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#1069682 - 02/27/21 07:26 PM Noise at 55 mph  
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TonyD Offline
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Not sure where to put this; if I don't get any responses I'll try drivetrain.

Original owner of an 85 SS. Just had the transmission rebuilt and on the way home from the shop I noticed a 'noise' and I'm not sure where its coming from. It sounds more like a 'droning', resonance or vibration at 55 mph. It is still there at 60-65; I didn't want to try it faster than that or for more than a few seconds. I had not noticed it before, I don't drive it much and when I take it out its usually around the block; 45 - 50 mph for about 8 miles. The car has 85K miles and also just before I had the trans done I got new BFG radial TA's installed.

I checked the driveshaft because I had new U-joints installed and they look good, both the fwd and aft weights are on the driveshaft.

I also checked the rear end fluid and it was down a few ounces; took it for another ride and the 'noise' is still there.

As far as I can tell the car has a Detroit locker rear end, stock 3:73 gears. I've never changed the fluid or had the cover off.

So, it could be a tire, but it doesn't really seem like that to me. I don't think its the trans because as I accelerated the trans shifted at higher engine rpm's that what it runs steady at 55 mph.

Should I remove the rear end cover and see if something is going on there? Not sure what to look for...

Thanks

#1069683 - 02/27/21 08:42 PM Re: Noise at 55 mph [Re: TonyD]  
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BadSS Offline
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Take it back to the shop and get them to drive it with you in the car or ride with you. Could be a u-joint, could be as simple as they knocked something loose on the exhaust system. Also, make sure they flushed your converter and didn't replace it with a "stock" replacement - the replacement converters they use typically only stall up to around 1400rpm compared to the SS stall speed of 2000-2200rpm (foot on brake and flashing).


Original owner of 1985 SS black hardtop w/gray interior. Frame-on restoration in progress. 406 sleeper w/ heavily ported FIRST TPI. 1.875" headers and dual 3.5" Borla exhaust. TH400, Ford 9", anti-roll bar, and notched frame. Dropped 2", 18" wheels, and F/R disk brakes. 10-point cage w/swing-out bars, custom gauges, and audiophile stereo system.
#1069684 - 02/27/21 09:06 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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Thanks, I'll do that. BTW mine is black with gray interior also! No T-tops; when I ordered it in September of 84 I was told they weren't available.

#1069689 - 02/28/21 12:38 AM Re: Noise at 55 mph [Re: TonyD]  
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BadSS Offline
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Originally Posted by TonyD
Thanks, I'll do that. BTW mine is black with gray interior also! No T-tops; when I ordered it in September of 84 I was told they weren't available.


Mine was SUPPOSED to have been ordered as soon as they let the dealers put in the orders. I don't know when you could order them with T-tops - I knew I would eventually put a high-performance engine in and wanted a hardtop. The story behind mine is my dad went to high-school with the owner of a neighboring Chevy dealership and I got the car at cost plus $100. At that time people were paying sticker and above for them. About two weeks after the car was due, I started getting impatient. They gave us some song and dance, but one of the mechanics told me when I was there picking up the car, that "my car" had come in months ago. He said a dude followed the truck into the dealership and they sold him the car. I wasn't all that mad about the wait, but it did tick me off that they left off the rear window defogger option on the "replacement". Still, I was glad to FINALLY get it and they took off the price of the rear window defogger off the originally agreed upon price - I'd rather have had the defogger though - lol

It's not just because I have an 85, but I really do think that was the best interior year. Only year for the brushed black trim and I prefer the upper vinyl door inserts along with the seat material used over the later years. I sprayed my seats with Scotchgard as soon as I got the car home and have applied it a couple more times over the years. To this day the material looks almost new, but I have rubbed a hole in the vinyl bolster side getting into the car so many times - that's on the short list of things to "fix" before I get it back on the road.

Good luck on finding the noise - hopefully it'll be something simple that they can correct for you.

