ZF Synchro Repair Discussion

To follow up on this topic (5 years later)....

Tastes good, lasts a long time!

Rocky

Rocky. You da' man! Except when it comes to playing Cow Bell. Practice man, practice! It has to get better.

@rocky posted:

OBTW, I am using Red Line MTL 75/90 as Doug recommended.... Maybe that's what really did it? Or was it More Cowbell?

@davidnunn posted:

Rocky,

I just noticed this.

Redline MTL is 75W80

Redline MT-90 is 75W90

That was a recommendation from Gary Hall. I called him for the ZF part which he had at the time. He said to try this stuff first before I took the ZF apart.  I did and the issue disappeared.

There was only 32,000 miles on it at the time so it was difficult to concede that it was the second gear syncro.

This collection of ZF repair lore is priceless- thanks, Rocky. It seems that the main variables are part of the design. We are dealing with thousandths of an inch combined with metallurgy in high torque transmissions. In trying to save the expensive precision gears while replacing the all-steel synchro parts that wear faster, experience from WW-2 apply. Gear-steel just doesn't weld well. Some of the elements in gear-steel change phase or boil off at welding heat. It also doesn't plate well. I tried welding gear steels with a TIG and failed miserably. So easy backyard fixes were doomed.

Combine that with the fact that ZF gear-steel is 'different' from 8620, 9310 or common Ford gear-steel. Ford found that out in 1970 when, after complaining semi-publically, their own testing found that ZF's steel was 'better' than Ford's. Dunno if it was tougher, stronger, better-wearing or all the above but compared to a Ford Top-Loader or a Muncie, a ZF was 'better'. Is part of it the heat-treat? I know D Quella spent years working on transmission gears and synchros, not just for ZFs but Indy-car trannys etc. Glad to hear from Ron that he succeeded.

ZF as a company was founded in Germany by Count Zeppelin to make parts for his airships back in the1900s. Because at the time, he couldn't find any that were good enough. ZF later got into parts for vehicles, ships, submarines and other prime movers. Over the past 120+ years (plus two major wars for motivation), they obviously learned a bit about steel!

Hi all,

I‘m currently having my gearbox rebuilt. The cones are worn as described above and the plan is to replace them.

Since there‘s no surface to push/pull the cone off the gear it‘s not obvious to me how these can be separated without damage.

The only way I can think of is to use a bearing separator like this:

However, I‘m afraid using this kind of separator will cause the small teeth of the cone to crack.

A: gear

B: cone

C: separator

Is there a different procedure?

Or, do I have to machine features (e.g. threaded holes) into the cone to safely separate it?

Thanks and best regards

Philipp

The syncro on this ZF is part of the gear. It does not come apart. You need to replace the entire gear.

They are just a little bit different then what you will experience on US manual transmissions.

If CRM (contact info above) is still working, he machines the entire cone off the gear, and makes a new one.  You can see my description of his procedure in the thread above….

Like Doug says, I saw no way to get the cone off the gear…

Ron McCall / Dennis Quella also has a repair procedure they have used successfully on many second gears…

…or you can try to buy a gear and synchro from RBT…

My ZF is still going strong!

Rocky

@panteradoug posted:

The syncro on this ZF is part of the gear. It does not come apart. You need to replace the entire gear.

They are just a little bit different then what you will experience on US manual transmissions.

Doug, gear and cone are two separate parts that are connected by means of an interference fit. This photo shows a gear without its cone. The cone sits on the serrated surface on the right side:

This photo shows the cone and cone+gear-unit (additionally secured by welding):

Thanks Rocky. I´m from Germany, so unfortunately, having the parts machined at CRM is not convenient for me. If he machines the cone off the gear, I think this will be the way to go.

The old cone needs to be sacrificed in order to get a new one on your gear.

Best regards
Philipp

I have never needed to do the synchro, not yet. Maybe I will tomorrow? I hope not.

Others have tried and come up with various solutions. It is just common consensus here that they are one piece.

Machining a new cone and machining the old one off seems the obvious solution but I agree with the others here. For all intents and purposes they are integral.

You will get no argument from me on any solution. Necessity is the Mother of Invention. Best of luck on your results.

The only question that I have is what material should the new one be cut out of and will just a press fit stay put?

My cousin is out of the business of ZF repair…. but there was a guy on here (GT4Peter, Peter Bascharz (?)) that was doing ZF work.

I don’t know much more about him or where his shop is, but you might be able to track him down…. but it sounds like you have a good handle on things.  

Good luck.

Have you checked the 2nd gear cone against the first gear (unworn) synchro ring?  What was the clearance (with both the first and second gear synchro?).  Just curious !

Keep us informed!

Rocky

Peter Baschartz lives in Austria, I have his contact details if you want them.

Another much cheaper solution than replacing the cones is to use bronze synchro rings in repair size; Denis Quella sells them,

Peter Baschartz lives in Austria, I have his contact information if you want them.
Another much cheaper solution than replacing the cones is to use bronze synchro rings in repair size; Denis Quella sells them, in 2023 he sold them for $165 each but you have to adjust them to get the desired clearance:

and then lap them so that they match the pinion cones perfectly:

and here is the result:

That's what I did and for the moment my ZF works very well.

@rene4406 posted:

Peter Baschartz lives in Austria, I have his contact details if you want them.

Another much cheaper solution than replacing the cones is to use bronze synchro rings in repair size; Denis Quella sells them but you have to adjust them to get the desired clearance.

That's what I did and for the moment my ZF works very well.

This is a great solution.

Thanks Rocky, Rene and Doug for your replies.

The clearance of the 2nd gear cone against the 1st gear snychro was also way too small (approx. 0.2 mm). Hence, wear must have mainly occured on the cone, not the synchron ring.

I have my gearbox at a racing gearbox manufacturer. They also service gearboxes for historic race cars:

https://www.holinger.de/

We also discussed to use undersize synchron rings to compensate for the worn cone clutches. I liked this solution for its simplicity. However, Christoph, the mechanic in charge convinced me that ZF did use sinter steel synchron rings for good reason and they would last much longer.

Meanwhile, I separated 2nd and 3rd gear from their cones:

Cone and gear were not only secured by means of a press fit.

The external toothing of the gear wheel was deformed in such a way that a form closure was achieved between the cone and the gear wheel, thus preventing axial displacement of both components.

To separate gear and cone the deformed section of the gears external toothing needs to be sheared off. For both 2nd and 3rd gear a force of approx 50 kN was necessary:

Now the the gears can be fitted with new cones (available at ZF).

We still have to decide whether to secure the cones with loctite only or laser welding.

The ZF engineers used the sintered steel synchro rings for a good reason: they were supposed to wear out and leave the cones intact.

Unfortunately, experience shows that this is not what happens, so they were wrong and cannot be trusted absolutely.

I had also inquired about replacing the cones and was advised to fix them with laser welding.

Thanks, benzoyl for the pictures…

Interesting stuff.  You are repairing both 2nd and 3rd gears?

Rocky