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Jack Worstell

1937 Special Hot Differential/Rear Wheels

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Lately we have taken several 30-40 mile drives in our 1937 Special.     It has

 a "Lloyd Young"   overdrive that makes it a real treat to drive.

 

We have noticed after these drives that the differential case and the two rear wheels are hot.

I can lay my hands on them...but just barely.   At first we thought the rear   

brakes were dragging  but we checked this out and it is not the case.

 

Ideas  ?

 

Jack Worstell       jlwmaster@aol.com

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Yes...checked the fluid level   ( and I noted that the way the differential is made and the location of the fill plug....that the capacity

is probably no more than one pint....not very much...I would have thought it would have been more capacity ? )

 

Jack

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I am not sure about a '37, but my '41 has a capacity of 3 1/2 pints. Again, on the later years, the cover is not indexed for position, so perhaps yours was put on with the filler too low?

Keith

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Why don't you take an infrared thermometer and actually shoot the temperature and lets let some others do a comparision. I have never felt my differential after driving my Century, and I don't have an overdrive, but the brake shoes get the rear hubs fairly warm, and the heat spreads out over the wheels pretty well. I have no idea actually how warm it gets but I can check it in the near future. I drove my Century over 700 miles on a recent two day trip, so I am sure that however hot mine gets, it is not a problem. 

 

The differential should hold more fluid than you are estimating. I assume it is full up to the filler cap. I am also assuming the differential has EP rated oil in it. That is what it needs, but I have no idea if another oil would cause a difference in heat that you would be able to tell, non-EP rated oil would typically cause more wear. 

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 According to the Shop Manual the rear differential takes 3 pounds of gear lube. I think that would be about would be  approximately 1.5 quarts.

 

Carl

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Hmmmm     When I say about a pint...I didn't actually measure it.......just  "eyeballed"  the physical size of the differential 

and noted that the drain plug was at the six  o'clock    location  on the back cover.

 

Now I wonder if the back cover should be rotated such that the drain plug would be.say.  at the nine o'clock

position. ?

  I would guess that this might give me   maybe three  pints ?

 

The car and the shop manual are at the shop so checking this out will have to wait until Monday or Tuesday.

 

Thanks for the tips 

 

Jack Worstell

 

 

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Jack, the 1950 manual actually recommends rotating one bolt to obtain a larger capacity. I don't believe more than that is better, though. Might raise the level enough to stress the wheel seals.

 

  Ben 

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Does your 37 have the 4.44 gears? An overdrive slows the engine rpm down but HAS to raise the ring and pinion rpm way faster to achieve that pleasant 60 or 65mph cruising.  speed. Before I went to shallower gears I switched to Torco 85-140 racing gear oil and lowered then temp a bunch. A downer is It WILL find any potential leak spots.

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A friend of mine who was a rear end and transfer case specialist said the general rule of thumb is that the differential lube level should be  at the centerline of the axle shafts.   So I assume that the fill plug on most Buicks might be around the 3 O"Clock position.   The best way to drain the differential lube is to remove the back cover and check out the bottom of the case for any foreign particles before replacing and refilling.   Finally, I have replaced one bolt near the top, but not in line with the ring gear, with a bolt with a small hole drilled through it to allow for venting of the differentail case.

Joe, BCA 33493

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I had the opposite problem with my '41 Limited when I went to change the differential oil last year:

 

 

You'll note that during that project, I revealed myself to be a bit of an idiot by assuming that whomever was in there last put it back together properly. My drain plug was at the top, and it was MUCH too full. Some fellow forum members pointed out the error of my ways and showed me the evidence that was right in front of my stupid face, and I put it back together properly. I'm inclined to agree with Joe that about halfway up is correct--enough to keep the gears submerged at the bottom but not so much that it's running down the axle tubes. 

 

I used SAE 140 GL4 gear oil from O'Rielly's that's called Sta-Lube or Master Lube or something like that and have been pleased with it in both the transmission and rear end. My rear end runs quite cool (it was barely 120 degrees after the oil change and a test drive), although the Limited rear end is considerably larger than the Special. However, I do think that you're running it a little low and that more fluid would be a big improvement. Clock the drain at the 4 o'clock or 8 o'clock positions and see what happens. And be sure to look closely inside for signs of where it SHOULD be. On my car, there were obvious cut-outs to clear the ring gear that I didn't notice at first, as well as a clear line on the back of the differential cover that showed where the oil level had been traditionally (right under the plug, with the plug somewhere around the 8 o'clock position. Extra fluid won't hurt anything as long as it isn't running past the axle seals and contaminating your brakes, and the extra fluid will be a good heat sink to help keep things cooler. 

