'71 Mach 1 rear axle removed today for service

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Joined
Sep 12, 2015
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Location
SW Ontario
My Car
1971 Mustang Mach 1, M code, 4 speed.
I've been planning on pulling the rear axle for some time as I have no idea if or when the oil was changed. In July of 2017, I replaced the rear springs and checked the rear brakes while I was at it. I noticed an axle seal was leaking so the rebuild was put on the 'to-do' list. Last year was pretty much a loss due to a hip replacement. Now fit again and the car put to bed for winter, I decided to pull the axle today, a nice sunny day at 50 f, so not too bad to work on the car. As I only have a single car garage, it's a bit tight working on it, but I got the job done. As most of the bolts were removed recently, it was an easy job.

With the axle out and on blocks for now, I noticed two things. 1/ the axle tag was missing. 2/ the sealant around the carrier is BLUE! That tells me the axle has been apart before, but when? I have not yet tried to clean the casing, ran out  of time, but I'll try to see what if any other markings are on the case. The date code on the casting is not very clear, but appears to be 1 B 5. I'll look closer tomorrow. 1 B 5 would still be a match to the build date of the car, Feb 22 1971, so I'm pretty sure it is the original axle, hope so!! 

On Thursday, it will go to the shop. I want all the bearings and seals replaced and checked for ware. There are no unhappy sounds from it, so I think it will all be good.

It is supposed to be a 3.25:1 open dif and I really don't have a concern that it is not as it should be. I have been offered a completely rebuilt Trac-Loc for 300 bucks IF I want it installed. Thoughts?

Geoff.

 
Gotta get rid of that one tire fire!! Way more fun smoking 2 tires!! Lol.

On a side note, I don’t like to see blue rtv on oil seals. I usually run the black which is made for oil.

 
Unless your pinion seal is leaking I would not touch the differential. Change the axle seals and axle bearings. If not making any noise the bearings are good to go. Just wash out good and put new grease in. DO NOT USE SYNTHETIC GREASE. Local shop here that rebuilds rears had a huge pile of brand new gears that he has done under warranty for local dealers. It is due to the synthetic not performing. Usually pinion bearing goes which then takes the gears out. 

If you and not drag racing and do not need both wheels to pull I would stay with the rear you have. A traction lock can get you into trouble if you do not stay up on the wheel. 

If you do go with the traction loc be sure to put a bottle of the friction modifier in with the grease.

 
Gotta get rid of that one tire fire!! Way more fun smoking 2 tires!! Lol.

On a side note, I don’t like to see blue rtv on oil seals. I usually run the black which is made for oil.
 Still on the fence about adding the trac-loc. It's extra money I could use elsewhere. As for the RTV, I agree with you.

Thanks for the reply,

Geoff.

 
Unless your pinion seal is leaking I would not touch the differential. Change the axle seals and axle bearings. If not making any noise the bearings are good to go. Just wash out good and put new grease in. DO NOT USE SYNTHETIC GREASE. Local shop here that rebuilds rears had a huge pile of brand new gears that he has done under warranty for local dealers. It is due to the synthetic not performing. Usually pinion bearing goes which then takes the gears out. 

If you and not drag racing and do not need both wheels to pull I would stay with the rear you have. A traction lock can get you into trouble if you do not stay up on the wheel. 

If you do go with the traction loc be sure to put a bottle of the friction modifier in with the grease.
 Thanks for your opinion David. Synthetic oils or grease in a trans or rear end is a no-no for me too. I don't use it in the motor either.

  As I mentioned, as far as I knew, this was the only major component that has not been serviced...... until I noticed the tag was missing and the blue rtv. So now what do I have? Original or not. Why was the dif removed before? More questions than answers right now. 

The guy who will be doing the axle is a pro, rear ends is all he does and he will recommend what is needed or not needed. I will however consider your suggestion of leaving the center section as is, but my thought was that a 48 year old bearing and seal may be in need of replacing. As it is now obvious that this has been apart before, it may not be needed at all. As for adding the Trac-loc, I'm on the fence with that one to be honest as it's money that could be spent on other stuff I want to do. 

Besides, the rear underside of this car has never been touched or restored. It's in pristine original condition, but could use a good cleaning. I don't intend on "restoring" the floor pan as I want to keep some of that originality. The axle will get repainted though for sure, with markings if there are any to duplicate.

Then there is the springs, Grab-A=Trak 4 1/2 leaf standard eye. These are a higher load rate spring and hold the rear up too high, had to add lowering blocks which I want to get rid of now. First, I'm going to see about getting them re-arched if it can be done at the local spring shop. If not I think I'll buy a pair of Eaton's Boss springs. This bad spring choice is what prompted me to do the rear axle over winter in the first place as it's only one step more to drop the axle out. The Drum brakes will also get a total rebuild as well.

Thanks David,

Geoff.

 
Update: Yesterday I got my axle back from the rebuilder. I did go to the shop and check it out and talk about installing that Trac-Loc. What was found was the pinion bearings were getting worn, so they were replaced with new seals of course. The axle bearings were top quality replacements and in perfect condition, so they were left as is, no need to spend an extra 100 bucks or so. And yes, I did have the Trac-Loc installed, so next spring I'll find out if I like it or not for the driving I do.

