1942 Willys MB Transmission Slips out of Second Gear - Classic T-84 Issue

This video shows the classic symptom my 1942 Willys MB jeep has with a T-84 transmission that slips out of gear in 2nd gear. Ford GPW's also had the issue.

The transmission shifts and drives fine through first, second, and third gear -- the problem exhibits itself when you let off the gas or coast in second gear. The stick just slides out of gear, and power no longer is tranmitted to the axles. If you try to hold the shift cane in second, it begins to whine and grind. Many potential causes for this slipping -- my suspicion is worn rings in the synchronizer.

[F.Krueger-csvk]

Part 1. Own a 1944 GPW ford jeep. Last Sunday, went for a drive around the local area. As I accelerated away in first gear, I went to upshift into 2nd gear, there was a small explosion from the gearbox . I had trouble getting 2nd gear. Was a grinding crunching noise from the gear box = trouble. Able to upshift to 3rd, make it home. Removed gearbox/transfer case together. Separated the gear box from the transfer case. Stripped gear box apart. Found 2nd/3rd gear synchro blocking rings pitted on the outside, the ribs on inside worn away. Need internal ribs to allow smooth gear change . Found the 2nd speed gear damaged, the shift hub that the 2nd/3rd gear selector claw sits in, teeth badly worn/damaged facing 2nd gear side. The 3 little shift plates or dogs as some folks refer to chipped/broken. Rear counter shaft metal & bronze thust washers damaged. Machined surface on inside of the gearbox where the metal thrust washer sits against scoured/grooved/damaged. Ordered new parts from my jeep supplier. Reused the original case. Hands on enthusiasts get a good jeep technical manual. I recommend " The Complete MILITARY JEEP MANUAL", by Brookland Books. Covering Willys Model MB & Ford Model GPW. Everything you need to know about your jeep is in this manual. Its in yourself interest to understand how your jeep works. Problems arises & they will, paying others to repair is expensive. After i seperated the gearbox from the transfer case. i looked inside the top of the gearbox opening where the gearshift goes, I had no idea what i was looking at or what to do. Studied the gearbox section of my manual, looked at every vid on YouTube on gearbox repairs. I photographed each section as i pulled the gearbox apart so I'd know where parts go for reassembly. Manual has good diagrams/names of all components. Check out jeep forums can be helpful with bits of info. Don't be scared, concentrate/pay attention to what your doing. Also used a white ink marking pen to mark parts before dissembley if I couldn't get a good photo. Cheers.

[F.Krueger-csvk]

Part 2. Ok, rebuilt gearbox, attached to transfer case, installed in jeep. Went for test drive, all forward/reverse gears worked fine, no more crunching noises. Problem now, jumping out of 2nd gear rolling down hill with foot off the accelerator pedal. My biggest mistake, I only replaced damaged parts thinking that was good enough instead of checking critical clearances. Removed gearbox/transfer case again together & seperated. Strip gearbox down. Checked clearances as per service manual instructions. First up, checked main input shaft clearances at both ends for wear. Looking for under size wear at front end & over size wear at rear end of main input shaft. Clearances within specifications, input shaft reused. Checked diameter of needle roller bearings that sit inside the rear of input shaft cavity worn undersize, replaced new needle roller bearings. Checked main output shaft front end, worn undersized, replace new main output shaft. Found rear main output shaft main bearing loose fitting on the rear main output shaft. The main bearing must be a "firm fit". Replaced new rear main output shaft main bearing. New main output shaft bearing must be pressed onto new rear main output shaft using a press. Do not use hammer. Checked the brass pilot bush that sits in the center of the flywheel for oversize wear. Found worn oversize, replace new brass bush. The brass pilot bush supports the front input shaft. My advice, just replace 2 new poppet balls/springs, their cheap to buy. Checked 1st/reverse gear selector claw for slopinous in selector hub, firm fit ok, reused. Checked 2nd/3rd gear selector claw for slopinous in selector hub, found loose fitting. Replace new 2/3 gear selector claw. Check both selector shafts for wear, bends, anything that stops smooth back & forth operation in the gearbox case, was fine, reused. Also check the poppet ball recesses in the selector shafts for wear as well. Both selector shafts were fine. Important, you need a special jeep tool that looks similar to an allen key to remove the grub screws that secure the selector claws onto the selector shafts. If you use an allen key, you may damage the grub screws, get the proper tool, their cheap. It is critical to eliminate main input/output shaft side movement/vibrations . Side movement/vibrations of input & output main shafts as you drive along cause the selectors to jump out of either 2nd &/or 3rd gears. Dont forget to check clearances of counter shaft. Just replace new thrust counter shaft washers, they are cheap. After installing new front bronze thrust washer, new rear bronze & new metal thrust washer, check there is no side movement & the counter shaft spins freely. One important piece of information you will not find any mention in the manual. There is a metal pin that sits in a predrilled slot in the rear of the gearbox case. The pin holds the rear metal washer in position through a predrilled hole in metal thrust washer stops metal thrust washer from spinning around as the counter shaft operates. Over time, the pin moves back & forth in the case, becomes loose fitting. It then wears the bronze thrust washer that sits in front of the metal thrust washer & then eventually shortens in lenght leading to thrust washer failure, hence a grinding noise in transmission. When the pin has worn shorter, the metal thrust washer spins damaging the box internal machined surface the metal thrust washer sits against. Remove pin from case with small punch & small hammer. Tap pin gently out of the case & check lenght. If undersize in lenght replace with new pin. I drilled a larger hole in my case & inserted a larger diameter pin. I've gone from 0.125 to 0.157. I pressed the new larger diameter pin into the predrilled hole in metal washer before installation. The new oversized pin was longer than needed. I used an angle grinder to grind the pin overhang so the pin was flush with the rear case surface. I replaced another new gasket set. Use an oil resistant silicone sealer on any gearbox bolts that screw into the oil cavities, otherwise there will be oil seepage from the bolt. Apply sealer to all gaskets as well. Follow instructions on the sealer packet. I reassembled gearbox, attached to transfer, refit into jeep. Road tested the jeep. The gearbox is like new, even better than previously. Gear changes are smooth/firm, no jumping out of 2nd or 3rd gears. All gearbox clearances are in the gearbox section of the jeep manual. The name of the manual is mentioned in first post, part 1. Any questions ask. Cheers.

