All parts should be cleaned and, if necessary, properly lubricated prior to assembly and/or installation. Different types of lubricants are required in different instances. In some cases I deviate from the service manual, based on information gleaned from those with many years of successful rebuilding experience, because a superior procedure has been developed. There have been significant advances in materials and lubricants since these vehicles were first built and the factory service manuals published. Even without upgrading to a high-performance rebuild kit, there have been changes that require things be done differently.
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Even though parts are direct replacements for the original factory items, there may be design or material changes. Several of the items in our rebuild kit, including the friction bands, were designed significantly different from the original factory parts. Functionally, they are as good, or usually even better, but may require a different installation process.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #1
A typical rebuild kit includes gaskets, seals, O-rings, new friction materials, check balls, and even new sealing nuts for the band adjustment bolts. There may be extra parts if the kit covers multiple applications, so don’t get upset if there are leftovers. Just be sure you use the correct items for your specific application. Materials technology has improved quite a bit since firstgeneration Mustangs were new. These new materials provide better sealing for the transmission to reduce the likelihood of leaks, and these often increase the service life after a rebuild. Although not shown here, we also replaced some of the hard parts such as springs, the vacuum modulator, and even one of the friction bands. Some rebuild kits include more than others, most items are available individually as well.
When trying to determine which seal or O-ring goes on a particular part, it is best to first separate the new pieces by seal type (square seal versus O-ring, for example) and then stretch them in pairs to get the relative lengths of each. Start with the largest component of each type and install the seals with the appropriate lubricant after first ensuring the sealing groove is clean. While most elastometric seals are not directional (and O-rings never are) check to make sure that is the case before installing it. There can be special features on the seal that may require a particular orientation. Seals that are molded onto a metal or plastic housing generally need to be installed in a specific manner. Always use the proper type of seal installer and lube.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #2
Most of the spacer plates (or steels) are nondirectional, but some must be installed in a specific manner. If there is a bevel, such as that shown, here then it must face into the clutch assembly, toward the friction discs. This is usually necessary to clear the retaining clip that holds the whole assembly together. All of the friction discs and spacer plates must be lubricated with transmission fluid prior final assembly. This swells them slightly, so we need to make sure there is sufficient clearance between them after everything is assembled. For high-pressure items, such as thrust washers, assembly grease should be used. Sleeve bushings and roller bearings generally also benefit from a dab of grease in certain locations. A thin film is best, and the components should also be rotated without any load to ensure the grease gets spread evenly.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #3
The inner planetary gear set is an example of where multiple lubricant types should be used. The thrust washer needs to be greased while the gears themselves should only be lubricated either with transmission fluid or lightweight oil. Be sure to not only lubricate the thrust washer itself but the surface it will contact as well. In this photo, both the thrust washer in the drum assembly and the tip of the planetary housing are greased. Note how dabs of grease were used to hold the larger thrust washer onto the planetary housing, so it didn’t fall off when the planetary housing was turned upside down and installed into the drum assembly. Lube the splines also.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #4
The shift lever seal must always be replaced when rebuilding a transmission. It is simply pried out and replaced while the shift lever assembly is out of the housing. Do not simply tap it in with a hammer. Use the back of a socket or seal installer with a flat face that applies pressure evenly. The valve body must be removed to get the shift lever out, so this is definitely the time to do it. The new seal must be lubricated before the shift lever is reinserted. Proper installation of this seal will minimize the chances for one of the most common leaks. This seal has a particularly tough job because it is more exposed to contamination than most of the other seals on the transmission, plus the shaft only rotates through a partial arc.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #5
Reassembling the servos is not very complex, but a few tips apply. Be sure to lubricate the sealing surface and the shaft with a light film of oil. There shouldn’t be too much play between the shaft and its bore, but it needs to slide freely. Be very careful when pushing the piston down into the housing, so you don’t tear the edge of the seal. A thin film of RTV on the cover gasket can also help prevent leaks. It is also best to tighten the cover down slowly and evenly in several steps to prevent warping and leaks. Start with the bolts that hold the vent tube bracket and then go diagonally across in a star pattern to the final torque.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #6
After both servos have been installed, check their operation by applying an air source to the appropriate ports in the housing. Just a quick burst of air should be enough to verify the shaft isn’t sticking and there are no leaks. Be sure to not use too much air pressure or else damage can result. Here, you can also see the rear case bushing. If this is in good shape, it’s probably best to reuse it because these can be hard to source in the proper size. If there are any minor imperfections that need to be removed, lightly rub with a fine emery cloth or pad.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #7
Some front servos have a sealing ring, rather than a square-edged seal on the piston. The same basic instructions apply for making sure the shaft and sealing surfaces are lubed with oil. However, you also need to properly align the cover so the gasket properly seals a port. It cannot simply be installed in any orientation. Hold the gasket onto the housing with RTV or grease and tighten the bolts slowly/evenly. Some servo covers are also stamped with a letter to designate the firmness of the spring: “H” is normal; “R” is firm. Ours was “H.”
