JimGnitecki

I have run into a minor issue on my 1992 convertoble with automatic transmission, after changing from the factory 2.79 rear end ratio (in Dana 36 housing of course) to a 3.54 aftermarket ring and pinion, Ruchmond Gear american made high quality, and installed by a very careful and experienced installer at the best local high performance shop, who persevered til he got it pretty perfect in terms of setup.

This change resulted in the planned 2000 rpm at 60 mph in overdrive, while retaining 40 mph capability max in 1st gear, and no impact on actual top speed.

The good news is that the change made a FANTASTIC dfference in the feel of the car. It is super nimble now - feels as though it lost several hundred pounds. And, I even get a tiny amount of "engine braking" when letting off the gas at speed. GREAT mod.

But, I am experiencing a minor noise problem similar to what I experienced on a Chevy SSR a few years back, when I did a similar ring and pinion swap.

The nosie can best be described as a sort of "whine", that becomes audible at maybe 20 mph, is most noticeable at 50 to 60 mph, and either subsides or gets overwhelmed (I don't know which) by wind noise (convertible, remember) above 60 mph. The sound pretty much goes away if I let off the gas, and returns when I reapply gas.

The noise would not be objectionable on most cars, but my C4's stock exhaust is so quiet, and I have taken pains to ensure weatherseals as perfect as they can be on a C4, and there are no squeaks or rattle, so that the darn car is quiet enough, despite being a convertible, that the noise "stands out".

On the Chevy SSR, the problem was ultimately diagnosed as the lightweight aluminum factory driveshaft resonating and "amplifying" ring and pinion noise like a trumpet. A smart shop owner who read about my issue online at the SSR forum sent me a high tech driveshaft, an aluminum metal matrix composite (MMC) driveshaft, that absolutely wiped out the problem. It was a very intriguing driveshaft versus the factory one: when you struck the factory driveshaft with a metal wrench it would loudly "ring", but when you struck the MMC driveshaft, it would barely "thud" in comparison.

However, I have googled around, and it appears that that kind of driveshaft material is no longer available.

I'd love to get rid of that noise, as the car is really remarkably quiet (for a C4 convertible) other than that noise.

Any ideas or suggestions?

For example, would a different driveshaft material make a difference, even without MMC, just by having different resonance ranges? Would a different rear axle lubricant make a difference (I am running Mobil 1 synthetic plus posi fluid)?

A driveshaft supplier has suggested making a new drvieshaft with a cardboard sound absorber tube liner inside it, but I am wondering if the factory shaft might already have that feature (it used to be pretty common).

Ideas?

Jim G

94z07fx3

FSM says run 75w90 gear oil. GK says use 75w140 and two bottles of GM LSD additive.

I use Mobil 1 75w-140 and one bottle of LSD additive.

I never swapped gears but it may be a heavier weight would quiet it down. I noticed no difference in sound from the rear after changes but never heard the diff before anyway.

STL94LT1

I would look no farther than your newly installed gearset as the source of the whine.

WVZR-1

You have these options and I'd likely do the first and then the second or third with the 4th maybe shuffled up to third. You know that the condition you mention is often related to a "tight build" of the differential. Right?

1. Remove your drive-shaft and check condition of the dampener on the slip-yoke, the u-joints (replace likely)and have balanced. Balance on a extremely efficient higher RPM'd piece of equipment. They aren't all the same.

2. Remove your drive-shaft, replace the u-joints and the slip-yoke using a slip-yoke less the dampener, balance on same higher RPM'd equipment and move on.

3. Since you're familiar with the MMC product and if you really felt it would be a plus have one built. It's simple! The C4 drive shaft is quite short (less than 26" of tube) SO you purchase a used FOMOCO piece that is an MMC build and have one built using the MMC you're familiar with. There should be many available and likely a $20 or so purchase. A NOS FOMOCO new one would not be out of the question but why the expense. I believe I could supply the required information.

4. Have a 6061 built with the "dampening tube" glued inside. You would buy that shaft new with slip-yoke and joints, balanced and ready to go out of the box.

Who do you have build either one? I'd have local conversations and I don't believe I'd consider Denny's. I'd suggest if you couldn't find a local that you cared for a couple mid-west shops but I'm quite confident a local drive-line shop can accomplish it.

