I got a turbo 400 with a reverse manual valve body and a 9 inch rear with a spool in my truck. When I accelerate hard in first and hit second hard, (it chirps the tires), I get a strange drive line vibration. The vibration feels like when you go over those rumble strip on the highway and gets worse with acceleration.
To solve the problem, I have to come to a complete stop and then the vibration will go away.
I have engine braking in 3rd gear, and 1st and 2nd gear the converter doesn't lock up. I can let off the gas in 1st or 2nd and it will act as its like in neutral.
I can feel the vibration if I down shift and let the rpms fall to idle, so im figuring its not an engine problem.
If I dont hit 2nd gear hard, I have no vibration.
Also, the faster you go, the worse vibration.
I have narrowed it down to possibly a rear end problem.
. I had a problem with exact same symptoms caused by a constant velocity (CV) double universal joint in my driveshaft... hard shift would cause the alignment ball to jump out of it's socket... stop and it went back in... you prolly don't have a CV, so look for something else jumping out of position, such as engine, tranny, or rear end/suspension mount jumping out of its rubber...
. I was thinking this was a 'Vette, but it's a truck, so might have a CV joint at the center bearing support of the driveshaft... if it has all that...
Most RMVB do not have engine braking, unless you order a Vbody with it.
Not sure what you mean by the converter not locking. T-400 did not have a lock up clutch in the converter from GM.. There are a couple aftermarket designs with a clutch for racing apps
When I say not locking I mean in 1st and 2nd gear you can let off the gas and the rpms will drop to idle, like its in neutral. Give it some gas, and it comes up off idle and matches engine rpm with trans speed. I got a 2000 stall saturday night special from TCI.
I got a lock up convert in my stock s10 and 2004 malibu, and when you let off the gas, it slows the car down.
Im probably wrong about my understanding of a converter locking up. But I know in 3rd gear in my turbo 400, I let off the gas and it slows down alot. 1st and 2nd will just coast like its in neutral.
Reverse pattern Manual valvebody's have no engine braking in low or second gear... due to removal of intermediate band for one thing, but it is a fluid path revision in the valvebody itself. Nothing to do with the torque converter, it's in the transmission.
It may be possible to set a 4 speed OD automatic up the same way, with no engine braking in the transmission even though they use a lock-up converter...but I don't know if it is possible.
What kind of rear suspension do you have? Maybe the rear end is rotating up in the front when you hit second gear hard and causing the drive shaft to run at a high angle. When you put on the brakes to stop the rear end rotates back down and everything is in line again. Just a thought.
If it as you describe, that this only happens in 2nd gear when hard shifting (chirps), then I agree with Big Gear Head - you have something rotating out of place causing the issue.
The question is does this NOT occur if you are easy on it? If it does not, then that confirms that you have an alignment issue during hard acceleration.
This would be a great place for to use a camera mounted to the frame rail to watch the trans yoke and rear end. It seems like half the kids around have one of these cameras attached to there skateboard or shoe, I've never figured out why they aren't widely used in other areas.:thumbup:
My passenger side cal-trac traction bar was loose and expanded too far. I adjusted it and it pulled the rear end closer to the trans. I didnt have a vibration driving home after I hit 2nd hard. Felt different when I shifted too. More adjustment maybe needed, but it seems to have worked.
. Maybe the poorly adjusted CalTrac bar was causing the front half of the leaf spring to snap up into a different arc and stay that way... then hitting the brakes caused it to snap back down into its normal arc... kinda like the on/off situation I had with a CV joint...
Ok, my suspension adjustments did not solve the problem.
I asked a mechanic today about the vibration, and he said it could be when I bang 2nd gear hard, the clutches dont grab and rub against each other, causing a vibration. Does that sound like a viable explanation?
Doesn't sound reasonable to me, I've felt clutch shudder in several different rear ends, on both the track where traction is heavy and the street, and it is just momentary until forces equalize themselves, it isn't something that continues or forces you to stop the vehicle to eliminate.
I would still bet you have a suspension issue of some sort...weak leaf springs, possible broken leaf in the stack, spring too light poundage for the job, poor or loose bushings, improper driveshaft angles
. How about finding a road where you can coast to a stop without using the brakes? Bang second gear, when vibration starts, coast to a stop without brakes, then examine everything underneath...
Ok, thanks. After I thought of it again, It cant be the clutches. I can down shift it into Neutral and it will still vibrate.
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