I have two F35s, one has a shredded 4th gear and the other won't stay in 5th gear. I'm planning on pulling the 5th gear syncros from one and transplanting them into the other. I still have to get a gear puller so I've only made it as far as pulling off the syncro ring. I was assuming I'd see some better visible evidence of damage on the dogteeth, I do see what looks like could be damage, but I'm not certain. This is the "good" one:


This is the "bad" one.


I do see some marks and what-not, it's hard to tell. It's also worth noting that the syncro rings don't seem to be interchangeable. Is this by design or is it because something is damaged? Here's the rings with the "bad" one on the left and "good" one on the right"

Once I get a gear puller I'll get both gear sets off for a closer look as well. Lastly, why does the one syncro set have a different colored ring? I'm assuming its made out of a different metal but why the difference between the transmissions?

 

Interesting that the "bad" one doesn't appear to have brass synchros. The other transmission that I've known to ditch the brass (VW/Audi's) have to use a DMF, otherwise the synchros will destroy themselves.

 

I really hope someone can help me with this. I've gotten 5th gear apart on both of my transmissions and there are variations between the two. They're definitely not interchangeable. What I was hoping to find out is *can* I install the 5th gear from one into the other safely. Here's the differences I found:

First, aside form the synchro rings being made out of two different materials, the synchro's themselves are different:





Next are these springs:


They were seated along the outside of the synchro ring. One transmission had them, the other did not.



Next the dog teeth gears on 5th gear are different lengths:





I'm also seeing the thickness of the teeth on the synchro sleeve and hub are different width, I haven't counted them as they seem the same but the shape is different enough that they don't mesh if you swap sleeves:


Lastly, on the transmission itself the drive gear bolt is different. Either a different metal or a different protective coating. Are both 5th gear sets interchangeable with the drive gear or do I need to swap drive gears as well?



I'm a bit stuck right now as I don't want to assemble the whole thing, get it all back in the car and then have the transmission eat itself before I get out of my driveway or my first time on the highway. Any help at all would be much appreciated.

 

I don't understand why would a dual mass flywheel protect the synchros?

 

That's interesting and also kind of shitty. I assume one is an OE transmission and the other is sourced? AKA, one is LNF 3.82 and the other is 05-07 4.05?

I do know that LNF's did not get actual Quaife LSD's, while G85 LSJ's did. My understanding is that GM started manufacturing the LSD's in Sweden themselves for the LNF's. I believe Powell and some others confirmed this on a Saab forum.

Interesting that they apparently changed some of the basic workings of the transmission, as well.

It's an interesting debacle for sure. The DM flywheels have springs in them that "soften" the shock of the clutch engagement. Outside of that, I don't know. I just know that VW stopped using brass synchros and started using DMF's about 20 years ago (I think their DSG's still have brass synchros though; weird). People that swap to SMF's end up replacing their transmissions because the synchros eat themselves. I do not have personal experience. I'll try to look into it some more.

 

Yes, the transmission with the bad 5th gear is my original OE transmission from my '09 LNF. Unfortunately, I don't know the history of the replacement transmission nor where it was sourced from but unless the tag on it was swapped, it's the exact same trans with same 3.82 final drive.

 

That is especially interesting then... why change the design that near to the end of its production?

I've got two track days this week with my GTI, and then I will start working on the Cobalt. I'll try to crack one of my transmissions open soon - at least my OE one. 98% sure both of mine are from 2005.

I'm going to have to go buy some transmission tools. I've got bearing pullers, but I don't have any gear pullers.

 

So I was visiting my folks today and talking to my Dad about the transmission. He recognized the brass synchro. It's very similar to the synchros he replaced in a transmission he rebuilt years ago from a 1938 Buick Special, I actually helped him but I was about 8 at the time and barely remember. The brass material in this case is a single casting with the synchro surface milled into it. The other one is likely a hardened steel casing with a friction material adhered to it, likely to improve durability and handle more torque.

I picked up a set of 3 arm gear pullers from Harbor Freight for $30 and used my 20% coupon on them to save $6. Anyway, the 3 arm pullers needs to have one of its arm hooks ground down to fit under the 5th gear as there's not enough clearance. I do believe a 2 arm gear puller may work better for the 5th gear. I believe Harbor Freight sells a 2 arm gear puller as well.

 

Here's how I filed down the gear puller. It may be a bit hard to see but I just reduced it a bit and it didn't affect the integrity enough to cause a problem pulling the gear off. The top two hooks are untouched and the bottom one is ground down. I did it on a wheel grinder.

 

So I decided to toss on the 5th gear from the other trans. It all installed smoothly and so far engages just fine. I have a few other things I still need to do before I reinstall the transmission so it may still be a week or two before I get the car on the road again.

 

Thats awesome man! I love the tricks the old guys have to offer. I had a neighbor for 30 years that could figure anything out like that.

 

So some time has passed with this project but I finally got the car running today. I'm so happy to report that the 5th gear swap appears to be working just fine. The alignment is a mess and once you get up to speed the stability control keeps kicking in so I only tried 5th gear on a backroad at ~50mph and it held under mild acceleration just fine. It looks like everything will be just fine!