Minimum Synchro Clearance etc. etc. etc.

When you load it (squeeze the gears together)the gear assembly should freeze or at least drag heavily.

Where the cone shape presses on the gear is where the synchro action takes place.
They work like drum brakes.

What happens is that they wear together and eventually polish each other so that they become too slick.

Chances are when you pull the cluster apart you won't SEE a problem other than the cone on the gears look polished. That's where you are loosing the braking action of the synchro because of lack of friction between the two mating surfaces.

You can not roughen them up. It doesn't work that way.

Second gear is the worst because it is the largest gear in the cluster and is harder to slow down.

The shift gate through second is also used the most and is also the narrowest.

I'm not sure if the flats can be machined to give you more travel or if you can tighten them up by changing the thrust washer.
I don't think so.

The original Pantera ZF uses iron blocking rings/synchros were as the GT40 was brass and lasted longer.

Butfoy, the last I talked to him, had brass synchros made and if I recall correctly were $900 each. I forget. I could be wrong. It was some time ago I talked to him.

He gets $5000 to go through the unit PLUS parts.
There isn't anything in a ZF that is unusual if you have worked on manual transmissions before.
The clusters are all made the same way and disassemble similarly.

The difference is in the cost of the parts.
You can't even get the parts from ZF for these. Butfoy is the only one that has them.

By comparison, blocking rings/synchros for a T10 are less that $20 each.

Sometimes readjusting the shift linkage can fix the issue. Sometimes not. The shaft naturally has twist in it and I think over time looses some of it's temper and gets TOO flexable. Also check the trunion shaft support on the chassis. The bracket can bend and the trunion itself wears out and lets the shaft move enough to cause issues like this that you tend to blame on the synchros.

You can try double clutching second gear, i.e., clutch to move out of second gear into neutral, then clutch again to go into gear. This is how you would shift a transmission without synchros.

I think RBT also has a one or two year waiting period as well. Might as well do the entire thing yourself.

Ask Ron in Maryland. He's done a lot of them himself. Maybe he can help?

I've also found that contrary to RBT recommendations that synthetic MTL (manual transmission lube) tightens up the transmission and adds a friction modifier for the synchros and helps a lot to rejuvenate them.

It swells the seals and gaskets and does not cause leaks.

PM sent


Ron

this is the web site for the company that bought the rights /manufactures zf transmissions in texas
owners name is oliver ring


http://www.hpgear.net/

I spoke to Phillip at HPGear but they do not deal direct with the public and handed me onto RBT.

Wannabe, in that photo above of the gear synchro and the ring, the space you're looking for is BETWEEN the two sets of small teeth- the other side of the small teeth from your screwdriver bit. So no- you have zero clearance and the synchro ring shown is junk. It's likely the gear cone the ring is supposed to fit onto is also badly worn and needs changing. With so much metal missing, this ZF will never shift well.

I also see rust on the parts shown: have you been following the previous threads on changing ZF lube yearly? Currently, there are two ZFs in U.S shops that sustained over $5500 in damage just from condensation build-up in decade-old lube....

The screw driver in the photo is there to push the sychro against the cone. The space between the sychro and the dog gear is about .020" not zero as it may appear in the photo.

Rust is partly an issue but my problem is getting a straight answer from people in the know. I have some people telling me that my cones are worn out and Lloyd Butfoy telling me the cone only wears out when the synchro is run out. My worst synchro has .020" of clearance. I am inclined to go with what Lloyd has to say seeing that he owns the rights and has forgotten more about zf's than I will ever know.

I have managed to get a hold of Lloyd by email but it is a tedious process trying to photograph and explain a problem via email. Combined with the fact that I am in Australia with the time difference it is a day between questions and answers. And I don't think answering emails is Lloyd's strong point or mine for that matter.

At the end of the day I just want to know what parts to replace so I can put the bloody thing back together before I forget where everything goes!

Sorry to interject here but I think this thread needs more cowbell?


It doesn't matter to the synchro what that measurement is. 20 thousands is actually the correct answer to what it should be.

