ZF Synchro Repair Discussion

I wanted to finally close the loop on my second gear syncro repair.

Based on careful measurements, both manually, and by using the first gear syncro as a "gold standard", we determined that the cone, and not the syncro ring was what was worn.

A second gear (complete set) from RBT is north of $1000. I believe the general recommendation is that you can't just replace the gear with the cone, as the mating gear wear could be significant.

A second gear syncro is north of $300 from RBT. There are rumours of brass syncros for $150, but I heard they don't last long.

Based on a recommendation from this forum, I found a fabrication shop (CRM Fabrication, Gainesville, GA) that has tackled this repair for another forum member, with successful results.

CRM Machine

The CRM process is to machine the cone down and fabricate a replacement sleeve out of 01 tool steel, hardened to Rockwell 50. Once the replacement cone was fabricated, it was installed using an interference fit with remaining material on the second gear cone.

Once the new cone was attached, the new cone and old synchro were lapped in on a lathe at 90 RPM.

The new gear/synchro clearance is now back to 49 thousandths clearance and works beautifully.

Although the job was not cheap, it was substantially less than the cost of a new gear set and synchro.

Chris Mullins (proprietor of CRM Machine) is an incredible machinist and a brilliant guy. The phone # to his shop is (770) 983-7151.

I took my car out today, and it is GREAT to have a second gear that I can upshift and downshift without having to baby.

I am thrilled with the results, and I am very happy with the cost vs. the traditional repair process (new gear set and syncro).

I am not trying to cut RBT out, and I certainly owe him thanks for the advice (and parts I purchased) from him, but I think there is always room for alternate solutions.

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

WELL, I for one are greatly disappointed!

I was expecting photos of a sidegrinder, cast drain pipe and the wife's oven!

Yeah. I took the easy way out!

(...and let somebody who knew what they were doing handle it!!!)


Rocky

Marlin did say that (hard chrome) and I considered it, but....

I hadn't heard of anyone successfully doing it, and Marlin (great machinist that he is) isn't one for much chit-chat. I asked for a little more info, but I never was able to get high confidence that the hard chrome process has been proven on someone's ZF.

Rocky

quote:

Originally posted by PanteraDoug:
..The problem here in this forum is that most if not all of the real hard line builders and racers stay away and don't share anything that they know of or have learned...

Thanks, Doug,

But investigation won't help me... My ZF is done, with an effective (cost and function-wise) fix.

Rocky

I have been having "follow-up" discussions on my second gear cone replacement with a couple members.

I want to try and make things clear in my discussion.


This thread below goes into excruciating detail on the gear / cone relationship. It really was helpful to me to understand things.

Minimum Synchro Clearance etc. etc.

Trying to boil it down to the basics (as I see it...):

The cone and the syncro ring have mating surfaces.

One (or both) wear

As they wear, the syncro ring rides lower and lower on the cone. This is a secondary effect, but the measurement between the bottom of the synchro ring and the face of the gear is what you use to measure the ring / cone interface. Once one (or the other) wears, the braking action of the synchro on the gear is lost. Once the braking action is lost, the shift (up or down) grinds.

In my case (and in most ZFs) – the cone wears before the ring. My clearance between the synchro ring bottom and gear face was .000”. New it's .050", and a good used set is about .035".

I fixed my 2nd gear grind by having a new cone machined and attached to my gear. Now I am back to .050” clearance when the synchro ring is set on top of the cone.


The cone and synchro ring are just a brake… There is really not “synchronization” going on – the synchro stops everything from spinning at a different rate than the gear, so parts don’t grind when you jam it into gear.

Is that helpful?

Rocky

Cone (upper grey part with grooves) and Synchro Ring - disassembled. The ring is upside down.



Gear and ring in mounted orientation, showing the gap between the bottom of the ring, and the top of the gear face. The gap is due to the interference between the cone and the ring angled faces.

Sorry this is out of focus.

