I own a 1969 L68 with a 4-spd and a 3.36 rearend. I have begun to feel a bit of grinding when I shift gears (mostly into 2nd), and it happens most often when I first start the car and the choke is engaged, though it does it a little bit later when the car is warm if I accelerate aggressively. My guess is the synchronizer is bad or going bad. What do you folks think? and if that is it, what am I looking at in terms of cost to repair, assuming I need to have someone else do it (which I do)?
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Re: grinding gears
Anthony, The synchronizer or the gear itself can be bad, it's worse when cold because the engine idle is higher so the shaft is spinning faster and the syn has to grab and stop the gear before engagement. Check the clutch adjustment first.
I think if you remove and replace the transmission yourself, work could be done for 300-350. But, if it's open a complete overhaul should be done with the other gears, bearings etc. then of corse while your at it check the clutch, pilot etc... nice winter project but when your done you did it the right way and will not have to be bothered with this again.
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Re: grinding gears
Are you using any type of synthetic gear oil?
If so, get it out of there.
That could be your only problem.
I know I am going to hear from those who will disagree here, if so, just ask any other volume rebuilder of our ol' boxes!
The synthetics are "to slippery" for our poor old muncies that are not designed for that product, there needs to be enough drag between the synchro ring and the gear to slow the gear movement enough to smoothly engage, the older the trans, the more polished the synchro taper on the gear gets do to age and use, the more sensitive it is.
Stick with a quality brand of 75-90 W petroleum base gear oil
STAY AWAY from bargain chain store brands, no matter what the bottle reads as far as specs met. They have poor anti foam properties,
without going into it you can imagine what happens if your oil foams up!Comment
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Re: grinding gears
Do you have any other hang up with the gears with the engine cold? Reason I ask is that it is common for an old clutch to stick a bit when cold and not fully disengage. Mine is still original (clutch @ 44.5K) and after sitting for a week or so during the cooler weather, I always start with transmission shifted into Reverse and clutch in. Otherwise, it is a bear getting into Reverse that first time w/o grinding - and you know that the R-Gear is weak. I also pop the clutch pedal several times to make sure the disc is free before starting.
Stu FoxComment
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Re: grinding gears
Plus, if it turns out to be a transmission internal wear problem, there are better parts available today for repair: bronze vs. brass synchros and 'locking' sliders...Comment
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Re: grinding gears
Have to say I agree with Bill regarding the light weight synthetics. A shop put that stuff in my old muncie back in the early 90's and it's never been quite right since. To start with, my transmission began to leak (never did before), and the shifting was sticky. Also, the transmission became noisy (gear and bearing). I changed it back as soon as I found out and in an effort to quiet it down a bit. It helped some, but as I said; it's never been the same since then. It shifts better and is a little less noisy, but it still leaks and has that "needs a rebuild" sound.
Stu FoxComment
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Re: grinding gears
I remember when I had my T-10 rebuilt I replaced second, third and new input and cluster. Torque lock slider for first/second and new regular slider for third/forth. The only gear used over was first because the engagement teeth don't get hard use because the engine RPM is at idle when shifting.
Come to think of it, new reverse idler and small parts and shift forks, american made bearings, no wonder it works like new. I had better write this stuff down.
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Re: grinding gears
Stu,
Feel for ya,
What brand/ weight oil did you puy in after removing the synthetic?
First keep in mind its very difficult to remove all the oil from the trans when in the car unless you drilled out the lower boss and installed a drain plug. It does not take much left over to still give you problems.
The synthetic did not really "cause" it to leak, but because of its superior migration properties over the petroleum based oils, it just get by things the dinosaur oil does not. Especially the cluster pin in the front of the case. I find an almost gauranteed fix for that to be to unbolt the trans from the bellhousing and pull it back about a 1/2", using a fast dry solvent clean the case around the cluster pin well and its mating surface against the bellhousing.
Take some Permatex "Ultra Blue" RTV sealant (do not use silicone as its a waste of your time, it will NOT hold up to oil. )
and put a big thick puddle over the area around the pin on the case, reinstall the trans and it gets trapped between the case and the bell creating a positive seal after it cures, (about 24 hours so do not use car until after that )
Do not try and wipe off the excess that squeezes out as you will just make a mess, wait till it cures and you will be able to easilly just pull off the excess hanging.
Take a good look at the tapered pin installed in the case holding reverse linkage in place, thats another notorious leak spot, wipe that with solvent and put a spot of the same permatex product on top and bottom of the pin, works great. If the spot of blue is offensive, buy a silver caligraphy marker in any art supply store and just cover the blue with that, matches the case fine!