Everyone is misunderstanding what it does and how it works.

I agree with Butfoy. The cone on the gear is rarely worn beyond use. In fact, you won't even be able to tell the difference between a used one and a new one by looking at the cone.



What happens is that the inner surface of the synchro ring has machined grooves in it.

Most transmissions use a brass synchro in them so that you don't have same materials against each other. The Pantera version uses an iron syncro.

When you move the shift lever, the cone on the gear and the grooves on the synchros press together and it works like a drum brake and slows down the spinning of the gear.

The grooves on these synchros get polished. Polished to the point that they become slick and loose the breaking action that they originally had.

Usually mechanically there is nothing you can do to restore that. You change the synchro. Very rarely if ever the gear.

Second gear in almost all manual transmissions is the biggest problem because the second gear is usually the largest in the cluster and has the most mass and inertia to slow down.

Sometimes double clutching that gear is required no matter what you do. Double clutching meaning initiating the clutch to move it out of first gear, releasing in neutral, then initiating the clutch again to move the lever into gear.

Some trucks to this day you still have to do that too.



You will see this interaction of the synchro/blocker ring right on the bench when you sit the synchro on the cone of the gear.

Just by gravity action the synchro will stick to the cone.

On the worn one, you might be able to spin the synchro with your fingers...maybe, but probably not? With the new one you definitely will not be able to.

That's how close the tolerances are on these parts and really the reason why they are cut in cone shapes. That shape kind of adjusts itself for wear in the assembly.



The original design of this transmission (GT40) had brass synchros. The Pantera version got iron ones.

No one seems to know why.

Butfoy had the new ones made out of brass.



I have found, purely by accident though that synthetic MTL has some kind of a friction modifier in the stuff that restores almost all of the braking action to the synchros.

After you put it in, the box will feel tight and precise. It's really like magic.


The Red Line is also the type of synthetic that swells the gaskets to tighten them up and not cause the gaskets to shrink causing them to leak.

I would recommend it to anyone that before they tear these transmissions apart to do a very expensive rebuild, that they change the lube to this synthetic and try it. The rebuild might not in fact not be needed at all.



The worst possible thing that can happen to you is it does not help and you still need to tear the transmission apart BUT it could fix your issue.

I'll bet you that you will NEVER get this recommendation from ANY of the rebuilders. They would be just shooting themselves in the foot and loosing a very lucrative business.



This is the MTL. I had a guy, one of my parts suppliers no less, tell me I was seriously full of do-do and that there was no such thing as synthetic MANUAL transmission lube. Only Synthetic AUTOMATIC transmission fluid.

Well I can offer two replys to that. First I just emptied myself from last nights Lazania. Umm. It was good.

Second. Here's a picture of the container of the stuff that doesn't exist.

As the quote goes from Shakespears' "Julius Caesar", "there is more in Heaven and Earth than in your philosophy!"

I can tell you first hand, this stuff works.

Just trying to help out here and share what I know.


Hey! If you want to ship the ZF to me, I'll rebuild it for you too. And I guaranty that I will do it for $500 less than any other written quote than you can get.

I'm not stupid. I'll take your money.

This is a picture of a BAD brass synchro out of my Doug Nash five speed.

It is the same as the T10. These are less than $20 each new. The ZF are $300 new from Butfoy.

Look at the grooves machined into the inner diameter.

Those are what creates the braking action on the cone of the gear.

These grooves have been slightly polished and as a result have lost their braking action.

You can't even see that right? And you won't either.

You should be able to see AND feel the difference between the brand new one and the used one though.

The grooves on the new one will feel sharp by comparion.

The friction additive in the MTL somehow etches these synchros and returns the braking action/friction applying capabilities to the thing.

As the oil filter commercial says, "pay me now, or pay me later".

About $40 to $50 for the MTL or $5500 to pull it apart and change all of the synchros.

The answer seems obvious to me. Apparently not to others?

Here's the view from the other side.

I feel like Darth Vadar, "Luke, come over to the dark side!"

