Changing Rear Diff At Track

I carry a spare diff in my trailer.  I am looking to lighten the load and wonder how often they break at the track and is changing one at the track using jackstands something that can be reasonably performed in a race weekend to make the next race.  Example: It breaks Saturday afternoon, can I make the Sunday race working on it with just one or two other people?  Has anyone done it (Not necessarily a professional race team).

 

And yes, I know anything is possible, but will I get 2/3 of the way done, miss the race, then have a car that can't get on the trailer

Murphy's Law states "as soon as you remove your spare diff from the trailer, something will happen to the Diff in your car"

A diff change is a 45 minute job if you know what you're doing.

Thanks Tyler, that's what I was looking for.  I did not know if it was a 1 hour job on the ground, or 5 hour job and lot's of cussing.

only takes like 45 minutes to an hour to do the swap if you know what your doing. ive done it before between sessions. 

It helps if the diff has been R&R'd previous. The sticking point is PPT frame bolts that seize to the collars where it mounts to the front of the diff.

While experienced mechanics or a group of fellow racers can get a diff changed in about 45 minutes, I have also watched a group of racers spend 3+ hours changing one, granted they did not know what they are doing and were a little less mechanically inclined/didn't have all the necessary tools, they did get it done though. 

 

The nice thing with our class is normally if you ask around, someone would be willing to jump right in and give you a hand changing yours out as well!

Phrased another way, if you have to ask, it’s not a 45 minute job. Since you haven’t done it before, use the manual to create a bullet point list of steps ready to follow and keep with the spare.

Good replies.  I do all my own work but do not believe I have ever changed a rear diff.  I am less worried about it being a 45 minute job than 'can I change it and still make the last race on Sunday' kind of thing.  Example: a few weekends ago at Sebring, I got hit in the turn 3 debacle destroying my LF suspension, wheel, fender...  I was able to make the repairs (took me a while), but I was also able to make the Sunday race.

 

One day I want to get back to Road Atlanta and would hate for something to happen and ruin the weekend that I drove 8 hours to get to.

As touched on above, seized bolts can stop you cold. Even without doing a full dry-run for practice, it’s worth removing, cleaning and replacing the long rear PPF bolts one at a time, and likewise the spacer on the rear one of those, putting a bit of anti-seize on that. The two large nuts at the ends of the diff housing arms aren’t usually an issue unless seriously rusted but the small ones adjacent to those may strip or snap off the studs if not removed in years, and are sometimes forgotten when doing a rush job. “Why the F won’t this thing drop?!?”

Steve, once again good info.  I have had the rear diff 'ear' mounting bolts out, but now that I recall, one time I was doing something in the rear end the PPF bolts were not coming out, Maybe I can break them loose on the lift now that I have a bigger impact gun.  You say the pressed in 'nuts' have to come out as well?

...You say the pressed in 'nuts' have to come out as well?

After loosening, leave 3 threads of the long bolts inserted into the nut and smack the head of the bolt from the bottom with a hammer to pop them out. Don't do this on the trans side of the PPF, just the diff.

Actually, I wouldn’t mess with the top one at all, or at least all the way, they aren’t a problem getting out but can be damaged going back (lightly splined). I’m talking about the one at the bottom by the bolt head. It has two flats on it and even gaps for rotating and prying it down. It’s not threaded, just a press fit. That dude extends up through the PPF into the iron spacer so must at least come down 1/4” or so, It can be a real pain even if the big bolts cooperate, and it’s much easier the first time on a lift without tearing it up.

OK, I think I know what you are referring to, I'll take a look next time the car in on the lift, thanks guys.

Actually, I wouldn’t mess with the top one at all, or at least all the way, they aren’t a problem getting out but can be damaged going back (lightly splined). I’m talking about the one at the bottom by the bolt head. It has two flats on it and even gaps for rotating and prying it down. It’s not threaded, just a press fit. That dude extends up through the PPF into the iron spacer so must at least come down 1/4” or so, It can be a real pain even if the big bolts cooperate, and it’s much easier the first time on a lift without tearing it up.

 

I use a ball joint separator fork tool for that insert and it works great. I can get it out much faster than I used to with just a hammer and chisel.

I use a ball joint separator fork tool for that insert and it works great. I can get it out much faster than I used to with just a hammer and chisel.

Channel Lock pliers and turn it like a screw...comes right out no banging!