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #8
When installing the rear sprag, it may be necessary to move it around a bit to ensure it seats fully. The springs can sometimes stick together and/or contact the sprag, thus causing improper action. Therefore, these need to be greased applied to the necessary surfaces and check to make sure the sprag freely rotates clockwise. It should lock if you try to turn it counterclockwise. Also check the movement of the linkage going back into the case to ensure it doesn’t stick. Lubricate as needed.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #9
When installing the governor support housing, make sure the two tubes fully engage their respective ports in the main housing, but also that the bore of the housing is centered as well as it can be over the sprag assembly. To the extent possible due to the tolerances of the retaining bolts, move the housing around as the bolts are being tightened to provide the best concentricity. This will provide the best alignment of the tailshaft with minimal friction and potential for wear. After you’ve bolted this housing in, make sure the top surface and inner bores are wiped clean.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #10
When assembling the new rollers and wave springs into the rear sprag assembly, it may be necessary to occasionally rotate the inner race to ensure the springs seat fully. While grease should be used as lubrication between the thrust washer and the race, only oil or transmission fluid should be used between the race and the rollers. It’s best to squirt some at each roller after all the pieces have been assembled. Turn the race to spread it.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #11
Before installing any of the bands, soak them in some transmission fluid for a short while. This ensures the friction material has absorbed enough prior to first operation. Check the reverse band, shown here, one last time for excess wear at the points where the adjuster tips contact the band. A small amount of polishing is fine, but any grooving or cracking means for replacement. Before installing the rear drum, its outer surface should also be lightly sanded with fine emery cloth or a ScotchBrite-type pad to remove any imperfections and create a smoother, more even surface for the band to grip. There’s no adjustment.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #12
After proper inspection and installing new sealing rings, the tailshaft can be inserted into the governor housing and through the sprag and reverse drum. This will help line everything up for when we stack on the rest of the drums. Do not bolt the governor on yet. This is a good time, however, to put on the new band-adjustment sealing nuts and start the band adjustment bolts in their holes. Do not turn them in too far at this point; just thread them in far enough to not fall out.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #13
Slide the entire planetary gear and forward drum stack onto the forward part of the tailshaft. All internal parts should be lubricated as needed beforehand. Be sure that the retaining clips are fully seated. Before the drum assemblies are installed, visually check to ensure all retaining clips have been fully seated into their grooves. Failure to do so can result in binding and/or failure. The rear planetary carrier is especially susceptible to this issue. Loosely install the forward band, but only tighten the adjusting nuts enough to hold the band and its related parts together. We will adjust the band later. Our replacement band was a steel strap style instead of the cast design of the original part (similar to the reverse band shown previously). This design is less prone to failure because the steel strap does not crack as easily as the casting does.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #14
After verifying the input shaft is clean and free of any wear or damage, it can be inserted into the drum stack so its splines engage at the rear. The input shafts up to 1969 were the same at both ends, so it doesn’t matter which way the shafts go in. The 1970-and-later shafts have a different length spline, so you have to make sure you put the correct end in first. Use an alignment bolt to hold the front pump housing gasket in place; a little RTV on the back of the gasket helps, but you still need the alignment bolt to locate the pump. The pump should have been pre-lubricated and have a new front seal and new sealing rings. Use oil to lubricate the sealing rings and grease to lubricate the bushings for the input shaft and the torque converter coupling. If you have a seal on the pump housing, rub some oil on it too and be careful pushing the pump into the main housing so as to not tear it.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #15
The bell housing can now be installed. The bellhousing bolts also hold the front pump assembly onto the main housing and keep it from rotating, so these bolts are longer while the shorter bolts are for the tailshaft housing. The inner/input shaft transmits the engine power to the rest of the transmission. The outer splined shaft does not turn, so it just supports the torque converter. The seal is necessary because the torque converter coupling passes through the seal and drives the inner gear to drive the pump. A little bit of oil should be rubbed on the front seal and the torque converter coupling when they are assembled together. The converter will have to be rotated until it can be pushed all the way in because the coupling drives the gear via a flat relief that mates with a similar key on the inner gear. This ensures whenever the engine is turning the pump in the tranny is also working to build pressure.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #16
