Brake rotor balance

[ParadiseCruiser]

New brake rotor installation...

I have asked this question in conversation with a couple of you in the past, and also of several other DIYers, mechanics and machinists... and there appears to be a wide range of opinion...

When installing new front brake rotors on an 80...

1) Do you simply bolt up the assembled hub to the rotor and call it good;

2) Do you turn the rotor first, then bolt it up to the hub and install; OR

3) Do you bolt up the new rotor to the hub (without the bearings), have it turned as a complete assembly, THEN bearings & pack, and install it?

All of the best advice differs here as to which of these scenerios would lead to the least (or most) likehood of future warpage of the rotor. OR, to ask ithe question another way, how do YOU do it?

Cheers, R -

PS: I followed the best advice , but I am still curious as to what others have done - and how it turned out...

 

[firetruck41]

Definitely do not turn a new rotor. IMO the collective advice has been, never turn the rotors on the 80 series, as warping will soon follow. I have personally never heard of turning a new rotor, as it has already been machined to probably tighter tolerance than the local mechanic can do, plus you are taking away some of the life of the rotor.
Just bolt on your new rotors and repack the bearings and set the preload, you might want to do the full birfield repack as you're half way there already. I just did the birf job w/new OEM rotors and pads, feels like new, no more pulsing brakes The old pads had about the thickness of a piece of paper left on them :whoops:

 

[sjcruiser]

Option#1, since turning a new rotor is just useless.

 

[RavenTai]

Option#1, since turning a new rotor is just useless.

Agreed

 

[Junk]

I followed the best advice , but I am still curious as to what others have done - and how it turned out...

What type of are you?

You already followed the BEST advice so know want to know how we would do it? Gee, Sparky, please remind me to offer you help next time you need any.

 

[Beowulf]

Ron,
Great question. I've also heard that "best practice" is to true-up new rotors or at a minimum to measure the run-out.

Up to now, I've just mounted new rotors without testing them. The next brake job is going to be a major service on mine; new rotors & pads on all 4 corners, caliper rebuilds, etc.
-B-

 

[cruiserdan]

There is no need to turn new OEM rotors. Simply install them on the hub and torque properly. DO wipe the friction surfaces down with a de-greasing solvent as there will be a bit of residual cutting oil left behind.

 

[ParadiseCruiser]

Jeeze Junk, gimme a break

Warped rotors is an often repeated subject on this forum, there are are a lot of newbies, and there are conflicting opinions. Worth airing it again, IMHO.

In order to satisfy my curiosity, I called every machine shop - and tire shop - (not so many here, actually...), and posed the question. To the last of them, they insisted the only way to do it is to mount the hub with races, and turn the rotor as an assembled unit. And, that is the way every shop around here does it.

Personally, I believe this is coming from the perspective of what is technically correct, strictly speaking, what is best in terms of CYA, and also liability (these are all commercial shops, remember).

As a practical matter, it is not really necessary - and obviously wastefull to be cutting into a perfectly good, new rotor. That is why all of the DIYers here do it that way... and why I considered the "best" advice to be the most practical.

What I had hoped to accomplish was to determine the range of experience among others here - both from those who had shops do the work, and from other DIYers, and what their experiences were.

But perhaps J is right, some of these subjects are just better left alone.

Cheers, R -

 

[Junk]

Well the reason I got slap happy is because you said you got the BEST advice, now want to know what we think. Like WTF type of way is that to lead into a question.

Here's the flaw in your strategy though. You are asking machine shops right? Don't they have a vested interest in telling you they need to machined first?

You also hear folks ask if their rotors should be turned too, but that's a different question. The bottom line is that the warping is caused by either heat or over-torque. Cut off some of the surface and you now get heat to build up quicker. Not much thought there then on why it's a bad idea to turn a rotor unless you just want it to be good for a short period like you're Vintaging your cruiser on ebay or something.

 

[ParadiseCruiser]

Junk, my good man, you have read something into my post that was not there. Let me take the rap for wording it poorly, and say it another way.

>>I have asked this question in conversation with a couple of you in the past...

The first thing I did was to query this group because I consider it the best advice, and I respect the opinions of the folks here. I then mounted new OEM rotors (without turning them) with 100 series pads.

>> ...and also of several other DIYers, mechanics and machinists... and there appears to be a wide range of opinion.

I am constantly reminded that industry typically does things differently, tho not always better... and that there are differences of opinion in that regard. What I had hoped to accomplish was to poll the group to hear their experiences from having it done one way or the other.

>> All of the best advice differs here...

I never said the best advice came from elsewhere; that is what has been read into the post.

"All of the best advice [from this group] differs here [from what the machinists say]..."

The best advice came from the folks here I queried... and they knew that is what I meant by that remark. I'm sorry anyone else read something else into it.

