Strange Differential Chatter

Discussion in 'Drive Train and Tires: Repairs and Modifications' started by 74Corvette, Nov 27, 2018.

  1. 74Corvette

    74Corvette New Member

    Hi, I have a 74 corvette and I am getting a strange limited slip chattering coming from the driver’s side. What is strange is I don’t get the noise when turning corners. If I go to a parking lot and do figure eights and full donuts at slow speeds no noise and all is good. Clutches seem to slip without issues. Problem is AFTER the diff is warmed up, if I stop a light or similar hold the brake and give throttle, i.e. brake stand, then the driver’s side diff starts to chatter. Car is not moving, tires are not turning, just applying steady throttle, engine RPM steady at 2100 ish. What is also strange is rolling forward light throttle no noise, but rolling in reverse light throttle causes chattering (backing up into the garage). This only seems to happen once the diff gets warm. Using an infrared temp gauge the diff is usually at around 120F max after a 20 min rip on the freeway which seems ok to me. A little background. I have replaced both rear spindles, bearing and seals. Close to .002 endplay when spindles installed. Checking the wheels doing the hands at the 10 and 4 o’clock positions practically no movement is felt. Temp readings on wheel bearings show slightly higher (10-20F) then ambient, no noise etc. so I am pretty sure the wheel bearings are good. Also when I changed the spindles, all half shaft u joints got replaced. No movement or binding in the u joints that I can see/feel. Wheel cambers set as close to stock as I could.

    Any thoughts or ideas would be appreciated. I did change the oil out as much as I could using a fluid hand pump and replaced with royal purple 75W-90 gear oil. Before I go and start adding extra additives I figured I would see if anyone with more experience then me has any ideas what is going on. This doesn’t seem to me to be a standard chatter issue simply fixed with additives.
     
  2. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Add 1 bottle of GM Limited slip additive.
    Drive 50 miles on the highway.
    Check again at slow speeds.
     
  3. 74Corvette

    74Corvette New Member

    Thanks that is what I thought too and I will give that a go, but I just don't understand why or how the diff can chatter while not moving and throttle applied, ie brake stand. This makes me think something else is going on.
     
  4. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Check the Engine and transmission mounts.
    Check the entire exhaust system.
     
  5. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

  6. 74Corvette

    74Corvette New Member

    Ok thanks for the suggestions and links. Going to dust off my inspection scope and see if I can get a look at the gears/carrier before trying the additive. I always like to try to get the opinion of more experienced guys then myself before I just do my bull in a china shop back yard mechanicing.
     
  7. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    They had alot of issues with the 1963-79 C3 Iron Differentials throughout the years.
    Most common is Stub axle wear on both sides of the Diff. The ends on the later 1970s are soft and known to wear bad.
    The Posi unit was not the best.
    Some had snowflake style clutch packs.
    Known to fail break apart.
    Might be looking at a full diff rebuild.
    It's expensive.
    Pretty much the only parts reused are the center main housing and companion driveshaft flange.
    They solved all issues with the C4 Gen Dana 36 and Dana 44 1984-1996.
    Only failed then severe drag race use.
    I used to build the C3 Dana 44s 1980-82 & C4 D44 1985 -1996 for guys on Covette Forum and Digital Corvette.
    Gary GTR1999 is the best with the C3 Iron diffs.
    The Good parts have nearly dried up.
    Looking at $5 k to rebuild Gary's way but it's done right.
    Diagnose and use process of elimination.
     
  8. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    If it needs a rebuild do not wait too long.
    Premium parts for C3 Iron diffs likely around 1 year or so.
     
  9. gtr1999

    gtr1999 Member

    Hi Guys
    Brian covered it a lot. The 74 diff's were not too bad BUT there was not one perfect year for a vette diff from 1963-1982. The 63-4 were Dana's and very weak. The 80-82 I think are junk and won't even take them in, Brian does an excellent job with them though and would be the guy to do them but back to your 74.

    If it's original then the axles must be checked. The typical posi chatter shows up when hot in most cases and usually at a turn either way of the car BUT it can also happen going forward or reverse. 1 Bottle of the current GM additive is not enough, you have to use 2.

    What I would do is check the endplay in the axles, look to see if the axle has hit the housing yet and also check the snubber bushing for wear from a leaking pinion seal. Suck out some of the new oil and add the 2nd bottle of additive and do the figure 8's in the parking lot. Then see if it's still there. If the axles are not hitting the housing and the chatter is gone you are good for awhile. What would be ok axle endplay in an otherwise good diff? up to 040" is "normal" for a stock built diff. I set mine at 005-007" when I build them. Be aware that just changing out the axles will not bring them even close to that spec, the diff would have to be correctly built - not a common shop or vendor build but one where every part is checked. As Brian noted this is time consuming and a Blueprinted Diff good to about 450hp is about $1800 now depending on what is still good. A HP diff for up to 900hp is in the $5k and up range and yes the good parts are getting harder to get. This includes NOS GM use made posi cases, no longer around. I had 20-24 of them and I'm down to 3 and keeping those. The best spiders were Tom's heat treated 30 spline with his 30 spline axles- the real deal ones we used are LONG gone now, I have some stock on them as well but they will go into complete builds. The new spiders are not the same as these and not as good.

    If that doesn't cure the issue you might have weak springs along with the lousy factory setup and the diff should then come out for an inspection. I have a lot of threads with pictures on DC you can look at, I don't know if they are downloaded here or not. I see my work all over the net and have no idea how it got there but it is.

