Cart
Checkout Secure

Got a Question? Call Us

1-800-551-4754

Mon-Thurs 7:30 am - 5 pm | Fri 8 am-12 noon CST

GM Turbo 350 Transmission Removal Guide

Removing and installing transmissions can be a difficult undertaking. The vehicle must be lifted high enough to get the transmission in and out from underneath. This isn’t too difficult with pickup trucks; as a rule, they’re pretty high off the ground to start with. For most cars, however, the vehicle must be lifted and well supported.

 


sa215small
THIS TECH TIP IS FROM THE FULL BOOK :

GM TURBO 350 TRANSMISSIONS: HOW TO REBUILD AND MODIFY

For a comprehensive guide on this entire subject you can visit this link:

LEARN MORE ABOUT THIS BOOK HERE

 

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: http://www.cartechbooks.com/techtips/gm-turbo-350-transmission-removal-guide/


 

Support the Vehicle

A vehicle lift makes transmission removal and installation much easier. It’s simply easier to stand under the vehicle to work rather than lying under it with the vehicle raised by a floor jack and supported on jack stands or on a set of car ramps. Even so, for most of my adult life I did not have a lift in my garage or shop. I have removed more transmissions the hard way rather than the easy way.

 

Shown here is a 4-post lift. Having the vehicle on a lift makes transmission  removal and installation much easier. The lift provides a stable support and you can stand under it. I still remember the days of doing these jobs on my back in my driveway! The lift was one of the best purchases I ever made; I can’t believe that I worked for so many years without one.

 

I have raised the vehicle slightly and lowered the engine oil pan onto a couple of blocks of wood. This supports the engine when the transmission is removed. In most cases the vehicle’s exhaust system effectively supports the engine, but it can still tilt back a little. Some applications also require that the exhaust system behind the manifold or headers be removed to have sufficient clearance. This necessitates some support for the engine.

 

 

Another option is to make an engine support from a piece of 4 x 4 and use a floor jack to raise or lower it. Although it appears a bit crude, it is an excellent engine support. If a suitable engine support that goes across the shock towers is not available, this is a nice option for front-wheel-drive transmissions. The wood 4 x 4 is actually attached to the flat plate on the floor jack with 1/4-inch lag bolts so it does not slip.

 

A screw jack can be used as an engine support if your shop’s lift has a movable center-jacking beam. Screw jacks are in the spare tire area of nearly every car sold in the past several decades, which makes them readily available at most salvage yards. They require much less clearance than a hydraulic bottle jack and have plenty of capacity to hold an engine in place while the transmission is removed.

 

 

Here’s a common problem with some vehicles that have a rearlocated distributor. If the engine isn’t effectively supported, it can lean back and break the distributor cap; in extreme cases it will bend or break the housing!

 

A transmission jack is essential when using a lift. The jack holds it in place for hours and allows the transmission  to be lowered slowly to get past obstacles.

 

It takes a lot of clearance to lift up large trucks and SUVs. I had to modify one truss in the shop for cab clearance when lifting larger vehicles, even though I had 131⁄2 feet of clearance under the trusses.

 

If the transmission is not equipped with a drain plug, just remove the transmission pan to drain it. It is best to leave two bolts in place on one end of the pan or the other, and allow it to tilt downward to drain most of the fluid from it.

 

Large trucks and four-wheel-drive vehicles with additional ground clearance may require more height capabilities. Accordingly, I added an extension to the transmission jack.

 

Even if a lift is not available, you can still do some things to make the job easier and safer. Always support the vehicle with a good set of floor jacks once it is raised into position for transmission removal. There is no such thing as too much support. Large oak or hardwood blocks also make excellent support fixtures. Whether using jack stands or blocks, make sure that the vehicle is supported well forward of center and on the vehicle’s frame or main crossmember. You cannot have too much support and you can never be too safe when it comes to supporting a vehicle under which you are working. For example, a truck with a solid front axle is a great place for support. With few exceptions, the engine also needs to be supported; the transmission and rear transmission mount generally help to support the engine. When the transmission is removed, the engine is not free to pivot forward or backward on its engine mounts. Few engines have mounts positioned in the middle; they are more typically toward the front. Unless you take steps to provide it with additional support, the engine’s heavy weight tilts it backward when the transmission is removed.

