Worn Synchro Blues... Flathead to 39 Trans

I think I've come to the conclusion that the synchros in the gear box in my AV8 are worn out. 8BA to '36 case with later gears. I bought it as a working trans for $100 so I'm not too surprised. A quick check showed clean gear oil and no chipped teeth but I suppose I should have known better.

It grinds/clunks/ when shifting about 80% of the time, even between 1st and reverse. I've adjusted the clutch linkage to both extremes to no avail. My only other thought is that maybe I have the wrong pressure plate or something? Any thoughts?

I have a nice 78 case and several 40's trans here. I tore them down this morning to put together one nice trans. Do these synchro blocker rings look good to use? Any other parts I should check out carefully?

 

That blocker ring looks great. One of the things that cause the trans to jump out of gear is end play. Both on the cluster, and the second gear when its all together. There are different thickness thrust washers to take up end play on both. Try to mix and match to get the end clearance down. Double check the shifter to make sure the trans is getting it all the way into gear, and the detent is holding it there.

 

Thanks Don, it doesn't pop out of gear ever, it just clunks or grinds a little when going into gear. Like the synchro isn't matching the speed quick enough or the clutch isn't disengaging all the way.

I had planned on building a fresh trans for this thing anyhow, I was just hoping to get by using this one for a season. I don't think that's going to happen.

 

I'm running one of those "good from a running car" 39 trans in my roadster.... it grinds/buzzes into 2nd and 3rd... i figured it was some extra play or something with the synchros.... hasn't affected the workings though... stays in gear just fine...

1st and reverse are smooth though if the clutch isnt dragging...

been this way for a couple years now and not gotten any worse..... of course my "driving style" has calmed down dramatically from when I first built the car

 

I plan on driving this car a LOT, so I'm not taking any chances. I really should have checked this trans out before I slapped it in there.

It definitely grinds going in 1st and reverse when the car is not moving. That's why I thought I might have a clutch/pressure plate issue. Hmm...

 

The synchro looks good. Wish mine looked that good when they went in a few years ago.
Are the teeth on the shaft a little buggered? Hard to tell in the pics.
I get a little grind going into first from a stop. Probably need to adjust clutch, linkage.
Found that Van Pelts book was really helpful for my 3 tranny build.

 

If it grinds going into 1-R from neutral after first putting it into 2-3 look for a dragging clutch. First step there do all the fingers set even? Have seen a disk that is too big installed that rubs/drags on the cover when released. should have about .060 clearance between those little teeth on the synchro ring and those on the mating gear,.030 is the absolute minimum there for good action.

 

I thought these looked good, just wanted confirmation from some others who have "been there and done that". The teeth on the shaft are good, just greasy.

I'll check and see if it still clangs going into 1 or R after 2-3 tonight. Yep, the fingers are even. I'll check the clearance on the new synchs also.

Thanks!

 

Man, the hardest part is already behind you- taking the trans. out of the fringin' car. I'd take a little extra care to go through it and make it right. No fun exploding a trans. 100 miles away from home.

End play can be a problem with these boxes. If the rear thrust surface is grooved or indented, look for a new box.

I think I have an original Ford service manual for transmissions I'd be happy to loan you or get you the end play specs. Really check this and be tighter than looser. Too much end play allows the cluster to move around and in essence, bind up. This is a majority of the reasons why an old Ford box grenades.

Maybe I'm too anal for some hot rodders' thinking but, since it is such a pain in the ass job to take out a trans. compared to how easy it is to replace the snychros those snychro rings, I'll look to replace them.

Here is the catch-I've heard from more than a few guys that you got to replace them with NOS or known good replacement parts. Some of the off shore versions are garbage and no better than worn out ones.

It's up to you.

Another bit of advice I'd pass along-If possible-replace the entire cluster/gear set (washers and all) from one trans to another. This way you'll know with a good deal of certainty the parts are all correct and go together.

Ford used numerous thrust washers and could have been swapped around by the numerous mechanics who have worked on this things over the years. When you find one of those seemingly virgin side shift boxes, snag it for you've got all the makings of the nice top loader.

Good luck.

 

Thanks much for the info! Unfortunately, the trans in question is still in the car! The pics are of the gears from the 40 box I'm sacrificing for it's gearset. The empty 78 case's thrust surfaces look pristine, surprising since the gears I removed were completely worn out. I'm gonna screw this thing together tomorrow so I can yank the engine, swap the trans, and plop it back in there in one fell swoop. I've been told that the way to make one of these last is to shim it up REAL tight. I have the specs around here somewhere but thanks again for the offer.

 

First of all, there is NO SYNCHRO on 1st or reverse . . . so this issue has nothing to do with the whole synchro question.

If it is grinding into 1st/reverse at a dead stop, then your clutch is NOT completely releasing . . . so when you try to slide the non-synchro slider gear into first or reverse, you're hanging up and causing the grind noise.

 

I suspected this as well, just wasn't sure... Why would it not be releasing? Wonky flywheel maybe? I've even adjusted the clutch all the way out, I'm getting plenty of travel there. At this point, I'm building a nice fresh trans for it regardless, so I guess I'll get a first hand look at what's going on in there when I swap it out.

