Just bought a '51Merc

If it's not the U-joints, the aft cover pan is relatively easy to remove to have a look in there. The Dana 44 has been one that has lasted for many years so stuff it available for repairs. There are at least two types of pinion seal in the early to mid 50s and I think they are interchangeable in sets but I still find the early type out there as well. The Mercury and F1/F100 pickups all used the Dana 44 in that time frame as well as Ford station wagons & Police cars. They are the 19-spline axle variety in those early years of the Dana 44 use. Hopefully your gears are still good. That set of gears is the most expensive part in there.

If it's a pinion bearing set that's bad, the pinion will move around and make all sorts of funky noises. Randy's Ring & Pinion should have a replacement set for the tall gears like yours. A lot of folks look for the gear sets taller than the 3.91:1 ratio that the overdrive cars used but the ratio has to match the carrier diameter. Yours should already be set up for tall gears.
 
rotorwrench said:
If it's not the U-joints, the aft cover pan is relatively easy to remove to have a look in there. The Dana 44 has been one that has lasted for many years so stuff it available for repairs. There are at least two types of pinion seal in the early to mid 50s and I think they are interchangeable in sets but I still find the early type out there as well. The Mercury and F1/F100 pickups all used the Dana 44 in that time frame as well as Ford station wagons & Police cars. They are the 19-spline axle variety in those early years of the Dana 44 use. Hopefully your gears are still good. That set of gears is the most expensive part in there.

If it's a pinion bearing set that's bad, the pinion will move around and make all sorts of funky noises. Randy's Ring & Pinion should have a replacement set for the tall gears like yours. A lot of folks look for the gear sets taller than the 3.91:1 ratio that the overdrive cars used but the ratio has to match the carrier diameter. Yours should already be set up for tall gears.
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Thought that this is a automatic and has the 3.31:1, why would any change even be considered or contemplated?
 
There's a salvage yard here in Minnesota that specializes in classics and they 2 rear ends for a '51 Mercury and both are 1:4.27
Do you think I should buy one of those?
 
What rotorwrench was stating is the lower ratio rear axles may not except the high ratio ring and pinion gears. At least without modifications.
 
Do you think 4.27 would be insane at 65 mph with the Merc-O-Matic? I'm guessing it's a huge difference from 3.31 .
 
"Taller gears" is a reference that a lot of folks use to describe higher road speed gears for less engine rpm.

There are four different differential carriers. The 3.31:1 and 3.54:1 Merc-O-Matic ratios used the 1M-4205-B carrier case. When the ring gear gets smaller for the low number "higher speed" ratios, the bolt circle gets smaller too. You can use those high speed ratios if your axle has that carrier case. The Merc-O-Matic was designed to start out in intermediate gear then shift to high gear unless you pull the shifter down into low gear. With the stall capability of that big torque converter and decent low end torque of the V8, it makes for a good city and highway combination. The higher speed axle gearing compensated for the inefficiency of that big old torque converter. If you go with anything slower than 3.54:1 your going to get out of the highway range pretty quick. It will be OK for city but the rpms will be too high to keep up with highway speeds.

Lets just hope that your gears are good. You won't want any 4.27:1 ratio. Keep what you have in case you just have a bad axle bearing or something of that nature. All it will cost you to check yours out is Dana 44 pan gasket and the work it takes to do a good shake down on everything to see what's loose in there. It likely could use some new gear oil in there anyway. Hell you might find something rattling around in a brake drum. It could be something simple. Always do the easiest thing first when troubleshooting.
 
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WABOOM said:
Doesn't appear to be the U joint. The pinion seal is casting off oil too. I think its the pinion bearing.
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I agree with checking the drive shaft first though. Put it in neutral and try to move back / forth by hand. Or, hold the brake at idle and switch from drive to reverse at idle...cheap enough diagnostic. It problem still can't be found, put the rear axle up on jack stands. With foot on brake , engine idling, put in drive. Still at idle, foot on brake again, put in reverse. Rear clunk will show up pretty pronounced if problem there.


'Rust belt', hm. I'd suggest that you wouldn't want to be responsible for ruination of a beautiful classic merc , by subjecting It to harsh salty conditions !
Yeah, I can garage it for you in SoCal gratis ! When you vacation here, you can ride in style and not feel guilty about ruining a classic , eh !
On the 'left coast' they don't even allow salt to be sold, just because.
 
Beautiful Merc you have. My 52 has the original aluminum sill plates but they are well used and dented. Have you tried jacking up the rear end and turning a wheel by hand? My 53 parts Merc had some scary noises coming from the rear axle that turned out to be a piece of broken brake hardware grinding against the shoes.
My 52 also had a loud whine on deceleration that turned out to be a loose nut on the front of the diff. Tightened it up and no more noise.
 

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Where are you in Minnesota? I just bought a 49 Ford and I live in Fargo. The car is at our lake home close to Pelican Rapids


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The first car I ever drove was my dad's 51 Merc 4 door. No , I didn't have a drivers license, I was only 15. I will turn 75 on my next birthday- you do the math !
 
I opened up the rear end and there is a lot of play where the axles meet the differential. That's what is making so much noise.
Is that axel bearings?
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The axle shaft bearings allow for a little play due to the type of bearing but not much. If you put it up on jack stands, see if the axles will chuck in and out very much. They are allowed to float but the bearings will have more movement as they wear out. Replace bearings that have too much play or roughness in rotation. The gears look to have some wear but no corrosion pitting or spalling that I can see. The spider gears float a bit in there so there can be some movement on them but not a lot. Shake the pinion side to side and in and out. There should be no shake or chucking movement I with it. The Dana 44 is a reliable unit or it wouldn't have been in service as long as it has.


The rear axle ring & pinion set are set up with around .011" of gear backlash when new but it gets to be more clearance as the gears wear. The Timken bearings should all still have some preload and show no signs of shake or movement. Wear reduces the preload over time. Used bearings can never be set up with as much preload as new ones. I general replace all the Timken tapered rollers & cups when I do an overhaul but I don't do an overhaul unless something is too loose in there.
 
Thank you for your reply. The axles have very little play as I push/pull on the wheels. But they do have play when I rock the wheel at the 6 and 12 o'clock position.
So I guess the axel has "shake" and not "chuck"
 
I just took another really close look at it and the play is where the spider mate in the carrier housing.
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