Hello, I own a 1992 Volvo 740 wagon, non-turbo. Super solid car up until a month ago when it developed a grinding sound and vibration when slowing down from 15-0 mph. There is no noise or pulsating at any other speed when I apply the brakes. This happens with tranny in N or D. I replaced the front rotors and pads about a month before this started happening. I suspected the rear brakes so I also replaced the rotors and pads but I was still getting that grinding/ vibration. The next thing was to replace the hub/bearing assembly, I only did the drivers side because I banged it up pretty bad when replacing the rotors. This also had no effect on the grinding. I also noticed that when driving at moderate to fast speed I hear a humming noise, almost like big truck tires make. This is especially noticeable when letting off the gas and coasting. Could this be a tranny issue? Any help/suggestions/ideas are greatly appreciated! Thank You for reading.

 

There is always the possibility that some gravel got in there, just a pebble in the right spot could cause grinding... I know, not happy with that myself either. Also, "vibration"?
How are the tires? A lump somewhere on a tire? Internal belt separation? Also a long shot, are the pads seated in correctly? Sometimes the springs can hang, rub... Are the caliper pistons OK? How's the brake pad wear, even?

I would recheck the front brakes: Pads seating, pins sliding, pistons operation, etc.
I doubt it has anything to do with the transmission...

 

Have you checked your u-joints

 

Hello Lev, thanks for your reply. The pads look even, both front and rear. I also went back and re-greased all 4 pad pins in the rear, and all sliding/contact points in the front. Tires look good, normal wear and no visible damage/bubbles. I will check the brake piston operation and belt condition tonight. What I don't understand is why do I only get the vibration/grinding from about 15-0mph, I would think it would be happening all of the time. I though maybe the new rotors were warped but this would also give me vibrations at all speeds, correct? Thanks again Lev for your response.

 

Hello eddie62,
I have not checked the u-joints. Not sure what the procedure is to check if they are ok. Do I grab the two ends and try to shake to see if there is any looseness there? Do you think it could be the center driveshaft bearing/support assembly? Thanks for your reply.

 

I can't see how a u joint problem would cause what you describe. Usually problems worsen at speed as things out of round get more so, odd that you only suffer at 15 MPH and below!

Defective rotors MIGHT be the cause, still, why only at such low speed? I'd change the rotors if all else is OK, never mind the driveline, u joints etc.
What about hard braking from higher speeds?

 

Sometimes when they start to go bad you will only get noise or vibration at low speeds. With your car on ramps, slide under your car on your back and grab the drive shaft with both hands and twist it one way then back while watching the U joints. They should rotate with the drive shaft with no play or sloppiness. Look at the bearing caps where the arms of the joint goes in, if you see any rust-colored dust the u-joint is bad.

 

Lev/Eddie62,
Thank you for your suggestions. I just found Brembo rotors for the front at RockAuto for $15 each, crazy low price. As soon as I receive them I will throw them on and see what happens. Not so painful at that price. When braking at high speeds all is well, no noise or vibrations, very strange. I have the car on jacks right now and will inspect the u-joints tonight when I get home. Thanks guys for your help. I will let you know what happens.

 

the brembo rotors I put on my 92 740 turbo wagon are someo fthe best brakes I've ever had on a volvo. NO throbbing or pulsing even on repeated hard stops with a heavy load.

 

Thank you everybody for your feedback. I checked the u-joints this weekend and all checked out. While I was underneath I noticed that the rear differential pinion seal was leaking and had to add about a quart of gear oil to top it off. I am dropping the car off at a local indie Volvo service shop to get the pinion seal sorted out, I don't think I will be able to get to the specified 147lbs/ft torque on the rear bolt with my measly muscles. I will update post as soon as hear back from the shop. Thank you all again for helping out!
Pierce, I have to agree with you. I always use Brembos on all family vehicles.

 

When they do the pinion seal they will have to drop the driveshaft. That would be a good time to re-check the u-joints. To properly check them, it's best to do it with the shaft off so you can verify there is no binding when you flex the u-joint. When my daughter's 240 u-joint went bad, she thought there was a problem with the brakes 'cause you would only get the shuddering when braking. Long story short - it ended up being the u-joint just in front of the differential was binding. You could drive the car all day at speed but braking was really annoying.

 

Binding U joints? Why, yes! I didn't think of that, only of the joints being "sloppy", worn laterally... which would produce a clunk, but binding (stiff) joints could produce vibration as well. Unfortunately I don't know if they cannot be checked without taking them out or may me duplicating the problem running the car on a lift?

 

Thanks act1292, sounds like the exact problem I am having. They are putting the car up on a lift tomorrow, I will be sure to mention that, thanks again! I will def post the results once the problem is diagnosed.

 

Talked to the mechanic today and this is the diagnosis: one u-joint is bad, center shaft bearing and support are trash, the cross member that holds up the center support is completely rusted and finally the rear diff pinion seal and bearing need replacement. Not sure if one of these issues caused the others but I'm really glad it's getting sorted out. I want to thank you all again for your replies! Only 105k miles on the clock, let's hope for at least another 100k.

 

So, is the vibration gone?

 

phew, our 240 has gone like 400-500k miles, its needed the center bearing&bushing replaced once or twice, and the transmission rebuilt once, but has never needed a U joint.

 

The car will be ready next week but the mechanic is pretty sure it is the u-joint binding up that is causing the grinding/shudder. The tranny mount has collapsed so that will be replaced as well. Pierce, I hope mine lasts that long!