Maybe try another oil change. Be sure and use a brand name oil of 75-90 weight, do not be tempted to add the heavier oil thinking it will quite it down, depending on the brand, the anti-foaming additives in the heavier weight leave much to be desired, first consequence of aerated oil is its full of bubbles, they do not help much when they are between our gears and will actually make it more noisey. Needless to say the lack of lube film does the gears no good either.
Second POTENTIAL consequence is the oil aerated so much its volume increases and will actually cause an overfilled condition and leak right out the front of the bearing support, and all over the clutch disk, yes, another hard knock learned. So much for what specs the bottle says it meets. Been thru this with customers, a hard lesson. This is also a consequence in your differential if using the same oil, the rear WILL become louder. Again, hard lesson learned. Synthetic seems to work just fine in the differentials and I continue to do that and still add the Posi additive, have not had any problems.
Interesting note, Tremec transmissions (KEISLER) has a disclaimer with the trans to the installer stating that if synthetic oil is used it will absolutey cause hard shifting and if memory serves, also voids the warranty, recommended oil is GM syncromesh product . That trans always sounds noisey to me but at least after a few hundred miles it does shift like a dream.
Good luck and keep us informed if you make any progress!
BillComment
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Re: grinding gears
Thanks to all you guys for your responses. I don't know what gear oil is in the transmission. I've had the car only a year and have never added any. I will see if I can figure that out, and put the right stuff in there if that is my problem. I haven't noticed any other problems other than what I originally described. It happens only when I'm shifting up, never when shifting down. It has happened only when going from 1st to 2nd, and rarely when shifting from 2nd to 3rd. I haven't had a problem going into reverse, though I have made a point of shifting into 2nd before trying to go into reverse. If there isn't a problem with the clutch, including no need for adjustment, assuming I need to replace the synchronizer, how involved is that to replace? I'm hoping I can have my mechanic repair this issue for under $500. How likely is that?
Thanks, TonyComment
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Re: grinding gears
Tony,
Not likely unless you can do most of the labor yourself. Once the trans is apart, it makes no sense unless to address just one item, rebuild the entire trans, kits, which include all bearings, seals, synchro rings, etc are under $200, hard parts extra, might as well check the clutch while you are in there also.........
BillComment
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Re: grinding gears
This doesn't sound like a synchro problem. The synchro has to work much harder in a downshift than an upshift. You could probably upshift without synchros and not get a crunch. I would look into the clutch disc hanging up on the trans. input shaft and not freely releasing from the flywheel. (I'm assuming that you upshift a lot faster than you downshift, and that's why the synchro can increase the input shaft speed without a crunch on a downshift. )Comment
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Re: grinding gears
Bill,
I disagree. The synchro assembly does not know if you are upshifting or downshifting, input shaft speed would be the key variable as far as engine speed.
Although a clutch not completely disengaging will keep speeds up and input shaft loaded which would be a problem.
Distinctive patterns of synchro problems only on upshift or only downshift are usually associated with an internally broken center bearing support plate. There is a very thin wall ( and its aluminum, = soft ) which the retaining ring for the bearing seats in, if that breaks it is not visible outside but it will allow the entire mainshaft assembly to walk back and forth quite a bit. It also allows the nose of the mainshaft assembly to rock up and down With the shifting fork trying to move the slider towards the selected gear the main shaft can "pulsate" back and forth as it is directly attached to the drivetrain and will either be loaded forward in the trans or rearward depending on whether the vehicle is accelerating or
decelerating.
Usually during shifting the drivetrain is a bit "relaxed" but still very sensitive to that pulsating back and forth beyond design limits do to the broken shoulder. I find this condition tends to usually be associated with the trans popping out of a gear its already in, usually second. But have also seen it cause erratic issues.
Another real problem area I see often is the transmission yoke and can cause erratic problems. Its purpose goes beyond simply attaching the trans to the driveshaft and allowing for movement in and out. It also serves a critical purpose.
It is holding the entire mainshaft in perfect alignment with the input shaft and of course, the rest of all the innards. It does so by the OD of the yoke riding inside a wide bushing pressed into the end of the tail housing, its just behind the oil seal. A little wear here allows a LOT of movement up at the other end, allowing that end to "whip", as you can imagine this clearly is not good. The input yoke and the bushing need to be in good shape and are commonly pretty worn, replacing the yoke without the bushing is wishful thinking and wasting money.
You may ask, if the support plate is broken then what stops the mainshaft from coming out of the back of the trans further?
Not much, just the fact that the yoke is attached to the driveshaft preventing it!
I am always amazed at the simplicity of design and manufacture of these transmissions and the abuse they take and actually still keep running but keep in mind, they are all getting OLD, and, temperamental. Requiring at times special attention to worn and tired areas.
Hmmm, seems like something I have heard before...............
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