Knocking Under Acceleration

nickvash0104 · 11-03-2006, 12:41 AM

Hello everyone,

On my 87 NA Automatic, I'm getting a knock under acceleration. The noise is coming from around the transmission / driveshaft and I'm suspecting a bad u-joint. The engine was replaced in April and I've had no problems since then. Some points to consider:

*It occurs intermittently.
*Usually happens in the 2200-2700 RPM range in drive.
*Does not occur in neutral, reverse, or park.
*All fluids topped off.
*When letting off the gas, it stops instantly and usually does not resume when giving it gas again.

What just confuses me is that it happens intermittently, seemingly without a pattern.

Suggestions?

Bill UK · 11-03-2006, 07:18 PM

Do you here a knocking noise from cold start up and then it disappears until you fev it to about 2K.?

nickvash0104 · 11-04-2006, 12:22 AM

Nope.

Doesn't matter if the car is warm or cold.
Doesn't happen at idle.
Only under throttle (any amount of throttle) in the 2.3-3k RPM range.
Very rarely 1.7-2k range.

Bill UK · 11-10-2006, 10:20 PM

Initially I thought big end bearings but you would get the knocking noise about 2K and at start up but it sounds as if it could be the crankshaft pulley; they are known to come loose.

nickvash0104 · 11-13-2006, 02:39 AM

Question though, how could it be the crank pulley if the sound is coming directly below / behind me? Correct me if I'm wrong, but isn't the crank pully in the front of the engine?

Bill UK · 11-13-2006, 09:31 AM

Yep! crank pulley is at the very font of the engine, I only mentioned it because knocking noises are associated with big ends or something like the crank pulley coming loose.Also location of noises can be deceptive, as it was easy to check I thought it was worth mentioning the pulley, and it seemed to be related to eng revs. At least it keeps your thread on the front page.

Drag0na5h · 03-26-2007, 01:32 AM

It's possible your u-joint in the drive shaft has worn out. Mine did the same about 2 years ago with roughly 200,000 miles on it. It would knock during initial acceleration at 2k-3k rpm or if I was cruising and then sped up causing the drive shaft to break loose from the u-joints worn out bearings. Try getting under your car and jiggle the shaft near that joint. If it feels really loose then replacing one shouldn't be so difficult. 4 bolts to the diff and 2 holding the u-joint up and the shaft slides out from the tranny. You might want an extra pair of hands to hold that thing up while you bolt it off and on. I have an 87 Auto N/A btw.

f00g00 · 03-26-2007, 08:01 PM

sounds like the center bearing that connects the two small driveshafts together. If you change it yourself be careful to mark the way they came off so you don't get the driveshafts out of alignment or you will get some serious vibration problems at around 60 mph. The driveshafts and center bearing are balanced at the factory.

11-03-2006, 12:41 AM	#1
nickvash0104 3" Exhaust Join Date: Aug 2005 Location: Dallas, TX Posts: 78	Knocking Under Acceleration Hello everyone, On my 87 NA Automatic, I'm getting a knock under acceleration. The noise is coming from around the transmission / driveshaft and I'm suspecting a bad u-joint. The engine was replaced in April and I've had no problems since then. Some points to consider: It occurs intermittently. Usually happens in the 2200-2700 RPM range in drive. Does not occur in neutral, reverse, or park. All fluids topped off. *When letting off the gas, it stops instantly and usually does not resume when giving it gas again. What just confuses me is that it happens intermittently, seemingly without a pattern. Suggestions? __________________ Black '87 N/A Auto

11-04-2006, 12:22 AM	#3
nickvash0104 3" Exhaust Join Date: Aug 2005 Location: Dallas, TX Posts: 78	Nope. Doesn't matter if the car is warm or cold. Doesn't happen at idle. Only under throttle (any amount of throttle) in the 2.3-3k RPM range. Very rarely 1.7-2k range. __________________ Black '87 N/A Auto

11-13-2006, 02:39 AM	#5
nickvash0104 3" Exhaust Join Date: Aug 2005 Location: Dallas, TX Posts: 78	Question though, how could it be the crank pulley if the sound is coming directly below / behind me? Correct me if I'm wrong, but isn't the crank pully in the front of the engine? __________________ Black '87 N/A Auto

03-26-2007, 01:32 AM	#7
Drag0na5h 3" Exhaust Join Date: Jul 2005 Posts: 67	It's possible your u-joint in the drive shaft has worn out. Mine did the same about 2 years ago with roughly 200,000 miles on it. It would knock during initial acceleration at 2k-3k rpm or if I was cruising and then sped up causing the drive shaft to break loose from the u-joints worn out bearings. Try getting under your car and jiggle the shaft near that joint. If it feels really loose then replacing one shouldn't be so difficult. 4 bolts to the diff and 2 holding the u-joint up and the shaft slides out from the tranny. You might want an extra pair of hands to hold that thing up while you bolt it off and on. I have an 87 Auto N/A btw. __________________ Last edited by Drag0na5h; 03-26-2007 at 01:35 AM.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Hard Engine Knocking	86SupraMan	MKIII Supra	10	09-14-2007 05:39 AM
funny knocking sound on 7mge	Jeff_5_7	MKIII Supra	11	09-09-2007 01:22 AM
Help with knocking on front end supra96	dini_the_owl	MKIV Supra	8	09-03-2006 10:24 PM
knocking block, want to build solid bottom, what should i use	alcbarrios	MKIII Supra	1	04-14-2006 04:16 AM
acceleration problem 91 2 litre supra	sexy91tt	Non-Generation Specific Questions	2	01-28-2006 09:43 AM

11-03-2006, 07:18 PM	#2
Bill UK AEM EMS Join Date: Jul 2006 Location: UK Posts: 891	Do you here a knocking noise from cold start up and then it disappears until you fev it to about 2K.?

11-10-2006, 10:20 PM	#4
Bill UK AEM EMS Join Date: Jul 2006 Location: UK Posts: 891	Initially I thought big end bearings but you would get the knocking noise about 2K and at start up but it sounds as if it could be the crankshaft pulley; they are known to come loose.

11-13-2006, 09:31 AM	#6
Bill UK AEM EMS Join Date: Jul 2006 Location: UK Posts: 891	Yep! crank pulley is at the very font of the engine, I only mentioned it because knocking noises are associated with big ends or something like the crank pulley coming loose.Also location of noises can be deceptive, as it was easy to check I thought it was worth mentioning the pulley, and it seemed to be related to eng revs. At least it keeps your thread on the front page.

03-26-2007, 08:01 PM	#8
f00g00 12psi boost Join Date: Aug 2005 Location: Kuwait Posts: 292	sounds like the center bearing that connects the two small driveshafts together. If you change it yourself be careful to mark the way they came off so you don't get the driveshafts out of alignment or you will get some serious vibration problems at around 60 mph. The driveshafts and center bearing are balanced at the factory.