Rear end fluid
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update - I was just on BG's website. seems there are two 75W-140 gear oils, #752, and #753. the 752 does not have the limited slip additive whereas, the 753 does. so, we've got to ask, what gear oil did they use? I would tend to think that if they referenced any type of application data, they might have chosen the "additive" version. what I don't understand, is BG does offer product #751, which is a 75W-90 synthetic gear oil with additive. seems to me that would have been the more correct product to use.
https://www.bgprod.com/catalog/drive.../#bg-product-1
from what i'm reading, the 75W or 80W-90 is more for regular duty usage, whereas the 75W-140 is more for heavy duty applications. if the OP's fill does include the additive, i'm not sure i'd panic at this point.
https://www.bgprod.com/catalog/drive.../#bg-product-1
from what i'm reading, the 75W or 80W-90 is more for regular duty usage, whereas the 75W-140 is more for heavy duty applications. if the OP's fill does include the additive, i'm not sure i'd panic at this point.
Last edited by Joe C; Apr 25, 2017 at 03:27 PM.
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From: LeClaire Iowa
UPDATE: The rear end started making noise within 20 miles. I did not take back to the shop. I don't trust them anymore. I am changing myself like I should have done. I have sucked out the old fluid. First question: I used a hand pump and got out about. 1 1/4 quart. I then taped a 3/8" clear hose to a shop vac and worked for a hour sucking. I got about 1/8 quart more. I can't seem to suck anymore. I am still 1/8 quart from what a full fill of 1 1/2 quart is. I guess this is the best you can do. The oil I pulled out really smelled bad. It seemed very thick compared to the Mobile 1. Stunk up the whole garage. Will fill with Mobile 1 75w-90 and one 4oz GM additive. Question 2: I see some recommend 2 bottles of additive. What is the correct answer. Thank You, Dan
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UPDATE: The rear end started making noise within 20 miles. I did not take back to the shop. I don't trust them anymore. I am changing myself like I should have done. I have sucked out the old fluid. First question: I used a hand pump and got out about. 1 1/4 quart. I then taped a 3/8" clear hose to a shop vac and worked for a hour sucking. I got about 1/8 quart more. I can't seem to suck anymore. I am still 1/8 quart from what a full fill of 1 1/2 quart is. I guess this is the best you can do. The oil I pulled out really smelled bad. It seemed very thick compared to the Mobile 1. Stunk up the whole garage. Will fill with Mobile 1 75w-90 and one 4oz GM additive. Question 2: I see some recommend 2 bottles of additive. What is the correct answer. Thank You, Dan
Last edited by Joe C; Apr 30, 2017 at 06:11 PM.
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I don't think the C4 model year differs on the service requirements for the differential. this is my personal method for service --
using a (cheap, harbor freight) transfer pump, and slightly warm differential, remove as much fluid as possible. again, using the transfer pump, add approximately 1/2 quart of recommended fluid. add the contents of the GM additive (4 oz bottle) to the remaining 1/2 quart container, and transfer. add an amount from the second quart bottle to the maximum fill level. it should take roughly another 1/2 quart. approximate fill - 1.5 quarts (including the additive). install, secure, and torque the service plug. off the top of my head, i'm thinking 30 ft-lbs on the plug - double check and verify per your FSM -
using a (cheap, harbor freight) transfer pump, and slightly warm differential, remove as much fluid as possible. again, using the transfer pump, add approximately 1/2 quart of recommended fluid. add the contents of the GM additive (4 oz bottle) to the remaining 1/2 quart container, and transfer. add an amount from the second quart bottle to the maximum fill level. it should take roughly another 1/2 quart. approximate fill - 1.5 quarts (including the additive). install, secure, and torque the service plug. off the top of my head, i'm thinking 30 ft-lbs on the plug - double check and verify per your FSM -
Thread Starter
Safety Car
Joined: Mar 2017
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From: LeClaire Iowa
I don't think the C4 model year differs on the service requirements for the differential. this is my personal method for service --
using a (cheap, harbor freight) transfer pump, and slightly warm differential, remove as much fluid as possible. again, using the transfer pump, add approximately 1/2 quart of recommended fluid. add the contents of the GM additive (4 oz bottle) to the remaining 1/2 quart container, and transfer. add an amount from the second quart bottle to the maximum fill level. it should take roughly another 1/2 quart. approximate fill - 1.5 quarts (including the additive). install, secure, and torque the service plug. off the top of my head, i'm thinking 30 ft-lbs on the plug - double check and verify per your FSM -
using a (cheap, harbor freight) transfer pump, and slightly warm differential, remove as much fluid as possible. again, using the transfer pump, add approximately 1/2 quart of recommended fluid. add the contents of the GM additive (4 oz bottle) to the remaining 1/2 quart container, and transfer. add an amount from the second quart bottle to the maximum fill level. it should take roughly another 1/2 quart. approximate fill - 1.5 quarts (including the additive). install, secure, and torque the service plug. off the top of my head, i'm thinking 30 ft-lbs on the plug - double check and verify per your FSM -
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From: Ashland, OH
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FOOLISH - unless maybe they reimbursed you their charges. Did they?
