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Help with 4-whl Discs!


Guest kmorg

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:o:( I'm new to the forum. Installed the Steeltech 12" kit on the front and the rear disk system on the back of my '78 Avanti II. My mechanic (Air Force moved me mid project) can't get the calipers to engage until the pedal is nearly bottommed out. He thinks the stock Master Cylinder doesn;t have enough volume to engage fully activate the pistons.

Any ideas? Is there a different Master Cylinder to try?

Starting to grasp at straws!!

Thanks for any help!!

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I don't know about master cylinder volume being a problem...never heard of that with these systems, but is the system fully bled of air? Also...would there be any chance of silicone DOT 5 brake fluid being mixed in with non-silicone DOT 3 or 4 fluid? That will create all kinds of problems...they simply do not mix. Look at the brake fluid in the reservoir and see if it looks cloudy or congealed...a sure sign of the wrong fluids mixed.

I would completely flush out the lines and calipers and make sure they are completely dry and use fresh fluid. Avanti Motors used silicone fluid at least since 1970 according to their advertising brochures. It's an easy mistake to make mixing silicone with non-silicone.

Most, if not all, performance cars specifically say do not use DOT 5 silicone fluid now. It aerates in hard maneuvering, causing a mushy pedal. Avanti's that use the screw-in brake light switch (the original type) that is not mechanical will have problems with silicone fluid.

I think many knowledgeable people now say to leave silicone fluid to museum cars and not cars you drive.

Hope you find your problem quickly and get it taken care of. Let everyone here know in case someone else runs into the same thing.

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:o:( I'm new to the forum. Installed the Steeltech 12" kit on the front and the rear disk system on the back of my '78 Avanti II. My mechanic (Air Force moved me mid project) can't get the calipers to engage until the pedal is nearly bottommed out. He thinks the stock Master Cylinder doesn;t have enough volume to engage fully activate the pistons.

Any ideas? Is there a different Master Cylinder to try?

Starting to grasp at straws!!

Thanks for any help!!

Call Stelltech about the master cylinder or porportioning valve, they should know. Did you bleed the master cylinder? Sounds like there is still air in the system to me. Watch the caliper for movement as someone slowly applies the brakes. The caliper piston should move immediatily, if not you have air in the system.

Jim Wood

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IndyJimW--Thanks for the quick reply--I'm pretty sure that the mixed fluid isn;t the issue--Mike (the mechanic--REALLY good!)--told me that they've run a couple of gallons of brake fluid through the system bleeding and troubleshooting--I think that I had mixed the fluid before I installed the new stuff but I never put any pressure on the system.

Jon Meyers(?) told me to try the earlier Avanti booster and MC because fo the larger bore (1 1/8) and volume---$$$$!!

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Are the calipers installed so the bleeder screws are at the top? If not there may be air trapped at the high point that cannot be bled out. Doubtful the volume is a problem. The calipers don't completely drain back into the master so the fluid in the master is really pushing on fluid already in the lines and in the caliper.

Ernie R2 R5388

:o:( I'm new to the forum. Installed the Steeltech 12" kit on the front and the rear disk system on the back of my '78 Avanti II. My mechanic (Air Force moved me mid project) can't get the calipers to engage until the pedal is nearly bottommed out. He thinks the stock Master Cylinder doesn;t have enough volume to engage fully activate the pistons.

Any ideas? Is there a different Master Cylinder to try?

Starting to grasp at straws!!

Thanks for any help!!

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Can't answer the issue directly, but...

Which M/C is Jon Myers referring to? The original 63 Avanti M/C? Or was there a change during the 70's?

If the pedal feels hard, not spongy, once it reaches the end of it's travel, then mixed/aerated fluid is probably not an issue.

If I'm not mistaken, there is some adjustment at the booster linkage rod that pushes against the M/C... perhaps it can be adjusted (extended) a bit to give a higher-pedal/earlier starting-point to begin pressurizing the fluid. See page 15 of the brake section of the Avanti shop manual. You might also check to be sure there's no slop in the pedal mounting/pivot joints.

Edited by WayneC
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I guess the first question is, did you JUST replace the brakes at the wheels, or

did you replace the master cylinder also? I am running the early 70's Avanti II

master cylinder on my 63 Avanti with 4 wheel disc, & the fronts are two piston!

I havent had any trouble with low pedals. Prior to that I had the 11 inch GT on

the front and single large piston - also no problems. I was concerned about it

needing a different master cylinder with the 13" Cobra brakes & 2 piston calipers

but everything works perfectly together. If the master was replaced, check the

depth of the piston in the master relationship to the pin coming out of the brake

booster like Wayne mentioned. Check the old and new masters depth. Air is

the one thing that makes sense here. Call Steeltech.

Tom

cobra_brake_testdrive007a_thumb.jpg

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:o:( I'm new to the forum. Installed the Steeltech 12" kit on the front and the rear disk system on the back of my '78 Avanti II. My mechanic (Air Force moved me mid project) can't get the calipers to engage until the pedal is nearly bottommed out. He thinks the stock Master Cylinder doesn;t have enough volume to engage fully activate the pistons.

Any ideas? Is there a different Master Cylinder to try?

Starting to grasp at straws!!

Thanks for any help!!

I haven't seen it listed in any of the replies but I may have missed it.

But it sounds like the master cylinder wasn't properly "bench blead" prior to its instalation.

This must be done and done properly or the symptoms will be exactly as you describe.

Charlie Rqb-3921

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  • 4 weeks later...

:) Thanks for all of the inputs. Jon Myers (and Mike the super mechanic at the shop in OK) was right about the Master Cylinder size being the problem. I ordered the early (4-bolt) booster and MC from Myers Studebaker and it worked great (the shop had to fab up a couple of new lines).

When I get all of the back from my shop I'll pass it all on to Steeltech so he can let other guys know about this issue--the 12" big brakes need the early Avanti II Booster/MC combo if also combined with rear discs!

Now the new question, which Lokar part number should I order for a new e-brake cable to work with the Steeltech rear disc brakes?

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:) Thanks for all of the inputs. Jon Myers (and Mike the super mechanic at the shop in OK) was right about the Master Cylinder size being the problem. I ordered the early (4-bolt) booster and MC from Myers Studebaker and it worked great (the shop had to fab up a couple of new lines).

When I get all of the back from my shop I'll pass it all on to Steeltech so he can let other guys know about this issue--the 12" big brakes need the early Avanti II Booster/MC combo if also combined with rear discs!

Now the new question, which Lokar part number should I order for a new e-brake cable to work with the Steeltech rear disc brakes?

How long did it take you to get your steeltech brakes. He has had my money for 7 weeks and I still havent seen all the parts yet.

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How long did it take you to get your steeltech brakes. He has had my money for 7 weeks and I still havent seen all the parts yet.

I actually ordered the stuff last year ('05 xmas present) and it did take awhile. Then I got the early axel rear brackets instead of the later Avanti II ones (they're different). Also one of the front rotors was wrong--he corrected all of the problems without question. He's also a pain to get ahold of but he's always returned my messages (at least by the 2nd try).

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