Jumping out of 1st Gear

I have a 73 CJ5 with the 304 V8 and the 3 speed transmission. When the jeep is not under a load (just putting along in 1st gear), it tends to jump out of gear. It doesn't do it in second or third. Does anyone know what the problem might be and how hard it would be to fix?

Thanks!

 

could be lots of things. could be it isn't actually going all the way into gear or you may have a broken gear. you will need to go into it deeper and see. That should be a T15 transmission!

 

Usually it means the shift dogs or srings that support them are just worn or weak.. They cost $5.99 the last time I bought them for a T-15 but you gotta tear the tranny completely down to replace them.

BUBBA

 

I have had the same problem. '75 CJ5 w/t-15 tranny. I had the tranny rebuilt, but they didn't do anything with the shifter. It doesn't happen as often as it used to, but still pops out of 1st on occasion. The shifter is still really loose & floppy, so I think the springs/detens on the shift rails are probably worn like the author of the previous post suggested.

Time to find a new drivetrain shop that really does a complete 'rebuild' when asked?

 

Does it pop out on acceleration or decelleration?

This problem could be several things. I expect the condition of the gears and synchro parts are more likely responsible than the condition of the shift top. The shift top is pretty simple - you should be able to take it apart without any special instruction. Watch for detent balls that will come flying out when you remove the rails.

In the transmission, popping out of gear usually means that the bushing inside the gear is worn, or that the shift dogs (teeth on the end of the gear that the synchro locks to) are worn, or that the synchro hub is worn, or that the detents in the synchro hub are worn, or that the detent springs are missing or broken.

Usually the 3-speeds pop out of 2nd on deceleration, not 1st. I'm surprised that 1st could be worn enough to come out. 1st is on the opposite side of its synchro hub from 2nd, so I'd expect a worn 1st to pop out on acceleration, just from the geometry. When the bushing in 2nd is worn, the gear skews on the shaft on decelleration. This pushes the synchro hub away from the gear, and the dogs disengage from the hub.

If 1st is worn, I would not blame the shop. The bushing is part of the gear, and there's no aftermarket source for T-15 gears. Also, it's rare that a regular transmission shop would know enough about the Borg-Warner 3-speeds to understand and correct most of these problems. That's the price of owning a hobby car.

 

If it pops, it is always out of 1st gear, and always during acceleration - not necessarily hard acceleration either. I just thought it might have something to do with the shift mechanism because I can push on the shifter with a very light 1-finger touch and move from 1st to neutral. If it isn't solidly engaged in 1st gear, the strain of acceleration might pop it out.

The other gears require a bit more effort and I can feel the action of the springs and balls on the shift rails.

The transmission shop I used specializes in these types of transmissions and they show prices and part numbers for the gears on their website:

http://www.drivetrain.com/parts_cat..._kits/borg_warner_t15_t90_overhuaul_kits.html

Besides being a nationwide repair shop, they also happen to be located in my area of Las Vegas. I will have to check the receipt to see what parts they replaced, but I'm pretty sure they replaced the all synchros, small parts, gaskets and seals. According to their site, 1st, 2nd, and Reverse gear replacements are available.

 

I'm just gonna throw out there that there are different thickness snap rings for low and reverse gear, as well as 2nd and 3rd.
This can control endplay of the gears on the mainshaft.
I'm sure aftermarket gears can be obtained, although the country of origin and/or manufacturer might leave something to be desired.
I'll also say that if you told them what it was doing before it was torn down and repaired, they should have been looking very closely at the components involved, including the shift tower and shift fork(s).

 

Jim, I'm just repeating what I remember reading here - from Nick I think. The OP could ask Herm if T-15 gears are available. If gears are availalbe, my guess is that it would be cheaper to find a good used core transmission and rebuild that one, or put parts from the two together to make one good one. Gears are expensive.

LBOGRS, when they say "synchros" they mean the blocking rings, not the synchro hubs. Replacing synchro hubs would be expensive. The blocking rings are typically made of brass and meant to wear out, like a clutch disk.

 

since it's not grinding during shifting, I would assume the blocking rings are okay.
I'm leaning towards the shift tower/detent balls-springs/shift fork possibility.

 

I'm gonna take out the shift tower this weekend and see what's up. I think that's where my problem lies too. I did explain my theory to the shop, and they said they couldn't get parts for the shifter and that "all old jeep shifters are that way". Sounds like a cop-out to me. If I'm really determined, I'll get a machine shop to fix it. That's always been my last resort due to cost, but it has never let me down. Must be Mechanics and Machinists are two different breeds.

 

The shift forks could be worn or the sleeve could be worn not allowing full engagement of the gear. Also the detent balls or springs could be worn. Also the springs or inserts for the 1st/reverse synchronizer assembly could be worn or broken allowing the sleeve to move too easily.
I'd pull the top and with the top off the transmission shift the shifter through all the gears. It should feel "crisp" meaning you should feel when the shift rails go into the respective gear positions. If it feels loose or shifts back out too easily then the rails, detent balls, or springs are likely culprits. If the shifter top feels good then it's time to look at the transmission itself. While the shifter top is off try and shift the sleeves onto each gear. It should be a little difficult too move at first until the inserts and depressed then it should "Pop" onto the gear and it should stay on somewhat firmly, i.e. it should just easily move back off. If the sleeve slides very easily then you probably have an issue with the synchronizer assembly.
Also check the dog teeth on the gear. It's common on T-15's for the teeth to get worn and allow the sleeve to slide back off or get pushed off. The T-15 has ridges on the sides of the dog teeth to help hold the sleeve onto the gear, but these same ridges accelerate the tooth wear and can allow the teeth to wear to a point where the sides are no longer parallel.