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I would like your advice on the following. A couple of years ago I had my differencial rebuilt (1966 big block with 3.70 gearing) and filled the case with Red Line synthetic gear lube but did not add the GM additive. I have notice that the rear end makes a whinning noise at low to mid range RPM (1,500 to 3,000) and in speaking with a representative at Baer's in Pa. about this he suggested that I drain the Red Line and replace it with two containers of the 24 ounce GM gear oil along with 2 containers of the 4 ounce GM additive. However, after reading some of the recent posts concerning differential fluid and the positive comments about Red Line synthetic gear oil I am not sure what to do. These appear to be my options: 1) Just add GM additive to the existing Red Line in the case. 2)Drain the Red Line, add the GM additive then refill with Red Line. 3) Drain the Red Line and refill with GM additive and GM gear oil. What should I do? Thanks for your help.
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Re: Differencial Fluid Revisited
John-----
I don't think that the gear lube is related to your "problem", if you have a problem, at all. Basically, the GM additive is a "friction modifier" and its primary purpose is to prevent "chattering" and "clunking" caused by the positraction clutch plates. I don't think that the presence or absence of the additive will have any effect on the "gear whine" which you describe.
Also, the Red Line synthetic should work as well or better than the GM lube in your differential and I don't think that the use of it is, in any way, related to the "gear whine", either. If you wish, you can safely add the GM additive to the Red Line, but, usually, it's not necessary with the synthetic lube.
If you want to eliminate the lube as even a possible source of the whine, I suppose that sucking it out and replacing with the GM-sourced product+additive might be the best bet. I really don't think that it will make any difference, though.In Appreciation of John Hinckley -
Re: Differencial Fluid Revisited
John,
I don't believe that anyone is saying that a change over to synthetic fluid is mandatory, or that there are guaranteed benefits.
Keep in mind that all one million + Corvettes produced came from the factory with 'standard' GM fluids and probably 90% of those went through their complete service life with that original fluid. That normal service life may have been twenty, thirty or fourty years.
It's hard to come to the conclusion that an alternate fluid is better when the original seems to do just fine...........
I agree with Joe on his assessment of your diff., a simple change of fluid is unlikely to help much.
Mike
NCRS Quebec chapterComment
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Re: Differencial Fluid Revisited
I basically agree with Joe. Clutch chatter occurs when cornering and the wheels rotate at slightly different speeds. Chatter is caused by a "stick - slip" friction phenomenon which can manifest as a "growl", "rumble", or "snapping" noise. In severe cases the car can even lurch. The purpose of the friction modifier additive is to allow the differential clutches to slip smoothly at low rotational speed differences.
Hypoid gearsets are noise prone, but it is usually speed and/or torque sensitive. You mention noise in an RPM range. Is this true in all gears or just one gear? The Corvette differential is prone to transmit noise to the cockpit because of its frame mounting (despite rubber isolators) and its proximity to the driver. I've always noticed more diff noise when the rear compartment tool well cover is off. You'd be surprised how much this and the pad/carpet attenuate diff noise.
From you post it sounds like a case of "gear whine". You could go back into the diff and change the pinion depth and/or backlash, but it can be a tough gremlin to subdue. When I bought my '88 MBZ 190E 2.6 I noticed it generated a high pitched gear whine under "float" conditions at highway speeds. For example, if I would lift slightly to maintain speed on a slight downhill freeway section it would start to "sing". Float is when the input torque equals the drag torque which allows the gears to vibrate back and forth through the backlash. I complained and they admitted to a problem in some 190s and replaced the diff with one that had be "tested for noise". No change. I wasn't happy, but I understood there was little more they could do. Dealers neither had the service procedure nor tools to go inside the diff and modify the pinion depth or backlash. About a year later when I was in for some other work they said they were going to swap the diff again with one that had a different tooth count, but essentially the same ratio. Don't really know what the change was, but it solved the problem. I don't know how much they spent fixing the problem, but if it had been on my own dime I would have probably just lived with it or sold the car, probably the latter.
Changing your lubricant is not an expensive or time consuming process, but at this point it I don't think it is the issue. One thing you should do is find a smooth stretch of straight road and drive the car with the tool well cover off. Determine the quality/quantity of the noise as a function of speed and axle load conditions of "drive" "coast" and "float", and come back with the results. I can probably give you a more definitive answer.
DukeComment
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Re: Differencial Fluid Revisited
Although I don't have experience using the Redline Oil products I agree with the previous replies to your question that the whine you are hearing isn't the result of what rear end fluid products you are using.
I've had ring & pinion gears changed in several cars and it is very critical that the correct amount of clearance or backlash be set between these gears. This is a job to be performed by an experienced professional using the proper tools and shims. Depending on how tight or loose the backlash is set will generally control the amount of whine you will hear. In addition, when used gears are employed it is very important to duplicate the clearances that existed prior to removing the gears since a wear pattern has occurred and changing the setup will cause the gears to generate noise.
Another factor generating the whine could be a bad carrier side bearing or pinion bearing, but if new bearings were installed during the rebuild they should not be a factor.
Good luck.Comment
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Re: Differencial Fluid Revisited
new ringear/pinion combo should be broken in under no load. we always put the rear end up on jackstands and ran the gears at at speed with no load for 15/20 mins. this will mesh the gears without generating a lot of heat and this lets the gear lube do it job without breaking down. also over torquing the pinion crush will cause a bearing howl. some gear makes are more prone to make noise than others. it may be the finish on the machined surface, because some gears are cut in 7 steps and some gears are cut in 3 steps and the 3 step cut gears seem to be noisier
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Re: Differencial Fluid Revisited
was the new gear a GM gear or a richmond one. I have been told that the richmond gears bmake more noise than the GM gears, this is why i replaced mine with a NOS one that was expensive , but makes no noise at any speedComment
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