So I installed my ring gear tonite. And it just didn't feel right.
Took the ARP bolts out and this is what I found.



The bottom .100" had all the threads ground off. Looks like I lost 3-4 threads. That's why they did not feel right. It seems the ARP bolts are quite a lot longer (.810") vs the GM OEM bolts (.650") so they go past the threaded portion into the OEM GM ring gear. In fact they almost bottom out, but not quite, maybe .035" left in a .845" hole. I can see in the ring gear that the threading stops before the bottom of the hole, but could not get a pic.

So opinions?

1. Run them as is?
2. Grind off the bottom of the existing ARP bolts so they will torque properly?
3. Buy a new set of ARP bolts?
4. Buy a bottom tap and bottom tap the ring gear holes?

I'm kind of leaning toward 3 & 4 and another delay.

 

911 for @GTR1999

 

Use a quality bottom tap with lots of threading oil. BE VERY GENTLE (I hate "digging out" broken taps!)
IF the majority of the bolt threads are good...grind off the damage so you will have at least 5/8" of good thread.
It couldn't hurt to run a die nut on the ARP bolts.

USE A DAB OF COPPER ANTISEIZE ON EACH BOLT THREAD !

 

I had no issues with them on my 71, but I also replace the gears with a set from Tom's. The biggest thing I knew of was making sure to put a slight countersink into the housing for the ARP bolt shoulder. Is your gear set a factory one?

 

What ARP part number bolt do you have? Should be 230-3001.

What ring gear do you have?

Did you check/clean the ring gear holes? As Sigforty asked, did you chamfer the holes?

Is the ring gear fully seated against the flange?

Respectfully disagree with doorgunner. Only use red loctite.

 

Pretty much what I was going to say. Those bolts should be .800" under head, sounds like the wrong ones. I have used 100's if not 1000's of them and they always fit a 10 bolt gear-GM or US. The only time I see this is when building a 12 bolt and you have to measure the depth of each bolt and machine fit them. I always test fit them before installing the gear on the case.

Case holes have to be countersunk if not they would not fully seat- this is not the case.

Gears are hardened, if you chase the holes be careful or you may bind and snap the tap.

Holes and bolts have to be cleaned with Acetone or brake cleaner and only Loctite #271 or 272 used- anything else will be an invitation to rebuild the diff again in the future.

 

My dimension appears to be too long (.810") vs the .800" GTR Gary mentioned. And the part # does not match the one 69L88 mentioned.
But the package says they are for 10/12 bolt.
Yes I have OEM 1972 GM gears. And the last .100" of the hole is not threaded.
Will investigate more when I get home. Can not reach ARP site from work.

 

Leigh, apologies for the MPN. I see I fat-fingered the entry. The correct number is 230-3001 so you are good. Again, sorry for the confusion.

 

OK it appears that I am in a situation where I will need to machine each bolt slightly for length, (.020") and deepen the threads inside the ring gear (.060"), New bolts and a bottoming tap are on the way. How or why this has happened I do not know. But I am sure glad I double-checked before I had an "implosion"

I am unwilling to use the damaged bolts.
One or two of the bolts jammed/bottomed out bad enough that there was an air gap under the shoulder when first torqued. (Al foil test) That's why they came out for inspection.
The posi flange holes were chamfered so that was not it. The ring gears involved (two) are 1972 and 1977 OEM GM ring gears. Neither are fully threaded. Neither is threaded deep enough for these ARP bolts without issues. I screwed them hand tight into the gear and they sit far too "proud" of the surface.

A 2 hour long measurement and spreadsheet analysis yielded several interesting facts.

