question on reusing bolts as part of rear caliper rebuild

[amblerman]

Hi Folks,

I am in the process of rebuilding the rear calipers on my 99 s70.
These are the ATE fixed calipers. One piston on each side of caliper.

I split the calipers to thoroughly clean and paint the caliper halves. That is going well.

Each caliper is held together by 4 bolts. I went to a decent hardware store to source 8 new bolts and discovered ATE made a really odd decision back in the day that is causing me grief.

They chose an M7x45 bolt. I really wish they had chosen m8 or m6 as M7 is quite hard to source.
in M8, McMaster-Carr has literally has over 50 choices in head style, material, finish, etc that would be appropriate.

in M7, they have 1 and it's not even an exact replacement as it's fully threaded vs the partially threaded that was in the calipers.

So.. I was thinking about reusing the old bolts.

Anyone have opinions on reusing the old bolts?

The bolts in question are these:

bolt.jpg (73.24 KiB) Viewed 712 times

I have found some older parts diagrams that list a number for those bolts but the sites don't list them for order (and don't show a volvo part number).

Current options for sourcing these that have found.
1) buy 100 for a decent price of $17 + shipping but they are bare steel so they will rust instantly
2) it turns out that modern XC40s apparently use a M7x45 bolt to hold down injectors or the fuel rail but they have a flange head (built in washer) that may not fit properly on my calipers.

I am sure the answers will be to keep looking and buy new bolts. I would have done that instantly if they were an M6 or M8 as they are everywhere.
Does anyone have a favorite source for odd bolt sizes?

Ugh.....

[volvolugnut]

Unless these bolts have a torque then turn spec for tightening, I would likely reuse the old bolts. Also, did you try OEM Volvo bolt sourcing?
Mcmaster-Carr is typically a good source for fasteners of various types. Also look at Fastenal.
volvolugnut

[Sveedy]

^ Agreed. Unless they are torque to yield, clean and reuse. I use a little thread lock as well.

[FireFox31]

Tangential question: What's the required torque for the bolts in question? I'm also curious about the torques for any front caliper bolts. I had mine powder coated but have yet to reassemble them. Thanks.

[454cid]

If the bolts are in good shape and can be cleaned effectively, I'd reuse them without any further thought.

Yes, I've heard that M7 is not common in the US. I have an old motorcycle that uses some M7. Thankfully in the case I needed to replace one, it was a through bolt, and I was able to simply use a high grade 1/4".

[abscate]

Din 931 partial thread m7 45 8.8 bolt…snap, ping , Belmetrics….

https://belmetric.com/m7x1-0-coarse-din ... BR7X45PCLZ

These bolts have to both hold the caliper halves together to seal, and also withstand 2x brake pressure over the pistons, every time you brake you are trying to stretch these with about 500 psi pressure.

Grade 8..8 is 8 MPa tensile strength or about 1200 psi, so 4 of them are safe up to 1000 psi working pressure , factor of 4x below tensile strength.

That’s a pre coffee calculation

Torque? I would use 20 Nm or 15 foot lbs

[abscate]

Oh yes, that internal o ring on the caliper halves was not available last I looked for it. Keep it safe!

No Volvo part number for those bolts. The calipers aren’t shown exploded in VIDA

M7 are used on the intake manifold and a couple of other places but I think those are all flanged

[amblerman]

Oh yes, that internal o ring on the caliper halves was not available last I looked for it. Keep it safe!

No Volvo part number for those bolts. The calipers aren’t shown exploded in VIDA

M7 are used on the intake manifold and a couple of other places but I think those are all flanged

Those orings were tough to find.
I found a source for the orings through a classic Porche site.
I will find that an post it here or in a new thread. When I took my brakes apart, the orings were still quite pliable and matched up to the new ones I got. I might have even found the link to the orings here or maybe on another volvo site.

[amblerman]

Din 931 partial thread m7 45 8.8 bolt…snap, ping , Belmetrics….

https://belmetric.com/m7x1-0-coarse-din ... BR7X45PCLZ

These bolts have to both hold the caliper halves together to seal, and also withstand 2x brake pressure over the pistons, every time you brake you are trying to stretch these with about 500 psi pressure.

Grade 8..8 is 8 MPa tensile strength or about 1200 psi, so 4 of them are safe up to 1000 psi working pressure , factor of 4x below tensile strength.

That’s a pre coffee calculation

Torque? I would use 20 Nm or 15 foot lbs

I watched a video rebuilding similar vintage Porche calipers (also made by ATE I think . very similar design) and the person in the video quoted a final torque of 17 ft lbs. So your pre-coffee calculation was darn close

Thanks for the link. I can't tell you how many sites I visited and failed. (or were now dead sites).

-A

[foggydogg]

Plus three or 4 on reusing what you have, if they're a bit crusty a soak in Evaporust should clean them up without aggression.