My bus has a Detroit Diesel Series 60 engine, so I know I can get the speed from the DDEC.  My Silverleaf VMSpc shows the current speed.  Anyhow, my bus appears to have had a new speedometer installed at some point, but it was the kind that used magnets on the front brake drum.  It was completely inaccurate, so I bought a cheap GPS to show my speed for the 1,000-mile drive home from the dealer.  I installed a GPS speedometer when I got home, but I am on the second GPS speed unit, and it is having problems. Post by: belfert

Should I install a regular electronic speedometer with a signal from the DDEC, or go with another GPS speedometer?  I assume a wire under the dash provides the signal for an electronic speedometer.  The wiring under the dash is such a mess that I have no idea which wire it would be.  Some are labeled with circuit numbers, but certainly not all.  Can I run a new wire from close to the engine and splice into that line, or is it bad to splice into the line?  I have the wiring diagrams for the bus.

Post by: luvrbus 

Buy a good GPS.  You will get into the digital and analog wiring from the DDEC.  The DDEC has both.  It is probably an analog device if yours reads from the front wheel.  In this case, there is no wiring from the DDEC.  The DDEC has to get a signal from the Allison speed sensor.  It doesn't read the speed directly.  Văn installs GPS speedometers.  However, I forgot where he orders from.  They are not cheap, but they work.  Give him a call.   

Post by: Van 

Brian, get the good GPS units from Auto Meter. That is all I install.  They are a little pricey, but they are of good quality and come with a warranty.  They have a few styles and sizes to match what you have in your dash now.  It is a simple install!
https://www.autometer.com/catalogsearch/result?q=Gps%20speedometer

Post by: Iceni John 

Another contender is the ISSPRO R8480M-SET I recently used to replace my original Teleflex when its odometer died.  I chose the ISSPRO because it has a resettable odometer, which may be unique among aftermarket speedos, so I didn't need to start over again at zero miles.   It's 3-3/8" in diameter, gets its signal from the front wheel, and can be programmed for complete accuracy. It has 2 MPH increments on its 80 MPH dial face, is made in the USA, and is way better than the miserable Teleflex ever was.   And it also works in tunnels!

Post by: plyonsMC9 

I put in a GPS speedometer in our DL3 and so far, there have been no issues. It's about 1 - 2 MPH, different from our trucker's Garmin GPS. However, I wonder if this would make getting a dyno readout impossible, as I have no functioning speedometer. We have a DDEC 2, and the few mechanics I've talked with don't have that interface.

Post by: luvrbus 

DDEC ll doesn't use the J1939 protocol.  There is very little out there in interfaces for the DDEC II.  To make an Allision World transmission work with that DDEC, it has to be programmed standalone. The translocators they made for communication between the ll and J1939 have been gone for 25 years.  It is a real problem.  The DDEC lll uses the J1939 protocol, which is the standard of today. 

Post by: Van 

Quote from: plyonsMC9 

I thought the dyno looked primarily for RPM, torque, and horsepower, not speed. I also see the same 1 MPH difference in speed between my truck's Garmin and whatever GPS speedo I use.

Post by: luvrbus 

A chassis dyno will look for speed, RPM, torque, and HP.  They show it all at different speeds.  WW Wiliams in Phoenix won't do a chassis dyno on older buses or an in-frame engine rebuild.  Bill at WW Williams told me that the repairs on older buses won't cover the dyno costs.  They will, however, run dynos on engines and transmissions out of the bus.  He did one on my Eagle years ago, after hours, and told me that if the drop box came out in pieces, it would be on me.     

Post by: richard5933 

I've installed two GPS speedometers from Speed Hut. They were accurate and reliable. The best part is that you can customize the dial to match your other gauges and pick the features you need on the speedometer. These units cost more, but to me, it's worth it.

Post by: belfert 

I had surgery on my hand this week, so I haven't done much with this yet.  I pulled out the wiring diagrams for my bus.  Indeed, the original speedometer on the bus used the speed signal from the transmission.  I am certain the speedometer that was used on the front wheel was a replacement.  For starters, the gauge said MCI on it.  Second, the cable going to the wheel was poorly run, as if it was added later.

GPS speedometers are great when they work. I bought a Dakota Digital GPS interface that also has an accelerometer, so the speed will still show in tunnels and other situations when the signal is lost. The problem is that the accelerometer is very sensitive, and even braking hard will cause it to go crazy and stop displaying the speed. The only fix is to disconnect the battery voltage from the unit. I think I might be just as well served by a speedometer fed by the transmission.

I have no issue buying the Autometer if I buy another GPS speedometer.

Post by: belfert 

I don't even have a Dakota Digital speedometer head.  I just have their GPS module sending the signal to an Intellitronix speedometer.  I see that Autometer sells only the GPS module, which I could use with any electronic speedometer.

I don't think the Dakota Digital GPS module would be a bad option for a car or motorcycle.  It is just that the accelerometer in their GPS module doesn't like the motions of a big vehicle under heavy braking.

Post by: RJ 

Quote from: luvrbus

That's interesting; WW Williams in Phoenix was the outfit that did the in-frame rebuild on my Prevost's 8V92 after the previous owner cooked the engine.

Will they do ANY work on the two-strokes anymore?

Post by: luvrbus 

No. WW Williams will only work on the stationary DD 2-cycle engines; they now have the 10-year-old vehicle “max” policy. In addition, they work on very few Series 60 now since they have been gone since 2010.

Post by: richard5933 

Interstate Power Systems still has locations that service buses and DD 2-stroke engines. My bus was serviced at the Milwaukee location—top-notch work but not cheap.

Post by: luvrbus 

Stewart and Stevenson will still work on 2-stroke engines in buses. They have locations across the USA, and they are not cheap either. 

Post by: Iceni John 

For any folks near Southern California, Dustin at J & R Diesel in Riverside only works on 2-strokes in buses (and occasional marine engines).   He rebuilt my engine last year, and I'm very impressed with his work.  He machines heads and rebuilds turbos in-house as well.   So far, so good.

Post by: luvrbus 

Times are changing with prices now.  I remember when a DD dealer's standard price for an in-frame on a 2-stroke engine was $100.00 per cylinder and $150.00 with new injectors and rebuilt heads using all OEM Detroit parts. A scan and sensor replacement on electronic engines will cost $1,250 for a $40 sensor.