• The GM bolts are .762" .788 in length but lose .100" for the washer so only .662" .688 is left
• The ARP bolts are between .800 and .812" in length under the head so they are 20% longer than the GM (.120" useable length)
• The ARP RG bolts have a tensile (strength) rating 33% stronger than the GM bolts (200,000 vs 150,000)
• The ARP bolts have 11.5 threads engaged in the RG vs ( 9 for GM) for 27% more thread engaged
• If the GM bolts were used without their.100" washer they would bottom out on the unthreaded section and never torque properly.
• The ARP bolts are long enough that they ground off about 3 threads going into the ring gear (.060-.075")
• I will need to bottom tap the holes (.060-.075") deeper to gain the last 3 threads of engagement
• The ARP bolts are long enough that they average about .015" from the bottom of the drilled hole, but some are as close as .003"
• I feel I need to grind off .020" of the bolt to alleviate the above (1/2 thread) to ensure that they torque tight and do not bottom out

What was that comment someone made about nothing fitting properly? Or only 50% of the time?
This is too much unnecessary work.
They should be engineered correctly in the the correct dimensions and just "bolt-up"
I am very disappointed in ARP..

Can some one measure a posi flange hole depth and tell me if that is my issue? Do your numbers match mine?
Or is it just because I am using ARP bolts on GM gears?
Or is it just ARP?

5/17 edited for accuracy

 

Do you mean ring gear hole depth? I have a new set of US Gear 3.73s and a bunch of OE GMs of varying ratios. I can measure them up tomorrow if that works for you.

 

I have to go back to my file to see what the last diff I built was that I reused the original GM gears and ARP's. As mentioned I never had this issue with 10 bolt gears, 12 bolts yes and I had to figure the thread engagement and machine each bolt to each hole. My son was over tonight building a 12 bolt spool for his vette and that took the ARP's without any machine work. I have some ARP made for Mark Williams that are a little shorter, I got them from Tom years ago and kept them since they are also for safety wiring.

 

The stock bolt in your picture looks to be chamfered too much, possibly done day one to use shallow gears?

Just found I had a bad NOS set of 12 bolt gears, backlash went from 006- 020- 006 so you never know.

Here is the last GM gear set I reused, 1965 gears. New ARP's no problem.

 

Is there anything wrong with using new GM bolts? I know the AFP are better, but why wouldn't stock bolts work in anything but a race car?

 

I was in my shop this morning so I pulled some bins of used GM bolts, "kit" bolts, and ARP.

The ARP & GM bolts are within 010" in length, clearly the GM bolts I have- 100's of them still, do not have a chamfer as yours does. The "kit" bolts I never use. They are fully threaded grade 8's but ARP are so much better then for $35 or so it makes no sense to use kit bolts- at least in a diff I put together.

I looked at some used c3 ring gears and all the holes are fully tapped.

I checked the spool my son is building and the ARP bolts fit fine. As mentioned some of the 12 bolts require them, mainly the 373's, but they all have to be checked.

I think you got 1970's GM parts, meaning the holes were probably shallow from day one and someone chamfered the bolts when assembling the diff. After all they just needed for them to last 12 months and out of warranty. Early 70's work was typically much better then later 70's but they sure weren't hand built custom units.

I would not try to tap the holes, they are hardened and the tap is brittle- there is a very good chance you will roll the tap, bind it and snap it before you cut many it any threads. I would not use that gear set if it was one I was building but that's your call.




New ARP RG bolt

801 underhead length - ok since using caliper

fully tapped GM RG

Bin of new kit rg bolts

box of used GM bolts

Kit-GM-ARP

GM & ARP

GM & ARP within 010

GM RG Bolt- no chamfer

12 bolt spool with the same ARP bolts

Toms RG on new spool

GM bolt 791 underhead

 

OK one mystery solved.
The short and tapered GM bolt was one-of-a-kind. My other 35-40 ring gear bolts were all about .020" longer and full threaded. Somebody's idea of a "fix" I guess. Looked like GM bolt markings anyway. There is at least 1 or two more threads on all the others. And they measure .781"


Second issue of ring gear bolt hole depth:
This pic looks a lot like Gary's but it is mine. Finger tight only.

I have two gearsets, a 1971 GM 3.36 and a 1979 dated GM 3.70. ARP Bolts go in this far on both before the threads stop. The exposed distance is .375" on a .800" bolt. So the threads stop .425" deep inside.

Please measure a bolt and see if yours are the same. But from your pic they look to be similar.


