Torque of steel brake lines

[Steve L.]

The AIM doesn't seem to show the torque of the bundy lines into the brass blocks and calipers. The rubber lines are shown as 110 lbs-in.

Anyone know what the torque is for the steel lines. I've always torqued them until they feel tight but I'd like to know what they are supposed to be.

[Duke W.]

Re: Torque of steel brake lines

I don't have a torque spec, but I recommend initially tightening them, then backing off and repeating at least two times so the flare conforms to the fitting to ensure a good seal, and ALWAYS use a tubing wrench to avoid rounding off the hex if an open end wrench is used.

Duke

[Stuart F.]

Re: Torque of steel brake lines

I agree on the use of tubing wrenches. I love them, but on old lines sometimes you need to use a vice grips to break them loose (after your tubing wrench rounds off the flats that is). And I hate that.

Stu Fox

[John H.]

Re: Torque of steel brake lines

The AIM doesn't seem to show the torque of the bundy lines into the brass blocks and calipers. The rubber lines are shown as 110 lbs-in.

Anyone know what the torque is for the steel lines. I've always torqued them until they feel tight but I'd like to know what they are supposed to be.

Steve -

Dunno about C3's, but all the fitting torques are shown in the Assembly Manual for 67's - there's a torque symbol next to the item number for each individual brake pipe; there are four ranges, all between 70-140 inch-pounds.

No torques are shown for the rubber flex hoses.

[Steve L.]

Re: Torque of steel brake lines

Thanks everyone,
I'm using new bundy, rubber lines and rebuilt calipers.

It's odd that the AIM didn't carry over the torque of the bundy lines from 67 to 73. but added the rubber lines.

I'll assume that the smaller fittings are 70 and the larger ones at the front or 140 Pound-inch.

I'll use Duke's re-torque suggestion. I'll have to do that anyways on the rear calipers since, like a dummy, I put the lines on before checking the caliper mount bolt torques. The lines are right over the bolts.

there are four ranges, all between 70-140 inch-pounds.

BTW, I'm sure you know this but there is a difference between pound-inch and inch -pound. Pound-inch is a measurement of torque(the thing we are discussing) and inch-pound is a measurement of power. The torque gauge I have at my desk correctly says "Pound-inch"

Same goes for foot-pound and pound-foot...but I digress from the topic.

[Duke W.]

Re: Torque of steel brake lines

Thanks everyone,

BTW, I'm sure you know this but there is a difference between pound-inch and inch -pound. Pound-inch is a measurement of torque(the thing we are discussing) and inch-pound is a measurement of power. The torque gauge I have at my desk correctly says "Pound-inch"

Same goes for foot-pound and pound-foot...but I digress from the topic.

Pound-feet or foot-pounds can either be a measure of torque or energy. It is not power. It's confusing because in the English system of units a pound-mass is the same value as a pound-force. This confusion doesn't exist in the SI (metric) system because the fundemental unit of mass is the Kilogram and the fundemental unit of force is the Newton, which is defined as the force required to accelerate a one kilogram mass at the rate of one meter per second squared.

Way back when, engine torque was expressed as foot-pounds, but changed at some point to pound-feet. I'm not sure how this happened, but I expect that SAE or some other standards organization decided to differentiate between torque and energy based on the word order.

A torque applied for a complete revolution per unit time or force applied over a distance per unit time is power. Horsepower was defined by James Watt as 550 foot-pounds (of energy) per second (now 550 lb-ft/sec) based on his time and motion studies of horses turning water pumps to keep English coal mines dry.

He needed a unit of measure as a marketing tool to sell steam driven pumps to mine operators based on the number of horses used to drive the existing pumps. So if a pump was driven by four horses, it needed a four horsepower steam engine.

In Europe torque ratings are specified in newton-meters and horsepower in kilowatts.

Duke

[Rich P.]

Re: Torque of steel brake lines

Don't forget to put a open end wrench on the brass blocks as you tighten to prevent galling, spinning or having the clip pop off.

Rich

[Steve L.]

