Hi guys, new to the site, but there seems to be a lot of knowledge(tried to search for my problem earlier didn't quite find it so heres a new thread)...I'm having grinding issues when I downshift or upshift at high RPMs. I just rebuilt this sag, it's behind a freshly rebuilt 350(only thing to add power was a new cam so we'll call it stock); new rebuild kit for the trans: synchros, snap rings, bearings, keys, seals, countershaft, etc. I even checked the clearances between the synchros and gears ~.06. Its got a Hurst shifter, and the shifter linkage is smooth with new bushings and clips to hold the rods on the brackets. When I originally installed the trans, after a few ride-arounds, noticed that the throwout bearing was in contact with the flexplate fingers all the time. Installed new return springs on the arm and now I have about .75" of free play in the pedal before the T.O. bearing contacts the fingers. O and newly resurfaced flywheel. I can't find the problem. I know that the clutch is releasing all the way!---Got on the road at a stand still and revved it up to around 4k and put it in first gear no grinding at all. On the road, anytime I get above 3k RPM and upshift, 1-2, 2-3, all gears, I can hear it grind. It's much worse downshifting, anything 2k and above and it grinds loud, even when I match the engine RPM with the wheel speed...please help, I've kind of exhausted the help over at the Nastyz28 forums...
What gear lube are you running in the trans? There's a lot of reports of shifting problems when using GL-5 rated lubes in older transmissions. They're slick enough that they prevent the blocker rings from being able to get enough "bite" to spin the gear up to speed for a smooth shift. This would also fit with the downshift being worse than upshift since downshifts require the next gear to be spun up to a higher rpm as compared to an upshift. The Saginaw was designed to use a non-synthetic GL-4 lube (not one with a GL-4/GL-5 rating) so if its got anything other than that in it now it might be worthwhile to change the lube and see if it helps.
This could be what I'm running into, I looked at the bottle I got from autozone...Valvoline Durablend API GL-4, GL-5 for Rear Gears....did some research on that too, different than old trans due to the "extreme pressure" rating of GL-5. I now see that it's not for use in "snychronizing" transmissions...yay, off to NAPA to get the Sta-lube stuff i guess, I'll try it out and see how it does; gona be a pain draining the thing without taking it off the car...
Did you check the gear shaft holes for roundness while re-building? They are known to go out of round and that could be your problem. There is a thread on here about the problem but I'm not sure if it was your model in particular.
You might be better off taking the trans. out and trying to flush that old lube out. With the additive packages and the way the new lubes cling, you'll want to get as much of the old stuff out before adding your new lube. I have no idea what type solvent you could use to cut the old lube out. Possibly Acetone.
BRAD PENN® Multi-Purpose 'Cl***ic'GL-4 SAE 80W-90 Gear Oil This is what I used for my recent rebuild of a saginaw 4 speed. Seems to work great.
When you checked out the synchro fit on the gears did you spin the rings and check the fit in several locations? Sometimes new rings aren't as round as they should be. Usually when you press a ring onto the gear the clearance is more like 40 thousands. 60 is ok is the rings are round. And the teeth on sliding hubs and gears are fairly sharp,not rounded? Of course the gear oil can cause a problem... I had to discard several "new rings" for this BW rebuild...Only NOS forged bronze fit properly, the repop stamped br*** fit poorly
Beat me to it! Keep us posted on how this works out for you. Short of pulling the trans you might at least pull the side cover to get as much of the current lube out as possible. Maybe spray the innards with carb or brake cleaner or some kind of solvent. Mop it out as best you can and dry it out with compressed air before you refill it. You might even run it with 30w motor oil for a spell and then drain it and refill with conventional gear lube.
loudbang - For the actual gears, I didn't check them for round when rebuilding...I'm guessing a micrometer or calipers would suffice but also having to tear down the trans again, I'll try to find that thread. Andamo - I should probably do this, to leave no doubt and cross it off the list would be good. For me and this sag it comes down to 'is it worth it?' bc I have another tore down waiting to be rebuilt... Truckedup - I did not rotate and measure in multiple places, just one place. This continues to get closer to pulling this trans... ClayMart - I was looking at the 80W90 GL-4 from NAPA, I think Sta-Lube is the brand. They have it in stock at my local store. Thanks everyone for your help and suggestions, I wasn't expecting this many responses so fast. appreciate it. -Mike
It's not the gears that go out of round it's the holes in the CASE where the shafts mount that get pounded out of round.
HMMM, had this same problem (OP grinding) with a 3 speed Sag rebuild, pulled out the trans and replaced with the 'good used' synchros that had been in there originally. Runs great now. Cosmo in the '49[/QUOTE]
I always lap synchros to the gears. just a touch of lapping compound and rotate by hand until I get good contact between the two. Then clean them really well to make sure there is no residue in the synchro teeth and then fit the synchro and gear together and give it a slight twist. They should lock together as soon as you twist. This has never failed to give me good service with my rebuilds. Worn gears and new synchros will rarely have much "Bite".
So far I've changed the fluid and it has actually helped quite a bit, drove it around for a good while the other day; town driving, going through the gears a lot, and no grinding. I got it up to about 4k RPM upshifting and it did fine, downshifting I only did 2500 RPM max and all was well. I have a feeling it has to do with the fitment of the synchros on the gears but this is a good start. I don't want to romp on it too much til it gets broke in more.
Thanks for reporting back. Sounds like the lube change has solved the bulk, or more, of your problems. Just try not to be too abusive with that Saginaw transmission. It's not as well suited to the "rough stuff" as a BW T10 or a Muncie is.
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