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Hi,

I'm looking to replace the front discs and calipers on my '91 940 Turbo. I've come across some pretty inexpensive refurbished calipers on Swedish Engineering Used Parts (hosted on eBay) and was wondering what I should check to make sure I'm buying the right thing and that the calipers are in good shape. I know my calipers are of the Girling type (with ABS).

Same goes for the discs. I found some Front + Rear discs + all pads for $120 (CAN$) on eBay !? Sounds a bit too good to be true. What about cross drilled discs? I've read that they give better braking power and cool faster but how will that affect pad wear and how will the ABS behave with those discs ? What about anti rust coatings ? Worth paying extra for that?

Any info is welcome!

regards,

TH
 

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As for the prices on 'discs', I have seen a large influx of 'Cheapo' China rotors in the past few years. In my experience, they are 'softer' then better brands, and therefore wear/warp faster.

As for "cross drilled discs", the ABS would continue to function normally, but in rare instances it would work more often as the vents keep the brakes cooler and working more effectively. Pad life might be slightly shortened since the rotor surface isn't as smooth. I can't imagine a 'normal' driver generating enough heat to make 'cross drilled rotors' worth the extra investment (unless you auto-cross or something). During normal driving rotors cool in between stops enough that performance isn't really affected. During panic stops, you would rarely hit the brakes often or long enough to generate the kind of heat that would cause 'brake fade'.

As for "anti rust coatings", mostly all rotors come with a finish on them to keep them from rusting before use. Most places wash this finish off before installation (some just let the finish 'burn' off the wear surfaces). You can't keep a coating on the area where the pad contacts the rotor. As for the other surfaces (Calipers, hub, vent areas, etc..), it would be purely cosmetic.

If anything, I would bleed your system out and replace with some 'fresh' brake fluid. DOT 3 and DOT 4 fluids will slowly become more suseptable to fade conditions as it absorbs moisture from the air (there is a small vent in the cap of the master cylinder to allow the fluid to rise and lower freely). The moisture that is in the fluid is heavier then brake fluid and tends to 'settle' to the lower parts of the system (which is why calipers and wheel cylinders can sieze/bind when the sit for a long time). That moisture in the system has a lower boiling point then brake fluid and can get hot enough during frequent heavy braking (racing, etc...) that it will expand while so hot and reduce the pressure that was applied (brake fade). The condition goes away when the sytem cools down.

Most master Cylinders have a removable 'reservoir' that we used to wash out (with brake cleaner) and top with 'fresh' brake fliud when we did a 'major' service (at the garage I used to work at). I only use DOT 4 fluid in my cars. I don't suggest that you use DOT 5 fluid, it isn't worth the extra money.
 
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