kuhar69

On my dashboard i have I think 3 mounting holes for gauges right now they have black mack logo caps over them. Can I pop one of those out and add a Boost gauge is this a good idea and is it hard to do??.

No to both questions. The Cab floor board has a section that is bolted in that is removable. You need to remove the floor mat, guards, throttle pedal (fold the pedal back toward the seat and remove the two bolts holding it down, be careful reinstalling as the bracket is aluminum and the bolt threads easily strip out). After removing the floor board bolts the plate has to be lifted and turned slightly to get the clearance needed to remove it from the cab. It takes some practice but isn't too hard. The pipe will not show bubbles with the engine running if there is a hole in it because the engine and compressor will both be pulling air in through the hole.

Mack made that simple providing the mechnic with that acess panel in the floor that was smart.

Ok I'll check that out tommrow.

ok rhasler I printed the page you provided for me thank you so much very helpful. Tommrow I will take a look at the truck.

You guys are a huge help this is what makes this country great.

By the way what is your name???

Mark

I have one of those 4 foot long cameras that are flexible and have a light on the camera end. Would this help me find a air leak under the cab maybe spray water on the line with a squirt bottle and with the camera look for bubbles.

If i have to take up the floor that sounds like my friend the torch has to come out and play??

Mark

Bobo seems to think i might have an air ride cab on my truck???.

I might be having an air issuie that might be related to the sagging cab if you look at my other post under engines Im being told that the cab may be pinching a airline that is restricting my boost???

My Pyrometer reads somewhere nere ???? PSI looking at the gauge the needle is always towards the left???

My Mechnic said to keep an eye on that make sure it does not read a lot of presure cause then we may have to service the aire filter which is brandnew.

I"m still wet behind the ears with this stuff its the first time i have ever owned a truck on my own.

So I might say something sooner or later that guys are gonna laugh!!

Mark

Ok BObo so i might have an air ride cab??. This is my 1st Mack so Im still learning!! My other truck is a kenworth.

How do i know if my cab is airride?

Yes, they are rubber and compress from the "hammering" they take during normal operation. Ask for a photocopy of how much torque to place upon the retention bolts for proper "squish" when the rubber parts are installed. Too tight and they split, too loose and they do not offer the slight cushioning effect they are for. The cab will really bounce and jerk if they are loose. You want a slight bowing out of the sides of the rubber when tightened properly. I'd say about 3/8ths of an inch would be enough.

Rob

Ok very good it sounds like an easy repair and it wont brake the bank at the same time. How long should that take to replace 2 or is there 4??

Ok so this is happening im not nuts. I dont have an air ride cab so I will have to check the mounts they must be rubber right???

I dont know if Im seeing things but I think my cab looks like it's sagging a little????. Is this possible??? another words when Im looking at the truck I sware the cab is sagging down towards the fuel tanks,

The weather is hot here in CT so I might be working to hard tell me this is not a bent frame or something??!!

Yes. It should be on the metal tag on the driver's door. If that tag is missing it should also be stamped on the right frame rail somewhere around the area of the shock absorber.

I sent you the vin number check your mailbox hopefully you got it.

Hey man thanks again!. Do you mean the VIN number??? where do i find the serial number

Guys I run a 2003 Mack RB688s dump truck with a E-7 350. I'm a owner operator.

Last month I had a loss of power problem I got on the site here and you guys all pitched in and fixed my problem. Rhasler had given me the exact problem and how to fix it I am gratefull for the help. Now that the truck is back on the road with a new speedo sensor and a new fuel transfer pump I didnt get the power that I thought I would gain.

Now the only thing I didnt do as was suggested was to bring the truck to a Mack dealer and have them turn off the parameter thats detects the tampering with the spedo sensor to prevent the derate power.

My friend has the same motor in a RD688 and he pulls a trailer with his machines on it.

My truck wont even entertain that idea!.

I just seem to have the RPM's to shift her to get her ass in gear.

Now when the truck is not loaded it runs like a bat out of hell.

Mark

Ok I will do that thanks again.