 

 

The engine’s exhaust system supports it to some degree, but it should not be trusted by itself to keep the engine from tilting backward when the transmission is unbolted from it. Some engines have rear-mounted distributors, and the distributor cap may be close to the engine compartment firewall. If the engine is allowed to tilt backward, the distributor cap could break and even bend or damage the distributor housing. If you are using a vehicle lift, you have several options for engine support. The four-post lift in the shop has a movable center support, so you can come in under the engine’s oil pan and use a screw jack and a block to support the engine.

Another option is to make support from a piece of 4 x 4 that can be raised or lowered by a floor jack. Although it looks rather crude, this makes an excellent engine support and a nice option for front-wheel- drive transmissions when a suitable engine support that goes across the shock towers is not available.

The best-case scenario for transmission removal and installation is to have a vehicle lift and transmission  jack. Most hobbyists do not have these items in their shops or garages, but in recent years both two- and four-post lifts have become much more affordable, and many people are installing them in their garages and workshops. They make excellent car storage when not in use, they quickly turn a one-bay garage into storage for two vehicles, one above the other. Most lifts, whether two- or four-post, require approximately 12 feet of clearance to the rafters to lift most cars high enough to work on them.

In my own shop, I had about 121⁄2 to the bottom of the trusses. This was fine for cars, but would not allow the cab of a truck up high enough to get underneath to work on it. I was able to modify one truss quickly and easily to provide enough room for the cab. To make sure that the roof still had adequate support, I doubled up support on each side and spread the load out to the two adjacent trusses. I also modified my transmission jack to provide additional lift when necessary. A transmission jack is just about mandatory when using a lift and standing under the vehicle.        

You can work off the ground with floor jacks, but a transmission jack made for that purpose is much better. Floor-type transmission jacks provide additional lift capabilities compared to a standard floor jack. They have more room for travel, and a wider base with the ability to strap the transmission to the jack, and can tilt it into position during removal and installation.

 

 

Prep for Removal

Once you have the vehicle supported and safety jacks are installed, you can begin removing the transmission. It is always best to drain the transmission fluid first so you avoid any spills out of the tail housing area or through the filler tube hole (if the tube is removed).

 

Battery Ground Strap

Remove the ground strap from the battery to make sure the engine isn’t started while the transmission is out of the vehicle. Removing the ground strap also kills the current to the large battery wire that leads down to the starter solenoid and prevents accidentally grounding it out when the starter is removed.

You may have to remove the starter to access the torque converter bolts. Doing so allows plenty of room from the front side to effectively torque them down once the transmission and torque converter are back in place. In most cases, the starter wiring can be left in place, and the starter can hang from a coat hanger or heavy wire during this procedure.

 

The ground strap should be removed from the battery to make sure the engine isn’t started while the transmission  is out of the vehicle.

 

You may have to remove the starter to access the torque converter bolts. Doing so allows plenty of room from the front side to effectively torque them down once the transmission and torque converter are back in place. In most cases, the starter wiring can be left in place, and the starter can hang from a coat hanger or heavy wire during this procedure.

 

If the transmission fluid isn’t drained, use a spare yoke to keep fluid from leaking out the rear of the unit.

 

As soon as the driveshaft is removed, wrap the rear U-Joint with tape to keep it intact. There is nothing worse than having one of the ends fall onto the floor and all of the needle bearings come out of it! 

 

U-Joint

Remove the four bolts and two straps that hold the driveshaft’s rear U-joint to the differential’s yoke. Push the driveshaft forward far enough for the U-joint to clear the differential yoke and slide the drive-shaft out of the transmission. When removing the driveshaft, make sure to take extra care not to lose the caps on the U-joint. If the caps hit the floor, the tiny needle bearings are easily dislodged. A couple of wraps with some electrical or duct tape keeps things together until the shaft is reinstalled and ready to hook up to the differential yoke. If a spare slip yoke can be obtained, insert it into the tail housing when the driveshaft is removed. it will keep any transmission fluid from leaking out if you were not able to drain it prior to transmission removal.

