welded 3rd and 4th

[BREEZE]

what is a welded 3rd and 4th. i have an idea but i want to know for sure!! any pics also??

[Marc]

The synchro hub is welded to the gear rather than relying on the stock press-fit. All torque must pass through this junction and a high-output engine (say, 130-150HP or more) is almost certain to "spin" the hub loose if it isn't welded on.

[ares650]

what about when they say keyed or splined. Is welding enough or not always?

[Marc]

<deleted>
...better answer below from Bruce2

[Bruce2]

When you see a reference to keyed or splined with regard to 4th gear, it refers to the manner in which the other gear that meshes with the gear in the pic above is secured to the pinion shaft. Prior to about 69, the fixed half of 4th gear set was located to the pinion shaft by a woodruf key. Later gearboxes used much stronger splines.

For the 3rd gear, prior to 73, all 3rd gears are the same. Then after 73, the third gears were revised so they don't interchange with the early ones. As Marc said above, prior to 73, the 3-4 shift hub is located by a woodruf key, after 73 it is splined.

[ares650]

So if a stock tranny would be welded (3-4), then anything after 73 would be really stong vis anything early.

[Bruce2]

After 73, the syncro hubs were furnace brazed on Beetle gearboxes. Bus gears were electron beam welded.
There were a significant number of poorly brazed 3rd gears in Beetles that failed, or could fail. But you will never spin a brazed gear. For HP use, you would not want to use the fine tooth Beetle gears, use the Bus gears, which come factory welded.
Both ERCO and Weddle sell late 002 type gears with a syncro hub electron beam welded just like VW did 30 years ago.

[arlo]

It may be usefull to note that Long Enterprises, where that welded hub picture cam from, also suggests using Loctite to secure pressed hubs. They recomend #609 I believe. This is made for pressed gears and hubs. There is an even stronger one in the same family.. #680. I have used this for other high torque applications at work and it is quite amazing stuff! The advantage of this over welding is that if you have a press (you need one to do other trans rebuild steps anyway) you can secure these hubs as a DIU step without having to weld and without risk of warpage. Also with applied heat you could still press them appart again if you ever had to.

[D JACKSON]

This may be a stupid idea, but here goes. Would it be possible to drill a slot between the gear and ring so you could install 3 rollpins that would be 1/2 contact with the gear and 1/2 on the ring. If the pins were locktited or peened in place to prevent movement it looks like they would work. Just thinking UNDER the box LOL. Don Jackson

[Csaba]

[quote="D JACKSON"]This may be a stupid idea, but here goes. Would it be possible to drill a slot between the gear and ring so you could install 3 rollpins that would be 1/2 contact with the gear and 1/2 on the ring. If the pins were locktited or peened in place to prevent movement it looks like they would work. Just thinking UNDER the box LOL. Don Jackson[/quote]


If you make them too small in diameter, they would cause stress risers which may lead to cracking. Too big, and you weaken the part, causing the same thing.

Just right, and it might be the shiznit...

IMHO

[arlo]

Also I think the hub may be hardened too much to drill. I think Loctite 680 is the best DIU option without precision welding.

[GARRICK.CLARK]

Can someone tell me the symptoms of a 3 and 4th gear spinning on the hubs .
Is it noisy.
Is it like a clutch slipping.
Thanks.

[Casting Timmy]

The real problem I think with spinning is that they separate and lock it into that gear. The gear and hub can no longer rotate freely in idle, if it didn't separate the spinning would eventually stop with the synchro hub welding to the gear.

3rd spinning locks itself between the clutch hub and 2nd gear, 4th locks between the clutch hub and the thrust washer/main shaft bearing on some (some don't have washer).

[Clonebug]

When I had to fix my trans due to the 3rd and 4th hubs I couldn't get it to shift anymore. It was really sticky going thru the gears.
I did it to two transmissions.

Since I had the first one rebuilt with 3rd and 4th gears hubs welded it has taken everything I have thrown at it.

[Bruce2]

Last summer I had a gearbox fail 4th gear. The factory brazing of the synchro hub to the gear let go. When it did, 4th gear became a neutral. No noise. With your foot off the clutch pedal, you could shift it from neutral into 4th with no grinding while driving.