Mountains and Tranny

[dmatz]

We have been traveling from NY to the mid west. Our first stop is Mesa Verde Co. While going west on rt 160 up and down the mountains of Co for hours I started a decent of about 12 miles from 10,800 feet to 6400 feet. The posted speed was 18mph over 33,000 lbs. I was in second gear with the exhaust break on and at the end I lost my speedometer momentarily and then about 5 miles later the tach and speedometer went out for a few minutes. About 50 miles later climbing another hill at about 45 mph I lost both speedometer, tach, and odometer. Revived message from in dash saying no data available followed by check engine at next stop. Then the check engine lite came on. I was able to pull over, checked oil, tranny and antifreeze all ok no speedometer. Drove another 24 miles to campsite and called prevue. They had me check connections on D Deck and module on Detroit engine. Did a reset on the dash computer all appeared ok. I was able to pull coach forward 75 or so and speedometer registered 10 mph. Prevo said could be a glitch may never happen again. Did not make me feel warm and fuzzy all is ok. We will be heading to Zion, salt lake, yellow stone ect over the next month. Any input is greatly appreciated.

[Jon Wehrenberg]

DDEC uses such low voltage to communicate with sensors and such that often the wierd happenings are attributable to something as simple as a bad connector, bad ground or bad terminal end on a wire. The bad news is a lot of those problems are intermittent so chasing the problem is an exercise in futility unless it fails completely so you know when you fixed it.

On my previous bus a weak spot in the system was the 28 pin connector at the transmission. As a result I took it apart and plugged it back in every time I was under the bus to "wipe" any corrosion off the pins and receptacles. Except for the first time I had a problem with that connector I never experienced another problem.

I do suggest when cleaning the engine or any area with plugs or receptacles to avoid getting them wet and especially avoid power washing around them. A salty environment, such as the rust belt, or along the coast near the ocean is a challenge for our supposedly protected connections and my problem was corrosion from the salt laden roads created a conductive path between two pins which in turn created many senseless error messages and eventually caused the transmission to lock in gear. Be particularly aware of keeping the space between pins or receivers clean and corrosion free. I do not envy you.

[dmatz]

Jon

Prevost tech said yesterday that the system works with 60 ohms and that the excessive heat could be the issue. That once it cooled down all was ok. Does this sound logical to you? I had a plastic storage bin in the las storage area riverside. It melted so I know it was very hot.

[Jon Wehrenberg]

I would have to defer to his knowledge. I have not heard of heat impacting good metal to metal electrical connections except in the context of when the connection is what is generating the heat, or if the heat and resultant expansion of mating parts changes the quality of the connection.

If he is correct that is a serious issue because as the buses have to meet more stringent standards for emissions I believe more heat is being generated.

[Ray Davis]

I had a similar situation happen, first time on the same day as your first post. Had driven out to Rancho ORA and spent a week. Started coach, intending to drive to Pechanga where we had a wedding on Saturday, the 7th. Noticed that speedo wasn't registering, but thought I might be not driving fast enough (still carefully driving out of the ORA park). Got towards the street and still no speedo, when I noticed there was a check transmission light, AND when I stopped I found the tranny was locked in first gear, and would not respond to any button pushing.

Checked the DDEC reader, no codes.

Checked via the tranny pad, oil level, and all was good. Restarted coach, made it to Pechanga without issue. 4 days later, drove from Pechanga to storage (45 miles), and when I arrived tried to put coach in neutral, and same problem, tranny locked in first gear. Restarted coach and was able to park it.

This time I did a code-read on the tranny pad, and came up with a 25-11 error, which turns out to be output speed sensor error, 0 rpm first gear. Have since purchased the sensor, and will hopefully look at coach again tomorrow. Other possible causes are loose or shorted wiring to sensor. I'm hoping I find the plug loose, but we'll see tomorrow. This will definitely shut you down if it happens.

Ray

[HarborBus]

Keep us posted Ray, I would like to know where the sensor is and what you found out.

[Ray Davis]

I did find a couple of online manuals for the transmission (or hopefully similar enough). There are actually three speed sensors. The one I'm having a problem is called the "Output Speed Sensor" is is located right near the shaft, at about 5PM if looking from the transmissiion towards the engine. The other two sensors are on the right hand side of the transmission. The turbine speed sensor is in the middle, and closest to the engine is the "Input Speed Sensor" which measure the input speed to the tranny.

