Drive Flange Bolt Size

[willincalgary]

I have been investigating the drive flange bolts on my Series II. It appears I have two different size bolts on the same rear axle. They are both 3/8" 20TPI but one is 1 3/8" and the other 1 5/8". I ordered replacements from a supplier out west and got new bolts of the diameter and thread but they are 1 3/4" long. How long are the bolts supposed to be? The issue is the new bolts bottom out in the hub before the head/lock washer meets the drive flange. I've measured the depth to the end of the threads to be 1 3/4" to 1 5/8" but there is junk in there making the measurement vary a bit. Anybody know what the original drive flange bolt length was?

[JimCT]

clean out the hole and measure

measure what you have yourself, does not really matter what someone else tells you.

I have been investigating the drive flange bolts on my Series II. It appears I have two different size bolts on the same rear axle. They are both 3/8" 20TPI but one is 1 3/8" and the other 1 5/8". I ordered replacements from a supplier out west and got new bolts of the diameter and thread but they are 1 3/4" long. How long are the bolts supposed to be? The issue is the new bolts bottom out in the hub before the head/lock washer meets the drive flange. I've measured the depth to the end of the threads to be 1 3/4" to 1 5/8" but there is junk in there making the measurement vary a bit. Anybody know what the original drive flange bolt length was?
[ATTACH=CONFIG]9105[/ATTACH]

[willincalgary]

JimCT

Okay. Let me rephrase my question. The new bolts measure to be as long as the threaded portion of the hole. However, the hole in the hub is blind, so it's not likely to be threaded perfectly all the way to the shoulder which I'm measuring (unless Land Rover really got in there with a bottoming tap). Should I go to the trouble of purchasing a bottoming tap to try to get the 1 3/4" bolts to fit, or should I try to source a shorter 3/8" 20TPI bolt to suit the hole as is.

Clear?

[I Leak Oil]

I "think" the earlier drive flanges were thinner than the later ones so if your SII has the original flanges then you may need to find shorter bolts. Or go with newer flanges. Either way clean out the threads as best you can.

Ulitimately Jim is right. You just need to find a size that fits. If you're 1 5/8 bolts work then find some of those. FWIW a general rule of thumb is you want 1 1/2 times thread diameter worth of engagement. EX: for a 1/2" diameter bolt you want 3/4" worth of thread engagement. More doesn't yield much advantage in strenght and less runs the risk of pulling the threads before the bolt would fail.

So measure the drive flange thickness, add 1 1/2 bolt diameter and that's your minimum length.

[JimCT]

cutting

you can always cut off a bit of the thread to keep them from bottoming out

I "think" the earlier drive flanges were thinner than the later ones so if your SII has the original flanges then you may need to find shorter bolts. Or go with newer flanges. Either way clean out the threads as best you can.

Ulitimately Jim is right. You just need to find a size that fits. If you're 1 5/8 bolts work then find some of those. FWIW a general rule of thumb is you want 1 1/2 times thread diameter worth of engagement. EX: for a 1/2" diameter bolt you want 3/4" worth of thread engagement. More doesn't yield much advantage in strenght and less runs the risk of pulling the threads before the bolt would fail.

So measure the drive flange thickness, add 1 1/2 bolt diameter and that's your minimum length.

[ignotus]

Will,
From the parts catalogue; set bolt (3/8" BSF x 1 19/32"), same size listed for the front.


gene

[greenmeanie]

you can always cut off a bit of the thread to keep them from bottoming out

I was going to suggest this but then I looked at the picture and noticed the unthreaded shank length is longer on the new bolt. He would need to measure the depth of the clearance hole of the flange to make sure this does not bottom out before the thread does.

[antichrist]

x2. Are you sure the shoulder of the bolt isn't what's causing it to "bottom" and not the bolt being too long?

[mearstrae]

Cap screws, in general, in these smaller sizes (I believe, under 3/4" dia.) have a standard of 1 1/4" of thread no matter how long they are. For example a 3/8" by 6" cap screw will still only have 1 1/4" of thread. So, you'll need to be sure the shank of the bolt is the proper length, so the threads don't bottom out in the blind hole before it's tight on the flange. Always clean out all holes with a #3 (bottoming) tap before putting in a screw.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[mearstrae]

oops !!!

[SafeAirOne]

Here's how that bolt is described in the SIII Parts Catalogue from 1988:



So it's the same as Gene posted. Not sure if he got his numbers from a catalogue for whichever series had the thinner hubs or not.

[I Leak Oil]

As for cutting the bolts, stick the new one through the drive flange to see if any of the shoulder sticks out past the mounting surface. If not you can cut 1/8" off no problem. If it does then you can't use the bolts without other machining to them or the hub. Easier just to source new bolts I would imagine.

Perhaps someone here can send you some used but in good condition bolts?

[ignotus]

Mark,

His signature indicates a Series 2(59) so I went with the Series 2/2a catalogue from 1964. However after all this time who knows what drive flanges he has............

gene

[I Leak Oil]

1.59375 long per the catalogue? Well by eye I can tell the new ones he bought are .00005" too long! Seriously, where did they come up with that number?

Anyway, like I said earlier, I "think" the earlier flanges were thinner but can anyone confirm or dispell this? Thought I got that from comparing them off a couple of my old parts trucks but that was a long time ago now.

[SafeAirOne]

1.59375 long per the catalogue?

It's the ever-popular 1 19/32 bolt. Must be pretty popular--they can't seem to keep them in stock at any of my local hardware stores.