• To ALL forum users - As of late I have been getting quite a few private messages with questions about build ups here on the forum, or tech questions about your personal project. While I appreciate the interest, sending me a private message about these topics distracts from, and undermines the purpose of having a forum here. During the day I wear many hats as a small business owner-operator and I work tirelessly to provide the absolute best service possible to you, our valued customer. When I created this forum I rounded up some of the best minds I knew so that any tech question you might have could be asked and answered by either myself or one of my highly experienced moderators, this way the next time this same question is asked the answer can be easily found and utilized by the next IH enthusiast having the same question. This allows me the freedom to run the day to day operations of the business and minimize the impact to shipments and shop activities that these distractions can cause. It is of the up most importance for me to complete the daily tasks in order to best take care of you our customer, all the while providing you a forum to get the level advice and input you have come to expect and deserve from the premier IH shop in the country.

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    Thank you for your understanding.

    Jeff Ismail

Rebuilding a Borg Warner T98 Transmission

Behold the mighty driver side PTO equiped T98! As found in my 1965 D1100 4x4, this transmission is the original model gear box for the truck however not original to this truck as evidence showed upon removal.

This unit displays several issues in that it leaks like a civil servant and also in hard shifting, making growling noises when being pulled into gear. This unit had a PTO that a shop removed several years ago in their laziness for not wanting to bend an exhaust around it. Its been sitting in a box since then. I will be performing a full overhaul with my transfer case now on the way back to the vehicle. Please note, I replaced my wheel missing in this pic, I wouldn't recommend doing this on stands of any kind other than a lift.

First up, removal, and PO forensics.
The first step is disconnecting everything and draining the oil, in my case a reverse circuit wasn't applicable, the 4x4 shifter must be unbolted from the passenger side (REPLACE THE BOLTS, THE HOLES AREN'T BLIND) and obviously drivelines must be removed, mine were already removed with my t-case. Up in the cab, there is a cover at the base of the shifter that must be removed, it can be missed if covered by mat, carpet, ect. Next I find the best way to get the shifter out of the way is to shift neutral and remove the lever from the top. The dome shaped cover at the bottom of the lever unscrews and the lever can be pulled out upwards, here take care not to lose the pin in the left side of the housing, it can fall into the trans. The last things holding the unit in the vehicle are 4 studs with nuts in the bell housing aft of the clutch. I found that a motorcycle jack was perfect for the removal process. I acquired this one from harbor freight for less than $80 with a coupon. To adapt the two pads on the jack to the trans, it was a simple piece of 4" thick laminated beam (several pieces of 4x4 board would work screwed together) with two 4x4 boards in front and behind the PTO adapter that hung down slightly. Because the bottom of the trans is not flat, there is a 1" thick slat used as a spacer in the back, and to begin removal, the jack is brought up easy untill the front block cant be moved by thumping a fist against it. Then the slat is wedged in till it no longer moves, again, thumped into place with a fist. I tensioned the jack a very small amount after that to relieve some weight. With this technique the trans was perfectly supported front to rear and in my case because I'm on gravel, the jack rolls on plywood straight to the rear.


With the jack supported the mounting nuts can now be loosened, two of my studs came with their nuts, you want the two top studs to remain in place wich mine conveniently did. These two help maintain alignment on the way out. The bottom two can be removed completely, I backed off the top two to the end of their studs, then, using a pry bar in the gap between the bell and the casing (shown above, just aft of clutch access) the trans started rearward quite easily.

This continues untill you build enough confidence in your jack to remove the last two nuts all the way. From here, the front bearing retainer slides free of where it bears in the bell housing, as seen here as that shinny edge centered between the bell and casing:

Now that everything is free (keep in mind adjustment of the jack may be necessary) the whole assembly should slide aft completely free of the truck and drop the throw out bearing in the bell housing.

The trans can now be easily lowered on the jack, one end picked up at a time and the blocks removed, then spilled off the jack. Note above the case is turned on its passenger side, I did not replace the 4x4 shift bracket bolts and residual oil went everywhere. After dragging my prize out one side of the truck, I noticed the oil spill was brass colored, upon closer inspection, evidence of metal particulate only got more obnoxious.