Hopefully tomorrow I'll see this up close and personal. First chance to use my jack stands I purchased from Jon two years ago!

Ray

[Ray Davis]

Well, this weekend, using the stands I purchased from Jon two years ago, I got under the bus, and replaced the output speed sensor. Major issue was the sensor was located at the very front of the transmission, right at the drive-shaft. The access was blocked by two sheet metal pieces, which almost made me give up. But, I removed one of the two panes, and was able to get a single hand up to the sensor. I was able to remove the sensor and install a new one ($80). Test drove it today. Good news is that I guess I didn't break anything, as everything worked fine. I won't really know if I "fixed" until it fails again, as it was previously intermittent. But, in several times of start and stopping, it worked flawlessly, so fingers are crossed.

Ray

[Ray Davis]

As a PS to this thread, it is helpful to learn how to read the codes from the transmission. Although this turned on the check-tranny light on the dash, it did not throw a code in the DDEC. I had to read codes using the transmission keypad.

Ray

[HarborBus]

Well done Ray, it's always satisfying to know you have fixed something yourself.

[dmatz]

I am finally at a place with wifi again. We have been from Cortez co, to Zion ut, to salt lake and now in Arco Id. The tach and speedo have failed a few times only momentarily the speedo twice has pegged itself and then came back to 65. Not much mountain driving. We are headed to yellowstone from here, expect there will be some elevation changes in route to Jackson hole then up to cotter bay. I have spoken to prevost several times and they believe it is heat related in a connection in the engine tranny area. I will keep you posted if and when anything is ever found. I will be pulling all the connections a parts looking for any corrosion and put back with dielectric grease when I get back to the east coast.

[dmatz]

The good news is all has been ok. I have been very careful not to build up much heat, using exhaust break as little as possible. I made it to Jackson Hole, the Tetons, Yellowstone, Cody Wy, Sturgis Sd, and now at Cedar Point Ohio all seems good. I guess that is the bad news as well. It's never good to not find a problem. Never know when it will pop up again. Do you think it makes any sence to have the codes read in the tranny and engine, or just wait for another issue?

[jj628]

For what it's worth---While at the Allison shop the tech told me that on my model if you back up it wipes out all of the transmission codes.

[Jon Wehrenberg]

Was he serious?

[BoaterAl]

That's a new one. Think about it ?? How could a transmission shop ever get a problem fixed if the codes were removed when you punched reverse.
John, there is supposed to be a great burger place in Nevada, I'am told ? Does anything come to mind. We run Hwy 71 often as the bus is kept in Peculiar ,MO. yes, that is the towns name. But the best town name has to be ..Tightwad, MO. There was a bank branch there years ago which did a brisk business opening checking accounts.
AL

[jj628]

Most important first--the burger place is the White Grill and has been serving the best cheese burgers in the world since 1938--grilled onions cooked with the meat on the grill.Never been a frozen pattie in the place. Suzie Q potatoes and you have your grease injection for a week. The bank in Tightwad is still in business as far as I know--it's a branch of a large bank. I know Peculiar well--aunt and uncle live there. When Charlie Findley owned the Kansas City A's he got into a peeing contest with KC and threatened to move the team to Peculiar to become the Peculiar Athletics. Oakland had a better deal I guess.
Lastly--the Allison Tech in Middletown CT told us exactly that--back up and wipe out the trouble codes. Later models don't have that "peculiar" problem. It made no sense to me either.

[Jon Wehrenberg]

We had a 1987 with the 5 speed Allison with ATEC. We had a sensor issue that locked the transmission in gear and as a result we ended up along side of the interstate. To get more to safety we managed to get it into reverse and backed up the shoulder to an on ramp away from the speeding traffic.

The Prevost tech with the computer reader came to us and hooked it up and was able to read the codes even though we had backed up about 1/4 to 1/2 mile.

At the time he read the codes the problem was not showing up so he was reading historical data. The problem was intermittent and turned out to be a bad 28 pin connector at the side of the trannie. Maybe some model year transmissions acted differently, but that is the first I ever heard anyone say to not back up.