 

Torque Converter

The torque converter must be unbolted from the flywheel and kept in the transmission while lowering the transmission. Remove the torque converter inspection cover to access the bolts. Removing the inspection cover also exposes the flywheel so you can turn it to gain access to all of the torque converter bolts. In most cases, you can use a big screwdriver or pry bar to turn the ring gear on the engine to gain access to the torque converter bolts. If not, turn the engine crankshaft with a deep-well socket and ratchet.

 

Remove the dust cover to gain access to the torque converter bolts.

 

Remove the shift linkage where it attaches to the transmission. Some applications also have a bracket under two of the pan bolts. Other applications may have the bracket bolted to vehicle frame, or farther forward on the transmission  bellhousing.

 

Use a big screwdriver or pry bar to turn the engine to gain access to the converter bolts; some applications have limited access to the front crankshaft bolt from the underside of the vehicle.

 

Remove the torque converter bolts. Many GM applications use bolts that thread into the converter. Shown here is an aftermarket converter using larger Grade 8 7/16-inch bolts and nuts.

 

Some applications have limited access or none at all to the front crankshaft bolt from the under-side of the vehicle. Large Vise-Grips (or other locking pliers) can also be used to turn the flywheel. Just be very careful clamping the flywheel so you don’t damage the ring gear teeth. The engine has to be turned one full revolution to access all of the torque converter bolts. Remove the torque converter bolts. Most TH350 and TH400 transmissions used torque converters that attached to the flywheel with three bolts. Some heavy-duty truck applications may have six torque converter bolts. Many GM applications use bolts that thread directly into the converter. Depending on the year of the transmission, the bolts could be either SAE or metric.

 

Remove the speedometer cable with channel locks or large pliers.

 

TH400s used an electric solenoid for downshifts. Remove any electrical connections to the transmission and safely secure the wiring out of the way.

 

Loosen and remove the transmission cooling lines. You must hold the transmission fitting as shown when removing the lines. With some applications, it may be necessary to lower the transmission slightly to gain access to the cooling lines.

 

Shift Linkage

Remove the shift linkage where it attaches to the transmission. Some applications also have a bracket under two of the pan bolts. Remove the rubber vacuum hose at the vacuum modulator. A long metal hose may run along the transmission up to the intake manifold on the engine. Make sure to either remove the metal hose, or unplug it at the engine so the transmission can be lowered out of the vehicle.

Locate and remove the speedo-meter cable using pliers or channel locks. Tie the cable to the frame of the vehicle so it is out of the way when the transmission is removed. Also remove any electrical connectors that are attached to any plugs on the transmission  case, as well as any electric wiring running down or along the transmission  and attached to the case at any point by wire holders. It is best to pull these items out of the way and secure them with wire, wire ties, or tape to keep them from getting caught up or damaged when the transmission is lowered from the vehicle.

 

Cooling Lines

Cooling lines can be difficult to access, and several different types of fittings were used. You must hold the transmission fitting as shown when removing the lines. Most GM TH350s and TH400s used 5/16-inch inverted flare cooling lines. With some applications, it may be necessary to lower the transmission slightly to gain access to the cooling lines. Make sure not to bend or kink them during this procedure.

 

 

Driveshafts

When working on a four-wheel-drive vehicle, you have two drive- shafts to remove, as well as a transfer case attached to the back of the transmission. The frame mount is almost always under the transfer case, not under the transmission. The transmission and transfer case can be removed as a single unit, or separated and removed individually, depending on the resources available. If the transfer case is removed fi rst, the engine needs suffi cient support to hold the additional weight of the transmission.

 

 

You must remove both the front and rear driveshaft for four-wheel-drive applications. The transmission is bolted directly to the transfer case, which supports the transmission. They can be removed as a single unit, or separated and removed individually, depending on the resources available. If the transfer case is removed fi rst, the engine needs suffi cient support to hold the weight of the transmission.

 

Two bolts attach the transmission’s rear mount to the crossmember. Once the crossmember and rear transmission mount bolts are removed, the transmission can be raised slightly so that the crossmember can slide out from under the transmission.

 

Six bolts attach the transmission to the engine. I recommended you remove the upper bolts fi rst, and leave the two bolts just above the engine dowel pins for last.

 

Crossmember and Bellhousing

Raise the transmission slightly and remove the rear crossmember. On some units it also helps to remove the rear transmission mount to provide additional clearance to get the crossmember out of the frame rails. The transmission jack must be in place at this time to support the unit.