The threads stop about .075-.085" from the bottom of the hole as seen here.


In looking closely at one of Gary's pics, it looks like the very end of the ARP bolt has hit the non-threaded area, just barely and flattened it out. Maybe 1/2 thread worth.

Gary's ARP bolt on right with .010" thread ground off.


My ARP bolt on left has threads ground off .065-.080" deep.

So I am for looking for why I lost .060-.080" !?

So if it is not the bolts, and not the ring gear, then it must be the posi flange. I found two clues.

First Clue:
Some of my ring gear bolts are sunk very deep, where the bolts are "recessed". Some are deeper than the others. Maybe a bad casting or bad machining?

Exhibit a .065" recess


Exhibit b .095" deep recess.


Second Clue:
Also my flange was warped and trued flat at the machine shop. Jeff said it was out by 3-4 thou. I do not think he took off anything like 30 thou but who knows?



Does someone have a posi where they could measure the flange this way? I think mine is thinner. Just not sure by how much.

Mine measured from .310 to .320" at the ten bolt spots.

I am looking for where the .060" went. Maybe here?

 

Good morning,

I mic’d up three cases, two are early “postage stamp” 1st design and one is from my 69 (2nd design).

Postage 1 - Avg .341, Min .337, Max .350

Postage 2 - Avg .344, Min .339, Max .348

69 case Avg .338, Min .329, Max .341

 

Thanks for keeping an eye on me. I was so concerned about the bolts seizing while the O.P. was test-fitting them....I completely forgot about cleaning off the antiseize once the problem was corrected

 

Thanks Kevin
Well I guess that answers that!
Your posi flanges avg 341 and my 10 spots avg 318. So I lost .028 there. It is either the deeply recessed bolts, or the trued flange, or likely a little bit of both.
So my fitment issue is an anomaly. It is not a normal occurance.
Since the flange is only 7% thinner I am going to assume this will not affect the strength.

However I am sure if I had tried to set the lash on the ring gear with a .004+ thou warped flange I would have driven myself in circles. So that was a good catch by my machinist friend Jeff.

When my new ARP ring gear bolts arrive, I guess I will be hand-fitting them and machining them to size. As Gary says he frequently has to do on 12 bolts.
I will attempt tapping the threads a couple threads deeper. I think I will try that on my spare gear, in case their is an issue. We'll see how that goes.

Once you start select fitting or "blue-printing" this stuff, it feels like the rabbit hole just keeps getting deeper and deeper!

I will get through it, thanks to all of your help!

 

I am signing off for a while. I have to go visit my first grandson in NYC. Only 4 weeks old now.

Kevin;
You have been so much help thru this that we have to get together at some point, when these two 500HP BBs are done. And terrorize the natives!
Hey MN is only 1000 miles away. Road Trip!
Leigh

 

OK I figured it out now.
I had an average of .065" ground off the end of the ARP bolts. (1.5 threads)

1. My posi flange is .028" thinner due to the truing operation.
2. The threaded bolt holes in my GM 336 gears are .033" more shallow than the 370 set I also have. (The gears are .150" thinner, so they cut the holes short) That means someone else using ARP bolts on GM 336 gears could run into the same problem.

Between the two items that is the missing .060" and about how many threads ground off the ARP bolts inside the ring gear. Plus they "bound up" and would not torque properly.

My 336 gear set is threaded so shallow that even the .100" shorter GM bolts only have 1 thread left over before bottoming.
The GM bolts only "use" 9 threads that are engaged in the ring gear.
Bottom tapping the holes is slow going, and I am only gaining a little more, maybe 0.5 to 1 thread more.
I will still have to trim the ARP bolts some. They have 12 useable threads but I should be able to use either 10 or 11. I think I'll trim around .040-.060" or 1.0-1.5 threads off.
That's still more threads than the GM bolts, and they are a way stronger material too.

Mostly I just want to make triple sure the threads are the correct length so the ARP bolts Torque down correctly, without binding up.

Progress!
Obstacle conquered!