I have noticed that in both my Haynes manuals and the Pontiac manuals that I have (For both my 85 and for 88 (Brakes and rear subframe info) that they most definitely have the wrong spec for tightening the banjo fittings that hold the hoses to the calipers.
They state between 30 and 35 Lb/Ft......I tried this on one front caliper when I was installing the 88 front calipers on my 85.....I cleanly removed the threads from the caliper! I have been doing some research and believe that 19-22 Lb/ft is a better torque spec...Remember, the fittings are threading into ALUMINUM brake calipers- not steel! I have crossed all of mine out in the manuals but have only pencilled in the 19-22 spec until I can conclusively prove the exact right spec.....
For most automotive work, I don't bother with the torque wrench. Except for things like bolting on a cylinder head, I prefer to rely on the feel... the feel of parts drawing together, making contact, and some squish after that. When you're stripping a thread, you feel that too.
Torquing by feel regularly helps to keep that skill honed and ready to go. Sometimes I'll check a hand-tightened bolt with a torque wrench to see how I did. It also helps for situations where a torque wrench's face (I'm thinking of beam-type torque wrenches) is not readable.
For my next project at work which involves a screwed-together assembly, I am somewhat planning on screwing a bunch together using my hand-feel, measuring the torque needed to tighten the screws a hair further, and then specifying that torque to the factory.
Torque specs for bolts are not necessarily the end-all-be-all. It's a way to approximately obtain some desired result (such as bolt stretch) that can be quantified and reproduced by different people. In the case of a banjo bolt, the desired result is a proper seal. So, if you've tightened the bolt, and it doesn't leak, it's good. I like to check my banjo bolts by having a helper (usually my dad) stand on the brake pedal while I look for leaks at the banjo.
I have to put a torque spec on the assembly drawing of said work project, because I can't just write: "Tighten screws using pmbrunelle's hand feeling." I doubt that would go over well with the factory...
[This message has been edited by pmbrunelle (edited 01-15-2019).]
I have noticed that in both my Haynes manuals and the Pontiac manuals that I have (For both my 85 and for 88 (Brakes and rear subframe info) that they most definitely have the wrong spec for tightening the banjo fittings that hold the hoses to the calipers.
They state between 30 and 35 Lb/Ft......I tried this on one front caliper when I was installing the 88 front calipers on my 85.....I cleanly removed the threads from the caliper! I have been doing some research and believe that 19-22 Lb/ft is a better torque spec...Remember, the fittings are threading into ALUMINUM brake calipers- not steel! I have crossed all of mine out in the manuals but have only pencilled in the 19-22 spec until I can conclusively prove the exact right spec.....
Yeah, the spec is 35 ft. lbs...
I've done this on my 88GT with new copper washers.
OK...the closest I can get with an on-line bolt torque calculator is 26 Lb/ft.......That is with 6061 aluminum as the material being screwed into........Put another way, a 1/2-13 bolt into 6061 goes to 63 lb/ft........To me something as small as 3/8 (10mm) into aluminum should not go up that high...Remember also, you only have a thread depth of 12-13 mm.......
I always did them by hand also....Until I was installing the 88 calipers.....(What got me thinking about being very accurate was the Caliper mounting bolts going into my aluminum adapters...I took them up to 60 vs 74)....
When the right front caliper kept leaking, I checked and had approx' 20 lb/ft on it....So I checked the spec in the book, then checked my other books........"OK...They say 33 lb/ft.....Seems really high for aluminum..." and stripped it right out.....Wasn't even close....
Originally posted by pmbrunelle: I prefer to rely on the feel..
That spec is stop 1/4 turn before it breaks/strips... you will know when you have gone too far!
Being serious... there are different torque specs for dry and lubricated threads. The reduction in torque for lubrication is in the 40% range. The service manual likely is the dry torque, so reduce it by 40% if there is any fluid on it.
Almost all GM specs are for Dry Clean threads unless FSM says otherwise for a given bolt/nut. Example some bolts need thread seal because goes thru the block etc and threads are expose to coolant or oil. Those bolts often have different torque specs because most sealers act as lube to tighten.
Banjo Bolts on OEM "rubber" hose ends... Torque the bolts to 31 ftlb (42 N-m), front or rear for 84-87 Torque the bolts to 33 ftlb (45 N-m), front or rear for 88 From 87 and 88 Fiero FSM
That said You can strip them very easy even w/ one hand and "standard" 3/8" drive ratchet handle (~ 7 to 8 inches long). Easier still when you have Fluid on/in the threads because brake fluid is lube to the brake system. Think like PB Blaster, 3in1, and other light oils in the threads. Maybe slicker then them even.
If you tighten "by feel" etc then check them after driving. Even a weeping leak that you don't feel at the pedal is still a leak and you fail the job and will leak more soon as hydro pressure, vibration and heat works the bolt loose. More so when people use crap SS lines w/ universal ends that allow the end to move very easy too.
Note that Leaking Brake Fluid for problems in/on the calipers can damage most alloy wheels. First will attack most finishes then that is done can/will attack the rim metal. Aluminum w/ Fluid on it can't use normal ways to fight corrosion and Fluid love water etc that will attack the metal.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Alright...I feel like a fool! Hadn't equated "Brake fluid" with "Lubricant".......(Remember, I was a govt worker for 35 years- have to keep up my "Qualifications"....(If I'd been any dumberER I coulda been a politician- but that would have required a lobotomy.......)
Rebuilt calipers won't take 33 ft lbs on the banjo bolts to the calipers. Those caliper housings have been cleaned with strong solvents, sand blasted and painted. Some calipers have been rebuilt many times. I tighten to 20 ft lbs and if I get leakage just use a bit more force until it stops. Once the copper washers are crushed the seal should be there. If the threads strip out then the piston must be removed, the bolt hole drilled and a Helicoil inserted.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Seems like it would be a delicate operation to drill and tap for Helicoil threads without nicking the sealing seat.
Any tricks?
I did this once a while ago and it worked. IIRC, that hole had a clear shot into the cylinder but I'll have to take an old one apart and check again.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
