Drilling and tapping 1970/71 drive flanges to remove roll pins - 90133220922

[Reubs66]

HI ALL

Please note - I haven't posted seeking scrutiny or speculation, just honestly seeking help as I know it can be done.

I've seen some posts whereby people have drilled and tapped / installed time-serts into 1970/71 drive flanges (part no. 90133220922) to conver the 2 rolled pin holes to M10x1.5 threaded holes to receive CV bolts.

Attached are a couple of photos I've located for reference.

I've spent much time seeking to understand if these flanges are through hardened or case hardened and what is actually required to drill them.

It is obvious a standard HSS drill bit won't work - we briefly tried in a friends mill.

So my questions if anyone is able to provide response from experience;
- Does anyone know what the actual hardness is, and if they are through hardened or case hardened?
- Will an M35 or M42 cobalt (5% cobalt or 8% cobalt) drill bit work?
- Or is a solid carbide drill bit required?
- Will a cobalt tap work?

Sincere thanks!

[nickelplated5s]

Why don't you just use a roll pin punch? Sort of hard to find but that's what they are made for.

[Reubs66]

Originally Posted by nickelplated5s

Why don't you just use a roll pin punch? Sort of hard to find but that's what they are made for.

Thanks for the reply - this isn't to 'remove' the pins - I already have them out.

It is to drill and tap where the pins were to receive m10x1.5 bolts - per the reference photos.

I've reworded my initial post.

Cheers

[jmz]

You could also put nuts on backside of the stub axles .

[Reubs66]

Originally Posted by jmz

You could also put nuts on backside of the stub axles .

Cheers - but still need to be able to drill the holes through - then would need to machine the back side to create a seat for the nuts if going that way.
The flanges don't have through holes to start with - refer photos.

This is why I am asking about the hardness and what people have used to do so per my initial post.

Thanks

[Jeff Higgins]

This begs the question - why? The roll pins have proven to be entirely suitable over decades of use by hundreds of thousands of cars.

[Reubs66]

Originally Posted by Jeff Higgins

This begs the question - why? The roll pins have proven to be entirely suitable over decades of use by hundreds of thousands of cars.

Hi Jeff

I wasn't wanting to go down that rabbit hole to be honest.

There are posts where people have changed to 930cvs - which is exactly what I am doing. There are photos of the exact drilling / tapping / time-sert and that is what I want to do.

The gearbox is a built gearbox with albins gears and modena lsd, now residing in a 1966 porsche 912 with an engine swap.

As I need to do custom axles regardless I am just putting 930 cvs in the car - along with drive stub adapters to suit. Makes it easy as plenty of axle makers use these splines.

[Reubs66]

Can anyone help with ACTUAL information please?

I haven't posted seeking scrutiny or speculation, just honestly seeking help as I know it can be done.

thanks

[Jeff Higgins]

Got it, thank you.

Have you considered, or do you have access to, something like EDM?

Perhaps going to a dedicated, professional machine shop (rather than a friend, or automotive machine shop) could provide answers.

I very much doubt that these would be surface hardened. There would be no reason for that. Assume they are through hardened. Any competent machine shop should be able to conduct a hardness test with the simple hardened ball and arbor press approach. They will know where to go from there.

[Reubs66]

Originally Posted by Jeff Higgins

Got it, thank you.

Have you considered, or do you have access to, something like EDM?

Perhaps going to a dedicated, professional machine shop (rather than a friend, or automotive machine shop) could provide answers.

I very much doubt that these would be surface hardened. There would be no reason for that. Assume they are through hardened. Any competent machine shop should be able to conduct a hardness test with the simple hardened ball and arbor press approach. They will know where to go from there.

Hi Jeff - thank you.

No access to EDM, and unsure of what be available in the part of Australia I reside.

Yeah, my friend is a machinist / fabricator, with multiple lathes and mills, although he does not have a hardness tester. We did the 'file test' which confirmed hardened, and to be sure did a light try with HSS bit on the mill and it didn't scratch the surface.