For now, it will sit on the garage floor till spring when the rear springs issue addressed, either the re-arched Grab-A-Trak or new Eaton Springs Boss 152lb will be installed as mentioned in another post. The drum brakes will also be totally new and no, I don't want, nor need, discs on the back. My choice I guess.

I'll revisit this when it's all done in Spring.

Thank to all for your comments,

Geoff.

 
That’s great Geoff. In my opinion you will not even notice the trac-loc back there during normal driving conditions. But you will look way cooler when you do a nice Smokey burnout!!! Lol. Keep us posted on what you decide for springs.

 
I am sure your rebuild guy told you to add the friction modifier to the rear? Also I would not use synthetic lube in the rear. Our local re builder here stays busy doing OEM warranty work replacing them due to the synthetic not doing very good. 

At about 125,000 on my F-150 I switched to synthetic in the rear and boom shortly after the pinion bearings went out. It was 2002 and not that old so it was cheaper to buy a complete rear out of crashed truck than to fix the original. I went back to normal grease and no issue and 300,000 + miles.

The only tricky thing to traction loc is be careful in turn if you give too much gas both tires spin and the car will come around in the blink of an eye. 

Since it works off friction not as bad as a Detroit locker but can be a little touchy.

 
Geoff, you will notice the trac loc just cruising around. When you are turning a corner like at an intersection your car will feel like it’s on rails. That’s what mine feels like at least. It used to kinda slide a bit if I had some speed going around a corner, but not now. I thought it was really quite noticeable and in a good way. Plus when taking off from a dead stop it will help to not spin the old peg leg, lol. I’m sure you will really like it. And like turtle said it’s much more fun leaving two black marks instead of one  :D

 
That’s great Geoff. In my opinion you will not even notice the trac-loc back there during normal driving conditions. But you will look way cooler when you do a nice Smokey burnout!!! Lol. Keep us posted on what you decide for springs.
Smokey burnouts, yeah don't really think so with a 3.25 dif. It may lay a bit of rubber though..... a little bit.

 
I am sure your rebuild guy told you to add the friction modifier to the rear? Also I would not use synthetic lube in the rear. Our local re builder here stays busy doing OEM warranty work replacing them due to the synthetic not doing very good. 

At about 125,000 on my F-150 I switched to synthetic in the rear and boom shortly after the pinion bearings went out. It was 2002 and not that old so it was cheaper to buy a complete rear out of crashed truck than to fix the original. I went back to normal grease and no issue and 300,000 + miles.

The only tricky thing to traction loc is be careful in turn if you give too much gas both tires spin and the car will come around in the blink of an eye. 

Since it works off friction not as bad as a Detroit locker but can be a little touchy.
 David, that was the first thing my guy mentioned, no synthetic and use only FORD spec friction modifier from a Ford dealer. I'll take his advice.

 My 72 Mach had a trak-loc, so I do know how they can catch you out.

Thanks for your input,

geoff.

 
Geoff, you will notice the trac loc just cruising around. When you are turning a corner like at an intersection your car will feel like it’s on rails. That’s what mine feels like at least. It used to kinda slide a bit if I had some speed going around a corner, but not now. I thought it was really quite noticeable and in a good way. Plus when taking off from a dead stop it will help to not spin the old peg leg, lol. I’m sure you will really like it. And like turtle said it’s much more fun leaving two black marks instead of one  :D
 John, I guess I'll find out next Spring. If I don't like it or have problems, I can always go back to a one-wheeler, just costs money!

Geoff.

 
Just a quick question; How much oil does the rear dif take? I've looked through my Ford manual(s) and can only find reference to the type, not the quantity. It does however say " with the car level, fill to the bottom of the filler plug hole" That's for all except the WER light duty axle. The axle is on blocks till Spring, but I want to add enough oil and Ford friction modifier so that there is no possibility of moisture getting on the new bearings etc. I bought 2 jugs of Valvoline 80W90, about 1 US Quart each if I did my metric conversion right.

I don't want to overfill it. 

Thanks in advance,

Geoff.

 
Last edited by a moderator:
Put the modifier in first and just fill until it gets to the bottom of the threaded fill hole. Sit the axle housing on to blocks on the spring pads to set the level close enough. Rotate a few time to get the lube in all the pieces. You cannot really overfill it will just run out.
+1.  Yep! What he said.

 
Put the modifier in first and just fill until it gets to the bottom of the threaded fill hole. Sit the axle housing on to blocks on the spring pads to set the level close enough. Rotate a few time to get the lube in all the pieces. You cannot really overfill it will just run out.
 Thanks David. The axle is sitting just as you describe. I think I was wondering about how much is held in the axle tubes as well as the dif.

Geoff.

 
Put the modifier in first and just fill until it gets to the bottom of the threaded fill hole. Sit the axle housing on to blocks on the spring pads to set the level close enough. Rotate a few time to get the lube in all the pieces. You cannot really overfill it will just run out.
+1.  Yep! What he said.
 Thanks,

Geoff.

 
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