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This is one of those true stories that reminds you of the importance of the fundamentals: attention to detail, and conscientious workmanship.

Most of you know that I had my rear axle ratio changed from the stock 3.73 to 4.56, a couple of months ago, at a respected high performance shop. The shop came with great references, and the owner assured me that they had plenty of experience with rear axle ratio changes.

Stupidly, at exactly the same time as it turns out, Chevrolet got my new backordered driveshaft in, as I had been complaining about the “tinging” I was experiencing with the original driveshaft (a documented problem – see plenty of postings on this board about it).

I violated one of my long terms rules, because I REALLY wanted both changes made, about doing ONE change at a time.

Sure enough, after getting both changes made, I noticed that I had a new sound, that first became audible at around 35 mph (only if you have the stereo system “off”!) and does not sound anything like any sound I have heard before. I have described that sound in another posting on here (“Ping Jim G if . . .”), but to summarize, it is a “ringing” sound, like you would get by exciting a metal object made of very thin metal. My intuition tells me this is our famous aluminum, thin guage, large diameter “pipe organ” replacement “tingless” driveshaft vibrating at high frequency, but of course this is hard to prove.

When I mentioned it to one GM mechanic, he took a superficial look at that first replacement driveshaft, agreed that it seemed to have a fair bit of play at its yoke end (i.e. at the transmission tailshaft), but insisted it was acceptable, and that the sound was probably just a byproduct of the stiff rear axle ratio. I did not agree, and had the driveshaft both foam filled and rebalanced at my expense to quiet it down. That DID reduce the volume, but did not eliminate the sound. Since it was not irritating enough to make a fuss over, I didn’t worry about it.

A couple of thousand miles later, the SSR developed a transmission fluid tailshaft seal leak, and so I went in to a different Chevrolet dealership and they replaced the seal. A few DAYS later, the NEW seal started leaking AND I noticed I was now getting a perceptible shake in a narrow speed range centered on 65 mph. The Chevrolet mechanic agreed that there was a shake there, and that it had probably totaled the new seal, but couldn’t pin down its cause even after using a spectral vibration analyzer on the chassis. Both the original shop that did the rear end work, and my new tuner (MTI Racing), suggested that I tell the Chevrolet mechanic to check that driveshaft yoke AND the tailshaft bushing closely. He did, and 2 hours later Chevrolet had a new driveshaft, a new yoke, and a new seal on order for me. However, contrary to the advice of my 2 mechanics, they elected not to replace the tailshaft bushing, because “it looked and felt fine”. Reese at MTI shook his head when I told him, and said something like “Bronze is softer than steel Jim. If the yoke was found to be the incorrect as the mechanic told you, then it HAD to have battered that bushing up.”

Yeah, you guessed it. The shake is pretty much gone now, but the ringing noise is still there. I figure I need to wait for the next reoccurrence of either a seal leak or a shake, and then INSIST that this time Chevrolet replace ALL the pieces that interact with each other: seal, bushing, yoke, and driveshaft. And, maybe at the same time, fight the battle to get a STEEL driveshaft that won’t act like a musical amplifier for every driveline sound, as one other SSRfanatic member who WORKS at a Chevrolet dealer HAS gotten.

In the meantime, I also told Reese about the fact that Motive Gear, the supplier of the new rear axle ring and pinion, had called for a target 0.008” backlash clearance on the gears, and a minimum of 0.006”, but I wondered if that was too large a clearance to minimize gear whine noise. Now, Reese has done LOTS of ring and pinion changes – it’s one of his specialities at MTI Racing in fact. He has done lots of C5 and C6 Corvettes, both stick and automatic, changing the ratios to as high as 4.11 (which with the Corvette’s smaller diameter wheels yields pretty close to the same highway rpm as the SSR with 4.56 gearing). More dramatically, he used to be a crew chief for a race team (Mobile One), and once changed rear axle ratios on a fleet of race cars 87 times within 3 months! He KNOWS rear axles.

He always sets up ring and pinion backlash at around 0.005”. He says he does that because the clearance opens up a bit with normal break-in wear and because you need it that tight to get optimal engagement and low noise. He says there is no reason to have a loud rear axle, even with a 4.xx series gearset. After driving my SSR specifically listening to the sounds, he is as mystified as I am about the ringing sound, but said with confidence that he could get the gear whine reduced. Although the gear whine I had was nowhere near loud enough to be a factor for me, I asked him to take a look at my axle just to assure myself that everything was reasonably fine there, and so that when I have my future discussion with Chevrolet about the ringing sound, they don’t try to blame it on the rear end. Turns out that was a great idea.

After opening up, examining, measuring, and correcting and optimizing my SSR’s rear axle housing, Reese had lots of news for me.

