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Old 04-23-2019, 03:31 AM   #1
ashgto
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another vibration thread, oh and AC

Hi everyone! I have been lurking on this forum since I bought my GTO last July and have learned alot from the group. I have searched and searched the knowledge base, read countless threads, and would like some input on some specific issues I am having based on the current status of the vehicle. Here is some background:



2006 gto, 6 speed, engine overhaul at 95,xxx before I bought the car due to failed oil pump/spun bearings.

Complete block refresh, eagle rods, stock pistons, billet timing set, melling oil pump, valve job.

The car also has:

Hinson engine and trans mounts

Ls7 clutch/flywheel

K&N intake (hopefully x-air soon)

JBA long tubes, full exhaust

Hinson 1 piece DS

Trutrac diff with full install kit

Mavman coilovers

stock wheels with BFGS, ace flow formed wheels with ps4s (using hub rings)

new rear wheel bearings

full pedders bushings, radius rods, control arms, sub frames, diff insert, etc

new dba rotors and hawk pads



The car was dyno tuned at 357/375 a few months ago.



The issues I am having are:

A vibration, seems to be from the rear end, 40 mph and up. Seems more prevalent coasting or even putting the car in neutral, feels like a hopping, thumping. It has done this with both sets of wheels and tires, road force balanced, i have hub centering rings on the new wheels. I followed the torque procedure for the lugs multiple times and have tried indexing the wheels. I also get an occasional squeek from what seems like right rear, possibly brake. My current thoughts for the vibration and the noise are: trans, ds, axles, inner stubs. The stubs were looked at when the trutrac was installed and seemed ok. When I replaced pads and rotors last weekend I removed passenger axle and noticed the inner CV joint to be clicking and not nearly as "Fluid" as the outer. I also measured hub runout on all 4 corners and got a max of 3 thousandths of an inch on the right rear.



Secondly, the AC is not working. It blows cold for a second or two, then hot. Seemed to be making a noise as well. Can not hear compressor clutch engage. I took it to the dealer yesterday and they stated that there is likely an obstruction in the system causing pressure readings to spike, compressor not engaging. They stated it was likely the compressor going bad, threw debris into rest of system. Quoted 2400 to replace AC.



I am fairly mechanically able and have done a good deal of the above work myself. I had a shop do the differential and dyno tune obviously. I have never done AC work and am leaning towards breaking the system down and inspecting parts as I go. Rock auto has compressor, condensor, TXV, and drier for reasonable prices compared to the dealer cost. I do not have the gauges or a compressor in order to diagnose things myself. I can get access to a compressor in order to clean out lines etc.



Any help that could be provided is greatly appreciated. I am starting to get frustrated with this as the vibration makes the occasional cruise less enjoyable, in addition to warm weather coming with no AC.



Thank you
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Old 04-23-2019, 04:30 AM   #2
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Can you describe the noise in more detail? Does it correlate in time with vehicle speed, or does it vary in intensity with say, bumps or irregularities in the road surface? It could just be a bad shock absorber.

Have the a/c system evacuated and check the expansion valve for debris. If you had a compressor self destruct, that's where shrapnel likes to collect.
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Old 04-23-2019, 04:36 AM   #3
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The noise sounds similar to a wheel imbalance, low pitch thudding, it seems when the drivetrain is loaded up it is not as bad, it is when I am off the gas I can really feel/hear it. Putting the car in neutral anywhere from 40-80 mph it is the most noticeable. I replaced the suspension with m man coilovers over the winter and it was doing the same thing before I replaced the suspension.

As for the AC, thanks for the tip. If it was the compressor can I just replace the compressor and Txv? or should the condenser be replaced as well? I have read that if debris made it to the condenser I could just kill another compressor. I planned to replace the drier as well as it comes in the kit from rock auto.
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Old 04-23-2019, 04:40 AM   #4
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If the compressor blew up and sent debris into the system, you should replace the entire system. Literally, except for the hardlines. You can probably blow those out with compressed air.

So, your rear dampers and springs have been replaced?
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Old 04-23-2019, 04:45 AM   #5
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got it, im not really sure that the compressor blew up, as it never made any bad sounds or anything, i just couldn't hear the clutch kicking in and out.

Yes, the rear springs and dampers were replaced. Along with all of the rear control arm bushings, wheel bearings.
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Old 04-23-2019, 04:51 AM   #6
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The a/c clutch can be visually verified. Fine the harness that leads to it and supply 12v. If the center hub of the pulley starts spinning, the clutch is fine.