It did not end with brass either, here I found what appeared to be part of a gear tooth:

This concluded removal, stand by for forensics of a PO swap.
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With the trans out of the vehicle, I did some wire brushing to expose and clean up casting numbers before I quit for the day, the first swipe across a crusty T98 revealed a spot of yellow paint.
From the paint, I can only assume the original tired gearbox was replaced with another from an unknown international 1 1/2 ton truck that was in 'FAIR' condition. . . sure. . . . the front face of the trans was coated with antiseize of some kind, and removal was far to cooperative to be in character for this truck. Thus I believe the swap was relatively recent in the trucks life. Now, how did they know, that it was in fair condition? Well, removing the top cover of course! And just my luck, PO never put on a new gasket.

Notice above, the way the gasket was clamped in there by the dirt.
Anyways, doesn't make a hill of beans difference now, the problems with this gearbox are getting nuked out of existence. First step, as you guessed, pull the top cover, here we find an intimidating looking clump of gears; don't be afraid, its actually quite simple. First thing I did was count and inspect the first gear teeth. Given the evidence of a swap, I needed to rule out that it might be a t18. 43 teeth on the first slider so it is a t98. There are 43 teeth, but they aren't necessarily good teeth:

This is by far not the worst gear that can be found, this damage is the result of one of, or combination of things. Through wear, the pin that prevents the shift lever from rotating along with a couple other bits makes distinguishing third from reverse difficult when upshifting from second. *crunch* The reverse idler also takes some punishment from this obviously. The other thing is that people don't realize is that these spur type gears(both first and reverse) should NEVER BE SHIFTED TO WHILE MOVING!!! Again: *crunch* the first gear is the only gear besides reverse that actually slides completely out of engagement with the cluster gear, the reverse idler interacts with the same bank of teeth on the cluster gear as first, as well as first itself. The cluster and reverse idler can't be seen well from an assembled state, I got lucky and the cluster looks much better than the first slider. Reverse also looks better but still battered. After consulting with some experts over on BP, I decided to run the existing gears and clean up the jagged areas of the teeth.

Disassembly is not too hard. I would do one thing differently in I would remove the yoke at this point. I did it later on out of forgetting to remove it more than anything, it didn't hurt anything, it just would be much easier. The cotter pin is removed, and with it in neutral, an impact driver removes the nut with some pulsing of the driver. The socket I used was a Carlyle
*note insert size*
And required grinding down the outside to fit in the yoke.
Much more to come, stay tuned!
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I disassembled my gearbox on the ground next to the truck. DO NOT DO THIS, unless you are planning a full overhaul. Contaminants such as dirt, dust, and road grime are not conducive to proper lubricity and long wear life. Since I will clean everything inside and out, it's not a big deal. I will note if I had to do it again, I would've moved it to somewhere I could pressure wash it prior to disassembly.
I will also note that I did not follow the service manual exactly. I took some pictures of the needed pages to reference from my phone during disassembly, since my phone is much easier to degrease than paper, and less susceptible to wind(remember I'm outside in a car tent, wich doesn't do much to stop wind).
The first step in disassembly is to remove the yoke as noted before, then I cracked all the bolts lose with a bar before proceeding. Next up, the top cover is removed. At this time I performed the previously discussed inspections and took some pictures of the safety wire arrangement in the shift fork/bar assemblies.

Once the wire is documented and can be easily reproduced, I cut them free with some dikes and began loosening the tapered square head bolts that locate the forks. First to go is the 1st/2nd fork, wich slides free of the bar easily.

At this point I found it prudent to remove the frost plugs. The first three are the ones at the rear, wich I drove out at an angle with a plastic mallet and a rachet extension(for the rounded corners). Once these are gone, the shift bars can slide to the rear fully out of the top cover once free of the other parts. The next part to come out is the tapered screw for 3rd/4th wich allows this shift bar to move rearward free of the top cover.