4-1 fault code is for the speedometer, not the engine position (camshaft) of engine speed (flywheel) sensors. Typically this code is set to derate the engine when there is no signal from the sensor (as a tamper detection preventative). With Mack transmissions, a sudden occurenece, in my experience, is related to a synchronizer failure. Remove the speedometer sensor fromthe output bearing cover & inspect it for debris & damage. Install the sensor as follows: screw all the way in, back out 1 turn, tighten jam nut to no more than 15 lb ft. If the nut is over tightened the sensor can crack, probably why they asked if you had replaced the clutch recently.

TRUCKNUT YOUR THE MAN BABY!!!!! You hit the nail right on the head. The speedometer sensor was the problem it was melted I went to the dealer they gave me a new one and the light is off and she runs good.

Now if i can only make up the work I missed for 6 day's.

Thanks again.

Mark

The sensor for the speedometer is on the transmission, not the dash. The 4-1 code will not set if there is a problem in the dash since that is a different circuit from the speedometer. Remove the sensor from the output shaft bearing cover on the rear of the transmission and check the sensor for damage.

Circuit #3 powers dash & marker lamps. If your other dash lamps and marker/running lamps are operational it's probably just the bulb. I believe your truck should have a small solid state rectangular telltale between the speedometer guage & the tachometer guage. If it's damaged you'll probably need to change it.

The sensor is on the tranny ok ok I'm sure the mechnic must know where it is. I explained to him what advise you gave me he said he would check that now in about an hour from now, I'll just explain to him it's on the tranny unless he knows that already.

Installation of lights should not have had an effect on the speddometer, the circuit that reads the speedometer is separate from the circuit for the dash lights. The lights should be on circuit #3, the speedometer has no circuit number as it is a direct input to the vehicle ecu.

Im just wondering if when the dash was apart if the speedo sensor got damaged.I'm not at all familar with the dash components.

As far as my speedometer light that light is on circuit #3. How do I check the curcuit??

That sounds like good information were gonna try that route. I did have L.E.D. warning lights installed on the mirror arms and the dump body so im wondering if when he had the dash apart that sensor got screwed up. The guy who put the lights in the truck is not a shoemaker he works for Whelen lighting so im sure it was just a mistake or maybe it got damaged from wear and tear. Ok I'm gonna try that I'll let you know how I made out.

Thanks so far.

It just dawned on me that a 3 months ago the speedometer light died which is anoying cause I can't read my trip miles very easy???...

4-1 fault code is for the speedometer, not the engine position (camshaft) of engine speed (flywheel) sensors. Typically this code is set to derate the engine when there is no signal from the sensor (as a tamper detection preventative). With Mack transmissions, a sudden occurenece, in my experience, is related to a synchronizer failure. Remove the speedometer sensor fromthe output bearing cover & inspect it for debris & damage. Install the sensor as follows: screw all the way in, back out 1 turn, tighten jam nut to no more than 15 lb ft. If the nut is over tightened the sensor can crack, probably why they asked if you had replaced the clutch recently.

That sounds like good information were gonna try that route. I did have L.E.D. warning lights installed on the mirror arms and the dump body so im wondering if when he had the dash apart that sensor got screwed up. The guy who put the lights in the truck is not a shoemaker he works for Whelen lighting so im sure it was just a mistake or maybe it got damaged from wear and tear. Ok I'm gonna try that I'll let you know how I made out.

Thanks so far.

Are you still getting the 4-1 code?

Yes Im still getting the 4-1 code.

I forgot to mention the speedo was all over the map...But it only did that one time. the dealer asked if I did a recent Clutch job? The clutch is fine.

Guy's I'm looking for some help here and FAST! I'm an Owner/Operator of a 2003 RB688S Dumptruck. The truck does not have any power to it. I have an "Electrical Malfuntion light on the dash.

I called the dealer and they walked me thru how to read a code. I followed the Instrutions they gave me. The truck is showing a 4-1 code.

Per the dealer i replaced the speed sensor's Bellhousing and the front of the motor.

We found a broken gear on the Fuel supply pump so we replaced that too. After running the truck we checked the status of the Fuel filters and found that the Main fuel filter is only 3/4 full and the secondary filter is full (Metric spin on filter's)

The light is still on and the truck still has little power.

The air filter is brand new and the oil is in the full range and the Radiator fluid level is fine.

Please lets put our heads together to figure this out PLEASE.