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9" Ford oil capacity - confused!
#1
Reading the Shop Manual it indicates that the rear end axle oil capacity is 2.5 qts (5 pints). Last night while I was refilling I pour 3 qts of oil and I am still under the fill plug. I am expecting needing approximately 1/2 a quart more. Granted that the center section is now a Truetrac instead of OEM, but I don't think this should make much of a difference in oil capacity. Also, I know my car when in the lift is 1" higher at the front, but again, I don't expect this too make such a large difference.
This probably explains the problem I had last year. Last year after I refilled it my pinion bearing went. I was expecting to need 2.5 quarts and at around that level I got a spill so I thought it was full. After the bearing went, I checked and I was able to pour one more quart in it, which showed me that I had underfilled it. I was confused because I never had a leak, but ultimately I had made a mistake when refilling it.
This said, could it be that my rear axle has a larger oil capacity. Since I bought my car 4 1/2 years ago I don't know if I have the original axle. I think the center section is original because it had the buck tag that matched the 3.00 gears that came with the car. Thoughts?

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
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#2
I always just fill till it runs out never have gone by amount. BTW do you have traction loc? If so you need to use the friction modifier in the oil. You can get at Ford little bottle.
I switched to synthetic in my F-150 PU and just shortly after my pinion bearing went. This was around 100,000 miles so not lots of miles. I went back to conventional oil and at 285,000 now. I will not use synthetic in engine or rear had bad experience with both.


When a man is in the woods and talks and no women are there is he still wrong??
Tongue
David
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#3
Just as David said fill till it runs out, and I assume you are running a different ratio than before so the ring gear size could allow for more oil. Most of mine have been 3 plus qts.
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#4
I know to fill it up until it runs out. The problem was that I had in my mind the 2.5 quarts and it ran out after that quantity. However, in hindsight, I had a spill instead of an indication of it being filled  Shootself . The lesson learned is to triple check to make sure it is really filled and not spilled. Now I know and I will recheck after letting it seat for couple minutes.

David, I hace a Truetrac which is a type of mechanical lock that doesn't need friction modifiers. Eaton recommends conventional 85w-140 oil.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
  Reply
#5
There is a possibility that has not been raised. Ford did not put fill plugs in all carriers, nor in all housings. It is possible to have a housing and a carrier with no provision to fill the rear axle with oil. When this occurs, the simple solution is to drill and tap the housing for a pipe plug. I know this to be true, because it is the way my car's rear end was done.

When the fill plug is added-there is no guarantee that it is at the right height. (Mine is, because I knew to mark the housing based on a carrier that did have the fill plug)

Different gear ratios result in different ring gear thicknesses High ratio gears are relatively thin and low ratio gears get thicker, all taking up volume, so as to make a specific fill measurement like 2 1/2 quarts inherently unreliable. If the fill plug is on the housing, measure it's location. If it is on the carrier carry on and ignore everything I said.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
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#6
This center section is new from Strange and it has the filler plug.

I understand what everyone is saying but one extra quart is a lot compared to what the manual says. Also, the instructions from Strange indicate 2.5 qts. Different gears should not affect the volume by that much. I just brought this issue up out of curiosity in case there are other axle housing capacities out there. And yes, I will be filling it up until it comes out of the plug. I need to buy another quart.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
  Reply
#7
Tony Muscle,                                                                                                                                 Probably does not apply in your case, but was your rear suspension loaded or unloaded at the time of refill ?                                                                                                                                  When the fill plug is located in the center section ones pinion angle COULD play a roll in refill capacity.                                                                                                                                    Not trying too hard to be an ass, but there are a LOT of variables.                                                   I have always bought three, and usually spill some and can never completely empty a quart container and always. transfer from one container to another, I always add the additive first, guessing that I have 1/2 pint left from 3.5 quarts total.                                                                                     Boilermaster
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#8
I really  need a new computer.                                                                                                       Boilermaster
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#9
(04-02-2019, 06:00 PM)boilermaster Wrote: Tony Muscle,                                                                                                                                 Probably does not apply in your case, but was your rear suspension loaded or unloaded at the time of refill ?                                                                                                                                  When the fill plug is located in the center section ones pinion angle COULD play a roll in refill capacity.                                                                                                                                    Not trying too hard to be an ass, but there are a LOT of variables.                                                   I have always bought three, and usually spill some and can never completely empty a quart container and always. transfer from one container to another, I always add the additive first, guessing that I have 1/2 pint left from 3.5 quarts total.                                                                                     Boilermaster

Valid point. I have a 2 degree shim that angles the differential pinion upwards. Also, I know the front is 1.5" higher than the rear when in the lift. So these factors may be contributing to increasing the "apparent" capacity

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
  Reply
#10
On the no fill plug?? I have never seen a rear that did not have a fill plug.
Maybe there were some models of 9" that had filler plug in the housing and some in the center section. Maybe yours was changed at some point and mixed the two. Would be a pain to have to pull an axle to fill it.


When a man is in the woods and talks and no women are there is he still wrong??
Tongue
David
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