Congrats Rocky.
Great job, and thanks for taking the added time/effort to share. I know it takes both....

quote:

What was the clearance with the worn gear (before repair) and new syncro?

That configuration never really existed, because I didn't buy a new synchro..... but....

I did test with the worn gear and the FIRST GEAR synchro, which (per Lloyd Butfoy) never wears.

Clearance was the same - .000"

This, and other measurements told us that it was the Cone, and not the synchro that was bad.

Rocky

I have seen some calculations that show that for every .001" of wear on (either the cone or ring), the end-gap will decrease by nearly .010"

Rebuttal:

quote:

The ONLY way to measure it is with an NEW syncro.

Not true. I have a table of detailed measurements of all my cones that clearly show the degradation of the second gear cone (the dimensions of the top and the bottom of the cone, and the deltas).

quote:

The second gear fix in the future HAS TO BE, that the new syncro must contain those grooves and the gear must be machined smooth.

While that may be a better design, that is the opposite of every -2 ZF that have ever been built. (UPDATE: OK, every ZF that I have seen - which is exactly one of them in the flesh, and about 5 of them on the interwebs!) Would you then go in and modify all your other gears too - while you are in there?

quote:

Sleeving the gear compromises it's structural integrity and you have modified the design to power of an unknown. This is like a friction weld solution as well.

I suppose it won't hurt anything anyway. If it comes apart it will just spin.

I agree - the worst that can happen is I start to get a second gear grind if the cone comes loose from the gear. BUT........ It is not like this is a direct linkage for all engine power. It is only braking the rotating mass of the ZF internals, and clutch disk.

quote:

Anyway it's a done deal

Agree here too.

There are two ZFs fixed by CRM that I know of. Quella has done a bunch of "laser cone welds" for other customers. I have not heard of any of the Quella repairs flying apart, and if they were, respectable ZF builders wouldn't keep going back to him. The basic fix is the same (new cone on old gear).

I will track things as I can, and will report out in 10 years.


The problem is with "armchair quarterbacks" that they have no skin in the game. No amount of $$$ (or schedule) is too much for them to pay to "do it right" - since they aren't paying.

"You pays your money and you takes your chances". I think I made a good bet.

quote:

The problem is with "armchair quarterbacks" that they have no skin in the game. No amount of $$$ (or schedule) is too much for them to pay to "do it right" - since they aren't paying.

"You pays your money and you takes your chances". I think I made a good bet.

Well, an 'armchair quarterback' WITH a vested interest. That's a big difference.

Why is it only 2nd in these zf's? I think I'll start in 3rd?

I am having trouble following this gear repair.

Is the "clutch" (which is the cone and the coupling teeth) sold as a seperate part or is it sold only with the gear wheel?

There is a slight difference between the reapir that Dennis Quella makes and the repair that was performed on Chuck's gear. Dennis presses the entire cone/tooth section off of the splined section of the gear, presses an entirely new part on and has it welded . The original part is pressed on and sometimes will get loose ( enough to fall off when the trans is disassembled).The welding eliminates the possibility of this. It appears that Chuck's gear had only the cone machined off of the toothed portion and a new cone pressed on. I have had Dennis repair at least 50-60 gears for me ( maybe more) and none have given me an issue in over 10 yrs. I'm not saying that there is anything wrong with the method that was used on Chuck's gear. I would have to have additional information before I weighed in on that. It will likely last quite a long time. The " spline " design on his new cone looks like it would last longer than the original version. And BTW, I recently flipped a BMW M1 transaxle for a GT40 customer which had a completely different synchro design on 2nd gear only!
Here's a picture of a gear that I just got back from Dennis.

Ron

quote:

Is the "clutch" (which is the cone and the coupling teeth) sold as a seperate part or is it sold only with the gear wheel?

Joe -

In a normal configuration, the "clutch" is fixed to the gear (that's what comes in the RBT gear set). Apparently, according to Ron's description & picture above, it can be removed, but it wasn't obvious to me that I could do it.