Re: Torque of steel brake lines

Pound-feet or foot-pounds can either be a measure of torque or energy.
Way back when, engine torque was expressed as foot-pounds, but changed at some point to pound-feet. I'm not sure how this happened, but I expect that SAE or some other standards organization decided to differentiate between torque and energy based on the word order.



Duke

According to wikipedia, some british guy, back in 1900 distinguished between the two. Apparantly it never really caught on so we are still living in this confusion.

[Steve L.]

Re: Torque of steel brake lines

Thanks for the open end wrench-brass blocks tip, Rich

[John H.]

Re: Torque of steel brake lines

BTW, I'm sure you know this but there is a difference between pound-inch and inch -pound. Pound-inch is a measurement of torque(the thing we are discussing) and inch-pound is a measurement of power. The torque gauge I have at my desk correctly says "Pound-inch"

Same goes for foot-pound and pound-foot...but I digress from the topic.

Steve -

When you're as old as I am, you go with what you've always been comfortable with and what the engineers put in the specs when these cars were built; if it was good enough for GM and the SAE, it's good enough for me. I'm not into Kilowatts and Newton-Meters or reversal of words I learned over sixty years ago .

[Bill M.]

Re: Torque of steel brake lines

confusion doesn't exist in the SI (metric) system because the fundemental unit of mass is the Kilogram and the fundemental unit of force is the Newton, which is defined as the force required to accelerate a one kilogram mass at the rate of one meter per second squared.

Duke

And energy is measured in Joules, not N-m (or m-N).

[Terry M.]

Re: Torque of steel brake lines

It's odd that the AIM didn't carry over the torque of the bundy lines from 67 to 73. but added the rubber lines.

I'll assume that the smaller fittings are 70 and the larger ones at the front or 140 Pound-inch.

Steve it sure is odd, because it isn't true. That is what happens when you assUme.

For the 1972 model year the torque values for the B-nuts on the brake lines are shown on UPC 5 (where all the brake stuff is) sheets B1 & B2. I don't have a scanner here at home, but you might want to check those pages in your copy of the 1973 AIM for the proper values for your Corvette. The 1972 AIM shows a value for the rubber line to the caliper as well.

I didn't look in the 1968 to 1971 AIMs, but if someone has an abiding interest in the history of the torque values for the early C3 brake lines I would be pleased to look them up for you -- assUm(e)ing they are in those AIMs. The devil made me do it.

Once you find those values, I recommend we have a discussion about how you are going to measure the torque you apply – that is for the last tightening after the first two or more tightenings per Duke’s most excellent suggestion.

OT BTW: I noticed at Wixom High Performance Build Center – where the LS7 & LS9 and some LS3s are assembled – that some of the torque tools make several runs at tightening the fastener before the final torque and then a certain number of degrees of rotation. Yes, I know that is for torque to yield fasteners, which is a whole different subject. VERY fancy tools – EVERY torque value is digitally recorded, and checked for accuracy (by computer) before the engine is allowed to leave the assembly line. But then maybe the go is more important than the woe? NOT. Next time I get into Bowling Green I'll try to remember to take a look at what they do to torque the brake lines on the new Corvettes. There sure are enough of them -- brake lines I mean.

[Steve L.]

Re: Torque of steel brake lines

Thanks Terry,
Using your hints, I found the info on the 73 AIM on UPC 5 sheet 1 as a general note that for inverted flare torqu to 120-180 lb-in but not more than 200.

[Terry M.]

Re: Torque of steel brake lines

Thanks Terry,
Using your hints, I found the info on the 73 AIM on UPC 5 sheet 1 as a general note that for inverted flare torqu to 120-180 lb-in but not more than 200.

It is good you did find someting in the 1973 AIM. At work today I scanned the two pages fron the 1972 AIM, but failed to email them to myself. DUH! So they are trapped on the computer at work until Tuesday. It is a 37 mile trip out there one way, so I think they will stay there until next week.

There were specific values for the fittings given as notes on the bottom of the page. Three different torque values listed inside a triangle. Most of the line fittings were 120-180 in-lb range. The rubber hose into the caliper was different though.

[Steve L.]

Re: Torque of steel brake lines

Terry,
Thanks for your efforts.