| Frequently Asked Questions Quality Transmission Service, Tempe, Ariz |
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| Frequently Asked Questions Quality Transmission Service, Tempe, Ariz |
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43- My older Chevrolet pickup truck makes a thump on acceleration after stopping.
The noise you describe is probably coming from the front drive line yoke splines at the transmission output shaft. It is very common that the wear in the splines causes "slop" that allows some "extra" rotation. When braking the vehicle, the drive shaft "holds" the transmission shaft back. When accelerating, the transmission output shaft "drives" the drive shaft in the opposite direction which allows the slop in the splines to rotate in the opposite direction and you hear this as a snap or bump. You can experiment to confirm this by letting the vehicle coast to a stop and then accelerating. There should be no noise. Then brake to a stop, and then accelerate. The noise should be present again. The harder the braking, the more pronounced the noise will be. The slop in differential gears will also contribute to this.
This is a very common in older/high mileage Chevrolet trucks, and my 1972 pickup has done this since 1976. Check the universal joints to confirm that they are in good shape and the play in the differential to confirm that it is okay. Otherwise, just keep driving and don't worry about it. Take comfort in the fact that you know the answer the one of the great mysteries of Chevrolet trucks. Most owners wonder, but few know the reason. BTW, the symptom in my truck has never gotten any worse, just very predictable.
44- My older transmission takes a long time to engage forward and reverse when the weather is cold.
Since the symptom relates to both forward and reverse, I suspect that the problem is thick fluid when its cold. When the vehicle sits overnight or a long time, fluid in the torque converter drains back into the pan area of the transmission. When the engine is started, the fluid is picked up from the pan to refill the converter. This process usually happens quickly and isn't noticed.
When the weather is cold, the fluid is thicker and takes longer to fill the converter. Any wear or pressure loss in the filter seals or the pump will cause the process to take longer. The torque converter transfers the power from the engine into the transmission and works like a fluid coupling using transmission fluid. So, until the torque converter is full, there will be no engagement of the transmission felt when it is placed into gear.
The first thing to check is the fluid level. If the level is okay, have the transmission serviced to replace the filter and its seal/s. But, if the filter is clogged with material, it could indicate severe wear inside of the transmission.
45- I did some work on my transmission and now it doesn't perform normally. Can you tell me what I did wrong?
This is probably the toughest question to answer because if you knew what you did incorrectly, you wouldn't need to ask. These faulty results could be termed "unintended consequences." You were simply trying to repair, modify, or perform maintenance on your transmission but the results were not satisfactory.
I'm not trying to be curt, but there is a big difference between diagnosing a problem in a stock configuration and one that has been modified or repaired. We have had vehicles in our shop with mistakes made during a repair that would not have been in our top 10 guesses. As Murphy's Law states: "If it can be done wrong, it will be done wrong by someone."
The best advice I can offer is to have a transmission professional review the work "hands-on" to determine what mistake/s were made. This basically requires re-doing the work and inspecting every step until all the mistakes have been resolved.
46- I am considering the purchase of a used vehicle. How can I check the transmission?
I suggest you take the van to a local ATRA transmission shop where the transmission can be evaluated "hands-on" to determine the present condition of the transmission. They should be able to point out any problems relative to the operation of the unit, and by removing the transmission pan, they can check for an accumulation of material that would indicate impending problems. Also, they can get an indication by checking the pan gasket whether the transmission has had previous maintenance.
Some of the "clues" that a professional transmission technician can use to evaluate a transmission may not be obvious to the average person. Also, a fresh pan gasket and new transmission fluid and filter may indicate an attempt to cover up signs of major wear in order to sell the vehicle. Few buyers will go to the trouble and relative inexpensive cost to have the transmission itself evaluated by a transmission professional resulting in a major expense shortly after their purchase.
When it comes to the purchase of a used vehicle, it's usually buyer beware.
47- I have a late model GM vehicle and the computer shows a P1870 code. What does this code mean?
Translated, the code means that the torque converter clutch is slipping. Beginning in 1980, GM modified their torque converters from a simple fluid coupling device between the engine and transmission by adding a piston to create a mechanical connection to increase gas mileage.
When these transmissions evolved into computer controlled units, sensors monitor the slippage in the torque converter. Theoretically, there should be zero slippage when the piston is applied, but in reality there is some allowable slippage that is acceptable. In time, valve bodies that control the functions of the transmission developed a wear problem in the area that controls the application of the piston. This wear allows the piston to slip beyond the allowable limits and sets the code in the computer.
If caught early enough, the valve body wear can be repaired and the transmission will work well. However left unattended, the torque converter will have to be replaced along with the valve body repair. (This will be evidenced by blue heat marks on the torque converter housing.)
While GM is familiar with this problem, don't look for any recalls.
48- I need to have work done on my transmission, but I want to know the "worst case" cost before I take my vehicle in, so I know I have enough money.
At first, this may sound like a reasonable request, but think about it. By taking your vehicle into a repair facility after getting a "worst case" estimate, you have essentially given your approval for the worst case cost regardless of the real repair cost. Do you really want to set yourself up like this?
Second, the worst case scenario is extremely rare. Taken literally, this means that your transmission is so badly worn that it is not repairable and will have to be replaced by another unit. And, if it's computer controlled like most transmissions are these days, the computer will also have to be replaced. How about additional sensors that feed the computer information? How about the engine and transmission mounts?
To answer this question accurately, the answer would have to include everything that could go wrong with a transmission along with any and all of its control devices.
The real question to ask is, "What will be the cost to diagnose my transmission?" If the answer is that it will have to be removed, disassembled, and inspected, then what is the anticipated cost range that I can expect? Many people get in too deep by getting a cheap inspection quote and not knowing the real cost of repair until their transmission has been removed and disassembled.
Now it's too late to decide that you don't want to invest that much money! The transmission is out and torn down. To attempt to assemble and install it, and expect that it will perform as well as it did before the inspection is not reasonable.
After a transmission is diagnosed while it is still in the vehicle, a repair cost range can be given. It is not accurate to the penny because an internal inspection has not been done, but at least you have a reasonable estimate to make your decision whether or not to proceed with the repair.
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