383vett

If you are sure the noise is coming from the driveshaft and not the gears, carbon fiber driveshafts are getting quite common in racing. They are not too crazy expensive. Here are just a couple of companies...

http://www.pstds.com/

http://www.acpt.com/Products/Composite-Driveshafts.aspx

JimGnitecki

I agree that the gear set is the source, but the question is how do I eliminate or attenuate the resulting noise. I do not want to give up the 3.54 gearing, and I know the install was done by a good installer, so having someone else fool with the gearset is not gonig to be helpful.

Jim G

JimGnitecki

I had wondered about this. If using the 75w-140 viscosity is not damaging, and at least one source recommends it, it is a realtively inexpensive and simple thing to do, so I should probably try it.

Jim G

JimGnitecki

The noise is almost for sure coming from the gearset - I cannot iamgine that the driveshaft is generating it - it's just amplifying what the gear set produces I think.

I agree that a carbon fiber driveshaft, could like the MMC shaft, eliminate that amplification, but there are some disadvantages that deter me from trying a carbon fiber shaft as the FIRST solution:

- Very costly

- Would almost certianly need to be custom made for me (no one makes one for a C4 as far as I know - hey, it's a 21 year old car), and a custommade carbon fiber shaft is going to be even more costly than one that is "on the shelf"

- If a heavy enough or sharp enough piece of road debris hits that shaft at highway speed, it will surely self-destruct rather spectacularly, leaving me stranded!

Still, it's an option if none of the other solutions recommended to try so far actually do the job!

Jim G

JimGnitecki

WVZR-1: As usual, you are the one who provides the most detailed and experienced advice!

Your suggestions are sensible ones, and I'm likely going to try them each in sequence as soon as I get back to Austin (I am currently 200 miles from home on a contract work assignment in south Fort Worth).

What do you mean by "the condition you mention is often related to a "tight build" of the differential." ? Did the installer make the clearance a bit too tight?

I have noticed the following: The noise is most apparent when the ambient temperature is high. It is either not present or at least not-detectable, when it is cold outside and the car is started and run the first few miles. It then becomes apparent as the car (and the axle housing of course) warms up, but is never as audible as when the outside ambient temperature is high.

I have noticed too that the noise level seems lower now, 3 months and about 4500 miles after I got the gear set installed. Could that be because the gear set is "wearing in"? Or, COULD this be just because the ambient outside temperature has dropped from 90s and 100s to 70s in the day and as low as 30 degrees first thing in the morning?

Thoughts?

Jim G

JimGnitecki

More questions:

1. What material is the stock driveshaft made of on my 1992 C4 automatic?

2. Is the factroy driveshaft cardboard lined already by chance? (I thought I should ask before getting a custom one made with cardboard liner )

3. Can you provide the required information you offered on what Fomoco drvieshaft to buy as a starting point for a new driveshaft? Either here, or if you prefer, to my email address:

JimGnitecki@gmail.com

Thanks!!

Jim G

WVZR-1

1. It's an aluminum tube and Spicer has eliminated the tube, end yokes and the slip-yoke information from their build specs. A good bit of early Dana and Spicer has been eliminated from information sheets I once had. I likely have it somewhere but I think it of no consequence. They would have ID'd the tube OD, wall thickness but probably not a spec.

2.Likely - I've had C4 drive-shafts that you could turn end to end and the cardboard tube would "thud" when it hit the end-yokes.

3. I need to research the FOMOCO stuff but I think it should be easy enough.

Everything that you mention regarding noise, heat and cold making a difference suggests that it's likely a "tight build" ring & pinion backlash related likely. If it were a "loose build" you would likely have the noise on coast and it would dissipate on acceleration.

I'd suggest a "ride along" with the builder and also a disinterested party that understands differentials. There are electronic sensors that can be applied to diagnose the problem. They're not often used but "most" dealers actually have them.

bassackwards

Plan on replacing it if you don't get it adjusted correctly

383vett

Some gear sets are made in a way that noise is a side effect. My 12" 4.35 gears whine like a jet on deceleration but aren't as noisy on acceleration (maybe partly because I can't hear much through the exhaust anyway). My differential man says this noise is a good thing.

cv67

Some gears are harder than others and are more prone to noise. Lower numerically may add to it. Still suspicious of the install it shouldnt whine. I mean you may hear a slight something being as youre sitting over the rearend practically but not "bad".