 

I agree with Bored & Stroked here. If at a dead stop it's grinding, your clutch is not releasing 100%. Steven

 

is the clutch disc sliding on the trans shaft easily enough?
sometimes those splines get boogered up from rust....
might be causing it to drag?

 

Hmm, it shouldn't be, the splines were nice and clean, the disc is new, and I put just a dab of light grease on the splines before assembly. I'll find out this weekend for sure...

 

Andy, Are you shifting fast? I had the same problem with my trans at first, These transmission don't like to be shifted fast. Did you try double clutching?

i know why your having trouble, your legs are too dam long for that car, you should give it to me.

 

yep, same thing with mine, a nice leisurely shift that includes a good bit of finding my way into gear usually results in a good shift.

and the most important part, always shift into second before any other gear.

 

Usually, 1 st to 2nd, no real problem, slightly slower. 2nd to 3rd needs a slower shift because of gear ratio change, same with 3rd down to 2nd. 2nd to 1st, forget it, I never got to pull that one off. For me coming to stop, down to 2nd gear, then clutch, brakes, don't pull out of gear, when stopped pull from 2nd then drop in first.

 

that's how I shift. never tried any other way....

 

"Andy, Are you shifting fast? I had the same problem with my trans at first, These transmission don't like to be shifted fast. Did you try double clutching? "

If everything is in reasonably good shape these transmissions can be full power shifted
so it sounds like a Lenco shifting. Thousands of people did it for years at the drags.
Nowdays rapid shifting is not recommended with them because of the big hp available.
The 25 tooth Zephyr gears would stand the most abuse because of the closer ratios.
With the symptoms you describe, you have a clutch release problem.

 

yep, when you could buy a dozen of em at the junkyard for peanuts without having to rebuild it. I remember reading how many transmissions it took gene winfield to learn how to powershift a toploader.......

 

That is because the clutch has warmed up and expanded and/or the lube in it has thinned. When the gear lube is thick, it acts like kind of a 'sychro' to slow things down so you can drop it into first or reverse.

 

You young guys have to remember how old this stuff is. It isn't going to perform like the new stuff. If you want to use it (and I hope you do)you have to remember that, and baby it. That said, if after a full stop it is grinding going into first or reverse from second you probably have a clutch problem. A young guy in my club said he had to fix the tranny in his 56 Ford truck because the syncro into first wasn't working. I had to tell him it didn't have syncro into first.

 

Okay, by adjusting my shifting technique and popping it into 2nd before going into 1st or reverse I have been able to lessen the frequency/severity of my gear grinding. It's still not entirely right though, downshifting from 3rd into 2nd grinds every time not matter how slow it's shifted or whether I double clutch it or not. Something is dragging somewhere. On top of that, my thowout bearing is sometimes making some groaning noises too. I'm going to proceed with building up a nice trans and figure out what's up with the clutch when I swap it in. For now, I'll just deal with the occasional "bump-n-grind". Thanks everyone for your advice and help, very much appreciated.

 

UPDATE!

One car garages suck for engine/trans swaps... especially if it's raining...



So as I had suspected, the sychros in this trans are shot.




I REALLY wish I would have checked this thing out a little better before tossing it in there, but I suppose it really wouldn't have mattered anyway. I would have been pulling this engine/trans anyhow.... ...here's why:

I'm a dumbass. I used a 9.5" pressure plate and flywheel from a early 50's ford with a 9" clutch disc to get the early spline count. I KNEW these pressure plates were incompatible with the early trans, but for some reason I thought it was a 10" plate/flywheel even though it's stamped 9.5 right on it! Dumbass!

Anyhow, the longer fingers of the later plate were digging into the throwout bearing carrier and face of the clutch disc. Bingo... there's the source of my noise/drag/grinding etc...




So... I'm off to get my flywheel redrilled and pick up a new pressure plate. At the least, I hope this thread saves someone a headache or two.

 

Just reading now, but thanks for the update.

I was searching around because the little detents in the 2nd and 3rd gear slider gave me problems this weekend. One of them fell out, and another cracked and bent up, jamming my coupe into second gear and stuck there. Goody Goody time to pull the engine/trans

Any advice on why they would pop out? When I rock the car in gear, I can see the large front bearing moving a little in and out of the front of the case, so there is a little play here opening up the gap between the synchros in front and the sliding ring.

 

I think you'll find you have a bit too much endplay in the shaft causing it to overshift and blow the synchro assembly apart.

My toploader did something very similar Elrod. So I swapped in another synchro assembly as I got sick of fishing the ball bearings and springs out of the bottom of the box every time it slid to far. Only problem is it didn't fix any of the problems, ended up it smashed the synchro blocker to bits (pressed steel type not the ball bearing) and in the process completely destroyed the synchro rings. Put a perfect 45° chamfer on both of them and destroyed the keyway where the block actually sits. Then after a quick patch up with new blocks and the least worn synchro rings I had I managed 6 months of light use before it jammed in gear. Currently I'm trying my luck with some new synchro rings (not N.O.S.) and blocks and so far so good, but I think I still have too much endplay but it is better. Just need to shift accordingly.

 

good discussion guys.....