Hi Folks, I have a 1954 3100 that I bought back in June with Little to no history. Its a great looking truck, and for the most part drives well.
My two problems with the drive train are: - Once the truck warms up, it has difficulties getting into 3rd without some "grinding" of the gears. When cold, it goes right into 3rd no issues - Putting the truck into first gear while the truck is in any motion, also results in some "grinding" of the gears. Is this typical? Is there a way to prevent this, or is this by design.
Your second question.... these trucks did not have synchronized 1st gear. First question....... your 3rd gear synchronizer is getting worn. You might have some success with changing the gear oil. Be sure to use factory spec non-synthetic lube. ðŸ›
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
Your second question.... these trucks did not have synchronized 1st gear. First question....... your 3rd gear synchronizer is getting worn. You might have some success with changing the gear oil. Be sure to use factory spec non-synthetic lube. ðŸ›
Thanks, Still new to these trucks, why do you recommend non-synthetic lube?
Thanks, Still new to these trucks, why do you recommend non-synthetic lube?
The synchros were not designed for slippery synthetic lubes, hence the synchros might not slow the gears quick enough to make a nice quiet shift. None of the first gears were synchronized so you must be at a complete stop to make it a grind free endeavor. If it is a sm420 4sp with granny low, 2nd gear is synchonized which is the gear you normally start out in if you are not fully laden.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Just need to wait a short while before putting into a non-synchronized gear, including when the light turns green, not wise to sit at a light with the clutch in, unless you like changing throwout bearings.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires. '47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle. '54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed. '55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
You might want to try hesitating a bit before actually shifting into third gear. Also the double clutching technique should be helpful. Apparently the fluid gets thinner as it warms up and your synchros have a problem with that. Going to a much thicker fluid may help a bit but I don't know if it would be good for the general lubrication of the bearings.
+1 for slow shifts. Shift into neutral, wait a second and then shift into next gear. Quite different from the last manual I drove; a Toyota Corolla. With the Toyota, you could shift as fast as you could. I can see why people want to install a T5...
I now pause an instant in neutral on my way to 4th gear leaving the clutch disengaged. I used to double clutch but my left knee should last twice as long now that I just pause.
34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
I do the pause, sometimes longer than others, and have tried to double-clutch as well with mixed results.
Just found it odd, that when the engine and transmission are cold, it goes into 3rd as happy as can be. I will look for SAE 90 Mineral Oil, to replace what is there today (synthetic), hopefully that will help.
Kevin, I have played around with many different gear oils and the best for shifting is the NAPA 90weight mineral oil. They sell it by the gallon, you will need a tad over 6 pints (granny low sm420). I've had a dozen or so sm420 opened up on the work bench this last year, playing with all the synchros on the gear cones and the mineral oil grabs these synchos the best, the worst was Redline 75-90 synthetic, it was too slippery. About 6 others just as bad as redline all synthetics too.
Last edited by sstock; 09/30/20197:10 PM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Kevin, I have played around with many different gear oils and the best for shifting is the NAPA 90weight mineral oil. They sell it by the gallon, you will need a tad over 6 pints (granny low sm420). I've had a dozen or so sm420 opened up on the work bench this last year, playing with all the synchros on the gear cones and the mineral oil grabs these synchos the best, the worst was Redline 75-90 synthetic, it was too slippery. About 6 others just as bad as redline all synthetics too.
Looking at the Napa Site, I did not see any mention of Mineral Oil. I see this one available online in 5Gal in Quarts. "NAPA Premium Preformance 80W85W90W Gear Oil - 1 qt", NOL 75210
Is this the right stuff? if not, do you have the part number?
Do you have a Tractor Supply near by? They have 90 weight Ford tractor transmission mineral oil which is the correct thing to use. Tractor Supply - Ford Transmission Oil
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Looking at the Napa Site, I did not see any mention of Mineral Oil. I see this one available online in 5Gal in Quarts. "NAPA Premium Preformance 80W85W90W Gear Oil - 1 qt", NOL 75210
Is this the right stuff? if not, do you have the part number?
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
$49.95. This is what I ordered threw PSC. Shipping is pretty fair and they have a ton on different stuff. I also got SEA 30 wt non detergent oil in gal jugs for my Babbitt motors also
Last edited by glenns towing; 10/02/201912:38 AM. Reason: opps
Picked up the ford sae 90 transmission oil from Tractor Supply. $60 for three 2 gallon jugs. More than I'll need in 20 years. Any 3100 owners in southern NH need some new SAE 90 transmission oil?
I changed the transmission oil to the new oil I picked up from Tractor Supply. It "might" be shifting a little better, but still has issues getting into 3rd when warmed up. Taking it to classic restoration garage today to have them replace the engine seal and check on the transmission. I'll let you know what they find.
To add to Kevin’s question: could a worn synchronizer cause a transmission to be difficult to shift OUT of a gear? Could an incorrect oil do the same?