When I talk about the gear, and the cone, I mean the part on the right.

In Ron's picture, you can see the welds inside the cone body, affixing it together.

Thanks, Ron - even more clarity is brought to the discussion.

as for second guessing repair methods...

by spot welding on a stressed fit, with those splinded stress risers, could make the piece suspectable to crack.

I would have thought a 150F delta interferance fit would been used. (and to facilate changing the clucth, a few drilled and tapped holes around the face for jack screws)

with the splines to transmit torque, a light fit might have been the original design and thus why some are found loose

quote:

Originally posted by r mccall:
There is a slight difference between the reapir that Dennis Quella makes and the repair that was performed on Chuck's gear. Dennis presses the entire cone/tooth section off of the splined section of the gear, presses an entirely new part on and has it welded . The original part is pressed on and sometimes will get loose ( enough to fall off when the trans is disassembled).The welding eliminates the possibility of this. It appears that Chuck's gear had only the cone machined off of the toothed portion and a new cone pressed on. I have had Dennis repair at least 50-60 gears for me ( maybe more) and none have given me an issue in over 10 yrs. I'm not saying that there is anything wrong with the method that was used on Chuck's gear. I would have to have additional information before I weighed in on that. It will likely last quite a long time. The " spline " design on his new cone looks like it would last longer than the original version. And BTW, I recently flipped a BMW M1 transaxle for a GT40 customer which had a completely different synchro design on 2nd gear only!
Here's a picture of a gear that I just got back from Dennis.

Ron

That gear is beautiful! Tough to get the originals apart though.

Ron would it be rude to ask what that repair costs on the gear?

My Strange axles on my GT350 when I first installed them, Strange recommended tack welding the wheel studs on.

They use 1/2"NF Allen socket bolts for studs, made by or for Strange for the application.

Just for caution I called them at the Tech line and they no longer recommended the tack welds on them, just loctite.

They said they had found welding on that axles alloy was not a good idea.


If this gear is a press fit, just some loctite might be safer?

quote:

Originally posted by PanteraDoug:

Ron would it be rude to ask what that repair costs on the gear.

If this gear is a press fit, just some loctite might be safer?

Dennis charges $475 to repair each gear.
As I said earlier, I have had Dennis repair 60+ gears over a 10+ year period including a transaxle in a Pantera which had 12,000 miles on it in 2000 and now has well over 200,000 miles on it with absolutely no issues.
I believe some of us may be overthinking this a tad. ;-)

Ron

You may thank Ford for some of the confusion on gear-cones. In the original GT-40 and most Mangusta transmissions, the gear cones were smooth and the synchro rings were grooved to hold lube. ZF changed that to the present backwards groove design, along with an almost complete redesign of the ZF transaxle in the ZF dash-2 variant. This was to placate Ford's fears of vast warranty problems. Per several ZF memos to Ford circa 1969-'70, the design differences between a Dash-0 or 1 (GT-40 & Mangusta) and a Dash-2 (Pantera) transaxle were:

1)- rotate gearbox 180 degrees (on bellhousing flange) and move ring gear to other side of differential case.
2)- relocate shift mechanism on same side of car as at present (left-hand side) in spite of the 180 degree gearbox rotation.
3)- Increase OD of bellhousing flange by 30mm. New bellhousing required by assembly rotation has one large view/ventilation port, rather than two smaller ones at 45 degrees to each other. The new bellhousing is also die-cast (smooth) rather than sand-cast (rough) as previously.
4)- revise internal lubrication & ducts as req'd for new position of gear assembly.
5)- increase front hole-mounting pattern from 4 to 6 bolts (+ 2 dowels).
6)- Use new clutch spline size (1-1/16" in dash-2 vs 1-1/8" in dash-1 and dash 1.5)
7)- replace aluminum axle side-plates with cast iron for strength.
8)- Relocate unit attach points from (iron) differential side covers/bellhousing to (iron) tail cover. Note- In 1972, the single rear attach point again moved to two points on the transmission case sides via new subframes & mounts.
9)- Transmission (1st, 3rd & 4th) & R&P gearing substantially changed & Ford-recommended gear steel used.

