39 ****** grinding 2nd?

Vanspeed

Vanspeed

Well-known member
Hey guys, just put a 39 ford transmission in my model a, behind the original banger using clings adapter kit. I rebuilt the trans and took it for it's first drive today. It grinds second gear when down shifting from 3rd to 2nd, not alot but just enough to be annoying. What do you think is wrong? I replaced the syncro rings. The syncro hub seems a little tight and I am running 140 gear oil in it. What do you think is the problem?
 
I run the same thing, my theory- the trans parts weigh a lot. The syncros are small...So I double clutch down to second... I also found that my clutch needed adjustment last week... Karl
 
Should you be able to slide the syncro hub back in forth with your hands? Mine is really tight and I was wondering if that is part of the problem.
 
This is the secong one I have done and the first one was fine, wondering what is causing this. Something is causing this to grind, I have no idea why it would. I put nos gears in it too. With the car off, when I shift the car between 1st and reverse, it is smooth and goes easy but when I shift it back and forth from 2nd and 3rd it is not as smooth or easy, more tension on it. Do I need it to "break in"? Should I be running 90W oil?
 
You might try the lighter weight lube. The heavier lube will have more drag making the synchros work harder to bring the gears up to speed before engagement.
 
I might try that, really frustrated about this as there is no apparent reason for it to be doing this. I don't want to double clutch it, as that is the whole reason I swapped this ****** into it.
 
The '39 transmission requires the lighter lube for the synchros to work properly. A guy here in the Dallas Club had problems with new roller bearings that was causing a similar problem. He took it back apart and the bearings came out in pieces. He is going back with used bearings.
 
If the synchro sleeve (the outer ring) is very difficult to move front-to-back, you may have a problem with the insert parts hanging up. We generally change them all over to the later style (3 insert plates with a bump in the middle and two round wire springs to retain them). You may also have some clearance issues going on. Did you check the clearance behind second gear after assembling the gear and synchro to the mainshaft? You mentioned using NOS gears....which gears did you replace?
 
Ed Pitts said:
The '39 transmission requires the lighter lube for the synchros to work properly. A guy here in the Dallas Club had problems with new roller bearings that was causing a similar problem. He took it back apart and the bearings came out in pieces. He is going back with used bearings.
Click to expand...

Could it be determined what caused these new bearings to fail? Did it appear to be a metal failure due to improper hardening or what?
 
Ross, the new bearings appeared to be improperly made and just came apart. They had less than a hundred miles on them. The failure caused a mis-alignment in the main shaft and thus the shifting problem. If new bearings were used, compare them to the old ones.
 
Use common sense on gear lube.These old transmissions were made to run thin lube in cold weather and heavy in hot weather. I know that heavy lube in cold weather makes the brass friction ring slip and not correctly grab the mating part on 2nd. rotating gear ond/or high gear mating diameter. Some of the very tacky lubes( speedway red lube) is too sticky for street use in these old units. Also like it was said earlier some of the new synkro rings are not worth putting in. The shifting is dependent on the small concentric v-grooves being just right. If the ring is worn or not made right the gear lube has nowhere to squeeze into the v-grooves allowing the tiny lands on the rings to brake enough to match speed between the two gears. Mac VP has very usable synkro rings because I just used them in a trans, of my own.
 
Most of the convential gear lube made are compatable with clutch type positraction limited slip differentials and have a slip additive in them to keep the Posi Clutches from chattering. This is fine for Posi Clutches but not for Transmission Brass Blocker Rings where you do not want them to slip but to grab the mating gear. If the container says Compatable with Posi Differentials or some such thing like that, it will have the Slip Additive.

For Many years, I have been using Red Line Gear Lube, 75-90 NS. The NS is for NON SLIP and it does NOT have the slip additive in it. It is made especially for Brass Blocker Ring Transmissions. This stuff is actually a lot thinner then conventional 75-90 Gear Lube and will allow the blocker rings to contact the gear better and work MUCH BETTER. The problem with it is if you do not really have the transmission sealed up well, especially the Counter and Reverse Idler Shafts, it will leak out.

Pennsoil and GM also have a Manual Transmission Lube that is formulated especially for Blocker ring transmissions. These seem to work just as well as the Red Line.

I have been using the thinner Manual Transmission Oils in all the old Ford transmissions I have rebuilt for about five years now with very good success.

This stuff also works great in steering gears BUT you have to have them sealed up real well or it will leak out.

One more thing, BE SURE your clutch is COMPLETELY DISENGAGING. Just the slightest drag on the clutch can cause the transmission to grind a little, especially in second. The early Ford Blocker rings were non too big and will not over come a slight drag in the clutch when it is disengaged.
 
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Thanks for all the info, my rings were bought from Mac's antique auto in N.Y. They seemed just fine. The gears I put in were from a 46 side loader trans, I used all of them as per Vern tardels book. The 140 I put in is really thick, my step dad thinks it is way to thick for the trans and suggested I put the 90W in it. It faintly grinds up shifting from 1st to 2nd too but not every time.
 
I don’t know where you live, but here in Southern California most like the way 140 up shifts better (1st into 2nd) than 90. Now the things that cause the gears to slow down quicker are probably going to work against you down shifting. You aren’t going to crash the box due to a lubricant failure with either, so try them both and see which you like better. However, even the better 39-48 synchros are not going to be great by modern standards. Personally, I ran 90 for many years; but I like 140 a lot better. Next time I change it, I am going to throw in a bottle of STP. (A 50/50 mix of 90 weight gear oil and STP is, by far and away, the best boat trailer bearing grease I have ever found!)

