Match the information from both! Complaint: banging, or erratic shift feel on one or all shifts, may correct temporarily if adapts reset but comes back, no codes present. Cause: Debris has stuck shift valve E in valve body. If you take valve body apart you may or may not actually find valve stuck, very sensitive, timing of stroke can create codes, this is extremely common issue.

Complaint: Allison transmission Erratic shifting in and out of lock up clutch at any speed. May have ABS light on. No transmission codes. Cause: Trucks equipped with ABS systems tie the lock up clutch operation into the ABS and you can have faulty wheel speed signals which can shut off lock up back and forth as ABS see missing or erratic wheel speed as wheel lock.

Check Ford trucks and International for rotted tone wheel which is part of brake rotors.

Symptoms of a Bad or Failing Transmission Speed Sensor

Can be confirmed by watching ABS wire signal in transmission data. Complaint: Truck will not back up, may or may not move forward, have upshift problems. May or may not have trouble codes. Cause: can be NSBU switch on shift lever. Can be simple problem here: transmission is low on fluid.

Alot of and up trucks are having cooler line fitting leak problems, usually right at bell housing fittings. Lube oil is not draining back into sump quickly enough causing pressure build up and venting. GM has updated dipstick Part which has vent slot added in it to vent more pressure out of unit.

This can happen in any Allison transmission, you can also drill small hole in top of fill tube by stick handle end. Complaint: Broken P-2 planetary and or broken C-2 clutch hub in spline area. This is due to driveline angle and or torsional vibration due to out of balance drive shafts and driveline problems.

On rare occasions this can also be due to engine miss fires due to injector problems, may or may not be noticeable or have trouble codes. Complaint: MLPS switch plugs wont come out, possible broken switch or connector upon removal up to model years.

Cause: Heat has melted the sealant between the plug and switch, you can usually safely remove the plugs if stuck by warming them up with Bic lighter or similar low heat source. Complaint: Truck will not upshift out of first gear, may or may not have codes.

allison transmission wont shift

Cause: can be output speed sensor is no good, TCM doesn't know truck is moving. Cause: One big problem here is the bolt pads on the torque converter crack and cause leaks, this can happen with reman converter and we strongly reccomend you only install Reman torque converters with an upgraded billet front cover to avoid this comeback after rebuild or replacement of the torque converter.

A small leak in GM pick up models can be you need to install bronze washers on the bottom bolts inside the housing to prevent weepage. Obviously you can have spun pump bushing causing a leak etc. Cause: The rear transfer case output shaft bushing is completely wiped out, this can cause the output speed sensor which is located in tail housing of transfer case instead of rear of transmission to grind into the speed reluctor wheel and causing harsh downshifts.

May also have trouble codes P, P in memory. Alot of times were seeing that the bushing is completly gone and the drive shaft yoke is grinding into the tail housing itself. Codes P sol. A stuck off, P sol.By williamhornFebruary 2, in Chassis. I have a Monaco Dynasty. We parked at a resort for a couple of months and started the motorhome to go into town to purchase propane. Everything went well until I started to put it in gear.

All at once the do-not-shift light came on, and the shifting pad blinked a couple of times and then went black. Every time I turn the key on, the N blinks a couple of times and then goes black. Nothing is lit up on the shifter pad, and the do-not-shift light stays on. The tach does not work -- sometimes if you rev the engine it will go crazy but does not work right.

Speedometer Erratic/Transmission Shifts Hard/3000 MH Allison Transmission

Start by verifying Like any computer, low voltage due to bad battery, discharged battery, poor or corroded connection, etc can cause some peculiar issues.

Next, query your Allison for diagnostic codes using your shift pad. Instructions in your Allison manual or here:. Also, a good idea to unplug and securely replug the two gang plugs at the Allision TCM and the shift pad. Though it does not fit your specific issue, be aware that if the idle speed is too high, the transmission will NOT go into gear. I have tried all of these things, someone told me if the tach isn't working the trans wouldn't.

I can't find out anything on the tach, how to check it out. So how long do you think it should warm up? It seems like it is idleing fine. I am really new to this Motorhome stuff. I have contacted some places about checking it out but they all want to tow the motorhome someplace. Two mechanics came out but knew nothing about what the problem is. My first thought, since you did not mention any check engine light, is cabling and connections to and from the modules.

You have been setting for some time. My first checks would be the area of the ECM as this is the starting point of the tack signal. There is a double headed sensor in the trans. What Engine does you coach have? You stated that when you start your engine, your transmission has fault codes. You also said that your tac was not working.

