Question about 1986 Volvo 740
Is the knocking a regular rhythm that is proportional to the speed of the car? Driveshaft center bearings generally drive you crazy with buzzing and grinding before they get to the point of knocking, but I suppose that is possible. Drive shaft and rear end bearings would not make noise as you start the car, however.
Is the knocking related to road surface or braking, and is it directly below your feet? If so, it is the control arm bushing. That part is bolted to the bottom of the car directly beneath your feet and it will knock when the rubber part fails and crumbles out. This is common on a car this old, but this part also would not knock as you start the car.
A knock when you start the car is more likely the exhaust pipe hitting the bottom of the car. This can happen if a bolt is missing from a hangar, or the pipe is bent, or an engine mount is broken. The engine mount on the passenger side is the easier one to see from the top, and is usually the one that breaks first, as I recall. I always suggest that engine mount replacement be left to professionals. That job is a good way to loose a finger.
Be sure and check the bolt in the bracket right at the rear of the engine. For some reason, this one works loose and the bolt falls out. You have to crawl under the car to see if that bolt has fallen out.
Another suspect is the transmission mount. Does the shifter move as you step on the gas and let off the gas?
Posted on Mar 26, 2011
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Posted on Jan 02, 2017
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