| Author | Message | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 10 Registered: 1-2009 Posted From: 76.0.172.15  Rating: N/A |
Hi folks, I'm installing a tachometer on my 1981 MC9. It's the kind that attaches to the "R" post on the alternator. My question is this: Is there an existing connection in the front electrical panel or close to the front of the bus that I can tap off of to get this signal connection, or do I need to run a separate wire to the alternator? I know there's a post in the back electrical panel where this connection is made, but that doesn't get me any closer to the front gauges (or does it?) I've looked at the schematics, but get a little confused, so thanks in advance for any help you electrically-minded folks can provide. Debo | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 960 Registered: 10-2006 Posted From: 76.202.165.190  Rating: N/A |
On most coaches there are extra wires built in . Just find one on the schematic and use it to run the tach. After 30 or 40 years of operation , what is the tach FOR? FF | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 11 Registered: 1-2009 Posted From: 76.0.172.15 Rating: N/A |
Hey Fred, Two reasons mainly. Number one is that the bus may have 30 or 40 years of operation, but I don't. After it's installed and calibrated I'll use it to check idle speed, fast idle speed, cruising speed, full governed speed, over-revving on downhill runs - stuff like that. It'll just help confirm what I can hear or feel the engine doing and give me a number to put with it. Second reason is that I'm also a pilot, so I've gotten used to having a lot of information available to me about engine sytems. I can use the information to spot a potential problem early, or confirm one doesn't exist if I have a hunch about something. More personal preference than a real NEED for one I guess. Thanks for ithe idea. That's exactly the kind of creativity I was looking for. | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 600 Registered: 3-2007 Posted From: 71.53.155.14  Rating: N/A |
DEBO the way you run a DD is Comfortable!! Both feet flat on the floor,and don't let up LOL That way you don't need anything but the speedometer to let you know when you need to shift up or down. Gomer | ||
| larry currier (Larryc)
Registered Member Username: Larryc Post Number: 281 Registered: 2-2007 Posted From: 205.188.116.203 Rating: N/A |
Since DDEC took over as fail safe, I even put tape over the engine gauges, but I've been sitting behind engines all my life. If I didn't have the experience I would likely enjoy some gauges, it would help me get a feel a lot faster for what I was rolling. Isspro sells a Pyrometer that I would like on the dash, but if anything gets out of parameter, DDEC is going to shut it down anyway, so I may as well just go until I get a trouble light and let it be. The biggest threat to a non computer engine is coolant loss and burning it up shortly there after. The pyrometer will tell you about that event. A coolant gauge will go cold when it loses contact with coolant and read 0. If you know that, then you know to stop from that gauge, but a pyro will also let you know the engine is getting hot right away. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1654 Registered: 10-2003 Posted From: 71.58.71.157  Rating: N/A |
Some GMC's have a low coolant sensor in the expansion tank to warn of low or no coolant. Looks to be the same system that GM used in some of it's cars. Tach is good to have, even with auto. Like mentioned above. How fast is the engine turning when you are running flat out? Is the engine running beyond its designed speed because of a mis-adjusted or malfunctioning governor? If speedo quits, you can use it to calculate speed till it gets fixed if you can't afford a gps. Watch for overspeed on downgrades, help calculate what rpm the engine is most fuel efficient with mileage checks. This will take several thousand miles to get an accurate idea; fewer miles for a general idea, and other benefits. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 962 Registered: 10-2006 Posted From: 76.202.165.190 Rating: N/A |
"Second reason is that I'm also a pilot, so I've gotten used to having a lot of information available to me about engine sytems.' If you like to scan instruments instead of look at the road , that's your way. BUT if all you want is the information you listed a visit to Daris's great site , with the tire diameter and tranny / rear axle numbers from Da Book will allow you to chart road speeds vs rpm in every gear , including reverse. Simple colored pips on the speedo will let you know downshifts /overspeed limits with no cost , effort or installation hassles or repair effort. Do it your way! FF | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 12 Registered: 1-2009 Posted From: 149.168.204.10 Rating: N/A |
A little perspective please. To imply that I'm not watching the road because I have a tachometer is a bit of a leap don't you think? Does that mean I shouldn't shift gears with the shift lever because I'll be distracted and "fiddlin' with somethin" too? Daris's site is awesome, and I've used it while making a decision about tire sizes, etc, but it's static information. A tach will give me real-world information as it's happening so I can make a more informed decision about the safe operation of my coach. It may not be your experience, but I have difficulty seeing how a little more information to make a better decision could be a bad thing. I have a lot of respect for you guys that can do it all by feel and experience. I'm just not there yet and I like a few more data points. I reserve the right to get smarter and "do it my way". I know some of you don't see the "need" for a tach or instrumentation. I do see a need for it and am going to be using it in my bus. You know if you really think about it, nobody really "needs" a 40-foot bus with a couch in it either, so exactly what point are we trying to make here? I asked a really simple question about a wire and got a good answer. Thanks again for that. Over and out. | ||