Ok if it is cowbell you want....

Doug you could not be further from the truth when it comes to the ZF.

Here is a pic of my actual 2nd gear. As you can see the grooves are on the cone, NOT the synchro. And if you look closely at the inner surface of the synchro it appears to have a coating, albeit worn looking. After a bit of back and forth with Lloyd it is indeed a coating. My concern was that it was rust that had been given a smooth over with use, but thankfully not.

Anyway from my observations and extensive experience with ZF's (Zero) it would be safe to assume that the synchro has a softer wear surface applied to the inner. This is a sacrificial coating, and once this wears away the hard sychro itself wears on the cone damaging it. That is why Lloyd always says in his posts, if it grinds into second "STOP", because you will start damaging the cone and in turn need to replace the gear. Not to mention wearing the teeth on the slider.

So we can safely say the sychro does indeed care how much clearance it has, A. because of wear of the coating, and B. because when the sychro butts up against the dog gears it ceases to apply pressure to the cone and not longer "Brakes" the motion of the gear wearing the slider teeth.

As for the fluid, the first thing I did was change the fluid to Redline Light Weight Shockproof. And before I did that I never had a problem, but a few months after that I did. Not sure what that says and I guess I will never know.

Another thing, second is not the largest gear on the cluster, first is. However second tends to wear more because you it gets almost as much use as first, but first generally is used when the engine is idling and the gear is moving much slower. Second however has to deal with 2000 odd rpm when being shifted into.

As I said these are just observations from some one who has no idea.

I like cowbell but not too much.

Actually, 5th is the largest gear on the input shaft. 2nd is the smallest gear that is not part of the shaft.


Ron

You're right, 5th is the largest on the input shaft. But first on the pinion shaft is much larger with a much larger synchro slider sleeve to cope with the mass.

PM sent.

I spoke to James about some of his issues and he thought it might me nice to post some of the details. There will be a few contrary points/observations to some of the information previously posted or brought forward by other experts. The information is a compilation of my personnel hands on experience, testing, logic, reading and talking to other experts about the issues in the following posts.

Most of the ZF work I have done has been rebuilding the input shaft gears and changing fifth ratios and it's no where near the other experts experience but I am extremely careful with each build and examine every re-installed component closely to make sure it will run correctly and if it is not good enough to re-install, I've always tried to discern why it failed in the first place. This has happened numerous times after removing worn out gear sets that are examined post mortem on how and why they failed. In an effort to find what was worn the worst, a new synchro was installed on the bad gear measuring the end clearance and then the worn out synchro was installed on a new gear measuring the end clearance. What I have found on every type 2 checked is that the old synchro will have far more clearance on a new gear than the new synchro will have on the old gear concluding that the cone was worn far more than the synchro so I decided to try and figure out the who-what-when-where-and most importantly why.

Spent quite a bit of time researching synchro history and designs and found some interesting details about how they work and the different manufacturing methods being used.

Getting into specific type 2 ZF synchro issues you have to look and the design being used the why it changed from the type 1. It appears type 0 and 1 sychros were cast and machined with lube transfer grooves on the inside similar to the try 2 gear cone pictured below and the type 2 synchro was made from a high pressure powered iron method and then coated on the inside surface. You can make a sophisticated design this way and it's far less labor intensive than casting and machining a similar part---basically cheaper. The down side is you have to groove the receiving gear cone which it's sole purpose is to dissipate the lube so the synchro will speed up or slow down the gear enabling it to lock into the shift collar. Synchro/receiving collars have a non locking taper and as long as the lube will dissipate---and in the case of this design, hydrolic into the grooves the taper will do the work no mater what the surfaces finish's are. Now things are working in milla-seconds and as the surface changes, so will the speed and shift pressures required to make the gear slow or speed up. Remember the gears are actually moving in the opposite direction of the shift for a split second as the synchro aligns with the cone teeth and shift collar. This is a bit wordy and hard to explain by typing so let me get to the hart of the issue.

