dog gear replacement ?

I'm currently rebuilding a 308 gearbox due to poor gear change in 2nd and 3rd , i have found some wear on the dog teeth and on the cones on the two gears is question, replacement gears are incredibly expensive , does anyone know if the dog gear can be sought seperately anywhere as it is only pressed on ?? the dog gears are marked "ZF 138". if anyone has a source for these do gears it would be greatly apreciated .

 

Dog gears are normally used in racing transmissions, I assume you are taking about a normal syncromesh style gearbox. Note I have not had a 308 gearbox apart so my comments on based on my experience with other transmissions. Having said that I assume you are seeing some wear on the teeth the sliders engage on. The gearboxes I have seen, these teeth are part of the gear and are not changed separately. Having said that, they rarely wear out to the point of needing replacement. The only time I replace them is if the car will not stay in gear on acceleration or more commonly it pops out of gear on deceleration. In those cases I replace the gear and the slider. Difficult shifting sounds more like a worn synchro issue. Generally I only replace the synchro in those cases.

Cheers Jim

 

the reason for wanting to replace the egagement part of the gear is because there are some slight groves forming where the synchro ring sits on it , there is some slight marking on the teeth i guess due to the reduced "braking" effect of the synchro ring . in the pictures you can see that they are pressed onto the main gear so was just wondering if the could be replaced separately as there are no new 2nd avaliable !!
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Here's what I've been able to find out, I'll be upfront that the following information is not verified by Ferrari and took some research and digging to acquire. Oh and it also will not help in terms of parts cost or replacement unfortunately.

The gears, baulk rings, etc.. are ZF-5-Ds25/2. ZF will not sell parts. ZF sold the rights and mfg to RBT transmissions, hence the lack of help from ZF. The above gearbox was used in the Ford GT40, Pantera, Mangusta, Bora, BMW M1 and a couple other exotic rare vehicles. Just our luck.

You could try contacting RBT for parts and they may have something but the cost is high, gear sets are over a $1k a piece.

I'm assuming you check'd the play and gap to the baulk ring against the WSM? The box I rebuilt last yr looked about the same but was thankfully still way within spec. Unfortunately it also needed a couple other parts, including a main shaft... it's real easy to hit $10k parts these days rebuilding these boxes. Bearings, selector rings, baulk rings, etc.. less available parts results in higher prices.

Honestly at some point the lack of gearbox parts will sideline the 308 long before engine issues will.

 

If those are the gears in question the dog teeth look perfect. If you are concerned about the slight wear on the syncro surface, don't be, that wear is insignificant. Those transmissions always work best with the syncros hand lapped to the gear. With iron syncros it takes forever for them to mate properly and by then the surface is often glazed and it will never work as well as it should. The glazing is a real problem if proper gear oils are not used. These are the reasons Ferrari for many years has had such a terrible reputation for poor shift quality. Take the time to hand lap them well with fine valve lapping compound, suffer all the cuts in your hands that will result and it will shift quite well assuming all the adjustments are properly made.

 

The dogs in a conventional transmission work in the same way and have the same name. They are a separate piece often only supplied as an assembly by the manufacturer. They commonly wear out needing replacement and has been done so by many of us for a very long time. When available it is a far less expensive fix to address the same problems. If it is an inexpensive and easily sourced gear it make sense to replace the entire assembly. When the gears are hard to find or a 4 figure part, replacing the dog makes a great deal of sense.

 

I am used to seeing a gearbox like a racing Hewland gearbox referred to as dog gears, although in cases like the 308 where the dog section is separate from the gear I can understand it being called a dog gear. Your experience is different than mine. Non of the gearboxes I have worked on have had the dog part separate from the gear. There have been several occasions where I could have used that.

Cheers Jim

 

thanks for all the comments guy's. i have found a company that have had good rate of success with grinding back and metal spraying the seat that the synchro sits on . these faces will be ground and matched to each new indivdual synchro ring that will be supplied to them ,they have done quite a few 308 gears and have good success with this process.i will keep you posted with the results of this process and how good the shift quality is once reassembled .