#1069690 - 02/28/21 02:06 AM Re: Noise at 55 mph [Re: TonyD]  
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AkronAero Online content
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Tony - Had a number of things done to the car early on including a 3.5" steel drive shaft to go with the higher HP crate and straight dual exhaust with only open Borlas. Had vibration problems at 55+ which were very hard to track down; noise is just another part of the spectrum of vibration. Swapped out a number of parts (my excuse for upgrades). Finally pulled the drive shaft and took it back to check balance. The original shop found it was out (really?) and just welded on another washer (gotta be kidding!). Still had the problem. Very suspicious. Decided on a rear end upgrade to 7.5" Truetrak with Moser 28 spline axles. Went to a regional drive line shop used by the serious racing circuit guys. While working on the rear he looked at the shaft. Putting one of the joints in a vice, he could easily play with the other end to show lots of slop. He said that for this joint all manufacturers are not interchangeable but for the joint on the other end they are. He was very serious that this problem occurs more frequently than one would think. I do not recall if it was the 1350 on the front/trans end or the 3R on the rear/diff end, unfortunately. He put in a new 3" DOM steel shaft with new yokes and Spicer non-greaseable joints and the vibrations disappeared! I should have documented before and just sent him a note and hope to have clarification on this next week.

Were the u-joints and transmission done by the same guy? Your original 2.5" drive shaft too? Might it have gotten bent while they were working on it? X2 on BadSS's recommendation to take it back right away to the transmission guy and confirm what you are hearing/feeling (then consider the u-joints). He is the best person to know. A good shop with a good reputation?

Keep us posted.
Thanks
Gordon


#1069691 - 02/28/21 02:19 AM Re: Noise at 55 mph [Re: TonyD]  
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86ttop Online grandpa
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TonyD, make sure that the support bracket to the Cat converter is fully installed and bolted securely and good luck!


Leo Paugh
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POW*MIA
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If things improve with age, I must be approaching magnificent. thumbs
#1069697 - 02/28/21 04:09 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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BadSS - a guy I worked with bought an 84 in white; I had my eye on the 'french blue', but they dropped that color for 85. With the 3:73 gears mine was quicker than his! The sticker on my car is $14,044 and I remember I got it for $15K 'out the door'. I do like the grey interior. I recall seeing one in white with gray and that looked sharp too. My car was stolen in 1991 and when I got it back it wouldn't shift out of first gear. My insurance fixed it and it wasn't until about 2005 when I was able to get collector car insurance for it (to avoid emissions testing) that I decided to look at the trans and found it was the wrong code! The serial number showed it was a 1981 trans. So they replaced my original instead of fixing it. I then found an 85 SS in a junk yard, verified the code and bought it with the converter. That's the trans I had overhauled and installed.

Do you know if there was a posi rear end option on these cars? When I ordered mine I was told no. This seems to be confirmed by the Chevy shop manual; in the Rear Differential section there is a special section for Monte Carlo SS - Detroit Locker. But I seem to remember people with these cars saying they have a posi, or are they just referring to the Locker rear end?

Akron - Yes, original driveshaft and the same mechanic installed the U-joints. I got them from RockAuto (ACDelco) that were advertised as fitting either the front or rear. This mechanic was recommended to me by a retired mechanic friend of mine. He also rebuilt the trans in my 87 El Camino SS (non-choo choo) and put the same U-joints in it and I don't have any problems with that car (368K miles that I bought in 1992 with 50K miles).

Are the U-joints supposed to be location specific?

Thanks for the suggestions, I'll let you know what I find.

#1069698 - 02/28/21 04:10 PM Re: Noise at 55 mph [Re: TonyD]  
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mmc427ss Offline
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Something i always do when pulling a driveshaft is mark it's orientation to the pinion. A china marker (crayon) marks the shaft and yoke before pulling the shaft. This is especially useful when doing AWD with multiple, odd angled shafts. Just takes that "it was ok before you worked on the car" possibility.