Be careful here as there is an interlock pin in the shaft you wont want to loose in addition to the poppet ball and spring. I held my dikes over the hole just because it was so difficult to get the shift bar to depress the poppet ball out of the way I thought it was under sufficient spring tension to hurt my hand upon flying free. In reality it was a buildup of metal particulate sludge at the base of the spring, no doubt not helping the hard shift issue. These can however still fly away with sufficient force, so wear some eye-pro, you may thank yourself later. Next the other two shift bars can freely move and disassembling them follows the same path as the first minus the interlock pin. Tapered screws removed, they slide free of the housing dropping their applicable interfaces and releasing a poppet ball and spring.


The above images show removal of the reverse side, the part in the second pic is where the end of the shift lever interfaces with the shift bar. The round plunger is spring loaded and in addition has its own poppet ball and spring that interfaces in one side of it. This gives the leaver the spring loaded effect when shifting into reverse, and these parts if worn enough can permit unintentional gear clash when reverse is mistaken for third on an upshift. This sub-assembly will be further disassembled later. At this point, the top covers remaining shift bar is removed the same way as the others, and the front plugs can be driven out with a punch and plastic mallet from the inside where the shift bars were. Lastly, there are two interlocks between the three shift bars. They live between where the poppet balls and springs are housed and are retained by goop. Be sure to save those, they can be pushed out with an allen key. With that, the top cover is completely disassembled. The only remaining shift fork resides in the transmission case, and operates the reverse idler. It is removed by driving out a pin located on the outside of the case as shown here:

From within the case, the pivot point of the reverse fork can be pushed outward slightly then pulled free by hand from the outside:


Above we see a tired rubber O-ring no doubt a contributing factor to the leaking problem. Once removed the reverse fork can be removed:

With all the controls removed, along with that pesky yoke I forgot, its now time to begin on the transmission core.
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For the lower case and gearing, the first step is pull off the front bearing retainer and remove the bearing. The retainer is easy enough, four simple bolts are removed and it slides off the end revealing the bearing. The bearing has a spacer and snap ring on the outside of it, and it can be accessed with a puller (that i don't have) by pulling the shaft forward after a light thump on the end with a wood block.
The input shaft is a tight fit inside the bearing, the outside is not tight to the case. Thumping the shaft rearward presses the bearing off the shaft slightly as it bottoms out against the snap ring and spacer. The problem is eventually the shaft bottoms out as well. So here, again, i don't have the right puller, I used a kind of hillbilly tactic, spacers that gradually increase in size
Untill those spacers weren't big enough anymore, so I got even more hi-tech:
In the last pic the bearing finally came loose by hand. This technique may make some cringe but keep in mind the amount of force needed to move the bearing in this case wasn't much. Just the weight of the wood block I was using swinging my arm under gravity made more than enough progress to be effective. I would NOT have continued if more force was required in moving the shaft out of the bearing. Now we see some lovely, clean(for a change) IH part markings:

At this point I was fed up with the case sitting at an awkward angle and removed the pto cover and subsequently the adapter/idler housing:

Once free there was more evidence of damage, this time more severe in the bottom of the case and caked against the pto cover:
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Cleaning that out, I replaced the cover on the main housing to prevent spillage of sludge and rollers later on.
With the case now finally sitting a bit more solidly I removed the rear bearing retainer, speedo drive gear(??? I thought it was 4x4! Oh wait... At least PO had the decency to find an actual cap screw rather than leave the speedo drive open into the case)


The output shaft can actually be pulled rearward by hand enough to get at the bearing. Now in this case I had a puller that would fit, although admittedly not the greatest one ever:

Once the bearing came loose it displayed the same nice markings as its friend up front.
The upper hunk is now free to remove, the input cluster actually pulls away from the output cluster(wich is obnoxiously heavy, hence the lack of pics here) dropping its rollers into the case and allowing the front of the upper hunk of gears to lift up in front and slid out of the assembly. This portion will be disassembled later.
With that out of the way the input shaft is easily plucked from the case, the rollers are recovered later on:

Next up the shaft retainer is removed and the cluster gear's idler shaft is, for lack of a better term, BLUDGEONED VIOLENTLY from its home, with a brass punch as the moderator/mitigator of abuse:

Above can be seen the retainer I used as a handle to pull the shaft free by hand. A look through the bore shows enough rollers to be mildly terrifying before the cluster is pulled:

I accepted fate and just dumped the cluster's contents into the case for later recovery:

For a device that has always intimidated me, its surprisingly easily disassembled and understood. Short of this, i honestly don't think I think I would've ever been able to figure out how one worked. More to come in the next two installments, stand by for complete disassembly! :icon_rotate:


The last hunk to come out of the case is the reverse idler, wich is retained by another shorter idler shaft. Disregard the directions in the service manual and proceed as follows. You will need, a nut, a bolt, a washer, and a piece of pvc pipe. They are arranged as a jack, the nut is loosened off the bolt wich pushed the washer and pipe like a press. This arrangement presses the idler shaft right out.

The reverse idler gear retains all its rollers within it, and lifts out with the shaft removed.

Now. The fun part:

The first synchro ring falls off the end, and next up is a snap ring, wich is followed by the synchronizer unit and third gear.

The brass synchro ring lifts off of third gear, and the synchro unit has two spring rings in each side that easily remove before the outer body of the synchro unit is pulled off the inner body. Once they are separated it will permit the three stamped detints to come out of the center body of the synchro unit:


Next at the other end of the shaft, the snap ring is removed, allowing the 2nd gear synchro/1st sliding gear assy to slide off dumping the second gear rollers:
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Once these items are removed from the shaft, the last part left is a snap ring. The 2nd synchro ring is then easily plucked from the 1st slider/second synchro group. Here I found increasing evidence of metal particulate:


To disassemble the first slider from the center hub, it is placed on a block to support the center, wrapped in a towel to prevent loss of poppet balls and the 1st slider gear is pressed down off the center body:

Here I found even more evidence of metal particulate, that had made a sort of cement with oil as a result of a centrifugal effect(only found in inside facing pockets and surfaces):

This material is very difficult to remove in a non messy way and once displaced has a property similar to glitter (DO NOT GET THIS IN YOUR EYES, oil in general would be bad, this would be far worse). With all of that done, disassembly is complete. The third gear bushing looks to be removable, however I have no reason to remove it and there is likely not a replacement available.

The next step from here would be disassembly of the pto, however there are so many important tech details accumulating (on what is in reality an incredibly simple component) I think its best to tackle that one once the trans is done as a separate rebuild farther down this thread or as a separate thread entirely.
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New member
Thank you for posting this. I am currently in the process of rebuilding a T-98 and am fumbling along. Have you begun the rebuild yet?
Yea, this is quite a bit farther along than this thread, it will be getting an update and some edits at the end of the week. If you need info, send me a pm, I'd be happy to help. Currently I'm about halfway through cleaning and paint prep.
Overdue update time! A few important points before tackling cleaning. First up, a fairly severe case of worn shift alignment pin along with socket damage.



The socket that the shift lever pivots in has a pin in the side that keeps the lever from rotating. In this case, the pin is harder than both the pivot in the shift lever and the top cover itself. Not only is the pin hole worn to the extreme and the surrounding metal cracked in a couple spots, the hardness of the pin has distorted the slot in the shift lever pivot. This raised a large bur over time resulting in a massive cavity growing around the pin hole as seen above. This is a large contributing factor to sloppy shift pattern.
In addition, several other factors can contribute, the shift bars fit to the tapered screws, the interfaces that join the shift bars to the lever both in their fitment on the shift bars as well as wear on the engagement surfaces that the lever bears against. In addition, the forks themselves can wear thinner than preferable. The solution in an ideal world would be new replacements. Sadly we live in the pessimistic and sad world devoid of oem parts known as reality. So here we rely on luck. Cast metal, while not impossible to weld is difficult at best. The t98 is largely obsolete, wich leaves us refurbished and used parts. . . .

And so I bought another top cover.