| John Lacey (Junkman42)
Registered Member Username: Junkman42 Post Number: 100 Registered: 3-2007 Posted From: 69.19.14.36  Rating: N/A |
Debo, when I started flying in 1960 I remember the old pilots saying why would You need a VOR? The real sailors mantra You do not need GPS use a sextant! And what do You do if the batteries go dead? It is possible that some are so old That They can not do two things at once. A tach like a pyrometer is a good thing. John | ||
| Paul Lawry (Dreamscape)
Registered Member Username: Dreamscape Post Number: 578 Registered: 5-2007 Posted From: 75.218.84.21  Rating: N/A |
I'm with you Debo, I like gauges. I also have a tach, just not hooked up yet. It's hard to hear the DD and I like the look of it anyway! | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1658 Registered: 10-2003 Posted From: 71.58.71.157 Rating: N/A |
Yeah, don't use any dash gages; just watch the rear view mirrors for flames or white smoke...overheated or fuel fire. Run with the traffic to replace speedometer. Rev it till it won't go any faster and then shift. Let it roll downhill. If it is over revving, you look in rear view mirror for parts coming out the back to let you know to slow er down a little. BTW, Roadway tractors had warning lights and only a speedometer in them. Although there may not be a specific wire for your tach output, most coaches have several extra wires from rear electrical panel to front for various options for the coach build that never were used. Just sort out with a test light and a small battery with coach batt disconnected. Also other ways to do this. There is a signal generator that does this too. Someone here may have the wiring diagram you need. Did you check the back side of the front panel cover? Look for wire posts with nothing connected to start. | ||
| Debo Cox (Debo)
Registered Member Username: Debo Post Number: 13 Registered: 1-2009 Posted From: 76.0.172.15 Rating: |
Hey John! Thanks for the sage advice. I actually have "da book" and that's exactly what I did. I checked the schematics again and found that the lavatory alarm circuit (which I'm no longer using) runs from the rear junction box to the front so I jumped a wire here and there, disconnected a couple of others, and used it. I just needed a little nudge to point me in the right direction, and you guys provided it. Thanks again. | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 603 Registered: 3-2007 Posted From: 71.53.155.14 Rating: N/A |
You go Big JOHN You got my vote~~ let -er-rip!! As I said before drive it comfortable. Gomer | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 963 Registered: 10-2006 Posted From: 76.202.165.190 Rating: N/A |
Most starting bus camper folks are delighted to shift sucessfully , not grind gears or stall uphill at stop lights and not knock down too many mailboxes on slim roads. The great driving tips from Mr Long on this board have changed many a novice to a smooth operator with a bit of practice. "To imply that I'm not watching the road because I have a tachometer is a bit of a leap don't you think?" The problem is not WATCHING the tach , it is the required thought to take what you observe and translate it into action. Just as cell phone folks have as many accidents as drunk drivers, my concern is with multitasking. To figure the proper down shift you will read the tach , remember the percentage difference in the next (or two) lower gear , apply that percentage to the tach reading and use that number for the target for the down shift. WHEW!!! Just looking at the speedo needle and comparing it to a colored pip to know the downshift is loads easier for me. Loong ago when I started as plumber on the DC-8 and had about 100 dials to scan , now MY WAY is as easy as I can . Of course doing it YOUR WAY , is the motto , so have fun. FF | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1660 Registered: 10-2003 Posted From: 71.58.71.157 Rating: N/A |
Now: put it in drive- push go pedal to the floor. Look out the rear view mirrors AFTER you make a turn to see what you ran over. Now that you are moving, put it on cruise, talk on one cell phone while texting on the other, and at the same time, punch in your address on the GPS and look for a decent radio station.................... | ||
| David Lower (Dave_l)
Registered Member Username: Dave_l Post Number: 228 Registered: 11-2007 Posted From: 67.58.201.14  Rating: N/A |
John you forgot one. I heard on Road Dog yesterday that a german driver had a crash because he was waxing his carrot and did not even stop when cops were questioning him until he went off! Dave L | ||
| clint hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 521 Registered: 1-2009 Posted From: 24.129.237.52  Rating: N/A |