- First, he noted that 2 of the housing inspection cover bolts had been stripped by his competitor’s mechanic, probably because that mechanic did not note that the SSR’s axle housing is ALUMINUM (like the driveshaft), and so had probably used an air wrench on the bolts, set to whatever he uses on STEEL housings. Reese repaired both of these, properly. By the way, they are METRIC.

- Secondly, he showed me with his dial indicator that the backlash, even though set and confirmed at the time at 0.008” by the competitor, was in fact now 0.012”. That would make it noisier.

- He checked the shimming, and found that it was close but not ideal, and speculated that that was because the SSR’s axle requires a different set of shims than Corvettes or Camaros, and that the competitor simply did not have the exact shims needed. Reese had his guy locate the correct shim set, and brought it in.

- He checked the spacers used elsewhere on the axle housing, and again, found that although close and acceptable, there was a special spacer set for our axle, and he procured and installed it.

- Then he checked the preload on the pinion bearings, and tightened it up, because with the aluminum housing, IF those bearings’ races ever got loose enough to rotate in the housing, they would go through that aluminum like butter, causing a quick failure.

- He checked the axle lubricant for any signs of metal, but found it was very clean, indicating that none of the deviations above had caused any undue wear.

- He had also checked the tooth engagement patterns, and was satisfied that they were acceptable.

- He refilled the housing with Mobil 1 synthetic axle lubricant.

The actual on-the-road results were interesting. The gear whine IS quieter, although I never found it objectionable at all before. To Reese, with his expertise and attention to detail, I’m sure that any excess at all would be an irritation. The ringing, just as I suspected, is still there and totally unaffected, proving that it has nothing whatsoever to do with the rear end, as we now have a rear axle that has been PERFECTLY set up by someone whose credentials would be VERY hard to dispute. So, when I next get either my seal leak or my shake, or both, I will say with great confidence to the Chevrolet folks “I want a completely new yoke, seal, bushing, and STEEL driveshaft”, since SOMETHING is making that ringing noise, and it’s NOT the rear axle. That new driveshaft assembly just isn’t quite right.

Reese says that a carbon fiber driveshaft wrap technology developed for race cars is now actually being commercially applied large scale to dump trucks. The reason is interesting. Apparently, some dump trucks that have 2-piece driveshaft (with a u-joint / bearing in the middle between the 2 driveshaft sections) experience failures in that center u-joint / bearing quite frequently, due to excessive driveshaft vibration. The carbon fiber is used as a dampening wrap to control the vibration. Reese says he could find out what the cost of that process would be for my driveshaft, but I am leaning towards leaving it bone stock until it causes another failure, so that GM doesn’t say the failure occurred because of “modifications to the driveshaft”.

But, getting back to the point at hand, MTI has effectively reminded me yet again that attention to detail and workmanship are incredibly important on a day to day basis. Extrapolate this thought. Attention to detail and workmanship in both design and installation are the difference between:

- SSR window seals that leak and window seals that don’t

- Auxiliary guage sets that work and those that get shorted and killed during installation

- Tonneau covers that seal and those that don’t (and so result in mildewing of the trunk carpeting)

- Roof hydraulic lines that don’t touch and scrape the roof, and those that do

- Driveshafts that don't ting or ring and those that do

- Etc., etc.

Makes you wonder how great our SSRs would be if GM actually HAD that attention to detail and workmanship. I’m not discouraged – I love my SSR regardless for all sorts of reasons. I’m just always looking for “great” rather than “ acceptable”.

And so evidently, is Reese at MTI. Gosh I am glad that Paul introduced us to each other. I wish there were more of us with similar values.

Jim G
 

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SSR Pit Crew
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Looks like a BIG steak dinner is in order for Reese! And don't forget to tip the waitress! :lol
 

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Detail

The things you mention just remind me why I like to do as much of the work myself so I know exactly what was done and how. Of course I understand that most do not have the aptitude or inclination for this.. It sound like you have found a true gem in the perofrmance world. Keep the stories coming!
 

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boy and I thought only I wigged about about stuff :cuss
 

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Jim, a few questions -- Why didn't you use the Moroso lube again? --- what spacers "that are used elsewhere on the axle" were you referring to? The SSR shop manual advised that they preferred a .005 to .007 backlash. You make some interesting points and I will be doing my own 4:56 gear change. Yes, I do have the knowledge and tools and the patience.
 