The pivot socket, while still worn, is in much better condition than mine along with the pin hole (still needs repair). My plan that I am currently exploring is to drill the original hole to round, use that size drill bit shank for a new pin, with the lever cut widened, then drill the other side and slot the opposite side of the lever pivot, effectively doubling the alignment pin's strength.
In the new top cover, I actually lucked out in that the lever interface parts were the mirror opposite of my wear pattern. Here you can see the two reverse interface parts, my original the one with the shinny rounded off edge the other is from my new top cover:

The forks on the donor are much more worn than mine, the tines are about 25-30 thousandths thinner than my original forks. In addition, the 3rd/4th fork that doubles as the shift lever interface is in much better condition on my original. Therefore I will simply reuse the originals.
Originals are right, donor spares are left:


Interestingly the interface fitment of the 1st/2nd interface was the polar opposite of reverse for the two assemblies,
My assembly was fine, while the donor was badly gouged. Fitment of my original tapered screws in my original shift bars was very tight, and I wont be messing with them. I kept the screws in the part they were in to ensure they go back in the same hole, when I reassemble I will simply swap the required parts.

In addition to these parts, a basic set of consumables is required. The parts are found in a top cover small parts set, which I sourced as a ford t18 top cover kit. There are fork bushings included that the t98 wont need, along with the large roll pins used to secure the t18 forks. There is also a round gasket used to seal a reverse switch wich I hope to add to my rebuild. The kit includes a bag of expansion plugs, the three interlock pins, the shift alignment pin (oem size) three poppet ball/spring sets, the reverse plunger spring, the reverse plunger retaining clip, and the large spring for the shift lever seal:

While we're here its a good time to point out that I've found some information that implies the poppet sets for the top cover and synchro clutch are the same parts, and I'm looking into that further currently. Now the remaining parts can be cleaned, gears and internals I personally prefer to leave oiled and wrap in rags or shop towels and store untill just before reassembly when I then clean them. The external housings and covers I will cover briefly here. I cleaned the outside for dirt and loose paint first by wire wheel. Once the outside is roughly clean, I filled a large heavy plastic storage bin with five gallons of diesel. I left the main case in there for about a week, rolling it around to a new side once or twice a day. This allowed the metal particulate sludge to loosen as the thick 90wt thinned in the diesel. At the end of this stage, dunking the case by hand repeatedly rinsed most of the particulate out of the housing and further rinsing with brakleen removed what was left along with 99% of the diesel. From here, I used shop towels and old used acetone to float off the majority of the paint. A more aggressive wire wheel job took care of what was left. The process was the same for the top cover. Twice. (I decided just before paint to replace the cover) I use a dremel tool with a small wire wheel to get in the hard to reach areas. The new top cover has a bit of rust, I plan on soaking it in evapo rust pre paint.
Once generally clean, I mocked up the retainers, top cover, and my pto adapter housing to inventory my hardware. All bolts and washers I'm replacing with new grade 8 zink flake coated bolts and Nordlok washers.

Now to paint prep and paint. The front and rear bearing retainers and yoke I did in a cardboard box, red oxide primer followed by IH red for the retainers, black for the yoke. The main case on the other hand required much more finesse. The first paint prep step was to thoroughly clean all the threads, wich I did one hole at a time with some cheap .38/9mm and .30 cal pistol/rifle bore brushes, acetone, and some rags. 99% of these holes are pass through and must be CLEAN to ensure seals. I kept track one hole at a time using a marker.

Next I used shop towels and clean acetone to wipe the entire case clean. I then removed lint from the shop towels with a clean stiff bristled paint brush. Now the clean work/paint environment is essential to good paint, so final cleaning and taping was done on a clean folding table in my garage right before moving it to the paint area.



Now to the paint booth! But wait, too poor for a paint booth? Look no further! The ghetto paint booth returns!

Important note: DO NOT VACUUM PAINT FUMES! This vacuum has a second hose port allowing it to blow filtered air. So, clean bag, cleaned out hose, a vent and Bob's your uncle!

Some time later:


When in the sun, internal temperatures reach roughly eleventybillion degrees, wich helps the paint dry quite quickly. As always, refrain from standing in front of the blower tube. It may feel good in the heat, but its not worth the time it takes to clean the bright red butt print off your nice craftsman garage stool. :mad2:
To be continued. . .


Active member
Have you ever tried oven cleaner for removing grease, oil and paint prep? It works great and the grease washes away with water. Easy Off is the brand I use. Paint sticks great the etched surface it leaves.