Wonder if a damper (dont know if the LTx cars had one like the L98 cars) could help.

I always use the heavier weight oil period.

bob guzzy

For my 2 cents, I do remember years ago when you went to an after market gear set you got noise.

Since the aftermarket gears were intended for race purposes the gear noise was not noticeable with open headers and was acceptable.

I would talk to the folks that made your gears, they may have been intended for racing, the gear noise comes with them.

I had an old chevy van with a noise something you described, it was due to the pinion bearing allowing the pinion to drop back when you left off the gas, it was quiet as long as you were accelerating.

93 ragtop

Jim, I used to have a dana 36 with 3.54 gears. They were as quiet as the factory 2.59. IMO 99% of gear noise is due to poor gear setup. Sometimes it will shorten the life of the gears and other times its just a nuisance. Unless they were some form of racing gear, usually designed for dedicated drag cars, there should not be any noise. Its a poor setup, no matter how professional the installer is supposed to be. Also, FWIW I bet you cant even find a racing gear for a dana 36.

tunedport85inject

Hi guys,may be here someone can answer to a question.Since i had my C4 (2004) this car had a bad vibration coming from the tunnel.I always thought about a woobling converter or driveshaft.Vibration becomes highier with high rpms.With trans in D in the 4000 rpms range you can feel something rotating unbalanced then shifting manually in OD it quiets down a bit.May be the driveshaft unbalanced?

JimGnitecki

Thanks for all the replies, guys.

The gear set is a Richmond Gear set, which I bought specifically because it is American-made. The installer is supposed to be very good - he's been doing ring and pinion installations for a lot of years.

On my 2004 Chevy SSR retro pickup, I ran into a similar noise issue but way more noticeable. The "extra"contributors there were:

- went from 3.73 to 4.54 (I know this sounds like a lot of gear for the street but the SSR weighed 4900 lb with driver and fuel, and the tires on the 10" wheels were large enough that even WITH the 4.54 gears, rpm at 60 was still barely over 2000 - certainly no higher than 2200, as I recall

- The only gear set available at the time was Motive Gear, and they were not known for being quiet

- The factory SSR driveshaft was a POS - very lightweight aluminum with a very heavy steel damper with rubber damper that liked to disintegrate in this application. The dealers were doing driveshaft replacements more often than annually in many SSRs, including mine, because of the poor quality of that factory driveshaft

That SSR gear install too was done by a pretty experienced installer, but was noisy all the same.

But, the MMC driveshaft instantly and totally eliminated all noise on the SSR. It was so dramatic that 2 minutes into the first test ride with the new driveshaft, my buddy and I looked at each other and both said simultaneously "Where did the noise go?" I ran the SSR for another 30,000 miles before selling it with zero driveshaft or pinion issues.

Now the change I made on the C4 is bigger percentage-wise: going from 2.73 to 3.54 is close to a 30% change!! So, both the pinion gear and the driveshaft are rotating 30% faster. That makes driveshaft balance and gear set up BOTH much more critical. In addition, the rear axle housing on the SSR was much further from the driver - the rear axle housing in the C4 is right behind the driver.

There's also perception. The C4 factory exhaust is ridiculously quiet, so a noise level that would be imperceptible on a car with a louder exhaust will really manifest in a stock C4.

If I wasn't trying to keep the car as close to factory stock as practical, I'd simply change the exhaust to one with a more normal sporty sound level, and the gear / driveshaft noise would probably be imperceptible. But, I'm really trying to keep the car pretty stock, at least to the casual observer, AND I really do like the quiet - it makes the car an eerily "glide like" experience compared to other sporty cars I've had.

I think I'm going to try the things that WV-ZR1 has suggested, in the order he has suggested. His track record on solutions is darn good.

Jim G

cv67

Maybe have him take a ride as suggested.
The factory gears are a little softer and will always be quieter from what I gather
Run the Motive gear was told the opposite re: Richmond.
Oh well thats hot roddin! Unless its super obnoxious enjoy the increased fun factor.
Tall gears suck!

JimGnitecki

WVZR-1: Have you found that info yet on which Ford MMC driveshafts are good starting points for a new driveshaft for my C4?

Jim G