There are several problems with worn gear cones, one being the wear pattern is unfortunately not flat so a new synchro will not engage the entire surface---they may shift fine but will wear faster cutting it to the same taper as the old worn gear cone. This is not a big difference but you can clearly see the problem when you put a new synchro on the old gear cone and it rocks. This does not always happed so you can install new synchros on old gears so long as the clearance is adequate. Second---as the grooves wear down, the lube can not dispatch as fast allowing the synchro to grab the gear--remember this happens in fractions of the second. Also the groove tops will mash a bit and splay into the groove opening closing off the area a bit more. Think of it as tire tread moving water---if half the trade is missing and the rubber has mashed sideways from a long burn out closing off the grove a bit more, the tire can not more the water from the surface---just like lube on the cones.

In short by studying the problem extensively---IMHO---, cones on the type 2 gears wear much faster than the synchros because there is half the surface receiving the synchro's inside scrub surface. Now I have not tested the hardness of either component but will show you the wear results and the newer design up-grades.

I will start with the close-up of a damaged shift cone. Take notice of the left to right ware pattern---left rings are worn much more than the right rings---look at the width difference of the ring surfaces. If you were to install a new synchro on this cone, it would rock and primarily drag on the right side groove rings. If there was adequate clearance between teeth surfaces, (.030 would be great but with this much damage even a new synchro might have only .010) the new synchro will wear out much faster from not having a good surface match from previous wear damage and only work properly for a shot time.

Here is a newer/slightly used first gear synchro cone. You can clearly see how it should look. It has close to .040 end clearance.

This is the inside of the type 2 synchro---the rings/grooves/lines in the surface are just print from sitting on the gear cone---the surface is flat. You can clearly see the added scrub material added to the powered metal synchro.

This is the new cone design on first through third. You can see the surface is polished with the lube grooves designed to drive off the oil rather than hydraulic the lube into the groove spaces. This design moves the lube faster and more efficiently and does not wear the cone surface nearly as fast allowing the synchro to be replaced rather than having to replace the gear synchro cone or the entire gear set.

By the way that first gear was used so the cone surface has some scrub wear lines. Here is the synchro for the new cone design. The lube grooves are in the synchro like the earlier type 0 and 1 trans synchro designs and with the oil cuts in the cone, the lube grooves do not have to hydraulic the oil to create the necessary drag to align the teeth and shift. The cone cuts help move the oil out of the synchro grooves much faster so it can grab the gear quicker.

This is a forth gear that still shifted OK but for how long??? It had about three thousands left before contact.

Last post tonight. Here is a first with good clearance---close to 40 thousands. You can clearly see the difference.

Forgot---please add any thoughts, explanations, corrections what ever you have. This is simply my personal observations from maybe 30 rebuilds. I like doing the transaxles because it's fun and thought provoking.

The only thing that age with the increased desire for knowledge tells me is that the more I learn the less I really know.

As always Kirk fantastic write up. Thank you so much for adding your experience and knowledge so that all can learn. Me included!

Thank you James---hope the information helps.

I measured a new synchro to a new gear tonight and found it had .051 clearance. The general rule is .030 minimum. Here's a shot of the 5th with the new synchro installed.

I took a shot of a synchro collar removed to show you how it looks removed from the gear. The replacements are laser welded when they are re-installed. Occasionally a synchro collar will break loose from the gear---I have seen this maybe a half dozen times mostly on second or third. The laser weld helps to assure the new collar will not break loose when the gear is rebuilt. Dennis Qualla started this procedure year ago.

Second gear less collar.

This is the back side of a new synchro. The inside surfacing material collects on the back side but is of no use. I usually remove the excess material to gain another 1 to 2 thousands. There is an effective removal hand method that works quite well.

Here's a synchro with the back side cleaned up a bit.

There are 2 styles of type 2 synchros I am familiar with not including the newer M1 type with the grooves built in. The 2 in the photo are for the earlier generation type 2 box. The one on the left is the newer style---you can see there is a slight difference in shape and the number of teeth.

