Transmission Replacement: What You Need To Know.

So Murphy’s Law has caught up with you; your cranky transmission has finally broken down altogether- just at the moment you can least afford it.  The cost estimates from your local repair shops give you nightmares; your next pay check is two weeks away, and even if you wanted to go with the lowest estimate (from Acme Transmission Repairs) of 6-8 hours of labor at $120 p/ h, plus the cost of the transmission, you just know you are not going to be able to make ends meet next month of you do go with Acme Transmission Repairs, or anybody else, for that matter.

What to do? Do you buy a used transmission form the local junk yard, or do you spend more on a rebuilt unit? While used transmissions can usually be had for only a few hundred dollars, you never know what you are getting; for all you know it may be in a worse condition than the one in your car- the one that left you stranded on the highway in rush hour traffic.

Rebuilt transmissions on the other hand, are always significantly more expensive, but they also always come with a warranty that goes way beyond anything the junk yard is likely to give you, which makes a rebuilt unit the better choice by far. If money, or the lack of it was not an issue, you could off course turn the problem over to Acme Transmission Repairs but in this case, money is an issue, and you must consider the possibility of replacing the transmission yourself.

However, the most you have ever done on your car is replace the brake pads, and the prospect of having to remove the transmission is a daunting one to say the least. Well, it looks far more difficult than it actually is, and while this article cannot provide detailed instructions for the removal of all transmissions from all cars, the procedure is much the same in all cases.

All you need is a basic mechanical aptitude, full sets of wrenches and sockets that fit your car, a good repair manual, and the determination to do it yourself. However, not even the best repair manuals tell you all you need to know, so read on, and we will guide you through the process of a transmission replacement.

Required Tools.

You do not need a truck load of tools to replace a transmission, so if you not have full sets of wrenches and sockets, you can buy what you need for about $200-$250, which is about the same amount you would spend on a couple of hours of labor at Acme Transmission repairs. Most auto parts shops sell tools of reasonable quality, and unless you buy the cheapest brands, you will have them for many years to come. You will need the following:

  • A good repair manual for your car. Get one that includes step-by-step pictures- even if the pictures do not always tell the full story, they are invaluable nevertheless.
  • A set of wrenches from ¼” to 1¼” to fit American cars, or a set from 6mm to 32mm for European cars. Make sure the wrenches are open ended on one side, and ringed on the other.
  • A set of sockets in the same sizes, but with a ½” drive, which is the size across the flats if the square hole in the back of the socket. Make sure the socket set includes at least one 12”-long extension bar.
  • A set of suitable Allen wrenches since on some cars, the brake callipers, and some suspension components require the use of Allen wrenches for disassembly.
  • An engine holder. This is an essential  device to which you attach the engine on front wheel drive cars, and from which the engine hangs when cross members and engine mounts are removed. A proper engine holder is also adjustable, a feature that allows you to adjust the angle between engine and transmission when the time comes to mate the transmission to the engine on re-assembly.
  • If your car is a front-wheel drive, measure the nut in the centre of the hub across its flat sides. This nut holds the CV joint in place, and you need a socket to remove it. Buy this socket if it is not included in the socket set- which is entirely possible.
  • A couple of 8”-long flat and Phillips screw drivers.
  • A trolley jack that is rated for at least 2 tons. Some equipment hire establishments hire them out by the day for a small fee.
  • Four adjustable jack stands rated at 2 tons. If you cannot hire them, look for them on EBay. You should be able to get four at considerably less than $100. These are essential since you need to get the car at least 24-30 inches off the ground. Never use bricks, logs, plastic crates, or anything else but proper jack stands to support the car.
  • A container to hold the transmission fluid when you drain it. Old plastic one-gallon oil cans with one flat side cut out work great, but ensure it has its screw-on lid, or most of the fluid will end up on your paving.

Other Essentials.

  • Old clothes, since this is a messy job. Also, hire an assistant if you cannot commandeer one- a transmission is heavy and unbalanced, which makes it necessary to have an extra pair of hands to help with the heavy lifting once you are ready to separate the transmission from the engine. Make sure the assistant has old, disposable clothes as well.
  • A clean tarpaulin to lie on under the car if you do not have a mechanic’s crawler.
  • A clean, dry, level surface such as a garage floor, or a level paved surface. Do not work on sand, since there is no way to prevent sand and dirt getting into places where it will cause damage later on.
  • A clean one gallon bucket to hold all the bolts, nuts, screws, clips, and other stuff that you are going to remove. Place everything in the bucket as you remove it to prevent anything getting lost. (Repair manuals never tell you this.)
  • A good camera or smart phone to take as many pictures from as many angles as you can during the removal process. The pictures in the manual will only cover the main points, which means that you may be at  a loss to find holes for all the bolts and nuts that you have removed. Taking lots of your own pictures will help you in ways that no manual can, since manuals do not take into consideration the fact that the people using them might never have removed a transmission before.
  • Replacement transmission oil or fluid.
  • Lots of old rags to wipe tools, and off course your hands.
  • Good quality hand cleaner.
  • At least one full day of free time.

Getting Down To It.