The factory manual details the procedure for adjusting the band(s) in your particular transmission. Generally, you turn the adjusting bolt a specific amount until you feel tension. Then you adjust it from there to the final setting. Always use new sealing bolts with a small amount of RTV applied around the seal itself as extra insurance against leaks. This is easily the most critical adjustment you will make when rebuilding the transmission, so be extra careful to get it right. An improper adjustment will cause all kinds of problems, from excessive wear to complete transmission failure. It’s also a lot better to do it now than in the car.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #17
Use air pressure to blow out the appropriate port for the front servo to ensure the band functions properly when the whole assembly is assembled. You can clearly see the difference in design here between the steel-strap-type band and the original-style cast band. Beyond the advantages previously mentioned, the steel strap design will apply more even pressure and thus be smoother and wear more evenly, assuming it is properly adjusted. Squirt a small amount of transmission fluid on both bands and at the gaps on the planetary gear and drum cases to ensure some lubrication at initial startup.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #18
Install this small screen filter in the governor support housing. The governor assembly is especially sensitive to any dirt or debris in the fluid, and this helps catch any that may be headed toward it. Blow out the passages with an air nozzle to try to dislodge any dirt. Then clean it in a parts washer or with a suitable spray, dry it, and install it. Replace it if it’s damaged in any way. Make sure the mounting surface for the governor is clean and smooth before you install it. (These machining marks, seen here, are fine.) Torque the retaining bolts evenly and slowly, preferably in a star-shaped pattern.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #19
After having a new seal installed and putting a little RTV on its gasket, the tailshaft housing can go on along with some of the smaller items such as the vacuum modulator (don’t forget the steel rod!) and the fittings for the transmission oil cooler lines. Depending on how you plan to install the tranny, you can also install its mount. Sometimes, it makes more sense to wait until the transmission has been lowered into the car before you put the mount on, to avoid it contacting anything and to have more room.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #20
Use light pressure with a mild abrasive pad to clean up the separator plate for the valve body. This helps it seal better and removes any minor imperfections. Do this after you make any needed modifications (like drilling extra holes), should they be required with your rebuild/highperformance upgrade shift kit. Make sure you wipe off any residue and otherwise keep the plate as clean as possible.
MUSTANG RESTORATION: AUTOMATIC TRANSMISSION ASSEMBLY – STEP #21
Reassemble the valve body with the filter. Be sure to put all check balls back in the proper locations in the valve body and check to make sure all plungers move freely and do not stick. Do not use any type of sealer on the valve body gaskets. You need to make sure everything is clean and dry when it goes back together. Do not overtorque the bolts because it could warp the valve body or crush the gasket and cause leaks. Put the shift lever in the proper position (usually straight up for Mustangs), so the valve body can be lowered over it and line up the manual control valve with it correctly. A thin film of RTV on the pan gasket can help avoid leaks but use as little as possible; you don’t want bits of RTV squeezing into the transmission/filter.
The finished transmission now has the neutral safety switch, the downshift control cable, the vacuum modulator hard line, and the shift linkage added to complete it. We’ll add the mount and dipstick/tube after we lower it into the car. Don’t fill it until it’s fully installed and be sure to use the correct type of fluid. If you’ve made any modifications, you should add additional cooling and/or use a compatible high-performance fluid just to be safe.
As the transmission is assembled, verify operation or functionality. This could mean anything from simply moving a lever or shaft to make sure nothing is binding, to using air pressure to ensure proper function of a servo. This helps ensure components are operating as intended so you do not have to tear the transmission apart again in order to fix something. Even though the fluid will not be at pressure, many functions can still be checked, at least in a basic sense. It’s also a good idea to move things so lubricants put on during assembly are evenly distributed before the transmission is operated under load. This can help prevent problems on first use.
The final stages of assembly include not only the installation of major parts but also various adjustments beyond those already mentioned. The factory service manual is the best place to find out what particular adjustments apply in your case. I’ve provided a few reminders and also briefly described some of the remaining steps.
Written by Frank Bohanan and Republished with Permission of CarTech Inc