It may be pressure that is too high on the high press side or too low on the low pressure side preventing the ECM from commanding the clutch to activate. If you want to diagnose yourself, it would be worth it to get a good set of gages.

Are the rear springs and dampers still stock? Have you tried rotating the wheels/tires to see if the effect moves with them?
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Old 04-23-2019, 04:55 AM   #7
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If it still has the stock axles with that mileage, it wouldn't hurt to just rebuild them. Those CV's are pretty prone to wear. If you do not dragrace often, just getting the gforce rebuild kit is worthwhile.

The stubs shouldn't cause a vibration with the stock LSD. I have heard of some stubs fitting a little loose with aftermarket carriers. I'd do a search on it, i might later when i have a chance.
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Old 04-23-2019, 04:57 AM   #8
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The rear springs and dampers are mav man adjustable dampers and springs with height adjustable perches. I tried rotating the stock 18s and the effect did not move with them. Still seemed to be passenger rear. I cannot rotate the flowformed wheels as they are staggered with directional tires.

At this point I am considering the passenger axle/cv, or the driveshaft. The stubs looked fine both inner and outer.
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Old 04-23-2019, 04:59 AM   #9
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I do have a trutrac in it, not the stock lsd. But the vibration was there both before and after trutrac install
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Old 04-23-2019, 04:59 AM   #10
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If it still has the stock axles with that mileage, it wouldn't hurt to just rebuild them. Those CV's are pretty prone to wear. If you do not dragrace often, just getting the gforce rebuild kit is worthwhile.

The stubs shouldn't cause a vibration with the stock LSD. I have heard of some stubs fitting a little loose with aftermarket carriers. I'd do a search on it, i might later when i have a chance.

As far as the DS, check the old seat belt bolts rubbing on the DS issue.

As far as any other ideas, i would think that with the car coasting or in neutral, with the subframe having some movement due to the stock bushings, that something is moving just enough to cause the thudding. If all else fails, look for witness marks.

You may want to invest in subframe bushings.
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Old 04-23-2019, 05:01 AM   #11
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subframe bushings already replaced with pedders. seatbelt bolts have been ground down and are not contacting ds. subframe was aligned using the tool when bushings were done.
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Old 04-23-2019, 05:01 AM   #12
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Hmmn. I wonder how i did that one. Looks almost like i tried to edit but just made a new post.
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Old 04-23-2019, 10:14 AM   #13
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I dont have a lot to add, except that you really should get some gauges ($50 @ Harbor Freight or borrow some) to see what is going on.

The only AC work that I've done on the GTO was to replace the internal control valve on the compressor (without removing the compressor). Had I not done my research, I might have replaced a perfectly good compressor for no reason. I'm not saying that it's YOUR issue, but the symptoms are in this video and the link to the part follows:


https://www.sherco-auto.com/gm-harri...alve-each.html

Also, here's a long list of t-shooting steps for the AC.

https://www.aa1car.com/library/2003/ic50350.htm

Good luck!
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Old 04-23-2019, 10:31 AM   #14
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Quote:
Originally Posted by ashgto...View Post
The noise sounds similar to a wheel imbalance, low pitch thudding, it seems when the drivetrain is loaded up it is not as bad, it is when I am off the gas I can really feel/hear it. Putting the car in neutral anywhere from 40-80 mph it is the most noticeable. I replaced the suspension with m man coilovers over the winter and it was doing the same thing before I replaced the suspension.

As for the AC, thanks for the tip. If it was the compressor can I just replace the compressor and Txv? or should the condenser be replaced as well? I have read that if debris made it to the condenser I could just kill another compressor. I planned to replace the drier as well as it comes in the kit from rock auto.

Sounds similar to the issue i am having. 40+ theres a vibration apparent. Significantly worse around 50s and cruising. Put power down and it becomes less apparent. I havent figured out mine yet but im on a stock driveshaft w/ new guibos and carrier bearing. So i was thinking it might be that still. I havent done my subframes yet or diff bushing. Also have mav man coilovers and now whiteline engine mounts and mavman trans mount. Was hoping those were going to fix it.
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Old 04-23-2019, 10:51 AM   #15
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wonder if a bad bearing in the trans could cause something similar...
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Old 04-23-2019, 10:55 AM   #16
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...maybe tailshaft bushing?
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Old 04-23-2019, 10:55 AM   #17
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Quote:
Originally Posted by Nothubertjfarnsworth...View Post
wonder if a bad bearing in the trans could cause something similar...

Its definitely possible. I tried wiggling my output shaft and didnt see anything abnormal on mine. I still have a few things i want to replace and then try rebalancing the shaft or get a dss as last resort.

