IRS Differntial War

[Tree]

Today I have been trying to get the rear differential for an modern IRS in with my helper. Good grief Charlie Brown!!! I kid you not, I am bleeding from 6 different places after this battle. Looks like I lost a fight and I am not sure I did not.

I never seem to learn as I just kept hitting my head on the underside of the frame. Maybe each subsequent shot to the head just made it tougher to remember, not sure. The most memorable experience would be when I dropped the dif on my face. Real smooth like. Don't worry, I have never made a cent off my looks and I was not expecting to start anytime soon.

Eventually we got it up there but then had a heck of a time getting everything lined up. I currently have the two front bolts in and the rear passenger side bolt in. The rear driver side just does not seem to line up and I am not sure what I can possibly do with three bolts in. I think the mount may just be an 8th inch off or so. Not sure what to do at this point. Really don't want to bring the differential back down as I had such a hard time getting it up there to begin with.

Where the bolt goes into the differential is threaded. For now, I have another bolt, which is slightly narrower threaded in. The narrower bolt fit okay with the 1/8th inch misaligned gap and did thread in, however, it is not the right size bolt and it slightly undersized.

What do you guys think? I know I read that others found it to be a tight fit as well and EdwardB used the tapered bolts. I am worried that the mounts are about 1/8th inch too close together and no maneuvering is going to get all four holes aligned. I did try losing the three bolts that were in to get any play I could. No mater how I seem to arrange it, I can't seem to get both rear bolts in at the same time.

Should I got back to war or use the smaller bolt I have in there now and add on a good amount of Locktight. The narrower bolt is snug and does need to be screwed in and out in case that matters.

[JimLev]

I had the same problem. I pulled the bushings out and then used my bench grinder to shave one side of the bushing OD down so they were effectively eccentric. This allowed me to set the spacing so I could get the bolts it.

[edwardb]

Get the two rear threaded bolts started first. That means taking out the front ones for the moment. Put something undersize in the front that holds it up but still allows it to move. That gives you maximum wiggle to get the rear threaded ones started. Once they're started, go in far enough for them to be solid but not tight. Then work on the two front unthreaded ones. I've had great luck with the tapered bolts as you mentioned. For my #8674 build, I too was convinced the mounts were off 1/8-inch or more. Wrestled with it for several hours and no luck. Called it a day and came back the next day with the tapered bolts and I was done in several minutes. Used them from the start on the Coupe build and had the diff in and bolted up in no time. After wrestling into place of course. Others have used different methods. But this has worked for me and I know several others. I'd try it before cutting anything.

https://oi867.photobucket.com/albums/ab234/edwardb123/Factory%20Five%2020th%20Anniversary%20Mark%204%20R oadster/Independent%20Rear%20Suspension/th_IMG_3351_zpsrfmo05qr.jpg (https://s867.photobucket.com/user/edwardb123/media/Factory%20Five%2020th%20Anniversary%20Mark%204%20R oadster/Independent%20Rear%20Suspension/IMG_3351_zpsrfmo05qr.jpg.html)

[JimLev]

I spent hours trying to get the diff bolts in. After a few minutes turning the 2 bushings down the bolts slid right in.
Either way works, grinding a poly bushing was quicker than doing the bolts.

[Tree]

Went back to it today and we were able to get the bolt in. I did end up grinding down and old bolt to tapper. That seemed to give me a tiny bit of movement but that was what I needed to get the real bolt threading in. It sure is tight and over the recommended torque but that was what it took to get the bolt all the way in. I am confident that the mounts are a small bit too narrow which puts a lot of stress on those two rear bolts. However, I think the bushings will handle that force and everything should be good now that it is in there.

I hope to put the rest of the rear together soon. I think I read a recommendation to grease all the fittings before installing the arms but I don't actually have a grease gun, so I guess I will run out and buy one. Any recommendations?

[Dave Tabor]

The IRS install was the hardest part of my build.

I used 3/8" socket extensions- like 12" long ones- a pair- as pins/levers to pull the thing into alignment- those and ratchet-strap.

Dave
GenIII Coupe #17

[CraigS]

Geez, I would have expected FFR would have fixed this by now. It's been what 3 years?

[JohnK]

I feel a little guilty for saying this. I had read all the reports about how hard this was and was prepared for the worst when installing my IRS. I had made the tapered pins like Edwardb showed. I had invited 4-5 friends over. We literally had it installed in like 2 minutes without a single scratch to the frame. Never even needed the tapered pins. Having 2-3 guys hold it in place and wiggle it around while another person is starting the bolts made it super-easy. As others have said, if you start the rear bolts first, then get the front bolts through the bushings, then come back and tighten the rears, it actually goes in easily. Then again, I've come across so many frame misalignment issues on my build so far that I'm not discounting the possibility that I just got lucky and my frame mounting points for the IRS were straight while others' are off. I guess my main takeaway on this task is... the more bodies you have on hand the easier it is.

[Tree]

Yeah, it was doable for me but it sure was not easy. I am sure more guys would have helped get it up there at a minimum. There probably is a little variation from one frame to another due to heat warping while welding, however, it seems like everyone is able to make it work eventually. I am happy with it now that everything is up there. I have my rear suspension and brakes in now too. Took a little doing to get everything together there as well. A couple things to note there. I needed to bend most of the mounting tabs for more clearance to get parts together. I would recommend just bending each of the tabs before you start. I think they pretty much all needed it on my build. On the brakes, you may want to compress the caliper piston before putting in the pads. One of my rear calipers I could not get over the rotor. I ended up needing to take it all apart and use a c clamp to compress the caliper piston to gen enough space between the pads to slide the caliper over the rotor.