Doffer

thanks guys, I haven't got a chance to check anything out yet. Im trading the truck in for another one tomorrow, so hopefully the mechanic will get a chance to check it over before he trades it off. Sometimes it sucks because it feels like its not going to start

Oh really? I didn't know this. I was pretty much just thrown onto a truck after I got my CDL and they said "Good Luck!" LOL

I would love to polish my rims, but I dont have an air compressor strong enough to remove them

Every once in a while my 2003 Mack MR688S cabover truck takes about 10 seconds to start up of continuous cranking. Other times it just starts right up.

Is there any way to test certain things on the engine to determine what is bad without Special Service Tools, or hooking the truck up to a computer ?

What would be some good things to check out ?

Thanks!

My Engine brake isn't disengaging when its cold for some reason. When I am using the engine brake and then hit the throttle the exhaust makes a weird noise (kind of like the engine brake is still engaged, but only partially), blows out all kinds of smoke and bangs and pops blowing flames out the exhaust then the engine brake turns off and it runs normal. When the engine warms up, there is no issue with the engine brake.

Its a 1999 Mack RD688S

What is causing this ?????

Okay, well I went up and picked up the valve today and it was $85.49 with a $25.00 core.

got to my shop, and started trying to get the brake pedal off the truck. Holy cow that was difficult to do!!! The pin that the pedal is attached to the bracket was seized in place. I ended up using a torch and heated up the bracket (catching the truck on fire once, but quickly extinguished with a water hose I had close by) and once it was hot, I drenched the pin with PB blaster and and broke free. I kept working it back and fourth and then started to remove the pin. got it out without breaking the bracket!!

then pulled the plunger and saw that it was in pretty bad shape, so I put it on the wire wheel and cleaned it up then coated it with antiseize. coated the steel pin as well, cleaned out all the dirt around the brake pedal area by blowing air in and around it and re-installed everything.

Tested the pedal and it now feels great!

Luckily the plunger was just at fault for now. I am keeping the Valve on my shelf just in case the valve body decides to take a crap on me.

I have a quick question. I am working on a 2003 mack MR688s and the brake pedal is rock hard, not spongy at all like normal air brakes.

I've tried to clean the valve, but it doesn't help at all.

Is this valve pretty simple to replace? I talked to a mechanic and he said that you should replace the bracket with the valve because the brackets tend to break.

What does the valve look like when removed?

Mack told me the part was like $60.00, but the mechanic said the valves normally are $200-$300.00 so I may have told him to get me the wrong part?

I told him I needed a treadle valve for the brakes.

ended up being the alternator was bad, and the connection to the starter was bad.

I'll try it out and report back

That is a new way of doing it.

do you think that would work pretty good?

I have an annoying air leak on my 2001 mack RD688S Cab-Over pump truck. The Secondary tank is holding air, but the primary is leaking off when sitting overnight. Can i dump some UV Dye into the tank and wait for it to leak off then check all the air lines with a UV light, or will the UV dye hurt something?

maybe, I would think unlikly through but it should be checked to see if it shorted, check the battery cables and end connections and the starter connections, if hitting it made a diffrence and you said the jumper cables provided power it is being lost somewhere the clicking I think is a circuit breaker, If it was me I would check all electrical connections and clean them for corrision and add some dielectric grease to keep out the moisture and corriosion.

BTW I think the alternator is probably good but since they are working in the front have them test it then you know for sure.

Yeah I told the Mech. not to spend too much time on the truck anyways because its going to be expensive with just the work thats being done right now. So he may not be able to find the problem. He said he was going to pull all the connections and clean them, test the alternator and check around the cab for bad grounds.

Well, I was looking around the firewall area under the hood and saw the starter relay was loose. I took the bolt out, cleaned up around it, and re-bolted it securely. Seemed like everything was good until I started driving it to a repair shop for weld repairs. While driving, first the volt meter started reading low (10V), then going about 55MPH, 16,000 RPM it was randomly cutting out (loosing power) to the engine, dash, radio, lights, heater. The dash needles were going from 55MPH to 0 then click sound, popping back up to 55MPH then 0 then stayed at 0 with no power at all. Pulled off to the side of the road, threw the 4 ways on. Which that did absolutely nothing..... and popped the hood. I had a vehicle following me, and I told them to pull up next to me and put jumper cables from the battery directly to the power on the starter. When I did that, I immediately got power to the cab volt meter was reading 14 and it cranked right over. Once it started, I sat for a minute, drove about a half mile, then it broke down again. This time I got pissed, and I took a ratchet handle and smacked the starter, and that gave it power again for some reason. I turned the headlights off and let it idle for a couple minutes, then started driving. This time, it made it the whole way to where I was going. One thing I did notice was that there was water leaking from the windshield onto the dashboard on the passenger side. I pulled the heater relay out and it looked wet underneath.

