Minimum Synchro Clearance etc. etc. etc.

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.