As Leo said check the cat support at the back trans mount, and condition of the trans mount.
Bob

#1069709 - 03/02/21 06:26 AM Re: Noise at 55 mph [Re: TonyD]  
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BadSS Offline
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Originally Posted by TonyD
Do you know if there was a posi rear end option on these cars? When I ordered mine I was told no. This seems to be confirmed by the Chevy shop manual; in the Rear Differential section there is a special section for Monte Carlo SS - Detroit Locker. But I seem to remember people with these cars saying they have a posi, or are they just referring to the Locker rear end?


I had bought an Edmunds book that listed options (and dealer cost), It showed the limited slip as an option and even the brochure showed the limited slip as an option. When I said I wanted it when the dealer was filling out the FIRST order-sheet, I ran into the same thing you did. The man swore up and down there was not a limited slip option available. He even went one step further and said he was sure it was standard on the SS and that's why it wasn't showing up as an option. Anyway, within about 2 minutes after leaving with the car,,,,,, it clearly was peg-legged - lol. I can laugh about it now, but between the long wait and it being peg-legged without a rear window defogger, I was not a happy camper at that time, but I got over it pretty quickly!!

#1069712 - 03/02/21 11:34 PM Re: Noise at 55 mph [Re: TonyD]  
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kma-85ss Offline
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Winter Garden, FL
Originally Posted by TonyD

Do you know if there was a posi rear end option on these cars? When I ordered mine I was told no. This seems to be confirmed by the Chevy shop manual; in the Rear Differential section there is a special section for Monte Carlo SS - Detroit Locker. But I seem to remember people with these cars saying they have a posi, or are they just referring to the Locker rear end?



I'm not sure, but I don't think Detroit Locker was available on these cars. Only the GM limited slip or the standard open differential. Look at the RPO sticker in the trunk. Do you see code G80? If yes, you have the limited slip. If G80 isn't listed, you have the open one. The shop manual reference could have been for a different car.


Ken

1985 Monte Carlo SS - Sold frown
2005 Impala LS
2014 Dodge Charger SXT
blackside
#1069721 - 03/03/21 05:48 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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kma - I have the Chevrolet Service Manual that I ordered from a form in the back of the Owner's Manual back in 1985. Its very specific: Section 4B Rear Axle, under General Description, has separate sections for Standard Rear Axle, Limited Slip Rear Axles (Disc Type, Cone Type), then Eaton Locking - SS Monte Carlo.

The only rear axle RPO code I have is GT4 which is: Axle, Rear, 3:73 Ratio.

Back in 2006 I ordered a data package from MSX International for my specific car (i.e. VIN) that included build information and in the Alphabetical Option Index, under Power Teams, it lists the 3:73 axle ratio as standard on the Mont Carlo SS. This is repeated in the MVMA Specifications Form which lists all the engine, transmission and rear axle combinations, for the Monte Carlo "SS", RPO Code Z65 (which I have), the standard drive axle ratio is shown as 3:73.

There is another MVMA Spec Form (I don't know what that stands for) specifically for the RPO L69 engine option, that also lists the 3:73 axle ratio.

The only other rear axle options available were 2:73 and 3:08, so maybe the only way to offer a high performance rear was the Eaton Locking?

#1069722 - 03/03/21 08:47 PM Re: Noise at 55 mph [Re: TonyD]  
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AkronAero Online content
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TonyD - Follow up on my earlier U-Joints/shaft comment.

You are likely OK if your shop replaced the entire U-Joint as one piece, regardless of manufacturer or style. My problems and that of many is that someone will reuse the cross/trunnion/spider and just replace one or more of the caps if they are bad. While the outer diameters of the caps are the same, the bearing set up and inner diameters are NOT. So there is internal movement, and wear. My shop says they see maybe TWO of these coming in EACH WEEK. Even if the same manufacturer, the internal designs could have changed over the past 35 years. Be suspicious if its not a full change out, although it sounds like it was?