There is a guy with a CNC locally, who via my friend quoted between $500-$1000 to do the 4 holes... but would need to know what they are working with to begin.

Another friend has the required gear to test surface hardness and can do both vikers and rockwell c testing, but has confirmed that will only confirm surface hardness not through hardness. We will be testing next Friday.

I guess part of my posting on the forum is due to seeing others posting it being done, and hoping to tap into the brains trust.

Cheers,
Reuben

[nickelplated5s]

Reuben, I'm running a 901 box with a 69S motor in a 67 chassis. It's fine. I did chip one gear in my 20's thinking the 7.2 rev limiter was good. I'm better at heel and toe and rev matching now though. There's a thread to stuff a G box in if you want. Listen to Jeff, his is more custom than mine which says a lot.

[stownsen914]

I had a machine shop do this exact mod years ago. I don't know how they did it, unfortunately. He did the work relatively cheaply, nowhere near the price you are being quoted.

In my case, I initially had the 4 bolt, 2 pin flanges mated to 930 CVs on a racecar with some hp. The CVs would puke much of their grease every track weekend. I finally realized most of the grease was leaking near the pins, I assume due to minor flexing of the flanges. I was initially surprised at this, but replacing pins with 10 mm timeserts and bolts solved the grease leakage issue.

[Reubs66]

Originally Posted by stownsen914

I had a machine do this exact mod years ago. I don't know how they did it, unfortunately. He did the work relatively cheaply, nowhere near the price you are being quoted.

In my case, I initially had the 4 bolt, 2 pin flanges mated to 930 CVs on a racecar with some hp. The CVs would puke much of their grease every track weekend. I finally realized most of the grease was leaking near the pins, I assume due to minor flexing of the flanges. I was initially surprised at this, but replacing pins with 10 mm timeserts and bolts solved the grease leakage issue.

Thanks so much mate. Very much appreciate you replying.

Yeah, I saw your post, and think they are your photos I shared.
And exactly why I want to install the other two bolts as well

I'll just need to keep asking around, although seems I'll pay through the teeth to have it done - even though only 4 holes.

[Dan J]

I have done it several times in a drill press with cobalt drills then tapping with the tap that comes with the time sert kit
It's been a few years but I don't recall having any real difficulty

[phunt]

Roll pins are stronger than the bolts. Contact renegade they have adapter and they use roll pins. The put Engines with over 500lbft of torque in 914’s. They make custom axles. Call renegade they know. I have renegade axles in my 66 912 with their adapter with roll pins

[stownsen914]

Roll pins are stronger and do fine resisting rotation. They provide no clamping force of course, which was the problem in my case. I assume for stock, lower horsepower applications the roll pins work well.

[PeteKz]

Check your flanges with a file. If the file easily cuts the flange, it is not hardened. If it tends to skip or not cut, then it's hardened. Then you will know how difficult it will be to drill through. I don't think the flanges are hardened, although the spline part may be.

For sure, the CV joints are hardened.

I will ask the same question Jeff did: Why do it? If you have to do custom work, it might be better to use different CV joints and flanges.

[oldie44]

I have worked on Porsche transmissions for many years and am fairly certain transmission flanges were made using the case hardening process. Case hardening produces a hard surface usually about 0.5- 1.0mm thick however this can vary depending on the process used. I have never done the work you want to do but I have had case hardened 356 mainshafts machined to reduce the diameter from 20mm to 18.5mm where they pass over the differential. I have watched a retired master toolmaker do the work and he had no problems but his cutting tool was best quality, correctly sharpened with correct cutting speed. I think you should be able drill out the roll pin holes and cut threads with very good quaility tools. You might face off the blind holes on the back of the flange with a grinder which may get you through the surface hardening. You might look for a junk flange to practice on.

[PeteKz]

^^ A junk part to practice on is always a good idea.