Just replaced pads/rotors and rebuilt calipers on all four corners, and flushed brake fluid. Factory service manual says 80 lb-ft torque for the front caliper bracket flange bolts, which seems really high - and I ended up stripping out the threads.

So either the torque specs are wrong, or my torque wrench is way out of spec (unlikely). What is the correct torque to use for these bolts??

 

I usually hand tight them with the ratchet never used more than 50lb in them?

 

Well, the damage is done.....so either use a helicoil insert or drill & tap to the next size.

 

It is definitely 80 lb-ft for the four front caliper bracket bolts, two on each side of course. Much like you, I changed my brake pads and rotors, rebuilt my calipers, changed my brake hoses (not lines), and flushed my fluid on my 1999 all around less than a month ago. I torqued all fasteners to service manual spec.

Your torquing instruments may be faulty or were improperly used, the female threads have weakened over time, the threads were lubricated/"wet" when they shouldn't be, or any combo of the above.

When using a click type torque wrench, especially when it has been sitting a while, you should torque a bolt (or bolts) at a few lower values (in steps essentially) up to your actual torque. This is to allow the deflection block inside the shaft of the wrench (if it is a standard click type design) to "free up" essentially as it is supposed to be. Example, your bolt spec is 80, start at say 20, then go to let's say 40, then 60, and finally to 80. Also, as im sure you know, you must hold the wrench where it is intended to be held, the actual handle part. Torque is simple, Torque (at a point) = Force (applied) x Distance (the force is applied from that point). Confirm your wrench is calibrated, test at your work bench.

Threads, especially when exposed to heating/cooling cycles, and corrosion, get weak. This is more ponounced in softer metals such as aluminum, but note that your dealing with forged steel here (forged as far as i know, but could be cast); still it happens. The female threads usually yield/give up first because the bolt is typically harder after treatment whereas the female threads are typically not. Blast it with dry compressed air right before hand threading the bolt too.

Fasteners are torqued under two conditions, dry or wet (not lubricated or lubricated). It is to be done dry unless otherwise instructed. Lubrication reduces friction as you know, and therefore the bolt will pull on the threads (including having more clamping force at the shoulder, more so when you also lube the shoulder) before reaching intended torque value. When torquing wet, you must adjust for reduced torque, which is significant (sorry, no equation on hand). You should clean the fastener, and make sure they're dry for your current task. There should be no grease, no dirt, but do not use a wire wheel and end up removing the anti corrosion coating (or what's left of it after all these years).

But, what's done is done, sh!t happens. Use a helicoil, aka threaded insert, or drill and tap out to a only slightly larger bolt, or change the knuckle.

 

Thanks for the help guys. I got a new bracket, not gonna mess around with cutting new threads. Actually I got two, I'll replace both sides.

I did work up, starting at 40, then 50, 60, the, at 70 ft lbs the threads came loose. I just cleaned them up and it's possible they were not 100% dry. Not sure though.

Heading out to reinstall now, I'm really afraid to try 80 ft lbs again if that is indeed correct.

 

Then don't do it... I never used a torque wrench for the bracket bolts, Always hand tighten strongly and never had an issue.. The odds of those bolts backing out are pretty low as that bracket don't see the movement the caliper bolts do.

 

I'd be comfortable with setting torque on those bolts to 70 ft-lbs on my vehicle, and feel comfortable that it won't back out. Worst case to satisfy my paranoia is that I'd check it a few days/weeks later (depending on how much I drive).

Out of curiosity, what brand/model torque wrench are you using by the way?

 

I ended up torquing to 65 lb-ft. Torque wrench is Tekton, not sure model #.

Just got home, wow what a difference. I use the acurazine special from Xlr8.

 

Glad you got good results!

It's probably the 24335, 1/2 inch, click, with a 10 to 150 lb-ft range. I've never used Tekton myself, but I used to hear good things when I still had contact with people who used them.

 

tech tip: store your torque wrench with 10 pounds of pressure set
that keeps a marginal amount of pressure to keep spring in correct tension = correct readings (advice from snap-on dealer on pricey tool- applies to all torque wrenches)
Left on 60-80 pounds and it will screw up the readings big time

in my experience of fixing a brake job dealer had just done- the caliper to bracket! bolts were at 130 pounds! (ckd them after first one came out with threads attached)
Tech BLASTED them on with the air gun set to max power!!
guess what the wheel torque was- that same 130+ instead of spec 80
Dealer replaced both brackets with a shamed face~

I use autozone numbers which are slightly less than 60 brackets and 40 calipers, rears are even less!
too tight is not only bad for the bolts structural integrity, it makes it hard for calipers to move properly in action

 

that torque ~spec~ is know by some as hand tight with ratchet/wrench and a light smack of the hammer to tool arm- the bolts are fine and wont come off or be way over- tight

 

another tech reminder
TL brake bleeding is LF RF RR LR = that's driver front then clockwise around the car and yes its that important!!
something about ABS plumbing,
AND IF lines were open- ie replaced calipers or lines replaced
THEN YOU MUST do 2 ABS fully active full stops from 45mph!!!
accelerate and repeat 2nd time stop to full stop

IF 2nd time had firmer pedal there was air hiding in the abs = it happens!!
Repeat the full bleed LF RF RR LR, air is probably waiting for you in LF but do all to be safe

reminder: brake fluid should be fully changed out = fliushed - once a year!, or max allowed is 3 years
Helps preserve the internal parts condition and makes for better stopping when fluid is good and no moisture contamination from age

 

I followed the order of bleeding, however I had forgotten about the ABS stops. I went to a gravel parking lot to do them this morning. The pedal *is* firmer now, so I assume there was air in the system that now needs to be bled out?

I know the recommendation for flushing the system however this is the first time I've done it, and the car is 12 years old. It looked dirty for sure, with some sediment. The internal parts looked fine, no rust or corrosion.

 

YES if 2nd ABS stop in gravel resulted in firmer brake pedal you need to bleed the system one more time, then good for a year~

you are lucky no caliper decided to rust up inside from hygroscopic action
Often the reason a pair of calipers gets replaced, seems to effect rears first on the TL