...while it may be true that nobody doesn't need a 40 foot coach with a chesterfield in it, but eye do need at least one, as I am a bus nut, I also find extra data from sensors is welcome redundancy, which is a option and not a vital urgent need; bus option come install to those that make the effort to install them ... - I do plan to install one when at some convient point in the process as the speedo does not tell me everything in a mechanical bus with automatic and it is often just to quite to always here what is going on way back there, though not all buses are as equally vibration quiet as these old MCI's | ||
| Nellie Wilson (Vivianellie)
Registered Member Username: Vivianellie Post Number: 322 Registered: 11-2008 Posted From: 75.178.92.43  Rating: N/A |
Debo - Considering the vintage of your bus, I'm guessing you run an 8V-71 (like mine) or 6V-71? If so, you (we) don't have a lot of the whistles and bells - auto cutoffs and such - that the newer engines have. So, for me, a tach is important. Call me an idiot, a novice - or whatever you wish - but I LOVE my 'clock,' an ancient technology for sure, but it's great! Greyhound called it a 'tachograph' (kind of a predecessor to computer printout devices). This thing contains an odometer, clock, speedo and MOST important, a tach - with a big fluorescent needle - and it records everything. Contrary to certain opinions voiced here, RPM seems to have been a major concern to Greyhound and certain fleet operators? Whether true or not, it's absolutely essential to me. My bus is relatively small and light, making it easy to run past the governor. Contrary (again) to some previous posts, I drive - and shift - strictly by the tach. My speedo clocks 6 miles fast at (true) 30 mph, and 8 miles slow at (true) 65 mph. I'm gonna rely on that? No thank you. The tach, however, is dead accurate. Why? I dunno, and I don't care. I just know I can trust it. If my pedal gets mushy, I check the tach. If I get a stutter or a warning lamp, I check the tach. If I feel I'm starting to lug, or the temp creeps up, I check the tach. What the heck is a speedo (even an accurate one) gonna tell me? Nada. This macho 'flying by the seat of your pants' jive just ticks me off. That nonsense went out with Lindburgh. As Clint noted (I paraphrase), these things ain't easy to hear and they don't vibrate (sounds almost like a song). And if we start to belch smoke, it won't be coming over the hood and into our windscreen... we won't see it until it's too late. Okay, a tach won't help me see the smoke, but it might warn me there's a problem BEFORE the smoke starts. You think FF has EVER been on a boat without a tach? I surely doubt it - unless it was a dinghy. Or one of those little matchbox sail boats. You rock, Debo. Get your tach, hook it onto your alt. post and go cruisin'. Hey... I just noticed you're kinda new to the board (so am I). Welcome aboard and enjoy the journey. Some of these fellows get a bit crusty  but they all mean well. They truly do... even moi. Nellie Wilson | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1722 Registered: 12-2000 Posted From: 76.71.103.244  Rating: N/A |
Ok, settle down y'all. You've driven me to drink heavily to finish this post... If you want a tachometer, install one, if you don't, then don't. Stop hurling insults. For the novices, the issue is: you need something to indicate it is time to take some gear changing action. Whether that is measured in RPM or MPH or KMH, doesn't matter. The gauge in question needs to behave consistently. Nellie, get your speedometer fixed. When we're talking 2 stroke DD and only 4 or 5 gears, the discussion is somewhat moot, you need to grab the next gear down as soon as you reach the governed speed for the next lower gear, because DD doesn't like to pull in the lower revs without a ton of heat being produced. Since there is very little overlap between the gears, effectively, the place you have to change gears is at the same RPM and at the same MPH/KMH every time. Be quite a shame to install that tach and then find that the speedo does the same job... So, whether you use the speedometer, or the tachometer, you will be upshifting and downshifting at the same RPM or MPH/KPH. Again, you do what you want to do, it is your coach, just go easy on the judgmental crap, and remember the poor novice that is trying to figure out what they are "suppose to do". With my auto, I shift it myself. I downshift into 3rd from 4th at 52 mph, down into 2nd at 38 mph, which is governed speed on the way up. No tachometer here, and I'd only bother to install one if I had enough gears for significant overlap, or if i was bored and had nothing else left to do. But that's just me, install a tachometer if you want, but don't feel you have too. happy coaching! buswarrior | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 975 Registered: 10-2006 Posted From: 76.202.165.190 Rating: N/A |
"The gauge in question needs to behave consistently. Nellie, get your speedometer fixed." No need , if its constant weather it sez 2100 in a gear is 35 mph or 45 mph doesn't matter for use as a shifting guide.But it MUST be consistant. Boat tachs , at least in smaller boats comes from an alternator output, the reading will change with belt age , belt load and even with different brands of belts. Useful only as a guide , go full bore , cruise 10% or 300rpm below that .And easier to re find the sweet spot where noise and vibration are least at no cost in speed. IF the bus alt were gear driven , it might be calibrated to be accurate . FF (Message edited by FAST FRED on October 02, 2009) |