    If you want to go over any questions you can call email me directly at gtrvette1999@gmail.com- just remind me who you are since I get calls and mails daily from around the world.
     
  10. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Less Good Stock You have than I thought Gary.
    C3 Will have to be Low Hp Cruisers soon.
    No choice.
    I disagree with you on the C3 Dana 44s.
    My late bud Bill had a 1981 Corvette with the Aluminum Dana44.
    572 Ci BBC packing over 800 Hp Normal aspirated on pump gas.
    I rode in it many times.
    We were Street Racing at night.
    No Pussy Footing.
    Power was full on.
    Racing Dodge Vipers.
    Vortech Supercharged 5.0 Stroker Mustang that ran 9 seconds 1/4 mile.
    Turbo Porches.
    He only lost to me street racing 1/4 mile with my 1970-1/2 TA.
     
  11. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    C4 Corvette and C7 will be the 1/4 mile battle Vettes.
    C4 Reborn again.
     
  12. 74Corvette

    74Corvette New Member

    Thanks again for everyone's input, I have read horror stories about C3 diffs and the chattering got me concerned as I didn’t think they could chatter in straight lines. When I did the half shaft u-joints I noticed the inner axial had movement but I didn’t measure it. I would guess it would be in the .050-.060” range. When I put her back on blocks for inspection I will check that too. The re-building of the diff is an issue. It probably needs it although other than the chattering thing it sounds and runs perfectly. Where would be a good place to go for a proper re-build? I came across a post on another site (www.corvetteforum.com I think) very detailed outlining a re-build gone horribly wrong. Of course I want to avoid that. I am also concerned because I am starting to get the HP up there and don’t know what the “limit” on stock is. My vette is full car, i.e. full interior, etc and last summer I was running 12.2et’s. Would the “std” diff rebuild be ok or would I have to do the “hp” rebuild? I only ask because with unlimited funds I would do the “hp” build. But 5K to 2k is a big difference. I don’t plan on trying to lower the et’s beyond this. Just got snow last night so it is probably going to be a while before I can see if the extra additive will eliminate the chatter, but I am starting to think a re-build is in order.
     
  13. gtr1999

    gtr1999 Member

    Hi Brian
    No problem with you disagreeing on the 80-82 Dana's, I will refer them all to you. At this point of my life I will stick with the 63-79's and that suits me fine. I know you like them and others do as well, I don't like the pinion design with the square shoulder, same as they used in the 63-4's only smaller. I have seen the 63-4 pinions snap in 1/2, I have one here I use for my seminars. I can't say I have seen that with the 80-82's but again I will never take them in, have you seen any snap? The 63-4 used a crush sleeve, not the shim setup the 80-82's did. Also the 3's and 4's didn't have the shims under the pressed on case bearings.
     
  14. gtr1999

    gtr1999 Member

    The are different levels of diff builds from guys like myself or Brian. We do not build the fast vendor type diff in 8 hours. The super 10 I just finished I put in over 40 hours on. What it would cost you all depends on first what shape your diff is in, next what you plan to use the car for? My son built his 75 as drag car so I had to build a 12 bolt conversion for it. He likes it because he hit the 10's in it but it beat you up driving it 30 minutes. I like my 300hp 72, everyone passes me by and I don't care. I take it out and get away from as many people as I can to just cruise and enjoy the car. The diff I built for it will handle 450hp all day long but it will never see it.

    A common vendor rebuild, bare bones, no axles, is about $800 now add axles and new gears and they are over $1200 and what do you get? New bearings, plain ring gear bolts, no posi tuning, about a base line as there is and they do them in about 8 hours. Many are sold like that but sure wouldn't use one. And that is based on the good vendors using new parts and doing what they say, it doesn't include those that cut corners you can't see and limit what they use in them. I can say that because I have repaired diff's from many of the "experts" out there both large and small you would be very surprised at what I have seen as "rebuilt"

    Read this as an example, it is from almost 8 years ago but not much as changed since then, if anything it's worse.
    https://www.digitalcorvettes.com/forums/showthread.php?t=148397
     
  15. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    Use Gary GTR1999.
    He is the Only Trustworthy with a C3 Iron Diff.
    I remember all those wanta Bee Clowns on Corvette Forum.
    They will Rip You off.
    Sell and build you Junk.
    Crap Sheet.
     
  16. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    The C4 Dana 44 was improved.
    Called actually the Super Dana 44.
    Thicker Pinion shaft.
    1.625" .
    Vs
    1.438 For 1944-1982 Dana Diffs gearsets.

    Is what it is Gary.

    Solid axle best for abusive drag race.
    Guys are too old to do that to a C3 today.

    Most C4 owners are young yet.
    On Facebook C4 groups.
    Why you never see DC C4 actiity.
     
  17. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    I have seen Chevy 12 bolt 8-7/8" Gearsets pinion heads shear clean off.
    Full Drag car.
    Power above 1000 Hp. Nitrous shots 400 Hp.
     
  18. gtr1999

    gtr1999 Member

    That will do it Brian. I have built 12 bolt vette conversions for up to 900hp at the crank but most are in the 600-800 range and so far are still out there. They will probably outlive me!

    Those 63-4 Dana's were a bad design and sheared the pinions with stock hp and some abuse. I still get them in though so they are still some out there. I always replace the posi and R&P with them.
     

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