Custom Transmission Rebuild
How To Rebuild an Automatic Transmission
- Automatic Transmissions have a lot of parts, and are not exactly simple, rebuilding an automatic transmission requires an experienced transmission mechanic specifically trained to do so.
- Cleanliness is of utmost importance. Any place where there is wind and dust and dirt is probably unacceptable. We have created a “clean room environment”, with excellent lighting for the assembly of your transmission.
- Likely a few of specialty tools will have to be purchased for the correct rebuilding of your transmission, and it is not entirely unlikely that those will be expensive tools. Of course, keep in mind that these tools tend toward manufacture supplied exclusively and that these new tools will be required to complete this rebuild correctly.
- We always have the current factory manual or access to current manufacturer updates and computer edits.
- You need an expert on this subject, and we are here to help.
With that in mind, it's time to break out the tools and get dirty. The following is an explanation of the common steps needed to rebuild your transmission, however since there are a never ending variations in transmission design this may not apply to your specific transmission.
- Transmission Removal: There are a couple of ways to go about doing this, and that’s the real danger! Improper removal will permanently damage the vehicle, and greatly shorten the life of the transmission. Basically, you drop the transfer case and remove it out the bottom, unbolt the engine mounts, unbolt the transmission from the cross member and then unbolt the cross member from the frame. Some cars you will pull the engine and transmission as a single unit following the transmission with a bucket to catch the fluid. The transmission is removed from the engine. In rare instances, you are able to save your torque converter and reuse it. After the transmission is out the entire transmission should be set with the tailshaft assembly pointed down to drain the remainder of the transmission fluid out into an approved storage container.
- Torque Converter Removal: With the transmission removed from the engine normally you will just pull the torque converter straight out. even if it is not being reused, it will be returned for remanufacturing and there is normally a core charge for the replacement torque converter.
- Transmission Oil Pan Removal and inspection: With the transmission upside down, we unbolt the pan. Many times, the pan will need to be pried off. If a previous repair was made by an inexperienced company we find RTV has been used to glue on the pan. Automatic transmission fluid will dissolve RTV, so consequently, we find a substantial amount of RTV stuck to the transmission filter, and floating around in the bottom of the transmission. We also look for an excessive amount of wear, cracks, and particulate matter. This will determine if we replace the torque converter.
- Valve Body: As soon as the pan is off you can see the valve body. This is the hydraulic brain for the automatic transmission. It is full of sliding valves, springs, and check balls. Rebuilding the valve body is fairly straight forward, but first, it has to be removed from the transmission. It is held on by a few bolts on each end and has the park lock rod attached to the manual shift by an e-clip. you can remove the whole valve body without removing the park lock rod from the valve body and the park lock rod just slides out. When a substandard mechanic rebuilds a transmission, they fail to properly rebuild this vital control system, and we often find them full of particulate matter. Judging from the dirt that we routinely clean out of the valve body’s I don't think other companies ever even had them apart.
- Rebuilding The Valve Body: This is no more complex that taking the valve body apart, cleaning it carefully, and putting it back together, except for one detail: The valve body can have over 100 different parts and they all look more or less the same. This is where access to the current updated information is critical. We laid each part on a clean table, labeled what it is, and then proceeded to do the next part. Then carefully clean each part, setting the clean parts on a clean table. We use APPROVED solvents that will not leave a residue. Lint left in mechanisms can cause problems so we never use either shop towels or paper products that will leave lint behind to clean the valve body (or any part of the transmission for that matter). When everything is properly cleaned and dried lint free we will reassemble the valve body in reverse order torquing everything to proper specifications as per the manufacturer.
- Rotating Assembly Endplay Measurement: Both the input shaft and output shaft endplay need to be measured before the rotating mass is disassembled. This is because a selective thrust washer is used to determine endplay and it needs to be determined whether the selective thrust washer needs to be replaced, upgraded or if the transmission case itself is not rebuildable. Once again, the end play specifications are in the manufactures information.
- Tailshaft Assembly Removal Inspection: On the rear of the transmission there is a short aluminum housing that adapts the transmission to the transfer case. It also houses the park mechanism, the governor, a ball bearing, a seal, and some of the output shaft. We remove the bolts that hold the tailshaft assembly to the main case and slide the tailshaft assembly off. The ball bearing is removed, and the seal is removed with a seal pusher. We then remove the governor, which is a small valve assembly that is held on the output shaft with a pin that goes through the output shaft. The governor is bolted to the park mechanism which rides on a spline on the output shaft. Once this is all apart we professionally clean it and reassemble it.
- Accumulator Piston and Spring removal from the case is the next step.
- Front Pump Removal: Commonly there are several bolts holding the front pump to the transmission case. After we remove them, and while the front pump is now still in the case, we must tighten the front band until the front band is tight around the front drum. This keeps tranny guts from bouncing out and bending or breaking. Depending on the manufacture a specialty puller or a slide hammer may be used. Other ‘home made’ methods used in the transmission can cause hidden damage that may not become evident until after the vehicle is driven for a while.
- When do we rebuild the Front Pump? When we are the first transmission rebuild we inspect and usually can rebuild the front pump. But due to the incompetence of many in this industry many times we don't have that option. The front pump is bolted to the reaction shaft support. The front pump and the reaction shaft support really need to work together as one unit. When we replace one we replace the other. If in good condition we can rebuild the front pump.
- Front Band and Front Clutch Removal We will pull out the complete assembly and leave together until it's time to rebuild it by loosening up the front band and sliding the band strut and band out the front of the transmission housing. We then remove front clutch assembly by grabbing the outside of the clutch housing, while being careful to NOT pulling on the input shaft as that can cause damage and should be done after the front clutch assemblies is removed.
- Input Shaft and Rear Clutch Removal: We then need to remove the input shaft and the rear clutch assembly hopefully it will slide right out of the case. There is a thrust washer that goes between the input shaft and the output shaft that needs to be retained and inspected. It may stick to either shaft or it may fall off into the transmission. Again there is a large number of parts that need to be disassembled, identified, cleaned and inspected, some of which will be reused and some replaced.
- Driving Shell and Output Shaft Assembly has machined surfaces that must be protected during removal. We are extremely careful pulling the driving shell and output shaft straight out of the case. The driving shell is a big bell shaped item. Care should be taken to protect it during removal, cleaning, and storage.
- Rear Band and Drum Removal should be performed according to the manufactures procedures; however, many will just Hammer it out with a punch. The potential for damage is real and may remain hidden until the vehicle is driven.
- Overrunning Clutch needs to be removed, it is basically a hub and a bunch of little springs and rollers that will not allow the rear drum to turn the wrong direction. We remove the hub, springs, and rollers and store them. The spring support may stay in the transmission housing unless the inspection shows it needs to be replaced.
- Front Servo Removal takes a fair amount of force. We will then remove the plug on the transmission housing that leads into the front servo bore. We then compress the front servo piston so we can place a tool in to hold the servo in place while we remove the snap ring that holds it in. These many times require two people.
- Rear Servo Removal is much easier to get out. Hopefully, with this one, we can just compress it and remove the snap ring.
We should now have an empty transmission case with a whole bunch of properly labeled and protected transmission parts on a clean work table. Now it's a matter of Cleaning, inspecting, and rebuilding the multiple assemblies. We will replace the multiple seals and clutches.
All of the above was to show the care and detail required by a professional Transmission technician.
Contact us at (918) 261-3656 for further information.
5649 S Mingo Rd F, Tulsa, Oklahoma, 74146
Call Us: (918) 261-3656
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