The Stovebolt Site Forums The Shop Area Driveline What causes bucking in a tranny?

Lucille's running pretty good lately. My question is, what would cause bucking in a tranny at low speeds? Low gear oil or wrong type of gear oil? I've got 80W-90 gear oil in her now. I believe someone recently wrote in about using 85W-140 in an old 216 three speed tranny. Any comments?

I vote for oil on the clutch. My '54 bucks until the oil is burned off.

90w is fine. I doubt you would notice much of a difference with anything heavier. As for the problem at hand, what do you mean by bucking?

Jeff

Jeff,
Good question!
As I try to describe "bucking" in a three speed '46 tranny it feels like a sudden back and forth banging that "only happens" at low speeds as I go back and forth on the foot pedal. 20 to 30 MPH. Accelerate and everything is OK until you let off the gas and then accelerate again and then something is knocking down there in what seems to be the tranny area. Would I be low on gear oil or is it something else? Like I said, something is "bucking" back and forth.
It's a hard thing to describe in words.

A bad U-Joint can cause bucking also. ???

oil on the pressure plate will do it too.

I have the same prob with my 216 and the 4 speed crashbox. Under engine torque or decelleration its fine but just at that fine area between torque and decell where you just need to cruse there is a bucking like there is too much gear lash or there is a squrt of gas from the carb that makes the engine jump a little. I would like to fix this prob is someone has an answer.
Rick

Check your engine aand transmission mounts. If one os loose it will let the engine move a little and the throttle rod moves when the engine does.

Had this problem on mine a while back and the drivers side transmission mount bolt had fallen out. Mine you would swear had kangaroo gas in it.

Oil on the clutch disc usually makes a clutch chatter on take off.

Another reason for "bucking" could be carburetor is out of adjustment.

Sounds like wear on the ring/pinion. I agree with elmer46 on the "gear lash". Hope thats not your case,Lucille.

Alvin,
Can you explain to me and others in simple terms "gear lash"? I've got my shop manual with cross sections of the 3-speed tranny and I don't have a clue what I'm looking at.

I'm really thinking it may be more of oil on the clutch since I am very suspicious of a leaking rear engine seal. There "is" a leak somewhere in that area. Trust me, the puddles on the cardboard on the floor of the garage are tell tale signs of something wrong in that area. I gave her a good run the other day when I saw you. That day I put over a 100 miles on Lucille and she did well performance wise, however, she lost 8 ounces (1 cup) of oil. Then I started to notice this "bucking at low speeds" issue.

Like you I hope it's not this gear lash problem that you and elmer46 mentioned. I just need to understand the terminology and what it all means.

BTW folks, LonnieC and InMy40s had suspicions about oil on the clutch and pressure plate. Just wanted to give them a shout out! How many people out there have had to deal with a leaking rear engine seal? AND what does it take to fix it without pulling the engine? Maybe I'm doomed to have to go through this ordeal. Any comments?

My leak isn't bad, so I can't give good info to you. I usually have a drop of oil hanging on the flywheel cover. I keep a pan under the drip to protect the floor. Never enough to lower the oil level.

Oil on the clutch usually makes the clutch "chatter". This is also usually only when starting off from a stop. Once under way you no longer "slip" the clutch.

The "chatter" is pretty rapid also.

If excessive gear lash is causing this "bucking" then the ring and pinion won't last long. Jack up one rear wheel and with the truck in gear move the wheel back and forth to see if there is a lot of play in the rear axle. Or turn the drive shaft back and forth to see how much it turns before the wheel turns. Just make sure the truck is blocked so it can't roll. Make sure the truck is well blocked so it can't fall.

I describe "bucking" as acting like it has kangaroo gas in it.