Torque for brake caliper bolts?

[Colin Lindsay]

Anyone know the correct torque for tightening the bolts that hold both halves of brake calipers together? I've been refurbishing sets of type 12 and 14 and it's so much easier to do with two halves, plus the small seal in the middle is easy to get these days, so I just need to know the proper spec for tightening the halves back together again.

TAF is the usual setting, but it may require RTAF...

[Pete Lewis]

its basically a hard fixing so std torque values should be fine , unless they are marked up as high tensile bolts 

whats the letter on the bolt head   is there a    r, s,  t , or v

but std   5/16unf  18-21   HT add 4 lbft

std 3/8"unf  26-31          HT   add 5 lbft

 

Pete

[Peter Bates]

I am intrigued by this topic and various others about splitting the brake calipers. A piston has seized in the ns caliper of my Vitesse which is why I am looking.

Back in the 70's when I had a 13/60 I had exactly the same problem. The only way to free the pistons was to separate the 2 halves of the calipers. And the O ring wasn't available. Anyway, to cut a long story short, I put the calipers back on the car and bled the brakes and bled the brakes and bled the brakes....However much I bled them I couldn't get rid of a certain spongy feel. The brakes seemed to work ok but just this spongy feel. So I rang Girling Technical Service Department. After a sharp intake of breath the gentleman at the other end said that you weren't supposed to separate the calipers. Under normal circumstances, he said, you wouldn't be able to tighten them up enough. What was probably happening was that when pressing the brake pedal the 2 halves were being forced apart slightly because they weren't tight enough. So I had a trip to the breakers yard to get some replacements.

I am now in the same situation and wouldn't have dreamed of splitting the calipers after that episode, but every thread I read on this and other forums seems to say it is OK.

Confused of Northumberland

[Pete Lewis]

this  suggests the girling bolts to join the halves may be torque to yield which may well be higher than std fixings , all a bit odd its the 0 rings that seal 

not directly the clamping force

I have a torque to yield torquemeter but no calipers to test on 

this idea would mean you cant re use the bolts   and looking at the pressures on the halves when braking i doubt bolts would be taken to their limit 

without a lot of testing or a good jab on the pedal could cause separation 

most caliper problems emanate from the piston seals  or hub endfloat causing pad push back 

not separating the halves 

just my take on this 

pete

 

 

[Colin Lindsay]

12 minutes ago, Peter Bates said:

I am now in the same situation and wouldn't have dreamed of splitting the calipers after that episode, but every thread I read on this and other forums seems to say it is OK.

Confused of Northumberland

I've never used the one I split; it's still in two halves however unless they used special one-use bolts to hold them together I reckon the correct torque could be attained, if we could work out what it is. For the caliper to be forced apart against the bolts, the pistons would need to be exerting terrific force against the pads; and if they separate under normal light braking it would seem they were never properly tightened up in the first place.

It's funny I never saw Pete's reply; must check the bolts. I don't mess about with brakes, they're not something you can even think of bodging, but it's something worth looking into. Wonder how the reconditioners do it?

[Badwolf]

I was always taught. Don't split the calipers. I think (and would need to check back) that when I refurbed mine in 2017 forumites here said ..don't spilt the calipers.  some even said, get new ones, don't even try to unstick a stuck piston. I did unstick the pistons and cleaned everything up. I did get new pistons though, due to the amount of corrosion on the old ones.

[Mathew]

Never split the caliper has been a long standing mantra. I have only changed the piston on one brake caliper and that was fine. If one is really rusted in i would get an exchange unit or new, just for time and skinned knucles saving.

[Pete Lewis]

there is the thought  well some plonker put it together  so some plonker can take it apart

operators on production lines were not scientists just guys doing a job to a process with supplied tooling and a  method sheet 

the two parts are not aero space just strong flat faces and 0 rings

i dont see the complications being complications 

clean yes

tight yes

hidden gremlins ...no 

dont forget in the 60s torque control as part of the quality drive were not recorded or specified for many parts 

in the 50s probably just head nut big ends and head bolt   in the 60s list grows to a dozen

70s the list grows to 100 

all to go with the evolution of process  tooling controls and methods of assembly

I was involved with all this back in the late 60s hey days listing out the fixing sizes and torques for every darn bracket and fixing on a wide range of trucks .   and then get it all implemented on the assy tracks  ...nightmare

Pete

 

[Clive]

I split the calipers for my car, and fitted spacers for vented discs.

I was concerned about teh bolts, as the originals had a big X cast into the head, and I could find zero info on the grade. The supplied bolts with the spacers were 8.8, but have been fine. I do wonder if finding a higher grade bolt may be wise though (had to do that on the prop, my diff uses m8 bolts, and the OE ones seem impossible to find, so bought 12.9 cap heads, had to chop the threads down so the joint between flanges was on the unthreaded part of the shank, but all has been well.)

[Mathew]

40 minutes ago, clive said:

I split the calipers for my car, and fitted spacers for vented discs.

I was concerned about teh bolts, as the originals had a big X cast into the head, and I could find zero info on the grade. The supplied bolts with the spacers were 8.8, but have been fine. I do wonder if finding a higher grade bolt may be wise though (had to do that on the prop, my diff uses m8 bolts, and the OE ones seem impossible to find, so bought 12.9 cap heads, had to chop the threads down so the joint between flanges was on the unthreaded part of the shank, but all has been well.)