I have had a similar thing happening in my coach. I would start the engine and nothing on the dash would work, but the engine still started. I turned the engine off and turned it back on and every thing worked. I have determined that I need to replace the ignition switch. Some times I have to turn it off and on several times to get every thing to come on.Typical problems of an Allison transmission include abnormal shifts, abnormal stall check speeds, slipping of the clutch and abnormal responses.

Other problems include the transmission throwing fluid out of the fill tube, excessive engine flares, intermittent noises and the retarder not functioning properly. Abnormal shifts in an Allison transmission happen during shifting at high and low speeds. At high shifting, this problem may be caused by a malfunctioning governor valve, leaking vacuum hose or broken mechanical actuator cable. A loose valve spring adjustment or stuck modulator valve causes problems during low and rough shifting.

allison transmission wont shift

Leaking oil in the converter housing originates from a defective real oil seal, spoiled input charging pump or cracked converter assembly weld. A defective clutch, leaking clutching pistons and transmission fluid leaking past the control valve are the probable causes of the clutch slipping and chattering in only one range. Low fluid levels, broken seal rings on the front support hub and open lubrication valves cause slipping of the clutch in all forward ranges.

If the shift selector linkage is unhooked, it may cause abnormal responses in the transmission. Failure to engage the shift selector at the selector valve also causes unresponsive movement of the selector lever. High transmission fluid levels and a failed vacuum modulator may throw fluid out in an Allison transmission. A loose dipstick, clogged breather, improper dipstick marking and water in the transmission are also probable causes of the problem. Weak trimmer valves and leaking forward clutch seals may cause excessive engine flares.

Lack of air supply, leaking air lines, malfunctioning check valves and a sticking pressure regulator valve are probable causes of a faulty retarder. Home World View. What Causes a Clutch to Burn Out?A transmission is a complex piece of machinery the runs of lots of complicated mechanisms. Upkeep and maintenance of these machines are tricky since the glitch with a tiny component can mess up with the gearbox.

What Are Typical Problems of an Allison Transmission?

Functional auto gearbox will shift up, down, and rest upon appropriate commands. But, when it fails to do so, there must be an internal hitch affecting the performance.

If you ignore the signs for too long, it could lead to a possible failure of the transmission. Overheating could be a reason for the gear to stick and the low fluid level is the culprit for making the transmission overheated.

Actually, low fluid levels are the source of several transmission-related issues. So, your first response to the gear-sticking problem should be to check the transmission oil. If the level is low, check for a leak in the input and output shaft seal, fluid lines, pan gasket, and the cooler. If there is no leak, flush out the old oil and refill the container. Sometimes, the cooler inside the radiator can leak and spoil the radiator coolant. A defective cable with excessive slack is likely to create issues with smooth shifting of the gears.

allison transmission wont shift

It may also totally stall the shifting. A faulty PCM powertrain control module will affect the transmission performance because it controls the gearbox mechanism in most car models. The PCM will have no input if the speed sensor fails. In that case, the transmission will not shift properly. To solve this problem, you have to check the speedometer to see that it is functioning.

Otherwise, replacing the VSS could be the solution. Tsukasa Azuma is an awesome car blogger of Car From Japan. He owns a car repair shop at downtown Osaka, and he put all that experience to good use in his sharing posts. Login with Google. Likes Followers Followers.

Import used cars directly from Japan. Maintenance Tips. By Tsukasa Azuma Last updated Aug 17, Tsukasa Azuma.

allison transmission wont shift

Show Comments CFJ Kenya. CFJ Mozambique.The transmission speed sensors are used to calculate the actual gear ratio of the transmission while in use. The first is known as the input shaft speed ISS sensor. The other sensor is the output shaft speed OSS sensor. If either of these two sensors falls out of alignment or experiences electrical issues, it impacts the operation of the entire transmission. After registering data, the two transmission speed sensors, also commonly referred to as a vehicle speed sensors VSSsend data to the powertrain control module PCMwhich compares these two inputs and calculates which gear the transmission should engage for efficient driving.

The actual gear ratio is then compared to the desired gear ratio. Should either or both of these speed sensors failyou may notice one or more of the following 3 issues:. Without a valid speed signal from these sensors, the PCM will not be able to correctly control the shifting of gears within the transmission. This may cause the transmission to shift roughly or more quickly than normal. It's also common that a problem with these sensors can impact the shift timing, extending the interval between transmission shifts.

