tap size for rear upper shock bolts

I'm going to attempt to drill out and tap the broken rear upper shock bolts out of my 2000 XJ. I know others have done this, so I'm wondering what size drill to end up with, and then what size tap to use to re-thread the hole.
I've got a dremel to start a divot in the center of the old broken bolt so I can drill it out with a carbide drill bit. Also, what would you recommend as a lubricant while drilling (if I need one)?
I'm also open to any other tips to consider before I begin this fun task!
Thanks for your help and such an awesome web site!

Size? I don't know - when you find out, would you let me know? I've been compiling a chart of bolt/screw sizes for ready reference, and I plan to code it into HTML as well...

Drilling? You probably don't need carbide - I don't suppose you saw the markings on the screw head before you threw it away? Or on the other one? Save your money - I'd be willing to be something like a TiN-coated HSS bit would be just ducky (and more durable!)

Lubrication? Since you're probably working overhead, oils are out. A dab of good-quality chassis grease, renewed at intervals (keep the bit "wet!") should serve.

Dumb question - but make sure you can't access the other side of that nut from inside the vehicle, which will make it FAR easier to work with! Also, if you're careful, you should be able to back the screw out, and not need to tap it when you're done - which is what I always try to do... There's a reason I've got a set of cobalt LH drill bits - they do come in handy from time to time. Cost me a bundle, but I've had them for 15 years, and they've certainly paid for themselves...

5-90

Left handed cobalt bits, eh? Where would a guy find something like that (local hardware?)?

The bolt heads were rusted beyond reading anything on the top of them when I removed them, or attempted to remove them I should say.

I would only be able to access the other end of the broken bolt from the top if I cut a hole in the foloor of the hatch area. I will attempt that ONLY as a last resort. The bolts go into a weld-nut inside the crossmember above the rear axle...

Thanks for the chassis grease idea for lubrication though.

Trout said:

Left handed cobalt bits, eh? Where would a guy find something like that (local hardware?)?

The bolt heads were rusted beyond reading anything on the top of them when I removed them, or attempted to remove them I should say.

I would only be able to access the other end of the broken bolt from the top if I cut a hole in the foloor of the hatch area. I will attempt that ONLY as a last resort. The bolts go into a weld-nut inside the crossmember above the rear axle...

Thanks for the chassis grease idea for lubrication though.

Click to expand...

I snapped 3 of mine off when changing the shocks and ended up just punching out the welded nuts with a punch and BFH, then taping a new nut to the end of a wrench and feeding through the openings near the mounts. Couple fo new bolts for the Shocks and wahlah!.. problem solved

I did what OBXJ had to do, but I used my air chisel and a punch bit. It takes a few seconds each to do away with a bad idea. I bought good quality shocks(OME Nitrochargers) and thru-bolted them with the "taped nut to the wrench" technique. Its a little difficult to access but if you go with good shocks you only have to do this every few years or so.

OBXJ
did you have to remove anything else to get in there to punch out the old nuts and how bad was the job of threading the new nut into that crossmember on the drivers side? I know there's not too much room on my 00' to wiggle around in there. Also, what size and grade nuts and bolts did you use?
I'm thinking I may have to file out the opening on my new bar-pin OME shocks to accomodate a larger bolt. Did you go with a bigger size bolt/not to fill the bigger opening in the crossmember?

Thanks a bunch for the idea..

If you're equipped to do tapping anyway, one alternative might be to punch out the nuts as above, but instead of using another nut, make home-made nuts out of pieces of reasonably thick steel, which you can cut long enough so that there's a tab sticking out that you can hold.

Last time I did this, I drilled and tapped, and it was a real pain, because it's very difficult to get a tap up to where you need it, and you can't use an ordinary tap wrench without continually changing the handle around. I ended up welding a tap to a long L-shaped rod. Now I've forgotten what size I used, but I think it was 5/16 coarse. Once you've drilled, you don't need to match the original threads as long as you have sound metal to tap into. Next time if there is a next time, I'll chisel the old nuts off and do my own.

5/16 or 8mm, that is what i remember anyway

Trout said:

Left handed cobalt bits, eh? Where would a guy find something like that (local hardware?)?

The bolt heads were rusted beyond reading anything on the top of them when I removed them, or attempted to remove them I should say.

I would only be able to access the other end of the broken bolt from the top if I cut a hole in the foloor of the hatch area. I will attempt that ONLY as a last resort. The bolts go into a weld-nut inside the crossmember above the rear axle...

Thanks for the chassis grease idea for lubrication though.

Click to expand...

"Local hardware store?" Fie! You're looking at an MRO shop or something similar... Google Is Your Friend (or does a better job remembering URLs than I do...)

