2004 A4 differential shudder/chattering - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 09-15-2019, 10:46 AM Thread Starter
 
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2004 A4 differential shudder/chattering

Hello. I have a 2004 A4 with 27k miles on it. Everything is stock except a LM2 exhaust, Superchips, and wheels. So this spring I got my oil changed at the nearby Valvoline Instant Oil Change. While I was there, the folks at VIC asked if I wanted to have my rear differential serviced; the fluid likely had never been changed by the first owner, and I didn't have it changed during the two years I've owned the car. I said sure go ahead, but it has an LSD and needs additive for that. They said yes we have that available, so I had them change the diff fluid.

After leaving the place, I immediately noted a little "da-da-da-da-da-da-da" feeling coming from the rear end when turning. Not a sound, just a vibration like you're going over a very minor rumble strip on the highway, but coming from the rear end only. I didn't think a whole lot of it, but was aware of it and was hoping it might go away on its own. And coupled with that is backing down the driveway, which is slightly curved there is an occasional light "banging" sound from the rear end too.

So after a couple months of that and nothing changing, I took the car to my mechanic and asked him to inspect the rear end and do a rear diff service on it. I mentioned to him too that it has an LSD and he said yep he understood about the additive. He inspected and drove the car and said he didn't find anything wrong, but he did the rear diff service as I asked. I got the car back from him, and all seemed well for a day, then back to the same vibration and banging from the rear end.

I've convinced myself after doing research on several GTO forums that both VIC and my mechanic probably put in rear diff fluid that may have had an additive in it, but they did not specifically put in a type F friction modifier. I've since then ordered some Torco RGO and Torco Type F friction modifier, so this upcoming weekend I'll change the stuff out myself.

My question is does driving without the right friction modifier in the rear diff screw up and damage the diff? I've put on a few hundred miles of around town driving, little bit of highway since having the diff serviced the first time at VIC, and I'd hate to see the rear end f'd up because of all of this. It wasn't like the diff was running dry or didn't have any additive in it, just apparently not the right additive.

Thanks.
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post #2 of 4 (permalink) Old 09-16-2019, 08:56 AM
 
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You’re assumption is correct. The shop probably threw whatever diff fluid they had on the shelf in not understanding the late model gto diff. Without Type F friction modifier to make the fluid, in essence “more slippery” you’ll get chattering and such. Over time this can wear our your differential. I would immediately drain it and put the right fluid in.

You are also correct in the fluid you got. Torco RGO 85/140 and half the bottle of the type F friction modifier. Just make sure you dont put too much friction modifier in because you’ll go the opposite direction and not have enough friction for the diff to bite and you’ll have a one wheel wonder. I believe 2 ounces is the number you’re shooting for. Its been a while since the last time ive done mine. I usually go a little under what i need, take it for a test drive and see how she feels. If it chatters on a tight radius turn i add a little more, essentially walking the fluid up to the ratio i need so i dont over shoot and have to drain and start again.

Also you’ll need a pump top screw on deal that goes on the bottle. Theres no way to tip the bottle upsidedown and pour it into the fill hole under the car. Just not enough room. You’ll need a way to pump it in. Something like this: https://www.amazon.com/Plews-55001-L...N97D551A99VXFE

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post #3 of 4 (permalink) Old 09-16-2019, 12:14 PM Thread Starter
 
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Thanks GTO44.
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post #4 of 4 (permalink) Old 09-20-2019, 08:01 PM Thread Starter
 
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Quote:
Originally Posted by GTO44 View Post
You’re assumption is correct. The shop probably threw whatever diff fluid they had on the shelf in not understanding the late model gto diff. Without Type F friction modifier to make the fluid, in essence “more slippery” you’ll get chattering and such. Over time this can wear our your differential. I would immediately drain it and put the right fluid in.

You are also correct in the fluid you got. Torco RGO 85/140 and half the bottle of the type F friction modifier. Just make sure you dont put too much friction modifier in because you’ll go the opposite direction and not have enough friction for the diff to bite and you’ll have a one wheel wonder. I believe 2 ounces is the number you’re shooting for. Its been a while since the last time ive done mine. I usually go a little under what i need, take it for a test drive and see how she feels. If it chatters on a tight radius turn i add a little more, essentially walking the fluid up to the ratio i need so i dont over shoot and have to drain and start again.

Also you’ll need a pump top screw on deal that goes on the bottle. Theres no way to tip the bottle upsidedown and pour it into the fill hole under the car. Just not enough room. You’ll need a way to pump it in. Something like this: https://www.amazon.com/Plews-55001-L...N97D551A99VXFE
I got around to calling Valvoline Instant Oil Change to see what they put in the car for me. They used Valvoline 75W-90 SynPower Synthetic Gear Oil. No additives were put in the differential. The attached product data sheet from Valvoline says it is a gear oil for limited slips, is appropriate for GL-5 applications, and does not require the addition of a friction modifier.

The GTO Owner Manual says to use 80W-140 synthetic gear oil, but does not say anything about a friction modifier.
The GTO Service Manual says to use 75W-140 synthetic gear oil GL-5, but also specifies a friction modifier to be used.

Interesting how the owner manual doesn't mention a friction modifier, but the service manual does. I don't know what my mechanic put it in, I'm going to assume something similar to the Valvoline. My Torco stuff supposedly showed up today, I'll have to check the front porch.
Attached Files
File Type: pdf US_Val_Syn_GO_EN.pdf (416.2 KB, 5 views)
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