Doffer

Well I have a different truck now anyhow. They keep making me give up my normal truck for other trucks, not fun

That's good information ! I really don't know a whole lot about these trucks beyond the basics, I've only been running with my CDL for 2 years now. When I had my issue popping out of gear we just brought the rig over to mack and they fixed it. They explained to me what they found / did so I tried to relay what they told me.. It ended up being $1200-$1500.00 I believe total.

Well I have bigger issues than a loud exhaust at the moment. I think my manifold just cracked or the bolts broke or something. Definitely and exhaust leak

I had the same problem happen on my MR688S but only 6th gear for me. I took it to mack and they replaced some assembly that the shifter (high / low) attaches to. They told me the assembly teeth was worn out, and it was also popping from high to low while driving. They said it could be from quick shifts where the transmission doesn't go into gear all the way, but you still power through the gear (only partially engaged). After you do this partial engagement for a while (powering the accelerator) it wears a flat spot onto the synchro assembly, and allows the transmission to push out of gear. Might be similar to what's happening to you.. My synchro assembly was changed at around 400,000 miles (14,000 engine hours)

Hah!! alright , well it sounds like it wouldn't be a great idea then. I commute between Pennsylvania, New York, Vermont, and Massachusetts... dont need to be getting busted every day because my truck is loud

Do you know if Pennsylvania or New York does? Thanks

Is it legal to delete the muffler on a 2003 Mack MR688S ? I love the open exhaust sound, but I'm not sure if its actually legal or not.

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

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?

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

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