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At the shop we use a 5 gallon drum pump with a piece of either 5/16th or 3/8th tubing hose clamped into the end and bent into a hook shape for diff fluid.
Advance Auto has fluid pumps cheap,$12. I used to remove and put new fluid in,but could only replace about 2.7 pints out of 3 pints that it holds,used Mobile 1LS fluid no need for GM additive.This was on my 94 base with Dana 36.Pump can also be used to suck out tranny fluid for partial fluid change and refill prior to doing a filter change for a more complete fluid change before dropping pan,suck it out,refill run awhile then filter change.
Last edited by A Peter C4; 10-04-2016 at 08:52 PM.
I change mine every 30,000 miles. The C4 differential capacity is small (1.5qt), it gets worked hard sometimes and there's a lot of shearing forces in the differential gears. So I used synthetic 75w90, I know the synthetic will perform great over the long-term. No leaks, no noises, all good.
those cheap, chinese, harbor freight transfer pumps work great and they're less than $6 (20% off and a free flashlight ). so cheap, they're damn near disposable. the same pumps are sold at advance auto for around $15. I always keep a couple around the shop - just in case. BTW, I service my differential with the rear up on ramps. I try to service it about every 36-50K miles, and my fluid of choice - castrol, 80W-90, limited slip, plus 4oz. GM additive -
Just want to bump this and say thanks! Just got done changing the rear diff fluid on my '84. No clue when the last time it was changed (I've only had it for about 1k miles), but at 120k on the odo I figured now was a good a time as any. Yup, that was some dirty oil that came out. Filled with Royal Purple 75W-90 til it dribbled out the hole and will test drive this weekend. Anything special to do driving-wise right after a drain/fill of the fluid to prevent any damage? Or just go easy the first couple miles and to be sure the oil has worked its way back in all the nooks and crannies?
Thanks,
Reed
I have read the bottom, center, diff bolt doubles as the drain. PO plugged mine with silicone, so I can't test. Had to pump it out with a mityvac.
On my 96 I originally thought so...but no that's just an old tale.
You could, I guess drill it out and use it as an drain...but there are kits that install a pipe plug...or just use a pump to pump out the old stuff, but you will never get all of it.
I installed a 1/8th inch allen head pipe plug in the lowest point in the differential, and change out the oil on a regular basis.
To answer the original question, the owner's manual says to replace the differential lube every 100K miles.
Sounds right. I replaced mine when I bought it at 56K miles. It'll be good until 150,000 miles.
After filling with fresh synthetic lube, just drive it. The oil will have run into "all the nooks and crannies" by the time you drop the car down off the jackstands. Even it it didn't, there is plenty of old, residual oil left on all the internal components. It's not like you can drain it dry......
If the car is used for street or occasional "spirited" driving, then something like every 50K miles should be OK.
As mentioned, it will have to be pumped out (get a cheap fluid pump from Harbor Freight) and the new oil will need to be pumped back in. Some parts stores sell gear oil with a pump already in the bottle.
Use a good grade of 80W-90 GL5 gear oil and a couple bottles of the GM posi additive. Some people like brands like Royal Purple or Amsoil, but for the most part, there is not need for anything special. I would not use a synthetic in the diff.
Originally Posted by Joe C
those cheap, chinese, harbor freight transfer pumps work great and they're less than $6 (20% off and a free flashlight ). so cheap, they're damn near disposable. the same pumps are sold at advance auto for around $15. I always keep a couple around the shop - just in case. BTW, I service my differential with the rear up on ramps. I try to service it about every 36-50K miles, and my fluid of choice - castrol, 80W-90, limited slip, plus 4oz. GM additive -
You'll never get that pipe easily into the bottom of the diff casing. I use a large oil syringe, and a length of 10mm silicon tubing. I mark the tubing so I know when its in.
Considering just boring a hole, letting the oil drain out taking any swarf with it, and tapping it with a gas thread and fitting a plug.
10-03-2016, 08:04 PM
). so cheap, they're damn near disposable. the same pumps are sold at advance auto for around $15. I always keep a couple around the shop - just in case. BTW, I service my differential with the rear up on ramps. I try to service it about every 36-50K miles, and my fluid of choice - castrol, 80W-90, limited slip, plus 4oz. GM additive - 