MSC Direct Industrial Supply Co.
J&L Industrial Supply
KBC Tools & Machinery
Small Parts, Inc.

For some oddball stuff, try Wicks Aircraft Supply or Aircraft Spruce & Specialty Co.

And, I sometimes find American Science and Surplus to come in quite handy, when I want to find something really odd...

5-90

xjtrailrider said:

I did what OBXJ had to do, but I used my air chisel and a punch bit. It takes a few seconds each to do away with a bad idea. I bought good quality shocks(OME Nitrochargers) and thru-bolted them with the "taped nut to the wrench" technique. Its a little difficult to access but if you go with good shocks you only have to do this every few years or so.

Click to expand...

+1. It's easy and works great.

I think that's the route I will go as well. Knock the old nuts out and replace with new ones... Next question-- I live in Rust Capital, Michigan, so- can anyone recommend good hardware as far as nuts and bolts to put back in there that wont sieze up again? I will use liberal amounts of anti-sieze on re-assembly as well, but should I use stainless nuts and bolts, or just standard grade (5?)? Any suggeations, and is anybody sure on the size of bolt?
Thanks again for the ideas and solutions!

Trout said:

I think that's the route I will go as well. Knock the old nuts out and replace with new ones... Next question-- I live in Rust Capital, Michigan, so- can anyone recommend good hardware as far as nuts and bolts to put back in there that wont sieze up again? I will use liberal amounts of anti-sieze on re-assembly as well, but should I use stainless nuts and bolts, or just standard grade (5?)? Any suggeations, and is anybody sure on the size of bolt?
Thanks again for the ideas and solutions!

Click to expand...

I think your safest bet here is to assume that they will seize no matter what you do. The stress on these mounts is actually not all that great (which is why they can get away with such a cheesy mount), and easily accommodated by standard grade coarse thread nuts and bolts. I'd get standard 5/16, and if you ever need to do the job again, just shear them and replace them routinely, as one does exhaust parts.

Trout said:

I think that's the route I will go as well. Knock the old nuts out and replace with new ones... Next question-- I live in Rust Capital, Michigan, so- can anyone recommend good hardware as far as nuts and bolts to put back in there that wont sieze up again? I will use liberal amounts of anti-sieze on re-assembly as well, but should I use stainless nuts and bolts, or just standard grade (5?)? Any suggeations, and is anybody sure on the size of bolt?
Thanks again for the ideas and solutions!

Click to expand...

Stainless should work (prefereably 300-series stainless - I think my local carries 304 and 306CRES,) and going undercar, I could see going with most brasses for fasteners torqued to under 50 pound-feet, and bronze for torque under 80 pound-feet or so without any trouble. Brass and bronze is nice because it does not seize against iron or steel!

CRES hex head should be rather easier to find.

5-90

CRES - Corrosion REsistant alloy Steel.

5-90 said:

Stainless should work (prefereably 300-series stainless - I think my local carries 304 and 306CRES,) and going undercar, I could see going with most brasses for fasteners torqued to under 50 pound-feet, and bronze for torque under 80 pound-feet or so without any trouble. Brass and bronze is nice because it does not seize against iron or steel!

CRES hex head should be rather easier to find.

5-90

CRES - Corrosion REsistant alloy Steel.

Click to expand...

Makes sense if you're retapping the original holes, but I think it's overkill if you're using a nut and bolt. As long as you can get a wrench on the nut at the top, just use cheap standard hardware and shear it off when the time comes.

or use anti sieze

EricT said:

or use anti sieze

Click to expand...

Also an option - but remember to reduce installation torque by HALF when using never-seez (most XJ's like rear shock damper nuts/bolts torqued to 44 pound-feet - so 22 pound-feet with never-seez...)

5-90

On my '01, I pulled up the carpet, drilled a hole through the broken bolts and also went through the floor so I could see where they are. I conservatively cut holes, carefully, around where the nuts were. Used a dremel tool w/flexshaft and cut out the factory garbage. Upsized the hardware size to 3/8 and used stainless bolts pointed downward with the necessary flat and lockwashers. Used one nut on the outside to lock the bolt in place, which now acts like a stud. Put on a flat washer to separate the locking nut from the shock, then added the new shock, another flat and lockwasher, and then the last nut to lock the shock down. Sounds like a lot, but is really simple and wasnt hard at all. I got some plain sheetmetal, treated it, cut it to size and put a lip around the edges with a pair of the bodyworkers vice grips. Added seam sealer to the underside of the lip and pressed the "patches' over each of the holes. They are now sealed for good, and with the carpet back down, you cant feel anything there. Like nothing ever happened.

get a letter h drill bit an an 8mm tap . will work perfect to reattach the shocks