Dunlop rear calipers...what am I missing? - Alfa Romeo Bulletin Board & Forums

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post #1 of 31 (permalink) Old 07-23-2012, 02:34 PM Thread Starter
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Dunlop rear calipers...what am I missing?

As best as I can figure out, when the brakes are pressed, the 'wheel' cylinder presses on the lower right rod. And in theory it pulls the left side in via the 'hand brake arm' and presses the right side in from the middle (the reason for uneven wear between pads).

That is, it would do this except for two small bolts - see arrows - which prevents this from happening.

Why-oh-why are those bolts there in the first place?

Or is there some mystical way the pads get pressed in that is way over my head?
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post #2 of 31 (permalink) Old 07-23-2012, 03:18 PM
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Manuals 930 and 976 cover the repair of the Dunlump brakes. Unfortunately, the manuals were only printed in French and Italian.

Pubblic. N. 930
Pubblic. N. 976
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post #3 of 31 (permalink) Old 07-23-2012, 05:53 PM
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Designed by Rube

Hard to understand how they work. And maybe harder to understand why the heck someone would design such a bizarre device in the first place.

The two upward - pointy brass things you see are springs. They - and the pad pushing arms - pivot around the pins part way up and are anchored by those screws you're talking about. These screws do not reach into the pad pushing arms so do not limit their movement. These springs act "flat" (left/right) in your photo. So, they are returning the pads to the resting (spread) position when you get off the brakes.

The slave cylinder forces its little rod out, pushing on the bottom of the large triangular aluminum arm piece, forcing the top outward but the pad inward. The upper rod on top is simultaneously pulled inward across the top of the disc, pulling the outside pad in toward the disc. Disc is pinched, friction happens and motion is turned into heat.

And we stop. Right?

Chuck
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post #4 of 31 (permalink) Old 07-23-2012, 08:05 PM Thread Starter
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Chuck, I would never have taken the brass parts as springs.

Do these brakes really work...or is it 'only theoretically'?

What is the best way to pre-adjust what I'm calling the hand brake rod? I gather it affects the overall braking on the side it is on...or is that not correct?

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post #5 of 31 (permalink) Old 07-23-2012, 10:08 PM
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Quote:
Originally Posted by Biba69 View Post
Chuck, I would never have taken the brass parts as springs.

Do these brakes really work...or is it 'only theoretically'?

What is the best way to pre-adjust what I'm calling the hand brake rod? I gather it affects the overall braking on the side it is on...or is that not correct?
They work surprisingly well, in my experience, at least as far as stopping is concerned. The only thing that really doesn't work as advertised is the self-adjusting mechanism--the ratcheted nut inside the large aluminum carrier, which holds the linkage rod which connects the left and right brake pads. As near as I can tell it's supposed to try to tighten up the linkage every time you release the brake, thus compensating for brake pad wear. When it's completely clean and well lubricated, it almost works. Fortunately when the self-adjuster doesn't your handbrake starts to get weaker, and it's fairly trivial to manually adjust the linkage.

What I've done to adjust the linkage rod (what I think you're calling the hand brake rod--presumably your term is as made up as mine ) is to bring the hand brake lever about half way to fully engaged, then tightened the ratcheted nuts under the inspection covers until they were snug. You can use a flat head screwdriver or even your fingers to do that. It's trial-and-error, at least for me.

Why Dunlop designed these things the way they did is beyond my. The front calipers are thoroughly conventional. I guess this rear setup saves you two hydraulic cylinders, but I don't think it's worth it. Incidentally, did you notice that some of the bolts on the calipers (not the ones that hold it to the axle) are metric while others are imperial (or maybe Whitworth, for all I know)? Just another little quirk.


Thanks,
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post #6 of 31 (permalink) Old 07-23-2012, 10:52 PM
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I think we call it "mechanical advantage" when you have the small piston pushing on the rod to actuate the levers to squeeze the pads to the rotor. Dunlop brakes have their faults but they will stop quick. These brakes were developed before most cars even had them. Jaguar and Alfa Romeo saw an advantage to market something unique and make the cars more safe. Be careful setting up the clearance of the pad to the rotor. If you get it to tight, the rears will lock up quicker than the front rotors. The fronts will rust up. Alfa Romeo made a change over to ATE in the middle of 1966 for this reason. The pistons were rusting in the bore and freeze up. The pedal got so hard you couldn't stop the car ( I know, it happened to me) so you use the hand brake to stop the car. Or the car would pull so quickly to one side it was frightening.
Good maintenance of the Dunlop brakes is essential to working well. The rear piston kits I hear are almost made of Unobtainium.