An automatic transmission is hydraulically controlled and designed to shift smoothly. When the transmission shifts hard, it can damage internal components including valve bodies, hydraulic lines, and in some cases mechanical gears. If you notice your transmission is shifting harshly or roughlyyou should contact a local ASE certified mechanic as soon as possible.

Since the transmission speed sensors monitor the input and output shaft speed, it also plays a part in monitoring the cruise control. As a safety precaution, the ECU will shut down the cruise control and render it inactive. If you notice that your cruise control does not engage when you press the button, contact a mechanic so they can inspect the vehicle and determine why the cruise control is not working.

It may be due to faulty transmission speed sensors. It also can indicate an increase in tailpipe emissions surpassing acceptable limits for environmental contaminants from motor vehicles. In any case, if you notice that the Check Engine Light comes onyou should contact a local mechanic to scan the error codes and determine why the Check Engine Light is illuminated.

Once the problem has been fixed, the mechanic will reset the error codes. If the problem rests with the speed sensors, depending on your particular transmission, the professional ASE certified mechanics may be able to replace the sensor. Some speed sensors are internal to the transmission and will require the transmission to be removed from the vehicle before the sensors can be replaced. The most popular service booked by readers of this article is Vehicle Drivetrain Inspection.

Our certified mobile mechanics make house calls in over 2, U. Fast, free online quotes for your car repair.This short guide is will hopefully help you diagnose simpler Allison Transmission problems. Allison Transmissions have been around for a hundred years and have set the industry standard for durability. Modern Allison Transmissions come with a limp mode installed. This is a different shift table that allows the transmission to protect itself from catastrophic failure.

This limp mode locks the transmission into third gear, and keeps the torque converter from locking up. It also keeps the transmission from going into reverse! Keep that in mind. The limp mode is often activated by things an excessive of slippage by the transmission. Here are some common conditions that can trigger a limp mode situation. Third gear should pull a load fast enough on the highway, but it can be challenging to get a load moving.

If you are noticing this problem during hotter weather, you may be able to keep it from happening by installing a transmission cooler. Heat issues are the number one killer of this transmission. Do your best to protect the investment.

Even just a little bit extra slip put into the tune, and an Allison Transmission can have problems. It should solve the issue for you. It could be a false positive. The best way to do so is to get a code scanner and scan the code to wipe it. Modern transmissions are computer controlled, but if you are working on your tank they made transmissions for them in WWII or your classic vehicle you may wish to take a look at the vacuum lines.

If it feels like it is shifting toward the engine red line you could have it hooked to the wrong port. GM sent a letter to customers advising them to bring it in and get it replaced.

Amazon has a pretty good compatibility chart on their TCM listing if you would like to check it out. Neutral safety backup switch issues are another common Allison Transmission problem on the GM Duramax versions. It is part number Make sure that you are performing the scheduled maintenance in order to get the most out of your transmission. Most GM automatics come from the factory with non-synthetic fluid. You should make sure that you are using Allison approved fluids and changing them when they recommend.Once logged in and you have uploaded your resume, it takes only a single click to bookmark any type of our content.

Bookmark this Unfortunately you need to be logged-in to use bookmark system. Login Register. This Allison automatic transmission is a model in a Thomas school bus that was running around on it's route when all of a sudden the transmission became stuck in first gear. Past experience with this condition told me that there was something wrong with either the output speed sensor, the connection or the wiring. Any time in the past when this condition existed the problem was always the output speed sensor.

In the video you see it mounted on the output shaft housing. It reads output transmission speed sending that signal to the transmission control unit. This determines shift points and is important data that helps the transmission run smoothly. The output speed sensor reads a tone wheel inside the housing.

Sometimes the wheel becomes loose if the output shaft nut at the yoke isn't torqued properly causing the pressure that holds the yoke, bearings and tone wheel to back off.

There is a specific torque specification for the output bearings that can be checked once the yoke is removed. There are tools available to adjust the bearings properly. It's a two piece device that secures the output shaft while torque is put on the bearing adjustment nut.

These procedures are in the Allison manual. This transmission featured is the New World series. I can say with confidence that most times when this transmission locks in first gear it will be a bad connection to the sensor or the sensor itself. The sensor in this case was at fault with an ohm reading of ohms. Normally the sensors read ohms. It was enough resistance to allow the transmission to shift normally but act up once in a while.


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