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I'm not cool...
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:thumbs the devils in the details :reddevil
Jim, do you think Reese would like to talk (post) about his 427? you know, how he does it & some specs we all might sorta understand?
thanks for all the info :flag
 

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Discussion Starter #8
Gary's 04 said:
Jim, a few questions -- Why didn't you use the Moroso lube again? --- what spacers "that are used elsewhere on the axle" were you referring to? The SSR shop manual advised that they preferred a .005 to .007 backlash. You make some interesting points and I will be doing my own 4:56 gear change. Yes, I do have the knowledge and tools and the patience.
I did not want to tell Reese what to do or use, as I wanted him to set this rear end up exactly the way he normally would. I am preparing for a return visit to the Chevrolet dealer, as soon as the tailshaft seal starts leaking again or I get that shake in the drivetrain again, and I want to be able to say with absolute confidence at that time "No, it is definitely NOT the rear axle, as I have PAID MYSELF to have it inspected and PERFECTED by someone who has more rear axle experience than any mechanic at a Chevrolet dealership could possibly accumulate, so you'd better finally give me a DRIVESHAFT that is CORRECT. I want a STEEL one".

I cannot provide any details on the spacers, but I will ask Reese.

I am glad you found that reference to a .005 to .007 backlash. This agrees with what reese has found, and proves that Motive Gear is specifying too much clearance with their .008" target and .006" minimum.

I am frankly not surprised that GM is having this driveshaft issue with teh SSR, as they basically took an engineered chassis, the extended version of the trailblazer, and shortened it about 16 inches as I recall reading. Then they also changed the diameter of the rear tires, and replaced the Trailblazer rear suspension with the link suspension. All of these changes, but especialyl the shortened length of the chassis and therefore driveshaft, have the effect of changing the angles between the tailshaft assembly, the driveshaft, and the rear axle pinion. If you do any research on driveshafts and u-joints, you will quickly learn that even just a ONE DEGREE change in these angles has a huge effect on driveline stability, and a THREE degree change is enough to cause destructive forces. Coupling that with a thin guage aluminum driveshaft is just tempting both destrcutive force and obnoxious noise problems.

This driveline noise issue is the only issue I have with my SSR. It may take me a while, but I am annoyingly persistent once I decide I want to solve a problem, and I will solve this one, as it is interfering with my enjoyment of the power characteristics that Reese has provided.

Jim G
 

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Hey Jim G, when my SSr grows up, It wants to be just like yours! :thumbs

I still think you need your own corner for your posts.
 

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Retired GM Program Manager/ Chief SSR Engineer
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A steel prop shaft would be dangerous in this application because of the higher prop shaft speed. Enormous forces can be generated if the the prop shaft is not correctly engineered for weight and stiffness. This is why long prop shafts are either large diameter aluminum or two pieces. Lighter weight, stiffer, carbon fiber would probably be OK. We did not find the angle change causing any issue. The current aluminum prop shaft might have an issue during any top speed run with this axle ratio. Since Jim changed the axle ratio, I'm surprised that GM is continuing to provide support for his efforts.
 

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freezer said:
A steel prop shaft would be dangerous in this application because of the higher prop shaft speed. Enormous forces can be generated if the the prop shaft is not correctly engineered for weight and stiffness. This is why long prop shafts are either large diameter aluminum or two pieces. Lighter weight, stiffer, carbon fiber would probably be OK. We did not find the angle change causing any issue. The current aluminum prop shaft might have an issue during any top speed run with this axle ratio. Since Jim changed the axle ratio, I'm surprised that GM is continuing to provide support for his efforts.
But that brings up the question, What is Chevy doing to correct the "tink" problem????? The present replacement isn't working for a lot of people.
 

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Discussion Starter #12
Freezer: There is no way that GM could dodge the driveshaft issue by trying to say its because I changed my rear axle ratio. Iwent through THAT math in my head a long time ago, and showed it does not pass even a superficial analysis.

The effect of the change was to merely raise the rpm of the driveshaft by 22%(4.56/3.73 = 1.22).

That means when I am traveling at 60 mph, in terms of driveshaft rpm, it is like an SSR with factory gearing traveling at 60 x1.22 = 73 mph. So a stock SSR can't travel at 73 mph without spinning its driveshaft too fast??? I guess when I went to California and back at an average speed of 79 mph on I-10, that was abuse?

The FASTEST I have ever had the SSR is under 100 mph, which in terms of driveshaft rpm, is like a stock SSR running at 122 mph. Is 122 mph a destructive speed for the driveshaft??? I don't think so. The governed speed of the SSR, based on TIRE RATING restrictions, not drievshaft rpm, is around 130 mph as I recall.

I did a google search on "driveline ringing" and came up with a BUNCH of references to it, including these:

From the Camaro IROC website:

http://www.iroc-zpostforum.com/Tech/Techrearaxletreat.htm

Quote:
For axle ratios of 3.73 and higher. At this point, you may experience some vibrations at the transmission slip yoke area where both the transmission and driveshaft can vibrate regardless of how well balanced a driveshaft is. To limit these left over vibrations, a special steel only shaft is available from the factory which incorporates a harmonics balancer on the slip yoke side. Otherwise, typically 50% of all F-bodies have drive line vibrations using 3.73:1 or higher gears.