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post #7 of 31 (permalink) Old 07-24-2012, 09:13 AM Thread Starter
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I have a pair of the rear slave/wheel cylinders, along with a MC, coming from Alfaholics. They appear to be longer in the photo than the ones I removed, so will have to see how that works out.

Yes, a mishmash of bolts required on these calipers, not at all helped by the fact that the plater lost several of them.

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post #8 of 31 (permalink) Old 07-24-2012, 09:38 AM
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Self-Adjusting Mechanism

The self-adjusting mechanism is a spring-loaded ratcheting thing. Press together the tops of the pad-pressing arms and it grabs a bite and wants to stay there.

Take one of these Dunlops apart and you'll start to see how it works. Now, if you come to admire its genius you might want to keep an eye out for the men in white coats.

And you better make some detailed sketches to accompany your many close-up photos of the thing as you disassemble it because you do not want THIS particular pile of parts looking up at you from your workbench without a clear map to lead you back to where you started. (For example, the many pivot pins are NOT all the same length...)

Hey, Alfa put them on GTAs and went racing!

Chuck
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post #9 of 31 (permalink) Old 07-24-2012, 10:20 AM Thread Starter
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Gee, I thought the above photo of the left caliper looked pretty good. This is a before photo of the left one. The right one was twice as cruddy.
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post #10 of 31 (permalink) Old 07-24-2012, 10:34 AM
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Q: Cleanliness is Next to _____ .

A: Impossible?

Everything works better when it's clean. Right?

Ok, well, at least it looks better.

Until the first mud-puddle...

Chuck
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post #11 of 31 (permalink) Old 07-24-2012, 11:04 AM Thread Starter
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Chuck, were you able to loosen up the pistons in the slave cylinders, or did you send them out to a rebuilder?

Your's look very nice. I went with black zinc since I've coated the front calipers with G2's (gloss) black caliper paint.

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post #12 of 31 (permalink) Old 07-24-2012, 11:33 AM
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The little pistons came out without issues, but I sent the slaves out to be brass sleeved, just as a "while you're at it" measure. (I hate to do things twice...)

New seals and dust boots were tough to find. But there are some genuine kits on Ebay right now, so I'd say GRAB some while you can.

ALFA ROMEO GIULIA 1600 DUNLOP GIRLING REAR WHEEL CYLINDER REBUILD KIT NEW! | eBay

I bought some from this guy, no problems. (Note that some of the slaves used a circlip instead of the metal "cap" to contain the little piston.)

Chuck

Oh, that's Eastwood's brake fluid resistant gray paint, applied after a phosphoric acid etch after bead blasting and degreasing.
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post #13 of 31 (permalink) Old 07-26-2012, 07:37 PM
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One thing to remember and watch out for with these brakes, don't let grooves get worn in some of the pins, as they then become very difficult to remove, hanging up on those grooves. I never liked those original brakes on the Giulia Sprint GT's, as the fronts were terrible in the wet, not grabbing for half a second if it had been raining, as it does in Seattle just once in a while, lol. I changed them over to the later ATE. No problems then.

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previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #14 of 31 (permalink) Old 08-16-2012, 11:13 AM Thread Starter
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39cub or anyone else, the return springs also did not come back with my plated parts. Could you give me - fairly accurately - how long the wound spring part itself is when unloaded and also the diameter? This is a pretty iffy way to determine as to how 'strong' the springs are, but was it a lot of work pulling it on when you were installing them or fairly easy, or somewhere in between?

I'm surmising the best way to adjust the rear calipers is once the brakes have been bled, is to adjust the upper arms so that there is, guessing, around ten thousandths space between pad and disc, then drive it and then adjust 'as needed'.

Ten thou is a bit much but since there is no brake bias unit, this should insure the fronts starting to stop first with the rears quickly following.
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post #15 of 31 (permalink) Old 08-16-2012, 11:30 PM
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Biba, in the middle of my post above, I caution you to not make these rear brakes to tight. I did that with my TI, everything was great if you did a slow stop. So, I tried a panic stop and the car swapped ends on me so fast I didn't know what happened. So error on the side of "loose". As you said, there isn't a bias unit installed as there is with the ATE system, so the bias is set up with clearances on the rear. Beautiful workmanship btw. Don't forget to turn the rotors

Christopher

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