1970 Chevrolet C10 Grandpa's -- My first truck -- In progress to shiny Follow the build in the Project Journal 1950 Chevrolet 1-Ton Dually "Ole Red Girl" In the Stovebolt Gallery More pictures here 1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's Parts trucks- 1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300
A synchronizer problem can definitely cause a grind when shifting. Its purpose is to match the speed of the gears just before the shift collar connects the input and output shafts together. In the case of 3rd. gear on a 3 speed, that collar simply connects the transmission input shaft which is splined to the clutch to the output shaft which is connected to the driveshaft. There's a lot of inertia contained in the spinning clutch disc and input shaft, and several orders of magnitude more involved in the spinning driveshaft, rear axle, and ultimately the whole vehicle. It's the synchronizer's job to spin the speed of the clutch and input shaft up or down to match the speed of the driveshaft to prevent gear grinding, in the few seconds it takes to complete the shift. A worn synchronizer blocker ring, and/or too-slippery lubricant makes the synchronization effort ineffective. The only option otherwise is to match the engine speed to the output shaft by either idling the engine down somewhat, or double-clutching. Double clutching is definitely an acquired skill, one that takes a great deal of practice.
Back in the dark ages when I was driving a rig with two transmissions and a gross weight approaching 40 tons at times, we would work our way up and down through 15 gears without ever disengaging the clutch except for starting, stopping, and backing up! All the shifting was done simply by matching up engine speed with road speed, and selecting the right shifter position (two of them) to slide in and out of gear with no load on the transmission(s). Fun stuff! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
To add to Kevin’s question: could a worn synchronizer cause a transmission to be difficult to shift OUT of a gear? Could an incorrect oil do the same?
No not out of a gear because the main shaft and gear are already meshed, and are turning at the same speed.
Last edited by sstock; 10/30/20191:38 PM.
1953 Chevrolet 3100 261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Would the synchro rings have anything to do with it jumping out of 3rd gear on it’s own? Mine does that often while I’m just driving along - all of a sudden I’m in neutral and have to clutch and shift back into 3rd. It’s not difficult, nor does it grind going into gear.
My '48 did that. It was caused by an extremely sloppy shift linkage. Once I fixed that, I no longer had the problem. Check for slop in all the connection points and joints.
I haven't tried brain surgery, but I ain't dead yet! Wanna be my first patient? LOL!
Quite often, a transmission jumping out of gear, especially high gear, is caused by sloppy bearings at the input and output shafts, and/or the pocket bearing where the shafts meet. The shafts get to wobbling, and the synchro collar works its way back and slips out of engagement with the input shaft splines. Eventually the splines on the input get worn or chipped, and the problem can only be repaired by replacing the worn parts- - - -usually the synchro sleeve and the input shaft. Loose transmission-to-bellhousing bolts can cause the same problem.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
So, I’m not sure if my question has been answered: what would cause it to be darn/near impossible to pull out of a gear? 3rd on a 4spd sm420? I learned to double clutch when I was younger and have gotten quite good at driving my old rig by feel and revs, but my wife wants to try it out. She can’t. My niece wants to take it to grad one day. She can’t. At times I’ve gotten into predicaments where a sudden stop is required and then I have to lug it a bit to get going and then slip it OUT of third. It’s a PITA. If push comes to shove, I’m changing the transmission to a parts one.
My bearings are good. I tightened up and refurbished my linkage. It seems pretty tight compared my parts trucks. Not a new Toyota tight, but it feels great for a 51 GMC.
1970 Chevrolet C10 Grandpa's -- My first truck -- In progress to shiny Follow the build in the Project Journal 1950 Chevrolet 1-Ton Dually "Ole Red Girl" In the Stovebolt Gallery More pictures here 1951 GMC 9430 1 ton dually--Shiny! | 1972 Chevrolet C20- Rusty- the puzzle box lid for the C10 | 1962 AMC Rambler American- my wife's Parts trucks- 1951 GMC 9300 | 1951-GMC 9430 | 1951- Chevrolet 1300
If it is a 4-speed the shift rails in the trans top/cover assembly have detents with little balls and springs designed to keep the shifter in the correct position. The springs can wear out or break and allow the shift rail to move out of position. Then it can jump out of gear.
Pull the shift tower, dismantle the lockout assembly and shift rails, and look for flat spots, bad springs, and/or flattened balls. It's a fairly precise relationship that keeps the transmission from trying to get into two gears at once. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I kind of gave up, and brought the truck to a restoration shop to have them look at the transmission. I will have them replace the rear seal on the engine at the same time.
If you open it up, it would be worth it to take a look at the clutch keys and springs of the 3rd-4th sliding gear.
My 4speed had trouble going into 3rd without double clutching or just waiting really long for shifts... Upon inspection, the synchro is not worn much and I think the most improvement will come from replacing the clutch keys and springs. They are what provides thrust force when you press the synchro, and if too weak will not push enough to match speeds.
I have not re-installed the transmission yet, but measuring the detent thrust force on the sliding gear, I've seen an increase from ~30 up to 50lb after replacing the keys and springs.