The transmission bellhousing bolts are the last items to remove before lowering the unit. Six bolts attach the transmission to the engine. I recommend removing the upper bolts fi rst, leaving the two bolts just above the engine dowel pins for last. Some upper bellhousing bolts can be very diffi cult to access from the underside of the vehicle. Gaining access to them may require a long extension, or a combination of extensions and universal joints.

 

Some upper bellhousing bolts can be very diffi cult to access from the underside of the vehicle. Gaining access to them may require a long extension, or a combination of extensions and universal joints.

 

The filler tube is held stationary in the transmission by one of the upper bolts on the right side of the transmission. You may have to remove the fi ller tube for some applications before the transmission is removed.

 

Two large dowel pins, one on each side of the engine, keep the transmission  in perfect alignment.

 

 

Filler Tube

The filler tube can stay with the transmission with some applications. With others, it must be removed first. It depends on clearance at the back of the engine and firewall area, because the tube may be too long and not allow the transmission to move back far enough to be lowered from the vehicle. Two large dowel pins support the transmission bellhousing. They help to align and support the engine and transmission and are pressed into the back of the engine block. The transmission must be moved back slightly before it is lowered. Just move it back far enough to allow the hub on the torque converter to clear the engine crankshaft flange.

 

Transmission Jack

Most transmission jacks come with a chain or strap, which is used to keep the transmission from sliding off the transmission jack during removal and installation. Make sure the transmission is effectively strapped to the transmission jack before attempting to lower it. If you are working on the ground using a fl oor jack (without a shop lift), or pure muscle from a couple of strong helpers, take care to avoid being injured as the transmission is lowered from the vehicle. A complete TH350 or TH400 transmission weighs nearly 150 pounds, enough to cause some pretty serious damage if it falls on you.

You can modify a floor jack into a transmission jack by welding a flat metal plate to a piece of iron pipe. The iron pipe must fit snugly into the recessed hole in the top of the floor jack. Drill holes in the metal plate and use bolts to attach the plate to a transfer case mount. The modified floor jack in the picture has been used successfully to pull four-wheel-drive transfer cases and transmissions as one unit.

 

Use a safety strap or chain to keep the transmission from sliding off the transmission jack during removal and installation.

 

You can modify a floor jack into a transmission jack by welding a flat metal plate to a piece of iron pipe. The iron pipe must fit snugly into the recessed hole in the top of the floor jack. Drill holes in the metal plate, and use bolts to attach the plate to a transfer case mount.

 

Most transmission jacks are out-fitted with adjusters to tilt the plate in both directions. These are used to help keep the transmission in alignment with the engine during installation, but also to help keep it in alignment during removal. It is important to pull the transmission straight back off of the engine dowel pins while maintaining correct alignment with the engine. It should also be tilted back slightly the entire time, which keeps the torque converter from falling out as the transmission is being lowered.

 

Lower the Transmission

Carefully lower the transmission to the ground while paying close attention to transmission cooling lines, speedometer cable, shift linkage, or any other items that could be damaged during this procedure. Some applications require that the filler tube and dipstick be removed prior to lowering the transmission. However, with other applications, it’s nearly impossible to install the filler tube after the transmission is in place, so it must stay in the transmission  during removal and installation. Once the transmission is safely lowered from the vehicle, remove the torque converter and completely drain the unit. Place the transmission holding fixture with the tail housing down, or lean it against a shop wall with the tail housing in a drain pan. Note the color and smell of the transmission fluid. Dark, black, or burned fluid can give a pretty good indication about what you’re going to find when you get the transmission apart.

 

Transmission jacks have threaded adjusters so you can align the transmission and engine perfectly during installation. This is an excellent feature.

  

Written by Cliff Ruggles and Posted with Permission of CarTechBooks

 

sa204

 

GET A DEAL ON THIS BOOK!

If you liked this article you will LOVE the full book. Click the button below and we will send you an exclusive deal on this book.Deal-Button

 


Older Post Newer Post

Here's What The Experts Are Saying...

Added to cart!
Free shipping when you order over XX You Have Qualified for Free Shipping Spend $x to Unlock Free Shipping You Have Achieved Free Shipping You Have Achieved Free Shipping Free shipping when you order over XX ou Have Qualified for Free Shipping