gearbox fix number 5

[Colin Byrne]

Hi guys
As I've mentioned previously I've had a pretty bad run with my purchase of a close ratio gear set from OSGieken through a supplier in the US.  Basically the story goes like this


- First run of new gearset was during the Winton 6 Hour, once home I replaced the gear oil and found 6 engaugment teeth on the sump magnet, pulled the box down to find 3rd gear had failed.  Purchased a spare (at cost price) from the supplier and rebuilt the box.

-   Next outing was Targa High Country, this time more serious, broke all the engagement teeth of 1st gear, syncro ring then popped out and went through the drive gears, damaging the lay shaft and first gear drive (we did however pull the box out on the side of the road, scoop out the debris, dremel the gears to mesh again, put the box back together on the tailgate of the support ute and finish the event in 4th place!)

-    Went back to the supplier who talked with OSG who determined that I had received a "brittle" gearset, they offered to replace the entire set if I sent back the original, pretty happy with that, put it all back together and everything seemed fine

-    On the next oil change (gearbox had done about 1000km) you guessed it more engagement teeth on the sump plug.

    Went back to the supplier again but this time was met with a very different response from OSG who where not prepared to come to the party, the supplier was however prepared to sell me a spare at cost price, when they where available

Well I was getting pretty sick of buying gears, pulling gearboxes in and out, and paying for posting heavy chunks of metal all around the globe so I went down to a heat treatment plant that does a lot of work for Hollinger to see if they could give me a root cause of the issue.  They took one look at it and commented on the case hardening being far too deep and covering nearly the entire cross section of the engagement teeth

I went back to the supplier with this new information and got a pretty strange response indicating that there are no guarantees in motorsport, it was obviously something I was doing wrong and not the product, Oh and by the way, OSG is no longer making that particular gearset, or offering spares for it so see you latter!

So unfortunately I was left with a really expensive set of broken close ratio gears with no spares, time to get all engineering on its ass!

The main difference between the Alfa gears and the OSG gears is the OSG gears are 1 piece where as the Alfa gears are a 2 part with a removable engagement gear.  A 2 part gear is much better as it can be repaired easily but also it allows the drive gear and the engagement gear to be heat treated differently, important as both gears are put under very different loading conditions.

Now when I say that the OSG gear is a 1 piece, that is not entirely correct, the are manufactured as 2 gears, but before the heat treatment process the two gears are welded together to form 1 part

        So it seemed to me that the ultimate solution would be to have the OSG gear outer with an original Alfa center that would allow me to use original, removable, Alfa engagement gears, so that's what I did, to 1st 2nd and 3rd gear

Firstly I machined the center out of the OSG gear until I was left with just a basic ring gear.  Then I got a selection of Alfa gears and machined the teeth of them so I was just left with the splined center (when I say machined there was a fair but of angle grinding going on initially to get through the case hardening!)

This is where I enlisted the help of some more professional machinists.  My dad took the modified parts to a specialist machine shop in Castlemaine who precision ground the parts to a very big interference fit, and pressed the gears together for me. They did a fantastic job and when I received the gears it all looked very promising.

Next part of the process was to very carefully Tig weld the two gears together, the interface between the two gears had been made on a relatively small diameter, this was good for keeping heat away from the gear surface, but meant I had to be very carful about not welding on the thrust face of the gear.  This ended up not being an issue and after a little carefully welding I had 3 very nice looking gears.

And that was pretty much it for the modification, the rest was very standard gearbox rebuild, apart from swapping a few shims to get all the gears to align.  I recently got my hands on an Alfeta transaxle which had 4 very good syncro rings in it, and out of the 3 parts boxes I now have I managed to source 3 very good quality engagement gears and selector rings, so it should have a nice crisp change motion.

I'm still chasing a small leak from the selector shafts, so as a last ditch attempt to solve the problem I spent considerable time polishing a mirror shine on the ends of the shafts and once again replaced the "sealing" o rings inside the case. I hope it seals this time, as the rest of the leak proofing I've done to the box has worked very well indeed.

So that's the story so far, once the engine is back together I can throw it all back into the car and try and this crazy Frankenstein gearbox!

[Colin Byrne]

and a few more pics

[Colin Byrne]

that third picture is what happens when your finger gets caught between a gear and a selector, don't recommended it!

[AikenDrum105]

Colin,

Magnificent.

Cheers,

[Steve S]

Very interesting, thanks for posting. I don't quite follow which pieces you welded together though. Did you weld the Alfa dog/engagement ring to the OSG gear?

I've been down this path too, I broke 2nd gear in my C530 box. The gears are 2 piece welded together and the weld failed. I had never seen this before, neither had anyone else I spoke to. I got one ludicrous quote to weld it back together so I just bought a new one and problem solved.

[colcol]

An Australian company called Holinger Engineering in Kilsyth are making a reproduction of the 5 speed ZF gearbox, the box can be had with synchromesh engagement or dog engagement depending upon the historic class the car runs in, Holinger Engineering DO NOT make the fragile transaxle's that the V-8 teams are currently having to put up with, Colin.

[pancho]

As always Colin - Excellent write up!

Very interesting and concerning as I've got an unbuilt OSG CR set still in the box myself. Was there a serial number on your set Colin? Do you think under limited 'spirited' road driving conditions the box would still have had the same issues?

[colcol]

The Holinger ZF replacement reproduction gearbox is a complete gearbox to replace the troublesome ZF used in rear wheel drive cars of the 70's, as you cannot get parts for these old ZF's anymore, most popular application was the Ford Escort rally cars, which are still very popular and are worth a lot of money these days, Colin.

[Colin Byrne]

Thanks for the comments guys

Pancho,  sorry no serial number, the two gear sets i've had problems with were manufactured in the last couple of years.  As for a road car, look it'll probably be fine the problem is the case hardening has effectively made the gears brittle so it's shock loading that is going to be a problem (missing a gear for instance)

ColCol, I've got to ask, what as any of that got to do with this topic?

[Mick A]

I was thinking the same thing!

[colcol]

Just my 2 cents worth on a proper fixup, as opposed to constant reworks, Colin.