Did you have any conversation with them after you questioned their service here? If NOT I don't understand the "I don't trust them".
I don't believe I've ever seen the Mobil 1 "in the book" - the terminology changes year to year maybe but GL5 is the only spec I recall being consistent.
Last edited by WVZR-1; May 1, 2017 at 08:04 AM.
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do it by the book and the book says 4 oz. (PERIOD!) (new sentence) mobile 1 75W-90 and 4 oz additive and you should be good to go.
Last edited by Joe C; May 1, 2017 at 08:22 AM.
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From: LeClaire Iowa
Going to dealer today to get the additive. I will also take my fill plug and see if they have a parts finch. My plug had the red plastic warning sign but no washer of any sort. Need to find out if it had one. Dan
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there's "no washer' the tag should be floating on the plug and being a NTP when installed there's likely 2 - 3 threads exposed.
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Just another data point.
A couple of years ago I changed the fluid in my '96. I bought some synthetic (I think it was a Pennzoil product) that said for limited slip and did not need the additive. So I tried it that way. After a few miles of driving I found very bad chatter. The chatter was worst when very slow and turning hard (like in my driveway or out of a parking spot).
I sucked out some and added the GM friction modifier additive. It worked. Completely cured the chatter.
As a side note, I used a hand transfer pump and while lying there under the car, the tube came off the pump. I got gear oil all over. What a stinky mess. Hope yours goes smoother.
Good luck.
A couple of years ago I changed the fluid in my '96. I bought some synthetic (I think it was a Pennzoil product) that said for limited slip and did not need the additive. So I tried it that way. After a few miles of driving I found very bad chatter. The chatter was worst when very slow and turning hard (like in my driveway or out of a parking spot).
I sucked out some and added the GM friction modifier additive. It worked. Completely cured the chatter.
As a side note, I used a hand transfer pump and while lying there under the car, the tube came off the pump. I got gear oil all over. What a stinky mess. Hope yours goes smoother.
Good luck.
Last edited by QCVette; May 1, 2017 at 08:55 AM. Reason: spelling
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, no washer - just a warning tag. BTW, how much torque on 2-3 threads exposed? 
. according to the 90 FSM, the drain/fill plug is 30 ft lbs torque, and the 96 FSM, is 9 ft lbs. that's quite a difference. off the top of my head, I don't know what size pipe fittings were used on the C4's. more research need to be done.
Last edited by Joe C; May 2, 2017 at 09:18 AM.
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Well, I guess I got all the old out because it took the full 1 1/2 qt. Took for a short drive to do the figure 8's and all noise in the rear end is gone. Thanks everyone. Only funny thing was the first chevy dealer I went to (largest in area) did not carry the additive. Dan
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Well, I guess I got all the old out because it took the full 1 1/2 qt. Took for a short drive to do the figure 8's and all noise in the rear end is gone. Thanks everyone. Only funny thing was the first chevy dealer I went to (largest in area) did not carry the additive. Dan
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From: Sacramento California
But the 140 is overkill -- you only *need* something that heavy if you are racing, or some other severe service.
Last edited by DGXR; May 1, 2017 at 06:54 PM.