3/4 synchro

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72-340-4speed

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I restored my 72 Duster #'s matching about 5 years ago.Total rebuild on engine and A-833 4-speed.After a couple hundred miles the 3/4 synchro failed,grinding badly on the downshift.Took it back to to the tranny shop where it was rebuilt and had it torn down and replaced synchro again. About a hundred miles later the same thing happened again.They said
the synchros all come from China now and they would not fix it unless I get an original one or one made somewhere else.The synchro is called a 3/4 Kingomatic.Can anyone shed some light on this problem or know where to get an aternative synchro.Thanks in advance.

72-34--4speed
 
Each gear has it's own synchronizer so 3 and 4 going at the same time?
Something else is wrong!
Too much play between the input and output shaft
 
Check the end play in the shafts. This happened to two of us using adapter shafts from (back then) Advance adapters hooking an 833 to a Jeep transfer. The play in the (same as) mainshaft/ and bearing allowed enough slop to tear up the 3rd gear syncro.

Check also bearing widths, snap ring groove placement and thickness, etc.
 
I restored my 72 Duster #'s matching about 5 years ago.Total rebuild on engine and A-833 4-speed.After a couple hundred miles the 3/4 synchro failed,grinding badly on the downshift.Took it back to to the tranny shop where it was rebuilt and had it torn down and replaced synchro again. About a hundred miles later the same thing happened again.They said
the synchros all come from China now and they would not fix it unless I get an original one or one made somewhere else.The synchro is called a 3/4 Kingomatic.Can anyone shed some light on this problem or know where to get an aternative synchro.Thanks in advance.

72-34--4speed
 
Called Passon performance and they stock the synchro as rebuilt original but also believe as you stated that it is likely something else causing the shifting issue. Don't know if I should go back to the same shop or try another,already out $1500.00 with these guys! Passon said that synchro Assembly is about $325.00.
 
It almost sounds like you're not declutching far enough and making the brass work overtime.
Or possibly the oil is too thick,too thin, or wrong type. If you are using synthetic, get rid of it.And we don't need 140wt up here; I run 50/50; ATF/80-90 EP.
If your slider is new, you just need the brass rings...... and maybe not even those.

If you lived next door.....I could fix you up in a jiffy.
 
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I also recommend a 50/50 atf/75w gear oil.

The syncros get sticky when you use straight gear oil. Check the fsm's.....
 
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I also recommend a 50/50 atf/90w gear oil if hot weather and straight 75wgear oil if cold climate
Wouldn't that be the other way around?

Also, you guys who are running the mix of gear oil and ATF.
What ATF do you use, Dexron, Type F or something else?
 
1. Just use 90 wt gear oil, it is fine until it get to -20 degrees
2. Did they replace the countershaft and needle bearings in the cluster gear? This puts everything back in the right relationship. Did they really rebuild the trans???
 
Here's the deal about the oils, in my experience
The brass rings are brakes. When you disconnect the input gear from the crankshaft, by stepping on the clutch,then all the gears on the mainshaft are supposed to be free to turn faster or slower. Supposed to be. Let's assume the clutch is working properly, and they are free. Ok now, the brass rings are brakes. or supposed to be. When you begin the shift, the fork moves the slider. That motion is transferred to the brass, thru the struts, by the springs pressing the struts into the sliders.. The brass is supposed to brake the chosen gear to match the driveshaft rpm, either speeding the chosen gear up or slowing it down. When synchronization has been achieved, the slider passes over the brass and the clutching teeth engage the gear. All this is supposed to happen in microseconds, as you slam the stick from gear to gear.
That's how it is supposed to work.With a fully disengaged clutch, and gears that are freely rotating.
Now, if the selected oil is too thick, too viscous, or too slippery, it takes more time, and if you are too forceful, grinding occurs.
And if the oil is too thin it is forced out too quickly and clashing may occur as the brass grabs the gear, and locks it between clutching teeth. However IMO this is a better situation than the first.
The cluster pin needs EP protection or it wears out prematurely. However it has 2 or more lives so I never worry too much about it.
Full Synthetic is just too slippery. Some guys use it, to some degree of success, But I couldn't make it work fast enough to suit me. And I really tried, modding my cones and brass with channels to get rid of it, and adjusting my brakes.
And about those brakes. If the brass won't bite the cones on the bench dry, you can bet they won't work installed. The cones have to be deglazed in a lathe with emery cloth to create the bite, and I bias mine to the upshifts, except first I bias to the downshift side. And the rings have to be round! If they rock on the cones they will be slow and or they will be the author of grinding. And finally; they have to sit high on the cones, else the clutching teeth will get together before the brass has done it's job. This is especially important on 4th gear, cuz it is usually a little further away from the slider's parked position in the first place.
And lastly lets talk about those energizer springs and struts. They have to be matched to eachother and to the slider. There are three kinds that will work in the A833; the early style, the late style, and the accidentally swapped in 3-speed style. I prefer the late style, but both A833 types work equally well on the street. Do not use a swapped in transplants from a 3-speed, They are not made to shift like lightning,lol. The A833 ones have long and deep humps on them that you can exploit with extra spring if you need to. Stock works for most. I stretch the crap outta those energizers before I put them back in. IIRC, I put an extra one in the 4th position to push the brass out a lil further, to initiate braking a lil sooner, cuz that gear is out there.

Back to the oils. 100% ATF works fairly well and IIRC was the FSM oil for a few years. 100% EP oils for me have been too slow although 75/90 is pretty good on my modded cones. So I mixed it 50/50 and it worked right away and so I didn't experiment any more after that. Those modded syncros of mine have about 60,000 miles on them now, or more;while I put over 100,000 on the used gears.The brass are older-than-Adam, used ones from the 70s.
 
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I don't know if they're all the same but I just had my 65 Dart 833 rebuilt in the Synchro gears weren't that bad and I still have them.
If interested for cheap

Dave
 
I don't know if they're all the same but I just had my 65 Dart 833 rebuilt in the Synchro gears weren't that bad and I still have them.
If interested for cheap

Dave
It's making me now think of what Synchro gears were put into my rebuilt transmission for $800
This project car ain't on the road yet
 
1. Just use 90 wt gear oil, it is fine until it get to -20 degrees
2. Did they replace the countershaft and needle bearings in the cluster gear? This puts everything back in the right relationship. Did they really rebuild the trans???
It almost sounds like you're not declutching far enough and making the brass work overtime.
Or possibly the oil is too thick,too thin, or wrong type. If you are using synthetic, get rid of it.And we don't need 140wt up here; I run 50/50; ATF/80-90 EP.
If your slider is new, you just need the brass rings...... and maybe not even those.

If you lived next door.....I could fix you up in a jiffy.
I'm running 80w/90 as well.Your right, it was not a complete rebuild as the repair order reads like this: 3/4 synchro assembly,gasket kit,seals and labor.As for shifting I have had several people drive it and all noticed the same issue. It was the tranny shop that said it was definitely a synchro problem when I took it back to them so they just replaced the synchro assembly the second time. Maybe it's time to try another shop!
 
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