 

I should also note that I like the straight 140 weight oil rather than an 85-140 simply because we don't drive in the cold. An oil engineer explained that when you have a multi-viscosity oil, it is based on the thinner oil's base stock with additives to make it act like a thicker oil when it gets warm. However, a straight-weight oil IS that thick without the additives. One isn't necessarily better, but I feel more comfortable with oil that's actually the thickness that I want rather than oil that's merely pretending to be that thick. Probably academic, but little peace-of-mind things like this are a big part of maintaining old cars, right? I also agree with mcdarrunt that the overdrive is probably pushing your rear end a little harder than it was designed to do. Not a lot and not a big deal, but more speed will always equal more heat simply because each tooth on the ring gear goes past the pinion more frequently and there's A LOT of friction on hypoid drive teeth.

 

Pull the cover and look around in there and see what you find. It will (hopefully) be obvious. Use good fluid and plenty of it and everything should be fine.

 

PS: Do NOT, under any circumstances, let anyone tell you that you need to take the whole thing apart and look around inside "as long as you're in there." If it's working OK, LEAVE IT ALONE.

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Decades ago when I bought my 90 Dodge diesel pickup (still got it 550,000 miles now) I was pulling a 26 ft travel trailer at 6000 lbs or my 26 ft Haulmark race car trailer at 11,000 lbs.  On my way to Madras dragstrip at the top of a long climb, Mt Hood, pulled into the rest area and checked things over. The rear end housing was too hot to touch. I decided to change to Amsoil synthetic. At that time $25 a gallon. After the races and before leaving to go back over that mountain I changed the lube in the pits. Stopping at the same rest area I checked and found the rearend  to be only warm to the touch,completely comfortable. Completely sold on synthetics for rear axles after that.

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1 hour ago, RiKi5156B said:

Decades ago when I bought my 90 Dodge diesel pickup (still got it 550,000 miles now) I was pulling a 26 ft travel trailer at 6000 lbs or my 26 ft Haulmark race car trailer at 11,000 lbs.  On my way to Madras dragstrip at the top of a long climb, Mt Hood, pulled into the rest area and checked things over. The rear end housing was too hot to touch. I decided to change to Amsoil synthetic. At that time $25 a gallon. After the races and before leaving to go back over that mountain I changed the lube in the pits. Stopping at the same rest area I checked and found the rearend  to be only warm to the touch,completely comfortable. Completely sold on synthetics for rear axles after that.

Agreed for modern vehicles, but the following explains why I don't use synthetic gear oil in older cars.  In 1997 I auditioned retirement by driving my 1936 Pierce-Arrow from Oakland CA to Cleveland OH for the wedding of a good friend's daughter, then on to Superior, WI for the Pierce-Arrow Society annual meet, then home via US 2 through the Dakotas, Montana (including Glacier Park).  I had a telephone conversation with a PhD chemist at Sta-Lube, who assured me that their GL-6 synthetic gear oil would pose no threat to the yellow-metal bushings and thrust washers in my differential.  So I used it.  Eastbound in Wyoming, about 900 miles from home, at a rest area I went to refill a leaking rear shock and found the differential to be as hot as the hinges of hell.  I made my way to a parts store and purchased a drain pan and GL-4 conventional gear oil.  The draining synthetic had the dreaded golden sparkles of disintegrating yellow metal.  Changed the oil again in Des Moines while visiting friends and saw only a minimal trace of the golden sparkles.  Must have caught it in time, because the car has many more thousands of miles with GL-4 and no excessive heat.

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If I recall correctly, my '38 Special differential cover only went on one way - it has a feature to accommodate the ring gear.  Yours might be the same.

 

Jeff

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Much more sulfur/sulfurous compounds in GL5 than in GL4, and *apparently* in GL6 synthetic.  And that stuff is hostile to yellow metals. 

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Afterthought:  My Jeepster owners manual is VERY explicit that although EP gear oil (GL4 and up) must be used in the differential, the transmission and overdrive must have only "straight mineral oil" or GL1.

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I'm going to take this in another direction.  You say your brakes are hot as well.  I would look for dragging brakes first.  If you rear brake hose is failing internally it will limit the brake fluid return to the master cylinder and keep the brakes applied.   The last time I had this problem, I cut the old hose open and the fluid passage had reduced to the size of the tip of a ball point pen.

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Some additional data from the 52 Shop manual and the 53 Product Service Bulletin. It seems the original fill for the rear axle was 3 pints.   In these references they indicate that differential with the numerically lower axle ratios should be filled with 4 pints of lube requiring that the back cover be rotated one hole higher.   Then in 53 early production they came out with a new back cover with the raised section for the ring gear.  The 4 pints will bring the lube to near the bottom of the axle shafts.

Joe, BCA 33493

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