This article is offered as a reference on how to swap an input shaft with the transmission remaining mostly assembled. Although I am making a special type of swap, a stock input shaft can also be replaced this way. Because it is possible to get some parts out of alignment badly enough that the transmission will require a more complete disassembly, these procedures are recommended only for those who are familiar with these transmissions and are willing to assume such risk.
If you would like more information on how to further disassemble a toploader or want to know how to upgrade the output shaft, I suggest this companion tech article:
http://www.fordmuscle.com/forums/tra...onversion.html
After being to the track numerous times, I was able to tune my suspension until my car could pull quite hard at the tree. Unfortunately a by-product of hitting the tires so hard was that I overpowered my small block toploader 4 speed transmission, specifically the stock 1 1/16” input shaft. While investigating some poor, notchy shifts I discovered that I had twisted the input shaft. After deciding that it might be a fluke, I installed a second small block input shaft and it too got twisted on its 2
nd trip to the track.
There was no doubt that it was time to take some serious action.
The logical thing for me to do (besides buying an expensive racing transmission) was to install a big block based 1 3/8” diameter input shaft, similar to what Ford put behind its 428CJ and 429Boss cars. Unlike the original big block input shafts found behind the big block, the aftermarket variety is made physically longer for usage behind a small block and so it is a direct replacement:
Note the much larger diameter of the new shaft. These large diameter input shafts are available for both the wide and the close ratio transmissions and they have 10 course splines just like the original big block stuff. You will need to ID which ratio you have before ordering parts. The easiest way is by counting the number of teeth on second gear, which is the third gear that is visible from the front of the transmission. See circled area:
A wide ratio transmission has 31 teeth and a close ratio will have 28 teeth on the circled gear.
Other parts that are required for this conversion include a new larger input bearing retainer (snout), a toploader gasket set with a new snout seal, a new larger ID throwout bearing, a larger ID splined clutch disk, and a special modified clutch fork. It is possible to reuse the old original front bearing, but I recommend installing a new one while you have the input shaft as this is a frequent wear item. Here is a photo of all the parts that were replaced in this project:
To do the big input conversion on a small block or 390 toploader, you will need to modify your small block to match the BB throw out bearing that is required. To my knowledge, Ford or the aftermarket does not make the required fork and one must be created using two different forks. I illustrated how to do this in this tech article:
http://www.fordmuscle.com/forums/tec...utch-fork.html
Note the CD—it was included with some parts that I bought from
Toploader Heaven and it is by far one of the best references for novices who are interested in rebuilding there own toploaders. Much of it is step by step and there are more than a hundred assembly pictures included. The clutch disc and the reproduction clutch fork that I modified were sourced elsewhere.
I also recommend a few tools to do this swap. A good set of retaining pliers to remove C Clips and either a brass hammer (or punch) should be used when you need to tap on parts:
Lets get to work. First, remove the transmission from the car. It will need to be drained of all its gear lube.
With the transmission fully drained and lying on the workbench, remove its top cover. A toploader gets its name because you access the internal parts through the top of the case. Use an adjustable wrench and put the transmission into neutral. Next, remove the 5 bolts that hold the tail shaft housing to the main case and carefully slide it off the output shaft:
At the front of the transmission, remove the 4 bolts that retain the front bearing retainer to the main case. Note that you can also see the end of the countershaft in the following photo:
Note that the front bearing retainer has a divot that faces down to aid drainage. That will be important for reassembly:
Roll the transmission over so that the top case opening is now facing downward. From the front of the transmission main case, again locate the end of the countershaft.
With a suitable hammer and punch (brass preferably), drive the countershaft into the case approximately ½-¾” and NO FURTHER in this manner. Next, carefully push the countershaft all the way through the rear of the main case using a dummy shaft. DO NOT try to remove the countershaft without a dummy shaft or the countershaft’s needle bearings will scatter. This is a very bad situation and it will more than likely require a much more complete transmission tear down in order to make the repair.