Hope OP can figure it out so i know where to look

Last edited by Sacrifice; 04-23-2019 at 11:25 AM.
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Old 04-23-2019, 12:44 PM   #18
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What? That's not fair I was hoping you would figure it out and let me know.

In all seriousness I am hoping to get some time under the car this weekend. My plan is to pull driveshaft and check u joints in Hinson 1 piece. Check trans output for play, and maybe even switch the rear axles and see if the vibration changes. I will also index the driveshaft 90 or 180 deg?
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Old 04-23-2019, 12:56 PM   #19
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Originally Posted by ashgto...View Post
What? That's not fair I was hoping you would figure it out and let me know.

In all seriousness I am hoping to get some time under the car this weekend. My plan is to pull driveshaft and check u joints in Hinson 1 piece. Check trans output for play, and maybe even switch the rear axles and see if the vibration changes. I will also index the driveshaft 90 or 180 deg?

Lol. I would try 90 deg first. Thats another thing im willing to try when i get the time.
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Old 04-23-2019, 06:00 PM   #20
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Quote:
Originally Posted by ashgto...View Post
What? That's not fair I was hoping you would figure it out and let me know.

In all seriousness I am hoping to get some time under the car this weekend. My plan is to pull driveshaft and check u joints in Hinson 1 piece. Check trans output for play, and maybe even switch the rear axles and see if the vibration changes. I will also index the driveshaft 90 or 180 deg?

Checking the u-joints isn't a bad idea. I thought the DS was new, so discounted the possibility.

I had a vibration that could be felt under certian engine loads in my truck. A few weeks later i started hearing the tell-tell clang when i put it in gear that told me that it was definitely a u-joint. It didn't really feel like what you are describing, though. I felt it in the floorpan, and it felt like it oscillated back and forth along the length of the truck body, but then again it did end up being the front joint.
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Old 04-27-2019, 08:08 AM   #21
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I pulled both axles. Passenger inner CV seems to get stuck in compressed position. Very notchy and catchy. Driver side does not have same issue. Going to swap them and see if vibration changes and order axles in the mean time
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Old 04-27-2019, 09:01 AM   #22
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Quote:
Originally Posted by ashgto...View Post
I pulled both axles. Passenger inner CV seems to get stuck in compressed position. Very notchy and catchy. Driver side does not have same issue. Going to swap them and see if vibration changes and order axles in the mean time

Rebuilding axles is super easy.

They like do develop divots in the outer race and cage over time, making for a bit of play and probably the notchy feel you're getting.
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Old 04-27-2019, 10:14 AM   #23
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Well, I swapped axles side to side and the vibration completely changed and is reduced. I made sure when I installed the questionable CV that I pulled out on the shaft so it was not stuck in the collapsed position. I think I'll be ordering some anti hop units. Dss or "hforce"?
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Old 04-27-2019, 02:42 PM   #24
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You think it was entirely the axles? How many miles on them?

I found some play in my subframe bushings so i need to get those replaced asap but i still cant imagine those causing all this vibration im feeling. But i dont want to waste money rebalancing a stock driveshaft either
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Old 04-27-2019, 03:00 PM   #25
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I think the majority of it is the CV joint. Not a typical CV symptom I guess but I could see if it gets caught In a position it could cause the axle to not spin symmetrically. Not sure how many miles are on them. They say unidrive on them so not sure they're stock and there's 96k on chassis. I already did subframes with peddlers. I'm full poly bushings so any vibration is just transferred right to me in the cabin
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Old 04-27-2019, 05:57 PM   #26
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Quote:
Originally Posted by ashgto...View Post
I think the majority of it is the CV joint. Not a typical CV symptom I guess but I could see if it gets caught In a position it could cause the axle to not spin symmetrically. Not sure how many miles are on them. They say unidrive on them so not sure they're stock and there's 96k on chassis. I already did subframes with peddlers. I'm full poly bushings so any vibration is just transferred right to me in the cabin

yeah, those are stock. unidrive did the stock driveshaft, too.
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Old 04-27-2019, 08:34 PM   #27
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Quote:
Originally Posted by ashgto...View Post
I think the majority of it is the CV joint. Not a typical CV symptom I guess but I could see if it gets caught In a position it could cause the axle to not spin symmetrically. Not sure how many miles are on them. They say unidrive on them so not sure they're stock and there's 96k on chassis. I already did subframes with peddlers. I'm full poly bushings so any vibration is just transferred right to me in the cabin

Im just under you. 91/92k. Ill take a look at mine too
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