How much Rear Diff Fluid?

[TboneMan]

I just ordered a Mag Hytec rear diff cover. How much fluid will be needed to fill it? I am planning on using Amsoil . I'd be interested in opinions on whether I should use 75W-90 or 85-W140. I do mostly highway driving year round and tow 6500# TT several time a summer.



Upstate NY temps range from -10 in the winter to upper 80 low 90's during towing season.

 

[Oil Ape]

We're running the Amsoil Series 2000 75w-140 and it can get down to -40 in Wyoming. It has a bit better protection for towing heavy and/or towing hot. If you weren't towing much at all the 75w-90 wouldn't be a bad choice. The 75w-140 is also a bit less likely to leak around the rear seals and honestly doesn't change our gas mileage much at all. At -40 F. All of your fluids are getting a bit stiff and peanut-buttery but to date no problems... We just liked the added protection...



I know a lot of the folks here recommend the 75w-140. I hope they chime in with their $ . 02 as well...

 

[JJW_ND]

75W90 does just fine for heavy pulling!

I have had great luck with the 75W90 in my 96 5sp. Tested every 40 - 50K. Pulled many many heavy (30K+) and long (80'+) loads. Rear tire wear is a good indicator and I ate rear tires.



I had a rear seal leak at 19K miles. Changed to Series 2000 75W90 shortly their after. Have a LSD and it is as tight as the day it was new. I have pulled in lots of summer heat.



Not sure much is gain with the 140WT fluid over a high quality full synthetic 75W90. Both should be changed ever 50K or sooner. My change interval is based on actual oil analysis. Wear metals have been almost none existent after the first change.



If not pulling over 20K trailers AND living in the deep south, 75W90 will provide all the protection needed.



I have 215K on my truck and it does get cold here!



jjw

 

[M Evan]

Did you guy use this limited slip additive with amsoil ? Amsoil say you don't need to, but just curious, if you use that anyway.

M

 

[BV]

How much rear diff fluid

I put in just under 5 quarts of Royal Purple 85/140w and it claims to have the limited slip additive in it. Just put it in 2 nights ago and haven't driven it yet to tell if there is enough additive or 2 much.

 

[Riflesmith]

TboneMan,

I was told by the Mag-Hytec people that a Dana 80 diff. holds 8 quarts with their cover installed. The Mag-Hytec cover is on my list of must-haves as well.

 

[JJW_ND]

I have always added two bottles of Mopar LSD additive in my 96 5sp. This last change I only added on bottle. No chatter yet.



I also drive a 2001 6sp for work. We changed the rear diff on that and added the two bottles. It seemed like to much additive as it is a much more "open" diff then my 96 is.



I read once on here that the clutch pacs on later truck were changed (to many chatter complaints) to loosen up the LSD. The older 94 - 97 trucks seem to have much tighter LSDs. Rarely if ever a complaint. Lots more complaints on LSD not working on new trucks.



I would use LSD additive only as needed in newer trucks.



jjw

ND