  • Something else the manual will not mention is the fact that you need to loosen the CV joint retaining nut before you even jack up the car. This nut is torqued to about 300Nm ( 221 ft/lbs), so use the weight of the car to prevent the wheel turning with the force required to loosen the nuts. You will not be able to loosen the nuts with the stuff in the socket set alone, so slide a length of steel pipe over the T-bar in the set to increase the leverage until the nut is freed. Do not use a torque wrench to loosen these nuts- you will almost certainly damage it beyond repair.
  • Retain the steel pipe- you will need it to retighten the retaining nuts on reassembly, but if you have access to a torque wrench, use it to re-torque the nuts to their specified values. Only use the pipe as a last resort!
  • A good manual will tell you where the jacking points on your car are. Never use other points, and never place the jack stands under the floor boards, or other soft points. Place the stands under hard points such as cross members, and ensure the car cannot slide off them when you remove the jack.
  • From this point on, you should be able to remove everything that is in the way of getting at the transmission. However, it is critically important to follow the instructions in the manual exactly to prevent damaging anything. For instance, if the manual says to remove the battery, do so in the manner prescribed because if you do not, you could easily short out live wiring- with possible fatal consequences for the electrical system.
  • Perform all steps in the exact order they are described in the manual, but remember that on older cars, some, if not all fasteners may never have been removed, which means that they may not be as easy to remove as the manual says. However, do not use excessive force- prevent skinned knuckles, broken fingers, or worse, a damaged nut or bolt head that may be impossible to remove because of the damage to it by taking it easy, and supplying force gradually until the fastener loosens.
  • Repair manuals always make things look easier than they really are, and unless you have some experience in transmission removals, you are bound to run into snags. Confined spaces, tools that seem too big to fit into them, and wiring, pipes, hoses, and suspension components that are in your way can make things difficult, which is why it is important to follow the directions in the manual exactly. Deviating from the order of things and taking short cuts will not help you in any way- all it will do is make an already difficult job even more so.
  • After about four hours or so, you should now be ready to remove the transmission from the car. However, be prepared for the weight of it as it separates from the engine. Repair manuals are usually silent on this, so place an old tire (without the rim) under the transmission to prevent damage if it should slip from your grasp and fall to the ground. With the help of your assistant, lower the transmission onto the tire, but beware of sharp edges that could leave you bleeding, which is another thing that repair manuals are also silent on, so take proper care!

Putting It All Back Together.

Your manual will probably say something silly like “ Re-assemble all parts  in the reverse order of removal.” At first reading, this might seem like a reasonable statement, but don’t be fooled. Unless you have some experience in this field, you will find that putting cars together is several times more difficult than taking them apart, which is where the pictures you took during removal come into play, but there are a few more things to remember, such as:

  • The replacement transmission will have no oil or fluid in it. So to make things easier, identify the filler plug and loosen it before you fit the unit, but do not fill the transmission at this point. In some cars, removing the filler plug is extremely difficult with the transmission in place, so by loosening it beforehand, you save yourself a bit of trouble, and the possibility of damaging the plug later on. However, make doubly sure you tighten the plug after having filled the transmission with the correct grade, and amount of lubricant.
  • When mating the transmission to the engine, make sure the mating surfaces are in full contact before tightening any bolts or other fasteners. On manual transmissions, the clutch plate can suffer serious, if not irreparable damage if the input shaft does not enter the hub in the plate cleanly, and attempting to “pull” the transmission into place by tightening fasteners prematurely can destroy the clutch.
  • On automatic transmissions, you have to keep the torque converter on the input shaft at all   times to prevent damage to the oil seal between converter and input shaft. Manuals do not always explain this, so if needs be, place the transmission on the trolley jack to prevent jerking movements that could dislodge the torque converter. By raising the transmission with the jack, while at the same time adjusting the angle of the engine by manipulating the engine holder, the transmission and engine can be brought into contact without damage to the oils seals.
  • Although most repair manuals are adamant that all fasteners should be torqued to specified values, the fact is that it is not always possible to do this. Even if you have access to a toque wrench, the confined spaces in modern cars more often than not, makes it impossible to even reach some bolts and nuts with a torque wrench. While all accessible fasteners should certainly be torqued, those that are not should be screwed down as tightly as possible- without damaging their threads.
  • If this is your first transmission job, take things slowly, and consult the manual with every step. It is also important to double check each step to ensure you have not missed anything on the one hand, and that you have properly tightened all fasteners on the other. The best way to do this is to insert and fasten one bolt or nut at a time before moving onto the next. This way you will not forget anything, and you will thus not have any parts or fasteners left over after when you are done.
  • On a front wheel drive car, you will have had to disassemble the brakes to remove the drive shafts, so before you re-assemble the brakes, make sure your hands are free of oil and grease to prevent contamination of the friction surfaces. There is little point in spending a day or more replacing a transmission only to end up with no brakes because of oil and grease contamination.
  • On a rear wheel drive vehicle, make absolutely sure you replace the bolts holding the driveshaft to the differential flange the right way round. If you get this wrong, the bolts can work themselves loose, with very serious consequences should the drive shaft detach itself from the differential.  Consult the manual, or even better, take your own pictures before you start disassembling anything.

And There You Have It…

Congratulations! You have achieved no small thing by successfully replacing a transmission, and provided you followed the instructions in the manual exactly, you should now have a fully operational vehicle with no parts or fasteners left over.  Moreover, you will have saved several hundred dollars in labor costs, but  to prevent a repeat of the above process, there are some  things to keep in mind when it comes to caring for your new transmission, such as the following:

  • Rebuilt transmissions are not necessarily leak proof, so be on the lookout for oil stains on the ground where you normally park. If you become aware of oil leaks, contact the supplier immediately, and do not drive the vehicle until the issue has been resolved.
  • If the new transmission is noisy in any way, or does not shift smoothly, contact the supplier and do not drive the vehicle until the transmission has been inspected professionally. There is no such thing a “breaking in” period for transmissions- if it is noisy or has shifting issues, there is something wrong with it, and it must be replaced. Transmissions do not “loosen up after a while”, so do not fall for this excuse.
  • On some automatic cars, there may now be some illuminated warning lights on the dash board. This is not necessarily a problem, since some management systems register the fact that certain electrical connections had been undone. Simply take the car to a reputable repair shop to have the lights turned off with suitable diagnostic equipment.

Happy driving!

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