In addition, the dash-1 Mangusta differential case (& interim dash-1.5 pushbutton Pantera case) is 4 lbs lighter than a dash-2, and the mainshaft is 1/2" shorter than in a dash-2. Dash-1 and dash-1.5 transmission mainshaft needs extended pilot bearing/bushing holder. Dash-2 does not. Clutch pivot shaft in dash-2 bellhousing runs in caged needle bearings rather than bronze bushings (dash-1 & 1.5) and is 1-1/4" longer than dash-1 & 1.5 shaft. Cross-shaft OD is larger, too. Throwout bearing release fork is also larger in all dimensions in dash-2.

Max input torque (dash-2); 325 ft-lbs @ 2153 lbs axle load (650 kp); Max engine rpms- 8000
Wt of ZF dash 1 type= 132 lbs (no oil or bellhousing)
Wt of ZF dash-2 type= 144 lbs (no oil or bellhousing)
Dash-1 holds 2.1 liters/3.5 pints 80W lube.
Dash-2 holds 3.5 liters/7.3 pints. Both can be hooked up to lube cooler via cast bosses.
Dash-1 (and dash-0) has ZF cam-type (sprag) self-locking (LSD) differential. Dash-2 has clutch-type. Dash 1.5 may have either type LSD.

And as far as 'brass' or 'bronze' synchro rings, I've never seen one from ZF or Butfoy. They are all non-ZF; there are dozens of types of brass or bronze formulations- aluminum-bronze, phosphor-bronze, red-bronze etc. No reason to expect them to be the same from various sources, possibly explaining the variant in lifespans reported for 'bronze' synchro rings.

Another subject mentioned by Lloyd Butfoy decades ago: 2nd gear synchro wears faster than all the others because in a street Pantera, the car spends most of its running life starting in 1st and quickly going to 2nd.... where it stays until the next stoplight when the sequence is repeated. 2nd gear is good for 70 mph with stock gearing & tires. The altered lube system noted above by ZF engineering for the upside-down Pantera ZFs may not be a perfect substitute for the original, either. The 2nd-to-neutral (or 2nd-to-1st-to neutral) shift is less stressful than upshifts and often is done at lower rpm. 2nd gear synchro is therefore used far more than the others, hence that cone & ring wear more.

Interesting that the so-called Super-ZF (M-1 type) got a redesigned 2nd gear synchro just in time to sell the whole ZF design & tooling to RBT. Thanks for that tidbit, Ron- I've never worked on one. Because M-1 shafts and bearings are also larger, piece-parts cannot be swapped into earlier ZFs. I'm told that with case machining, the entire M-1 gearset can be transferred to a lighter & less-strong early case, but it's not simple- nor cheap.

quote:

Originally posted by r mccall:
...presses an entirely new part on and has it welded
...Here's a picture of a gear that I just got back from Dennis.

Ron

Can the cone be replaced on a gear later after being tack welded?

I guess you verify the "proud" weld does not interfere with the movement of any internal pieces

JFB -

I can't specifically comment on your question, except to say that as I recall, all of the gears are "located" on the shaft via a series of snap rings or retained split washers (#211/212).

These retainers are close to the gear centerline.

The Syncrobody (216) and sliding sleeve are close to the gear, but on the outside of the cone (not where the welds would be).

I hope my description is clear...

Follow up report....

I have had my ZF back together for 1 1/2 years now.

The tranny is great.

2nd gear synchro action is great. I have put about 8-10K miles on the car.

If someone is working their own ZF, or has a very competent mechanic (like I did) helping you with working the ZF... I would highly recommend this route.

Not much point in going this route unless you are going it on your own... all the ZF experts have equally effective & proven solutions.

But in my case, the CRM solution works great and was cost effective.

CRM is highly recommended by Lyle and myself!

Rocky