Novice's Question


Jun 23, 2016
I'm trying to get my 68 Mustang on the road. The car has been sitting for 30+ years so I'm going thru the whole car replacing what seems to be worn or ravaged by time. I am a novice at this and also new to Mustangs. I am working on the rear end and have the brakes, axles, seals, etc. out and now am wondering if I should pull out the differential and if so, what should I look for? I have no clue. Thanks for any advise you can give me.
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Founding Member
Aug 13, 2000
League City, Texas
I would do just as your doing, seals and brakes. Also check the front wheel bearings and repack them. Then I would change all the fluids crank it up and let it warm up and check for leaks then drive it around the block and see where your at. If it seems like its doing ok I would drive it down the road a bit. Definitely listen to things as you drive such as a noise from the rear bearings, unless you opt to replace the rear wheel bearings. Also you could get harmonic vibes due to a bad pinion bearing. Also replace the pinion seal. Not sure how likely that would be though. If you do drive it ease into it as it hasn't been driven in a while. Just driving it a bit may give you indications whether the hogs head should be pulled. But definitely change the lube in everything!

If you don't plan on driving it much you may want use DOT 5 brake fluid in the system. DOT 5 does not absorb water (A lot of car collectors use DOT 5 for that reason as the cars sit for a while) as it is silicone based but you must bleed the system slowly. If you bleed it like a system with DOT 3 or 4 you could induce air bubbles that will be hard to get out. If you plan on driving the car regularly (once or twice a week in traffic, to work etc.) I would use DOT 3 or 4


Dec 15, 2004
What to do on a 50 year old car to get it on the road is a long list, but as far as your differential question goes:

My experience is that the rear ends in this generation of Mustang are fairly stout and reliable – especially in stock applications.

If there isn't any leaking and there aren't any issues such clunking, grinding or binding, were it my car, and I was just putting it back on the road, I'd leave it right where it is. That isn't to say that a 50 year old differential wouldn't be improved with all new parts or that there couldn't be an undiagnosed issue waiting to rear its ugly head when you get it on the road, but it is an ugly job and any time you open something up, you invite something to go wrong.

Realistically, if you aren't a skilled rear end technician, and there is something wrong, it's best to take it in to someone who is, because replacement of most components in the pumpkin require special set up and often special tools that aren't readily available at your local auto parts store.

Hope that helps.

Charlie Cheap

Jun 5, 2018
Abilene, Texas
I spent 50 years building cars from the frame up and if I did not see any leaks after cleaning the housing, I drained the axle and replaced the 80-90 with newer fluid, drove it around the block a few times to circulate it, then checked for leaks again. The seals and banjo housing (3rd member) are the places to check. ALWAYS rebuild the brakes on a car that has sat for over a couple of years. I pulled the plugs and shot a little oil in each hole, then spun the engine with the starter. If it turned okay, I cleaned/checked the plugs then installed them. Make sure the oil level is okay with NEW oil before turning over. Replace the oil filter, and check the is a 68, right? Look for any leaks where parts join (heads, intake, exhaust, etc.) and remove the valve covers. If sludge is everywhere and it smells like burned oil, TEAR IT DOWN! Depending on mileage, a good cleaning with new fluids may fix it. Just removing the head may expose a lot about the engine. If no deep top-grove (where the rings top-out) that catches your fingernail when dragging over the grove, you are good-to-go. Some say to run engine cleaner in the oil, but only for a few minutes to remove sludge build-up. I prefer to look inside with the head and pan off. No need to rebuild if things look good, just clean things up, replace fluids, adjust tunable parts to factory specs, and drive it. Sitting is bad for any car/motor, so think about what happens when not driven. Grease, oil, water, trans fluid, brake fluid, fuel, electrical current...does not circulate. Just stop and think. It has been a while but I come from a poor family and have owned many used cars. My Dad and older brother were machinists and understood metal surfaces and wear. They showed me what to do and it worked for me.