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The car is a 1971 142E with M41 with an IPD header and Simons exhaust system.
I have done a complete restoration on the car and as I have gradually eliminated most of the 'unnatural' noises following reassembly, I am now left with one persistent sound that I cannot diagnose. It seems to be originating from underneath the floor pan in the OD area or perhaps farther back. The noise occurs when the car is in gear and accelerating between approximately 1600 - 2400 RPM.
The noise sounds exactly like what I would expect from the knocking of the exhaust system on the body. However, when I grab the cold exhaust system parts and shake them there is no banging. Visual inspection doesn't show any contact points and in general there is lots of clearance between the exhaust components and the body.
I initially thought perhaps some kind of clutch engagement issue, so I did a test drive, sped the car up in second gear, let it coast down in second until the engine speed was about 1600 RPM and then reaccelerated. The noise was present so it is not related to the engagement of the clutch.
The noise is present in 1st, 2nd and 3rd gear at the same RPM so I don't think it is a drivetrain noise.
The rubber engine and transmission mounts are intact.
I am at a bit of a loss - any suggestions?
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I did the grovel around under the car thing today and poked at the driveshaft and the center mount. There is definitely nothing loose on the center mount or anything that appears to be out of order and there is no clunking in the U joints. But, I think that I may have figured out the source of the noise. I have about a 12" long tail piece bolted on to the header flange. The tailpiece has a 2" OD. The pipe on my Simons exhaust system has a flare that is 2 1/4" OD. The tailpiece butts up (no overlap) against the Simons exhaust pipe and the two are joined by a stepped band clamp. The stepped clamp appeared to provide a secure connection; however, when the engine shakes a bit, the coupling allows a little rocking in the tailpiece allowing the end of the tailpiece to, I believe, tap the end of the exhaust pipe which acts as a nice sounding board. The rocking is facilitated by the fact that I do not have a solid U bolt connecting the exhaust to the exhaust bracket off the transmission. The top of the IPD header sits about 1-2" below the bracket so I have a clamp with one of those rubber straps and the strap hangs from the bracket which allows some extra movement in the exhaust system. I think I need either a flex coupling or an overlapping coupling of some kind between the tailpiece and the front exhaust pipe.
When I did the shake test on the exhaust system, I grabbed the pipe and tailpiece together and moved it side to side to check for body contact and as a result there was no rocking motion at the connection and no noise.
Thanks to everybody who provided suggestions. I may be back if the exhaust system modifications do not resolve the problem.
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It sounds like you may have hit on it.
Since there is a quarter inch difference in pipe diameters would it be possible to install a sort of "transition" section of pipe with a 2-1/8" OD? At each of the two overlapped connections cut a couple slots in the pipe that happens to be on the outside so that it contracts when putting a clamp on. Just brainstorming.....
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)
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I found a transition stub at the local auto parts place that is roughly 2 1/8 OD and is supposed to fit over 2" OD. If I slot it as you describe I should be able to clamp it to the header tailpiece and then fit it into the expanded section of the Simons front pipe. The Simons is nominal 2 1/8 OD pipe which has an expanded section to allow a 2 1/8 " pipe to fit in. I will need two separate banded clamps on each side of the transition ( I hate U bolt clamps). Right now my main problem is sourcing some 2.25 - 2 " banded clamps in SS locally. Most of the vendors don't seem to have anything that small. May have to shop on-line.
If that doesn't work, Its off to an exhaust shop to get a flex fitting installed.
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Might these work?
http://www.princessauto.com/en/detail/2-06-in-to-2-31-in-t-bolt-hose-clamp/A-p8017013e
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I have 2" wide SS banded clamps already. Those Princess Auto clamps are a nice price. Wish I knew about them earlier. I have been out to Princess Auto a number of times and have never seen them. I may give them a try because I think my 2 " wide clamps are deforming a bit and relaxing.
I found a short stub adapter. 2" ID / 2 1/8 OD. Fits perfectly over the header tailpiece and in to front pipe of the Simons exhaust. I slotted the adapter where it fits over the 2 " tailpiece to ensure that I get a good connection.