That being said, I knew two older mechanics in the early 1960’s who had each worked as Ford dealer mechanic before and after WWII. One was still working for the same dealer! The both, independently, told me the same thing. They used to put the heavier differential lube in transmission’s, they were not supposed to; but they said customers liked it better. They both, independently, used the same words to describe that lube. They called it “tarry, sticky and nasty stuff”. For what that is worth!
Dave(Smith)
 
The lighter 90W will make it work better. The extra thick stuff doesn't let the syncros work as effectively due to the parasitic drag on the moose slime gear oil. Also if you used the one piece rectangles without the balls it will shift a little harder as well. But don't worry once you change the gear oil and put a few miles on it you should feel it working smoother. I'm running a similar combo behind my Banger with the Clings adapter. It's the best thing I've done yet to the A.


Good luck,
Tim
 
I like the 140 weight, too. I have a stock '37 Zephyr with a transmission that is essentially a stock Ford. With the heavier oil, I do have to let it warm up a little (mile or so) before single clutching up to 2nd, but after that, it's fine. With regard to downshifting, it's definitely *not* like a modern ******. But I'm much newer to all this than most of you, so just sharing my 2 cents.
 
Syed Razzacki said it best, "The manual transmission synchronizer design has been a real challenge, and is usually referred to as a myth and black magic. A mathematical algorithm and dimensioning and tolerancing scheme has been developed to dispel this myth. A unique and logical user-friendly method for designing synchronizer is devised. The knowledge that existed in the public domain is advanced to higher level to show that the design and calculations of physical parameters must go hand in hand. The calculations of synchronizer physical parameters should be supported by scrupulously dimensioning and tolerancing the components design to achieve the intended functional objective. A mathematical algorithm is developed which facilitates establishing the sleeve and blocker ring pointing angle relationship with the synchronizer size, coefficient of friction, cone torque, and index torque. The relationship is presented graphically in a unique manner identifying the clash and hard shift zones. As such, it allows sizing the synchronizer and selection of the parameters for a given application for comfortable shiftability between the two extremes of clash and hard shift. Synchronization episode is separated in to the following six distinct events: Event I. Strut contacts blocker ring Event II. End of strut loading, strut out of detent Event III. Sleeve point hits ring point, ring clocked Event IV. Sleeve chamfer passes through ring chamfer Event V. Sleeve tooth point contacts clutching tooth point Event VI. Sleeve tooth chamfer passes through gear clutching tooth chamfer Arithmetic stack and calculations are utilized to iteratively dimension and tolerance the components for each event so functional harmony is achieved in concert with the selected physical parameters. Event charts are presented with illustrations and necessary stack for dimensioning and tolerancing the synchronizer components. The components that play significant role in each event are identified and related to specific physical parameter."

caveman.jpg


Sounds easy to me.

So, the bottom line is: if it continues to grind after it warms up ... even with straight 140 ... and the clutch is in spec and adjusted properly ... and the pilot bearing/bushing is good ...

Then, your functional harmonies and physical parameters are messed up.

It can be very difficult to measure ALL the wear points in a flathead transmission. Just because the thrusts are correct with new bearings and synchros installed doesn't mean the transmission will operate as new. Your transmission may exceed the parameters of the mathematical algorithm.

When the functional harmonies are in order, you'll achieve the intended functional objective, and it will be a fine shifting unit.
 
Hoop said:
Syed Razzacki said it best, "The manual transmission synchronizer design has been a real challenge, and is usually referred to as a myth and black magic. A mathematical algorithm and dimensioning and tolerancing scheme has been developed to dispel this myth. A unique and logical user-friendly method for designing synchronizer is devised. The knowledge that existed in the public domain is advanced to higher level to show that the design and calculations of physical parameters must go hand in hand. The calculations of synchronizer physical parameters should be supported by scrupulously dimensioning and tolerancing the components design to achieve the intended functional objective. A mathematical algorithm is developed which facilitates establishing the sleeve and blocker ring pointing angle relationship with the synchronizer size, coefficient of friction, cone torque, and index torque. The relationship is presented graphically in a unique manner identifying the clash and hard shift zones. As such, it allows sizing the synchronizer and selection of the parameters for a given application for comfortable shiftability between the two extremes of clash and hard shift. Synchronization episode is separated in to the following six distinct events: Event I. Strut contacts blocker ring Event II. End of strut loading, strut out of detent Event III. Sleeve point hits ring point, ring clocked Event IV. Sleeve chamfer passes through ring chamfer Event V. Sleeve tooth point contacts clutching tooth point Event VI. Sleeve tooth chamfer passes through gear clutching tooth chamfer Arithmetic stack and calculations are utilized to iteratively dimension and tolerance the components for each event so functional harmony is achieved in concert with the selected physical parameters. Event charts are presented with illustrations and necessary stack for dimensioning and tolerancing the synchronizer components. The components that play significant role in each event are identified and related to specific physical parameter."

caveman.jpg


Sounds easy to me.

So, the bottom line is: if it continues to grind after it warms up ... even with straight 140 ... and the clutch is in spec and adjusted properly ... and the pilot bearing/bushing is good ...

Then, your functional harmonies and physical parameters are messed up.

It can be very difficult to measure ALL the wear points in a flathead transmission. Just because the thrusts are correct with new bearings and synchros installed doesn't mean the transmission will operate as new. Your transmission may exceed the parameters of the mathematical algorithm.

When the functional harmonies are in order, you'll achieve the intended functional objective, and it will be a fine shifting unit.
Click to expand...

Huh? Oh Yeah, now I get it???? Right!!!!
 
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