Hi,
I'm after some advice re my front brake calipers (91 Turbo).
Not long ago, (<1000 km) I stripped them, cleaned them (ie wiped them down), installed new rubbers, lightly (wet) sanded some rust off the pistons, greased up the pins, reinstalled them with new pads, bled them and started using them. Everything seemed ok, but recently there has been a vibration in the steeering wheel, worsened by applying the brakes.
In trying to diagnose the vibration, I now find one caliper is sticking, so removed it, and its pistons were jammed.
Blew them out and low and behold, the pistons have rusty brake fluid on the skirts, inside of the seal. The fluid I was using was good, so I am wondering where did this rust come from. Not from outside is for sure. 
 I don't mind stripping the calipers again and redo-ing but better to be sure there is no more rust in the lines, or wherever, first. 
 What can I do to locate / remove source of the rust ?  The rubber lines to the brakes are old, not sure if they are candidates.

In regards to the vibration, it could be a few different things.
It could be a warped rotor (for want of a better word). If you didn't replace the rotors, i'd recommend you do so.
you can get standard rotors from Brakes Direct in QLD for a reasonable price. Housemates Bimmer had a similar issues and I just replaced the rotors and the vibration was gone. If it's worse under braking, it'll probably be a rotor issue.
In regards to your calipers, when you rebuilt them, did you grease EVERYTHING with a rubber seal? that includes the ones that go in the piston pots. They need to be properly greased or they won't slide properly and can seize (I've made this mistake before). And the dust boot obviously need to be on to protect from contaminants.
If you had rust on your pistons, I'd probably have replaced them. I wire-wheeled my pistons and they cleaned up nicely the last time I did a caliper rebuild, but haven't come across rust on any of my brakes before.
Brake fluid doesn't cause rust, it's a hydraulic fluid. If there has been any water in the lines at some point that could cause your rust issue. If that is the case, I'm not sure of any way to salvage them, and would probably replace the calipers, etc.
Assuming you did a full fluid flush upon rebuilding the calipers, it may have been some residual rust in there, because that won't get out of the system through the bleed nipples...
 
tl;dr check your rotors, and possibly replace them. If a caliper is seized, there wasn't enough grease on the piston seals. Rust = bad. Most likely replace the calipers
 
hope this helps!

Hi SWTato, the rotors may be warped but before determining that I measured their thickness and found they were .7mm passed the wear tolerance, so have bought new rotors.  I certainly will flush the lines before changing back from Dot4 to Dot3. Speaking to a brake specialist when I told him about changing to Dot4 which in many cases is not an issue, he asked what make of car. He said Toyota's seals don't like Dot 4 as the rubber seals don't like the detergents in Dot4 and will swell. This may be why my calipers were sticking.
A good flush should remove any residual rust.
Also the grease on the pins looked like it was non-existent. The seal kits come with a little sachet of grease and he said probably not enough so get a tube of rubber grease and put plenty in there. 
 So with all these things contributing and now that my new seals have arrived, I will do the rebuild again, confident of a better result. cheers and thanks for your thoughts. 

Dot4 instead of Dot3?
What brand of Dot4 Fluid were you using?  
Maybe check it's specs. Some Dot4 fluids may be OK to use, or so the manufacturers claim anyway, and may also have better heat tolerance as well.
 
Steering vibration under braking or otherwise:
First check all front suspension components for slack, track rods, ball joints, wheel bearings etc.
A $50 clock gauge and magnetic stand could be a good investment and you could use it to check for hub runout. One or 2 thou on the flange outside the studs may be acceptable.
 
Surprisingly I have found that even new rotors may not be machined accurately and may actually have runout new out of the box that could be magnified if combined with hub runout. This could cause uneven rotor wear in future causing steering shake under braking.
Use the clock gauge to index the new rotors on the hub to minimize the total runout on the pad surface.
 
 
 
 
 
 
 

 Thanks RT,
  I am borrowing a dial gauge this week, and will check hubs, rotors, wheels for truth :o) 
 Yes I was surprised by the Dot4 being a problem. The brake guy made the comment about "Toyota" and seals swelling with Dot4, I didn't verify if it was all Toyotas or just old ones like mine. My research didn't pick up any such comments and it seemed you can simply replace 3 with 4, main benefit being extra heat, but since my road car will never get to the limit of 3, then I'm happy to revert. 
Anyway swollen seals may have been the culprit or the fine particles of rust in the fluid ?? 
I'll never know since I am dealing with both of them at the same time. Can't wait until the wheels spin freely, the steering wheel doesn't shake and the brake pedal is at the top, hopefully.  

FWIW, I personally have used Castrol React Dot 4 (used to be called Castrol Response) for many years now with no probs.
I change it about every year, including the clutch fluid, and have never seen any black sediment/rust to indicate seal cup probs.
From the Castrol website that may be of interest:
Corrosion protection: Outstanding protection against corrosion caused by absorbed moisture that can cause rusting and failure of components.
Rubber swell control: Contributes to efficient operation of the braking system components
Compatible with all other brake fluids that meet either DOT 3, DOT 4 or Super DOT 4 Specifications. 
 
BTW I am a fan of suction bleeding and have just ordered this off eBay:
http://www.ebay.com.au/it...-Bottle-/141547516884?
But I have previously used the hand pump type with success. Best way to do it IMO.

Thanks RT,
incidentally I was not associating the rust in the fluid with Dot4, it was only in there a few months. A good mate who is a mechanic gave me some advice to flush the old fluid using metho and then flush that with the new. I don't know if it helps move residual rust in the lines or is just easier to see when the rust is gone. 

Is the purpose of the metho flush to absorb any residual water from the DOT4 fluid?

Hi Fred, I don't really know, but there is unlikely to be any water in the lines since the Dot4 was only installed a few months back. It either has something to do with helping remove any residual rust, a cheap way to flush out the lines or a bit of both. I don't really know.