[darylrose]

Had the same issue with my T-90 when i purchased it, the previous owner advised me of the issue when i bought it. When a standard tranny kicks out of gear on the Decel, its not a synchro issue but the gear itself, the triangle shaped cones that engage the slider get worn and rounded off causing the issue. NOS Gears are available and reasonable depending on your vendor. The T-90 was an easy repair..there a pretty basic tranny to work on and great to learn on...Id vise you give it a crack. The cones do wear from grinding into rear, so relace your synchros while in there, 2nd tends to wants to grind more then 3rd. so i tend to ship up pretty easy or even double clutch to play it safe.

[allandanieldalabhanjan]

Sir I'm Jeep mechanic.yadgir, Karnataka, India.no need of worrying sir those catcher's are not holding the gear replace those no need of changing brass ring gear

[samhouston]

Had 1950 CJ3A that would pop out of 2nd gear too. Pain in the a$$. Loved her though. Wonder what transmission that might have had in it.

[tbs]

I had a 1948 Willy’s jeep and it did the same thing.

[thraherxbs]

Mine is fine, but there are lots of owners that have the problem and have learned to live with it. Also technically the Willys isnt a Jeep, it's a "Willys Truck 1/4 ton". The ford GPW got the nickname Jeep which spread to both vehicles. Of course some people believe that the vehicles were named after Popeyes pet dog. Either way these are amazing vehicles and each one has its own personality.

[championbeam]

In mine, I get reverse and first.... cant find second or third.... probably seized up from sitting 20+ years

[ranveer-ry]

Sir we can repair everything of this gear box india Maharashtra kolhapur.

[banm.umlong]

Pls show us how to shuft to special gear

[joefalabrino]

That's no way to shift a T-84 transmission and expect it work properly. The T-84 was NOT designed for the WWII military jeep but was for the Willys Americar sedan. It will not take the kind of treatment you demonstrated. Don't take my comments as rude, but as to help you understand that these transmissions are not strong. Jumping out of second is usually caused by the second gear bushing being worn. Then it can be the front & back bearings also being worn. All the worn parts enable the gear to have slop on the main shaft and then poof! she jumps out. Just shift slower & gentler when you get your next transmission.

[timothylangdon]

it just wear box out replace bearing and seals and most important replace synchronizer hubs the three collets on hubs and hair springs do not forget 1st motion shaft phospher bronze bearing flywheel bad bearings cause bad shaft alignment and layshaft teeth failure, modern gear oil too thin original oils like molasses

[brettduffy]

I have no audio on my phone I take it they were unsynchronized