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Author Topic:   Trans keeps breaking HELP!
Dirt Roller

Total posts: 7
posted April 25, 2004 09:19 PM  
We have broken two transmissions in two weeks. Also, broken one drive shaft and one pull bar. Before it breaks each time, I can feel a "vibration" on acceleration. I thought it was that I was breaking the tires loose since I'm a new IMCA driver, so I tried to feather the throttle. After about 15 laps, I broke the front nose off of one transmission and after about 1 lap I locked up a second transmission. Any thoughts, suggestions, help????

Dirt Forum Racer

Total posts: 92
posted April 26, 2004 06:02 AM  
Most likely the vibration you feel is the yoke coming out of the transmision and the drive shaft starts to whip. You need to run the long yoke.

Dirt Forum Champ
Total posts: 1363
posted April 26, 2004 06:04 AM  
it sounds like a driveline alignment problem. maybe too much pinion angle or the rear of the transmission is too low. the driveshaft needs to be angled down from the transmission to the rearend.

Dirt Forum Champ
Total posts: 755
posted April 26, 2004 08:34 AM  
Is this a powerglide?

Have you jacked the car up and articulated the rear suspension with the springs out to determine your required slip yoke length?

Are your dowel pins in the back of the block the proper length? If they are stock and you have a midplate, they are probably too short.

When you say "front nose", what are your referring to?

I've felt vibrations before and have always found it to be a crack developing in the powerglide bellhousing or a driveshaft ujoint.

[This message has been edited by NJantz (edited April 26, 2004).]

Dirt Maniac

Total posts: 192
posted April 26, 2004 10:25 AM  
As well as everyone else's suggestions, you should check the following:
Drive shaft length is correct, to short or to long will be a problem
Pinion angle Vs Slip yoke angle, I try and maintain as close as possible the same angles,
Also angle of pinion during acceleration and deceleration, If your Vibration is when you are on the gas, maybe you are binding a U-joint

Dirt Freak

Total posts: 270
posted April 26, 2004 11:37 AM  
What are you running for pinion angle and how much of the yoke is exposed at ride height. Is your car short or long links,4 bar, 4 /z, 3 link ? Are you running a short or long j-bar or shorty bar? All this makes a difference because short link cars have much more drive train movement. Dman

Ego Racing
Dirt Forum Champ
Total posts: 724
posted April 26, 2004 12:08 PM  
Busting the front is a clutch bellhousing alignment problem.

Dirt Roller

Total posts: 7
posted April 26, 2004 09:08 PM  
Thanks to all of you who are trying to help. It is appreciated. I’ll try to give you some more info and answer all the questions you gave me.

I am running a Saginaw 3 speed. My yoke broke the first time. We replaced with a new drive shaft and yoke from Smiley's. We made sure all "broken off pieces" were removed from the transmission. The new drive shaft is the same length as the old one (We believe this is the correct length since the car had been run all last season with this drive shaft.)

I am running a swing arm 3 link with a bisquit pull bar and a short bar.

We do have it angled down from the transmission to the rearend.

I am running the yoke that Smiley’s puts on their racing drive shafts. I don’t know if it is “long” or “short,” but I do know it is what they sold to me!

About an inch and a quarter is exposed at ride height.

About the clutch/bellhousing alignment problem: How would I know if that is the problem?

We worked on it tonight and checked the rearend. It looks fine. While investigating, we did find that the clutch may have been slipping from wear. This may have caused it to finally “catch” and place some major torque on the nose (input shaft) of the transmission.

Dirt Forum Champ
Total posts: 755
posted April 27, 2004 06:10 AM  
"About the clutch/bellhousing alignment problem: How would I know"

The centerline of the clutch and bellhousing all needs to be on the same centerline as the engine crankshaft. You could verify this with a dial indicator and magnetic base stand. You will be measuring total indicated runout. Or they do make alignment tools you can buy.

If you've got an off the shelf Smiley's driveshaft then it's the short yoke.

Did you take the springs out and cycle the rear suspension while watching the driveshaft go in and out of the trans? The amount of yoke showing at rideheight really doesn't mean anything. Whats important is when the wheel base is at it's max and min dimensions.

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