Cheers, R -

 

[RavenTai]

You seen worried about this I would put it all together and go myself, but if you want to go further to ensure long brake life the manual specifies 6 thousands of runnout

Front brake disc runout Maximum 0.15 mm (0.0059 in.)

To measure this you will need a dial indicator and a magnetic mount, build up everything and measure, if the runnout is below .006 you are done put the wheel on and go, if it is above it is either the rotor is misshaped or the hub is bent or bearing races are misshapen fix the root problem instead of cutting good rotors, more measurement with the dial indicator will bring you to the root cause

It has been my experience with other vehicles that turned rotors eventually warp (although I have never turned new rotors) I don’t know if it is because they are thinner and get hotter or if because the thickness is no longer uniform (new cut face relative to the cooling channel) causing stress as they heat or both

Even the cheapest new rotors will be truer than a field turning as they are made in a production environment. I assume you are getting Toyota rotors? Toyota’s sub contractors have do very good machine work you will not find a field machine shop that can improve on that on a “one of” job,

I guess the thought in turning new rotors is you want to true the rotor to the hub but if the hub is that far out it needs to be replaced/repaired

Measure don’t just blindly cut

Back to the title of this thread the rear rotors on my 80 (only OEM ones left on my truck, Dam PO’s) have a slight scallop at one edge I assume they dynamically balanced the rotor after all other machining operations were complete. After turning a new rotor that balance would be lost, probably not enough to notice vibration in the cab but something was lost nonetheless

 

[Junk]

Ron,
The way your original post was worded lead me to take it as an insult. As in, ok I got the best advice there is so now let me ask the second rate folks. Sorry dude, but that's the way it read.

The problem is there are too many unknowns. As Raven points out, it's more than just using an indicator, one would have to take into account everything else.

So, what does all this mean? Means just stick the new ones on there and wheel it.

 

[pound3151]

Ron, for what it's worth, I just did a complete rebuild of my brakes ( rotors, calipers, pads). All OEM. Went with the lick 'em and stick 'em theory, torqued to 109 lbs. on the lugs, and I'm outta there. (except for one piston, new one on the way from cdan)
--Brad

 

[Beowulf]

Brad,

Factory alloys on 95-97 trucks are 76 ft/lbs. 91-94 Alloys and Steelies are 109. (Edited)

-B-

 

[turbocruiser]

This is slightly off subject but, remember about six months to a year ago there was an advertising assault running about these do it yourself rotor turning things? They looked like little pattern cut pieces of 36 grit sandpaper that were inserted between the face of the old brake pad and the old brake rotor. The advertising asserted that these things would "turn the rotor on the car while you drive". I remember coming really close to crapping my pants the first time I saw that advertisement; I was thinking of all the many many many disastrous problems that would come with these things. First, if the rotor is already past safe spec and if the rotor is then turned thinner than before, that could cause serious trouble. Second, if the caliper is at all already out of operation, putting an aggresively abrasive pad on will only worsen the result of a partially siezed caliper that already squezes more on one side or the other, on the top more than the bottom, etc. Third, there is no way to truly tell how far to drive the car with these things on so even an extra thick rotor can turn to thin depending on so many factors. Fourth, there is no way to tell ( I'm talking average consumer without measurement methods ) after the process is over how much material was taken off. Fifth, even if the approximate right amount of material was taken off, you really cannot precisely abrade material off this way the same way you can precisely machine it off; the old pad would have to have a perfect face, the abrasive insert would have to have uniformity of unusual quality, the abrasive insert would have to have a perfect fit to the rotor, etc. It just seemed so stupid a method to do the brakes this way, I was amazed it made it past patent application. I have not seen the advertising at all recently, I wonder if these things were recalled? Anyway, the reason I mention all this is that part of the advertising I saw listed among many other advantages that these things true up new rotors as well as renewing old rotors. Strange stuff man!

 

[pound3151]

Damn, I missed the "steel" part in the manual. Anyways, it's a heckuva lot closer than the 220+ pounds that were on a few lugs when I got it back from the dealer. Thanks Beo --Brad

 

[firetruck41]

Brad,

Factory alloys on 93-97 trucks are 76 ft/lbs. Steelies are 109.

-B-

I've been told (I think by Cdan) the 93 (and maybe 94) alloys are 109 ft/lbs because they have steel inserts where the lug nuts seat. I just had to replace a rotor to hub bolt today and noticed the inserts on the back of the wheel when I was getting ready to put it back on. So all my lug nuts are @ 109 ft/lbs.

 

[cruiserdan]

Ben is indeed correct. Actually 91-94 wheels, both 15x7 and 16x8


D-

 

[Beowulf]

OK... I'll edit the above post.

Wouldn't want a Search to turn up wrong information and make me look like an eeediot.



-B-

 

[ParadiseCruiser]

Thanks to all for your comments on the rotors.

R -