Note that the shaft itself could be the problem. Its not hard to bend/twist the small diameter (2.5") shaft under heavy load. In my case, the shaft was crushed in when the first shop put it in the vice to work on the u-joints. Never put the shaft in a vice! Suggest you take a look for marks or a dimple near the ends where this might have occurred? You would get noise/vibration beginning at modest speeds, and this will lead to seal failures and yoke wear too.

If these two are OK, the the shaft/joints are not the problem.

Good Hunting!
Gordon

#1070074 - 03/25/21 05:51 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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Finally got him to look at my car. He's a one-man operation with the shop next to his house.

Put it on the lift with the engine running in DRIVE and saw the driveshaft oscillating at the rear end. After shutting it off, he was able to move the rear yoke and saw the washer under the pinion nut move. He was able to get about 1/8 turn on the nut which tightened the washer, but he says this is a sign that the pinion gear bearings are going bad in the differential. That nut does not come loose for no reason.

He lives in a rural area so when he took the car out for a drive after rebuilding the trans and replacing the U-joints, he only got it up to 45 or 50 mph because from the transmission point of view that's all he needed to do.

He said I would likely still hear the noise, which I did, on the drive back home.

So it will probably be another month before he can get me in to replace the bearings. Good thing I only put a couple hundred miles on the car per year! I take it out every other month but my 'route' does not include any highways so I can't remember the last time I hit 55 mph or better with it.

#1070075 - 03/25/21 07:39 PM Re: Noise at 55 mph [Re: TonyD]  
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Yes, but think how GOOD it will feel when it is done and you drive with no noise or vibration!!!!
Glad he could ID the problem.
Gordon

#1070082 - 03/26/21 03:49 PM Re: Noise at 55 mph [Re: TonyD]  
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I had the same thing happen to me. Mine had developed a whine while on a work trip, that got progressively worse, but I had to keep driving until I got home. When I got home, I found that the nut holding the yoke had come loose. I applied locktite and tightened, and it has been fine for the last 20 years.

Marc

#1071027 - 06/09/21 06:46 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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UPDATE: finally had some time to help me. Couldn't do the pinion bearing, but we pulled the driveshaft to check the balance. Sent it to a driveline shop and he found it to be bowed! Off by 1/8 inch in the middle!

They tried to straighten it but couldn't so the re-tubed it. The car is much better now, although we will still replace the rear end bearings. I hear what you said T5, but I still think the nut came loose because the crush sleeve is worn.

Not sure how the shaft got that way, no marks on it so its not like I hit something. Maybe it was made that way?

#1071028 - 06/09/21 07:09 PM Re: Noise at 55 mph [Re: TonyD]  
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I attributed my nut coming loose as a result of recent drag strip runs with bias ply slicks and a manual transmission. The nut hasn't come loose since and has been quiet.

The bow in your driveshaft is an odd one, indeed.

Do you still have any noise?

Last edited by T5montecarlo; 06/09/21 07:22 PM.
#1071029 - 06/10/21 12:24 PM Re: Noise at 55 mph [Re: TonyD]  
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Its better, but not resolved. There's still a faint 'rumble' at 50-55 mph.

I re-read the above responses and to answer some of the questions: there was a new trans mount installed when the unit was rebuilt and we checked the converter bracket, its bolted in correctly.

#1071608 - 08/14/21 07:20 PM Re: Noise at 55 mph [Re: TonyD]  
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TonyD Offline
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FINALLY got the car into his shop for the rear end work. Both pinion bearings were rough, pitted. Looks like the crush sleeve spun. The pinion shaft was also scored so we replaced it. Since we were in there we replaced the carrier and axle bearings too.

Rides much better now!

#1071611 - 08/14/21 10:07 PM Re: Noise at 55 mph [Re: TonyD]  
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That would do it! You must be relieved to have resolved the problem.


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