10.2 bolts are available. 

It always amazes me in the search for bling on a car some people dont consider the purpose of the bolt. A few years back on a different make's forum they were big into using stainless steal bolts in aluminium heads to hold on manifolds.  Now what could possibly go wrong with that! (I do know).

8.8 are a standard high tensile above the 7.2 you normally would be given, although quite often 8.8 are given out as a standard! Suppose if you ask for HT you get 8.8, so would have to specify 10.2 . Been a while since i needed to buy bolts as they are supplied at work and i have boxes of imperial at home from all the cars.

[RogerH]

2 hours ago, clive said:

I split the calipers for my car, and fitted spacers for vented discs.

I was concerned about teh bolts, as the originals had a big X cast into the head, and I could find zero info on the grade. The supplied bolts with the spacers were 8.8, but have been fine.

I fitted EBC vented discs to my 4A many moons ago.

The splitting of the calipers became interesting.

The supplied bolts began to stretch like` liquorice when I got near their supplied torque figure of 60lbs.ft. 

When I contacted EBC they said 'oh well, use 50lbs.ft see if that works' !!!!

I used the originals that were only just long enough. They have held very well ever since

 

Roger

[GrahamB]

Is 10.2 the correct designation for the bolts?  I read that 8.8 referred to a tensile strength of 80 kg/sq.mm ( I think the units are correct) and a yield point of 80% of tensile.  Similarly 12.9 refers to 120 kg and 90% yield.  If this is correct then 10.2 would indicate a very stretchy bolt.  To quote a previous post rather like liquorice.

[Pete Lewis]

well to me (that dosnt mean much) 8'8  10'9 is metric tensile ratings  

unified being   R S T V  etc. 

?????  pete

 

[Clive]

2 hours ago, Pete Lewis said:

well to me (that dosnt mean much) 8'8  10'9 is metric tensile ratings  

unified being   R S T V  etc. 

?????  pete

 

I get some stuff from Namricks, as 5 mins away from my house, or more importantly, garage.

They list UNF  cap head as grade 12.9. I wonder if they are simplifying the grades? Maybe using metric equivalent description?

[Pete Lewis]

Hi Clive so you remember the rstv codes     im not dreaming ,despite 2 jabs 

pete

[Clive]

I remember UNF were using S as teh code for high tensile. So yes, you are correct. Well, I assume so🙂

[GrahamB]

I worked for 6 months prior to university in the quality control lab at Automotive Products.  Back then every thing was still imperial so the high tensile bolts were all graded R, the weakest, to V the strongest.

R was 45-50 tons/sq inch tensile, but I have not calculated that out in kg/sq mm. 

Whilst checking on R grade bolts, it listed 10.9 grade as the intermediate between 8.8 and 12.9

Edited April 18, 2021 by GrahamB
Mistakenly quoted yield not tensile.

[Colin Lindsay]

I've checked three calipers today and none have any markings on the bolts.

[Mathew]

Thats whats on mine, no idea what the markings mean.

[Rabbit]

I have been reclaiming (?) brake calipers for the past 40 years. I was told NOT to split calipers but as someone had done just that in the past, why could I not do it. No information on the torque was ever found so I kept to 80ft lb and a new rubber seal every time. I NEVER has one leak in all that time. Seals were, and are available from MOSS, these are the correct square section ones and are quite reasonably priced. The only reason I chose 80 ft lb was because that was what the first one I did was set at. Critics will tell me I was doing wrong, well, tell me the right way then. 

[Colin Lindsay]

Whilst waiting for the oven to heat up I've been searching online.

https://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=3226  No torque details, I joined this forum so as to post that question, 13 years after the last reply...

https://mgclife.home.blog/2017/04/25/girling-brake-caliper-rebuild/       This guy advocates 40 on the outer bolts and 70 on the inner (type 16 with four bolts)

MGA site says: torque to a 'reasonable' spec.

https://www.tr-register.co.uk/forums/index.php?/topic/22966-girling-caliper-torque-setting/    TR Register says 50 - 70 depending on the bolt size.

Revington TR are not committing to anything:

Girling do not advise splitting these callipers (not single casting TR3 type). However, when you have split them and realized you shouldn't have, you will need an 'O' ring to put them back together.
We keep 2 types
509044TR3A seal inner to outer calliper body.
RTR4028TR4-6 seal inner to outer calliper body calliper. 16p type calliper
These seals are as close as we can get to the original, however, as Girling offer no information on them we cannot guarantee their fitness for purpose. In other words, use them at your own risk! 

The Lotus Elan forum is divided between splitters and non-splitters; some have never found it necessary and others think that if you split them you may forget to refit the rubber seal.

https://www.lotus7.club/forum/techtalk/triumph-spitfire-front-brake-calipers  This would appear the most specific so far; they recommend a torque setting of 30 lb/ft according to the Caterham / Lotus 7 assembly manual.

Incidentally what's an M O R torque setting?

[GrahamB]

In response to Mathew's photo, ARP is the manufacturer and T is the tensile designation.  I cannot find the definitive specification for T grade but I think it is 55-60 tons/sq inch which equates to 85-93 kg/sq mm.

If I needed to replace this bolt I would try to obtain a 10.9 grade if using the metric convention.