After the repair, the noise was gone. However, after driving around for several days and looking for bumps to try and shake things up, the noise is back; but reduced. A little poking around showed that the rubber strap on the flex hanger at the bracket at the front of the transmission had failed. I have to come up with a better mount for that location. It also looks like my 2" wide SS banded clamps from Canadian Tire have deformed and are releasing some of the clamping force. The Princess Auto clamps may be the answer.
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Another option:
http://classicvolvorestoration.com/volvo-1800-exhaust-parts-/3087-volvo-exhaust-clamp-54-56-mm.html
....and use a SS bolt/nut/washer.
If the connections aren't pretty close tolerance to begin with, then it's questionable whether or not you can get it tight without slotting. You could try it first without slotting and then cut slots if you absolutely have to.
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My vote is for rear-most U-joint. Even if new, an incorrect installation (which can go unnoticed when doing it) can totally cause premature failure, and you won't necessarily be able to notice it by shaking things around. Gotta pull the driveshaft from the rear and then you can check it for looseness or binding, and the other two joints for looseness.
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-Matt I ♥ my ♂
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Something else came to mind, although I'm not sure if this could be causing the problem or not...... When you connected the rear drive shaft to the front drive shaft, did you orient it in a way that it's properly phased (u-joint yokes aligned with each other properly)?
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)
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Yes the yokes were correctly phased and the driveshaft was dynamically balanced before installation.
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posted by
someone claiming to be blackjackmc
on
Tue Nov 1 23:24 CST 2016 [ RELATED]
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Are the engine and gearbox mounts original specs and the cross member original?. If the transmission and pinion are not in the same plane they will put stress on the drive shaft.
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The cross member is original. The mounts are new and I assume are to the original spec. I am not using the B30 mounts.
I do have slightly shorter springs (-25 mm). However, if alignment was an issue I would expect a persistent vibration that would get worse with speed. That doesn't happen.
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posted by
someone claiming to be blackjackmc
on
Tue Nov 1 02:38 CST 2016 [ RELATED]
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Could be loose muffler innards, and rattles with synchronous vibration at certain rev range. Drive shafts aligned properly?.
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Possible; but low probability. The mufflers are new (less than 2000 km) and they are the Simons flow-through style so there isn't much that could come loose in the muffler. When I am doing my center mount check I can take a rubber hammer and tap them and see if there is any rattling.
The U joints are correctly phased and the driveshaft was balanced prior to installation.
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Hi,
What is the frequency of the knock ? Like a woodpecker or a knock at the door ?
Will it knock in neutral at the same RPM ?
Peter
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No banging in neutral that I have noticed; however, I generally do not spin the engine up to those speeds when in neutral. Perhaps I will try spinning the engine to 2300 or so in neutral to see if the noise is present.
I do notice that I seem to get the same or similar noise when I shut the engine off and you get that little lurch as the engine stops rotatin. That made me think that it was exhaust rather than drive train related. However, the total absence of any contact points between the exhaust and the body is what has me mystified.
Update:
I just checked. No knocking present when I accelerate the engine with transmission in neutral.
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"...The noise is present in 1st, 2nd and 3rd gear at the same RPM so I don't think it is a drivetrain noise...."
I don't know if I would be so quick to draw that conclusion. In 4th gear, the amount of torque applied to the drive shafts is less than in the lower gears. Your getting the noise in gear 1-3 but not in 4th.
Have you grabbed the drive shafts on each side of the center carrier and shook them around to see if you can produce a "banging" noise within the carrier?
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)
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No; but, I can try that. Are you thinking that the rubber bearing mount is loose / faulty? All the U joints, support bearing and the rubber mount have less than 2000 km on them.
I was out driving it today and watched the gearshift lever when the noise was occurring. I have the original mile long lever so if there is any movement / rocking of the transmission, it is will be quite noticeable. There was no perceptible movement of the lever that corresponded with the noise occurring.
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Have you checked for the driveshaft hitting the top of the tunnel? Possible as 1,2,and three have enough torque to "roll" the rearend to where the driveshaft hits the top of the tunnel.
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I remember the front muffler mount on one of my 140s would sometimes bounce against the rear floorpan. I should have been more careful when installing the exhaust.
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