have! 

Do yourself a favor and replace the rear cab mount bushings, we just did on our '79 R model and gained more than an inch of height back. Makes a lot of difference when you're working in tight spaces.

Access to a helper is strongly recommended, there's a number of things that really need 2 people.

On 11/29/2023 at 6:36 PM, mjrays said:

Thank you for your help this is my first mack 688s been around truck awhile now picked this up short money was sitting about a year and half guy swears ran fine when parked (company closed up shit just sat ) 

Inquiring minds want to know how you're making out!

https://maps.app.goo.gl/ea5bGe6WJHoKPRKL6

A&R industrial is near you, no idea what their reputation is.

If you're confident you can do the repair yourself then get it apart, take your old clutch to them and they can order you a new one based on the parts you show them. Assuming they're the friendly and knowledgeable type.

If you aren't confident then you could just have them do the repair.

I'd plumb them in parallel, not in series.  In series, the first filter catches everything and clogs, leaving your other filters clean and useless. In parallel, the oil can go through either set of filters, so you're actually getting the use out of having that many filters.

Get it sorted out before you get a runaway motor that starts running on its fuel diluted engine oil...

I believe there's a fuel gallery plug under the timing cover that can work loose.  Not sure if you can get to it without taking the timing cover off.

If it doesn't already have one, it's worth putting an intake boost gauge on the truck at some point. The charge air cooler in front of the radiator cracks along the welds every once in a while. My E7-350 was only making 25psi boost and running hot on the pyrometer. Found cracked CAC, replaced, and now it'll push well passed 30, close to 35 psi boost. And much cooler EGT's.

But we'll sort out your current problems first.

That is a nice looking truck, I'm a sucker for R models.

About 3-4 screws on that top piece of the dash above the rpm/mph gauges and you should have access to those 2 little lights in the center. Looks like one "fell out" (tampered with most likely). Light socket will be laying just inside, and I believe it should have a little tag on it saying what its for.  Get a good bulb stuck in the Engine Malfunction Lamp socket and turn the key to the "On" position. EML 'should' turn on briefly then turn off, indicating that the light works and there's no "Active Faults". If it stays on then you have active fault codes which can be retrieved by holding the set/resume cruise control rocker in the down position. Count the blinks to get a 2 digit code, write the code down and rock the switch down again to retrieve the next code. Post the codes here and Joey will straighten you out! 

One thing worth noting is ECU locations:

 The Engine ECU is located under the stainless covers below the turbo. This ECU is weatherproof, but there is a recall on the Coolant Level Sensor because the sensor can fail and let coolant wick along inside the copper wire and corrode the EECU pins. Not sure if this problem affected the early ETECH engines or just the later ones. Be careful when doing any mechanical work, that ECU can get pinched when replacing engine mount bushings or replacing clutch etc.  A small dent in that ECU and it's toast.

The Vehicle ECU is located on the kick panel in front of passenger's feet.  DO NOT drill holes into that panel without first checking VECU location. Idk why you'd drill holes in the panel but I hear it's been done before.  The VECU is not weatherproof, and rain water can leak through windshield gasket/firewall and get onto the VECU, frying it.

These are great engines and I think it's one of the best computer systems you can have on a truck because of the blink code diagnostics.  There's no need for computer software that costs thousands of dollars to find out what's wrong with it. In fact, Mack/Volvo released the diagnostic software for these computers for free, you just need to download it from somewhere like "DieselLaptops.com"  and buy a roughly $750 device that has the cable ends and interface device to link a laptop and the truck computer together. Diesel Laptops also has their own program 'Diesel Explorer' that is pretty good. It'll give you a lot of data, it'll tell you what ECU's are powered up/communicating, which helped me identify why I couldn't get my 2003 ETECH to start.  The EECU wasn't getting power, and I didn't know that til I couldn't see it listed in their software.

59 minutes ago, Joey Mack said:

It may be best for me to leave this thread.  Good luck sir..   Jojo

Don't leave it, you know too much to do that. But he's gotta let us know if the EML light is working properly. I bought a 2001 RD vmac III once that someone pulled the lightbulb out to mask about 10 active fault codes. The blink code system is a great ally, if it's functional and hasn't been tampered with.

Before you go digging all around, you really should update us on the functionality of the check engine light circuit. If either of those sensors are bad it'll light up the lightning bolt dash EML.

Do you have any Engine Malfunction Light codes? Lightning bolt indicator should come on initially when the key is turned on. If not, fix that lightbulb so you know if you are getting a fault code.

If that circuit works and the light is on, with key on (engine can be running or off, doesn't matter) turn cruise control "off" then hold the set/accel / resume/decel rocker switch in the down position til the lightning bolt turns off. It'll then spit out a 2 digit blink code. Write the code down, hit the rocker again to request next code. Keep doing that til it loops and keeps playing the same pattern of codes.

Is there a parts source for individual parts like round fuel tanks, engines, etc?

I see AMT has an R685ST model with the 237 HP motor, but is there one with the engine mounted charge air cooler?  Toying with the idea of making a model of my dad's volumetric mixer truck.

Paging @SkippyMack the old timers want an update on the truck

The appear to only have the one form of electronic schematics, nothing older.

However if you run a broad search like this: 

Then you'll be rewarded with about 4 pages of different books for different years. Off on the left they list a few different age categories of trucks, I didn't search the Legacy category to see if there was anything there.

You'll be rewarded with things like this: 

That have an SKU that's completely useless to the dealer til they find it in the emedia search function themselves.

No, at my Dealer, Bergeys.

Can't speak for your truck, but the bottom picture looks like every pair of rear mount bushings we've had.  Torch or undo top of bolts, jack up the trans high enough you can chase out whatever remains of the old bushings, and then drop two rubber bushings and washers into the top two holes on each side in the frame bracket, lower trans most of the way, then put the bolt/washer/bushings in from the bottom and pit the nut on top. Its kind of a two person job.

Can't speak for the front engine mount bushings, the engines I have use a rubber donut around the front of the timing cover at the crank hub.

Snap a picture of the brackets you have and we can yay or nay one style or the other for grommets.