Drilling for Shelby drop

sparx · Nov 21, 2009

I am about ready to drill my 66 for the Shelby drop. The info I have read has stated to drill the final hole with a 17/32" bit.

Also suggested is to drill a pilot hole using a template and work up to the final 17/32''. It has been my understanding that drilling with a succession of bits can and most likely will throw off the center point and therefore place the hole(s) off location.

What do you think, how did you drill yours?
sparx

BarnStang · Nov 21, 2009

Here is a source for the template and drill bits. It would be more accurate to drill the pilot hole and the final size.

DazeCars, Shelby Drop, Klaus Arning drop, upper control arm drop, Falcon, Mustang, Cougar 60-70

sparx · Nov 21, 2009

Yes that is where I got my template, a very nice item BTW.
sparx

BarnStang · Nov 21, 2009

Hmmm, the writeup at Dazecars says to drill in steps...so there ya go. Either way should work ok. You would just need to check the fit with the UCA to make sure you get a good fit. If you have the template then you are pretty assurred of getting it right.

sparx · Nov 21, 2009

I have concerns about drifting off center.
It is said that the cars frames are not all perfect or identical so as long as the upper arm fits and the holes are drilled as accurately as possible there should be no issues.

Just looking for feedback from those that have done this.
sparx

RGS0907 · Nov 21, 2009

sparx said:
I am about ready to drill my 66 for the Shelby drop. The info I have read has stated to drill the final hole with a 17/32" bit.

Also suggested is to drill a pilot hole using a template and work up to the final 17/32''. It has been my understanding that drilling with a succession of bits can and most likely will throw off the center point and therefore place the hole(s) off location.

What do you think, how did you drill yours?
sparx

So what alignment specs are you planning on using?

sparx · Nov 21, 2009

To drill, the Daze template.
sparx

rbohm · Nov 21, 2009

rather than use a succession of larger drill bits, use a unibit for the initial stages of drilling the new holes. that way you only change drill bits twice, once from the initial pilot hole bit, and the second time to the final bit.

JonK · Nov 21, 2009

I drilled in succession and don't have any issues I can tell, the UCA bolts still slide snugly through the holes so they ended up the correct distance apart from center. I used the Daze template and bit. I bought some stronger bits from Fastenal locally as my 'carbide' bits from Lowes lost their bite and dulled quickly. The steel at the mounting point is double layer thick so use a good drill. IIRC I needed a 1/2" drill to mount the 17/32" so have one handy EDIT: I checked the pic on the Daze site and the bit is necked down to fit a 3/8 drill chuck, I needed the 1/2" for the larger bits I got from Fastenal, they went through like butter.
It took me a while to do both sides, a step bit did help to skip a few sizes.
Jon

zookeeper · Nov 21, 2009

Don't use 17/32" bits. There is no reason to use anything other than a 1/2" bit, since the studs that go thru there are 1/2". Any slop in the hole is a potential for the stud to move and wallow out the hole over time. The steel is also very soft, so use a center punch first, followed by a 1/4" bit, then a 1/2" bit. Do it accurately and you'll be rewarded with a snug fit and a nice job.

RGS0907 · Nov 21, 2009

zookeeper said:
Don't use 17/32" bits. There is no reason to use anything other than a 1/2" bit, since the studs that go thru there are 1/2". Any slop in the hole is a potential for the stud to move and wallow out the hole over time. The steel is also very soft, so use a center punch first, followed by a 1/4" bit, then a 1/2" bit. Do it accurately and you'll be rewarded with a snug fit and a nice job.

Is this really true? Why would anyone use a 17/32" then? What are original hole sizes?

zookeeper · Nov 21, 2009

This is very true. Every drop template I have ever seen says to use a 17/32" bit, but my experience as a machinist tells me this is asking for trouble. There's a lot of forces at work in your A-arms, and the constant jarring can move the stud in the hole. If there's no slop to start with, there's that much more support. While the difference is only a bit over .030", if it starts moving, it'll get a bunch bigger in a hurry. I know lots of people that have the 17/32 holes with no problems, but if you're starting from scratch, why not drill them 1/2" for a better fit?

sparx · Nov 21, 2009

Yeah, after I went to get a 17/32'' bit and failed, I measured the bolts, 1/2" is what is needed. WTF?

I will drill them with 1/2" bit.

I am going to go back and get one of the bits with the centering points and drill a tiny pilot hole as a center punch not passing thru.

Also some oil to lube and cool the bit will be required.
sparx

Opentracker · Nov 21, 2009

I've been drilling them to 1/2" for years. The reason to go 17/32" is on the early cars where the shim stack can be off from side side, making the bolts go in angled. The larger holes gives the extra room needed for the bolts when they are at an angle.

When I drill, no matter what template I use, I re-measure each time I go up in drill bit size. I always use a 1/8" first using a metal template, then jump to 1/4" - 3/8" - 7/16" and finally 1/2". Measureing each time. Going from 1/8" right to 1/2" doesn't work all that well for me. You can get the holes off by a good amount if the drilling is not done straight or if the bit is dull.

2+2GT · Nov 21, 2009

Very true- Use a 1/8" for the pilot hole, and break out the 1/2". If you need a few thousandths, get your large round file out. If you measured carefully, it won't take much. Don't forget the piece of plywood between the tower and engine, to protect your parts and drill.

sparx · Nov 21, 2009

More questions.

What is done to the rails on the inside, ground off so nuts can turn on the bolts? I am referring to those "raised lips" on the inside of the towers.

Not sure what "shim stack" are, I know what the alignment shims are.

BTW should I place the shims back in from where I removed them before I started?
Sparx

zookeeper · Nov 21, 2009

The nuts fit right into the lips, no need to do anything. Drill, assemble, smile...

2+2GT · Nov 22, 2009

sparx said:
Not sure what "shim stack" are, I know what the alignment shims are.

BTW should I place the shims back in from where I removed them before I started?

1) More than one shim, and more than one is normal, especially with the
"drop".

2) Yes. Then drive straight to get your alignment done.

sparx · Nov 22, 2009

After I get the entire steering system, suspension and engine and wiring and brake lines and gas tank installed.

zookeeper · Nov 22, 2009

Also I think it's worth mentioning that there are two different templates. The drilling template for the '65-'66 cars is different from the '67-up cars. Make very, very, VERY sure you use the correct one for your car.

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