My dummy countershaft is a simple piece of PVC pipe with an overall length of 8 ¾”. It has a .830” OD which is less than the countershaft’s .890” OD. Since it is shorter than the cluster shaft, it allows the cluster to drop in the case, thereby giving clearance so that the input shaft can be removed without disturbing the needle bearings found in the counter gear. Here is what my dummy shaft looks like next to an old countershaft:
Once the dummy shaft has been fully located inside side the cluster gear, roll the transmission so that the top opening is again facing up. Here is what the dummy shaft looks like once it has been installed in the countershaft and the countershaft is dropped slightly:
Now you can carefully pull the old input shaft forward out of the case. There will be 15 roller bearings located inside the input shaft and some of them may fall into the case. They are large enough to fish out with a long skinny magnet. The brass blocking ring may pull out also:
The bearing is held on the input shaft with a C-Clip and you must remove it. If you are going to reuse your old front bearing, remove the C-Clip and have the bearing pressed off if it does not slide off on its own.
When I remove a bearing from an input shaft, I use an old disguarded toploader case and a block of wood to drive the shaft out of the bearing:
REASSEMBLY:
Clean all the parts to get them ready for reassembly. Scrap any gasket remains off with a razor blade. Now it is time to install the bearing on the new input shaft. Again I use an old case for reassembly. I place the bearing in the case the opposite way than it is normally installed. Then I heat the bearing with a low wattage heat gun or hair dryer for 20 minutes. Use a low setting as you do not want to overheat the bearing. The heat allows the inner hole in the bearing to enlarge slightly which allow the input shaft to be installed by hand. Be sure to spray the machined area of the input shaft (where the bearing gets installed) with some type of lubricant before shoving it in:
Alternately, you could have the bearing pressed on in a shop or you could have the part of the input shaft that the bearing rests on turned down slightly so that it can be installed by hand without other tools.
Reinstall the bearing retaining C-Clip. Next it is time to install the 15 roller bearing on the rear side of the input shaft. Smear the outer race with some heavy wheel bearing grease and shove the individual bearings into the back of the shaft. I also put a layer of grease on the topsides of them:
Reinstall the brass blocking ring inside the transmission case. It has 3 notches that will match 3 synchronizer keys:
Now carefully slide the new input shaft assembly into the case, watching that the roller bearings and brass blocking ring remain in place. You may need to wiggle the output shaft slightly, but don’t go to extremes.
Carefully roll the main case back over so that the top opening is facing down again. Look inside the countershaft holes to ensure that the dummy shaft is still retaining the countershaft roller bearings. You may need to roll the main case a little more in one direction or the other to ensure that the dummy shaft is aligned with the holes in the case. You may also need to move the thrust bushings slightly to get them realigned. Getting all these things aligned is the hardest part of this swap and is why I recommend that
this swap be performed by someone who is knowledgeable of these transmissions.
For reference, here is a picture of an old brass thrust bushing and the case boss that it gets keyed into:
If you can clearly see the dummy shaft on both ends, it is time to reinstall the countershaft. It is installed from the rear of the transmission case:
By keeping it butted firmly against the dummy shaft at all times, it can be pushed by hand until the shaft meets the front of the case. Work slowly to keep the needle bearings and thrust bushings in their place. Once the countershaft contacts the inner front of the case and the needle bearings and thrust washers are in place, finish drive the countershaft with a piece of brass until it is seated in the case with the roll pin being located within the rear case boss:
If you haven’t done so, install a new seal in the front bearing retainer. It will install in the same direction as the old seal in the old retainer.
Next install the new bearing retainer on the front of the transmission with a new gasket with the aforementioned divot facing down. Be sure that the paper gasket divot also faces down too. I recommend using a Teflon pipe sealant on the threads of the 4 retainer bolts.
Now it is time to reinstall the tailshaft housing using a new gasket. This is also time to replace the rear seal and to inspect the yoke bushing that is found within the tailshaft housing. I also use Teflon sealant on the 5 bolts that retain the housing to the main case. To help with alignment, I suggest placing a driveshaft yoke on the tailshaft splines prior to tightening these bolts.
Now it is time to test your work. First, use a crescent wrench to move the transmission through its gears. You may need to spin the input or output shaft slightly for the gears to fully engage.
Next test the new throw out bearing on the bearing retainer. It should slide freely. If not, take a strip of emery cloth and polish the retainer. Slide the new clutch disk onto the input shaft. It to should also slide freely. If not, you should locate all burrs and file them off until the disc slides freely:
Finally, test your pilot shaft bearing for fit. Normally you will not have an issue with it.
It is easy to tell which toploader has been modified:
The good news is that with this modification I no longer need to worry about twisting an input shaft. I was able to complete the season with several new personal bests without worrying if I was going to get “shafted” again.
Today