Here is a shot of a type one trans synchro with the grooves compared to the type two. You can see the 3 tab design verses the teeth design. The gear locking collars are also different.

This is the inside of a type one with the oil grooves. I have had little experience with the type zero or one but it appears that the synchros wear out faster than the gear cones which is a plus. The type one design is more difficult to assemble but was told they shift better when they're in good shape---Lloyd Butfoy's opinion which I hold in very high regard.

I hope the information helps make the synchro issue more understandable. Please remember to change your gear lube--better option than replacing synchros and gear cones from being scrubbed off by dirt, metal and water intrusion blended into your gear lube.

Thank you for reviewing the information.

Kirk

Kirk

Thanks for sharing the synchro information. For us ZF novices thinking about opening af ZF up it's great stuff.

quote:

The type one design is more difficult to assemble but was told they shift better when they're in good shape---Lloyd Butfoy's opinion which I hold in very high regard.

I just made the switch from my original 40000 mile type 1 to a rebuild type 2. Both gearboxes are in good shape. In aggrement with Lloyds statement, there's is a marked difference in shifting smoothness - the type 1 being much smoother and faster shifting than the type 2.

Great info here in this thread! Thank you everyone, Kirk especially for all the detailed photos and descriptions.

quote:

I have found, purely by accident though that synthetic MTL has some kind of a friction modifier in the stuff that restores almost all of the braking action to the synchros.

After you put it in, the box will feel tight and precise. It's really like magic.


The Red Line is also the type of synthetic that swells the gaskets to tighten them up and not cause the gaskets to shrink causing them to leak.

I would recommend it to anyone that before they tear these transmissions apart to do a very expensive rebuild, that they change the lube to this synthetic and try it. The rebuild might not in fact not be needed at all.

Doug - You recommended Redline Synthetic MTL 75/80, saying it seems to help 'correct' some second gear issues. However, the Redline MTL is a GL-4, not the GL-5 recommended by ZF.

A friend has the dreaded 2nd gear issue and has 4 quarts of the MTL ready for a pre-Fun Rally oil change, but the GL conflict is giving him some concerns.

Do you have any other thoughts to share on the GL-4 versus GL-5 issue to put our minds at ease?

Thanks!
Garth

FWIW, when I interviewed Lloyd at a Fun Rally Tech Session one year and asked him about friction modifiers in ZF 90-wt, his response was, "They won't hurt and may help some ZFs". The subject was LSD chattering in slow corners- more noticable in wet weather or other low-friction road surfaces. We did not address synthetics at all.

I found this recommended in another post. Here you go... Redline 75W90 NS GL-5 Gear Oil

This may help too... See the directions section... Tech Info

Steve

So my new synchros arrived and I have had a chance to get the zf back together and in the car. Well I can confirm that Kirk, Ron and Dennis Q were right. As can be seen in the photos the new synchro barely gave second gear another 7-8 thou of clearance (old synchro first pic, new second). And after a solid hour or so driving I still get a slight clunk into second although third is just fine.

So my box will need to come back out at some stage. But despite not fixing the problem I am kind of cool with that. It was a great opportunity to work on the box without taking to big a bite. This is after all the first gearbox I have ever disassembled so I'm pretty glad I haven't damaged anything! When I next pull the box I will look at some new bearings and such. Baby steps.

Thank you very much to Ron and Kirk for your great advice and if you don't mind I will have more questions in the future.

Old

New

Wannabee, there's one more rather easy mod owners can do to reduce or eliminate the clunk during shifting: shift slower! Steel balk-ring transmissions as found in ZF and Porsche gearboxes can often be 'beaten' by the linkage, and may ALWAYS clunk if you attempt to shift too fast. In the U.S we call it 'speed-shifting' or 'bang-shifting' and it comes from drag racing. Panteras do not drag-race well. Try moving the gearshift lever a bit slower & more precisely and see if that doesn't help. The only other thing I can think of is using thicker lube for its shock-cushion effect, and that affects the bearings and how hot the assembly gets on long runs.