Do you think that the water dripping down could have been causing me all these problems all along? There definitely is an issue with the charging system right now, but the alternator looks almost like its brand new. I have it at a repair shop right now to change out the radiator, 2 brake chambers, windshield, and rear drums right now. I told him if he can figure out the problem that would be awesome too. But any suggestions I could give the guy would be greatly appreciated

well i haven't had a chance to look at it yet! I had to go on a job this morning. I'll check out everything tomorrow. nothing going on as of yet

I just thought of that it sounds like a bad ground. To check it take a pair of jumper cables and attach them to the cab and attach the other end to the frame and then try it and see what happens. If this is the problem, run a ground wire from the frame to the cab.

makes sense. I'll check all this stuff out tomorrow when im down at the shop. Hope its an easy fix!

The connection from solenoid to starter would cause the entire cab to have no power ?

Im having an issue with my 1999 Mack RD688S truck. I hop into the cab and turn the key to ON and wait for the 6 clicks... after the 6 clicks, I proceed to turn it to the START position. Well, the problem I am having is every once in a while when i turn it to the START position, it will make a click sound from inside the cab (relay) Then i will loose all power to the cab. No radio, no lighter, no buzzer, nothing. I'm not sure what is remedying this problem... what I've done to get it to start in the past was clean the battery terminals for one time. I bypassed the battery shut off switch (Bolted it together ... no longer has a shut off switch), and Wiggle the harnesses around for the other times. It just randomly will come back to life and start buzzing. Its very frustrating. the batteries have all been replaced recently, and I confirmed individual voltages on each battery.

If anyone has any thoughts, i would sure appreciate it. I really dont want to take it to Mack and have them fix it. For reference of the model, a picture has been attached of the truck

I noticed yesterday morning upon pre inspection my drivers side air tank has a pin hole leak in it, there is a sheet of rust Right next to the pin hole. Is there any way to cut the tank up and have it weld repaired?? Or Is that unsafe?

How much does a new tank cost from mack??

Trucks a 2003 mack Mr688s

Okay, thanks for the information!

I have been running a 2003 Mack MR688S the past month or so since the windmill jobs have been done, and I'm having some issues with my truck I was hoping you guys could point me in the right direction.

I remember before I posted a topic about the 1994 Mack MR688S I was running and asked about the oil pressure, and you guys said that it was OK being where it was.

Now on the 2003, the oil pressure is running when the engine is hot below 30 PSi at idle. Is this Okay?

Also, sometimes when driving up hills the turbo sounds like it stops spooling as fast as normal. I actually loose speed because the turbo quits working. I do not notice any smoke, and the engine RPM are usually steady between 1600 - 1800 RPM. What would cause the turbo to do this?

Finally, every once in a while my truck takes forever to start up, It usually happens when the engine is hot, but i've had it happen when its completely cold as well. I actually recorded a video and from the overall length it took about 6 seconds of constant cranking for it to start. I know these have the plastic bosche fuel pumps, do you think the pump could be getting weak and loosing the prime?? That would make sense to me, but it doesnt have any problems Revving up to while operating on the job, which kind of is throwing me off because when I had a fuel pump go bad, it started to sputter real bad, and this truck once it starts doesnt skip a beat besides the turbo while driving

engine hours are 13565.3, 133133 miles when i fueled up today

heres a video of it starting:

I really appreciate the help / comments so far, and would appreciate some help on the few issues im having currently.

Thanks,

Brandon

Great photos of your truck working!

How many yards in each base?

They are about 700 yards of concrete in each base!

Havent been logged on here in a while. I've been up in Ellenburg NY pouring concrete bases for windmills for the past 2-3 months!

Anyways, Ive been running a 2004 Mack MR688S Cabover. This thing is a SWEET ride. the only problem I had the whole time I was there, was the fuel pump took a crap. For anyone who hasn't delt with the fuel delivery pumps on the 2004 mack, it is a good idea to keep a spare on-hand since the entire pump is made out of plastic besides the center shaft which is steel. Even the gear is plastic!

For more info on the wind farm, check out http://www.noblepower.com/our-windparks/ellenburg/index.html

on the booms, its recommended to change the boom system every 10,000 yards. The cups need replaced around that also. The cups are the large Rubber Plungers attached to long hydrualic cylinders that push the concrete through the boom-line.

The boom line on the larger pumps is a smaller diameter, so it wears a lot faster and its right around 4,000-6,000.

These numbers are just recommended specs per manufacturers. A more realistic number for the smaller booms is around 15,000-20,000 yards before it needs replaced

The hopper, and the pumping components are all Hardfaced, so the parts last a longer period of time. The boom system is not hard faced though, so it tends to wear out quite quickly.

Not sure what the Yardage to Hours would be

Well that is good news indeed then! I just recently started running this truck, so i wasnt sure what the normal pressures were. On my other Mack, the oil pressure is higher, thats just why i was worried.

Heres a few pictures of her

I run a 1994 Mack Truck with a Schwing Concrete Pump mounted on it. I am wondering what the normal oil pressure is supposed to be, HOT while idling. currently its hovering right around 30PSI which seems too low to me. When cold its at or above 60Psi, but as it warms up it gradually gets lower. If i am throttling the truck, the oil pressure is OK. The engine has 21750 hours on it and it has 550,000 miles on the chassis.

The Engine Brake works great all the time if that helps?

Any input would be greatly appreciated.