End quote

From www.4xshaft.com:

Quote
There is in fact a foam fill the drive line "trick" referenced in a GM factory service bulletin. This is a referenced as a solution to the problem of a "ringing" noise from the drive shaft. The source of the problem is a result of a ring & pinion mesh or minor torsional vibration problem. Filling the drive shaft with foam simply deadens the noise. Although in the past, I have had problems with filling the drive shaft with foam, it seems that the foam may not harden in the airless environment. I have had better luck cutting the drive shaft apart and packing it with wadded up newspaper.
End quote

From Minneapolis Star Tribune newspaper car column:

QI have a 2000 Chevrolet Silverado extended-cab pickup with four-wheel drive, the 4800 V8 and a four-speed automatic transmission. Whenever I put it in drive, there is a clunking noise. This happens on the initial shift. I have taken it to the dealer and they have told me that the 2000 model is having this problem but there is no remedy. They have lubed the splines on the driveshaft slip joint and replaced the propeller shaft between the transmission and rear differential. This clunking sound is getting louder and very annoying. Is there anything that I should be asking the dealer to try?

AI spoke to Bill Prinsen, service manager at McCarthy's Chev/Olds/Cadillac in Forest Lake, about this issue, and searched my ALLDATA for bulletins. GM has published a service bulletin on this type of driveline clunk; it says that in most cases it is the result of cumulative run-out, lash or free play among all the mechanical components in the system. Thus, on a four-wheel-drive model, the potential for this noise is greater. Think of it this way: As the shifter is moved into the drive position, engine torque snaps all the play out of the drivetrain instantly. This includes the clearances between inner and outer splines on driveshafts and axles, backlash between the ring and pinion gears, clearances between gears in the transmission and transfer case, and the fractional play in all the U-joints in the system.

Thus, some clunking sound when shifting from park to drive is normal and in no way harmful. In fact, the bulletin suggests that it is unlikely that a single component is responsible for the sound. In your case, the first step would be to have a mechanic determine whether the clunk is a normal or not.

Prinsen added an interesting twist: He points to the large-diameter driveshaft as having a drum-like characteristic in amplifying and echoing the noise of engagement. He also pointed out that if the vehicle is not parked on a perfectly flat surface, the weight of the vehicle is, in effect, leaning on all the driveline components. In other words, all the play is being forced out of the system by the leverage of the parked vehicle. Then, when it is shifted from park to drive, the load is reversed and the total play in all the components clunks out of the system.

Prinsen says that it may be possible to reduce the level of noise by servicing the driveshaft. He has seen cases in which driveshaft shops have cut open the hollow shaft and inserted a cardboard "W" into the tube, then welded the driveshaft back up. The cardboard wedge acts as a dampener to reduce the ringing sound transmitted by the driveshaft.

Prinsen had two more suggestions: First, upon cold startup, wait a moment for the idle flair to fall toward normal idle speed before engaging the transmission. He has also seen some success in changing the transfer-case lubricant to the new blue synthetic fluid, and lubing the splines where the rear driveshaft enters the transfer case with this same oil.


Seems to me that GM IS well aware that not everything is wonderful in driveline land.

Jim G
 

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I was most concerned about the top speed issue with the prop shaft and your axle. There is a design limit for how fast you can rotate any particular propshaft. Beyond that limit it can fail quickly. You are OK at 100mph.

I sometime have a clunk on my truck a low speed when going from coast to drive. I ignore it since I do not know how to fix it. The clunk is a product of the slip fit clearances between the propshaft and the transmission. The factory fix tuned damper on the prop shaft eliminates a resonance at 54mph and does not fix the clunk. I have yet to hear something that sounds like a "ping".
 

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Discussion Starter #14
Gary's 04: I asked Reese about the spacers. he gave me a very rapid education on some of the rear axle parts.

He said that every rear axle has TWO sets of spacers or shims:

- The shims that shim the clearance between the pinion and ring gear

- The two "side shims"

It is the second set of shims he referred to when I said "spacers". They ARE actually spacers, but on the SSR rear axle, he says they are very clever. Each of the side shims is actually a "sandwich" consisting of 2 thick spacers with a thin shim in between. That shim comes in multiple thicknesses, so that the total thickness of the sandwich assembly can be set perfectly if you are persistent enough. That is what Reese set to perfection, along with the pinion to ring clearance.

Jim G
 

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Jim, the SSR shop manual says not to reuse the side spacers but procure shims of the same thickness and install the shims instead of using the existing spacers. That is why I asked what Reese installed.

I look forward to your investigations as I am not personally interested in cosmetic changes to the SSR but I am interested in the technical and performance changes offered on this forum. Looking forward to when you get involved with the transmission and torque converter.

Besides you choose a great color!
 
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