Hi , I found some new information that may help on this not uncommon problem…low pedal on disc conversions , --Maybe not specific to Nigel’s issues , but important to know
I have several AAJ kits, (GM fronts) installed in the past , no severe problems, after sorting out related issues with the car and things I did; Pedal never came out “perfect”, but safe and useable— = good braking, even if pedal travel a bit much. (Subjectively) . . . ------however I am having a bear of a time getting a high enough firm pedal on the present car .
It now has 4 and 10lb residual pressure valves, (RPV) new (last week) a 1.125 corvette master , although I never felt the later mopar master provided by AAJ (their full kit) was the problem. Car has Manual brakes , it has correct Mopar manual pedal arm, and arm ratio . The Mopar master supplied in the AAJ kit however had no RPV valves in it at all when taken out. . (I understood usually they are in it , for discs) ..but also was told many rebuilding shops toss them, “not needed” (!!) . Beware. Check with soft wire or toothpick before install , on discs . if no RPV , wire will pass right into bore of master. Valve will stop it. External valves probably better , you know what you have .Wilwood are aluminum, but after using those , found out someone else makes brass ones. Threads on adapters (brass ) to Wilwood aluminum threads not good engineering, IMHO< re leaks and worse.
Firewall on 57 can be redrilled for corvette two large bolt master ok. (Mopar are 4 smaller bolts )
We can SEE the front discs retracting maybe .030 (visual estimate) when you take your foot off, even with the new 4 psi RPV. (was a 2 psi) Pumping does not help--- discs just follow the pumping. GM front calipers are used on the AAJ kit. By happenstance , searching, I found out GM changed the caliper to a “low Drag” design about 82 -83 where the rubber seals are specially configured to pull the puck back from the disc. This was an attempt to improve gas mileage (?) I am told.(seems really trivial issue to me) ; discs are always knocked back a few thou+ anyway by rotor runout, prior to that change. The problem is that rebuilders may throw all GM front calipers into a bin, --apparently, ---and you can get the wrong ones in the box .. I am suspect. The early ones , I think 79-80 Malibu era are not self pull back. What you want to have , I think . The differences are in machining the internal rubber ring grooves, maybe rubber too. That is not obvious to anyone looking at a GM caliper sitting there. All this from various Hot Rod builders. Sorry not more definitive.
You can see this on your car , apparently, if after applying the brake you can slide like an .020 feeler in there. Mine move back more than that (back into housing ) ; looking at the math, the 2.5 “ GM puck is about 5 sq in, the 1.125 (corvette) master is about 1 sq in,(=5x) so say .05 travel at puck is .25 of master travel…and pedal is 6 x that , or 1.5” AFTER taking up all the other slack . so ? 2” + of pedal gone….?? If a smaller diameter Mopar master this is all even worse.
So maybe we get the wrong caliper at times by accident ; GM fixed this issue when this rubber pull back came out by some kind of two step master (“stepped bore” ) that moved a lot of volume at low pressure (takes up slack) then smaller high pressure bore took over . (like a wood splitter) We do not have that. Probably do not want it either. TBD
None of this is meant as definitive stuff ---or “the answer” to fixing the problems at hand –not just yet, but important info along the road.
Not knowing this caliper pullback stuff is a road to going nuts, if it does what we think it does . All this is information to process , not a recommendation. Use your own ability, sort out yourself… I know power brakes are more suited to that big Corvette master. But I want a good pedal. Even if I have to push harder. Will worry about that after I get solid brakes at ~ 1” down.
Comments or experience really welcomed…
Best,
John
PS, saw “big red” 62 H at Pa meet, I really checked that out. A proven 150 mph car was running stock manual brakes, stock Mopar single master , the right manual pedal arm . . Seemed to have worked fine. So only system level difference (effectively) is GM front discs. And discs take more fluid, even if not pulled back. .
From: Nigel Wright [mailto:nigelwright11@xxxxxxxxx]
Sent: Sunday, May 19, 2019 1:26 PM
To: John Grady
Subject: Re: [Chrysler300] 62 300 brake issue
The specifics of the front disc conversion kit from SSBC are on their site:
The MC has a smaller bore than yours. I had this done about 3 years ago, but last year I noticed at low RPM that the pedal seemed to stick near the top and having the power booster reconditioned corrected that problem. I don't think my guy tried to bleed the system yet, so i'll check tomorrow.
Still working on it . Put in 1.125 bore corvette master 4 and 10 psi wilwood valves . Better but not happy . Car still being worked on , manual brake setup. AAJ fronts What about you
Sent from my iPhone not by choice
You mentioned you are suffering with low pedal also -- have you tried to resolve the issue or are you just living with it?
It may take a few miles - as in 1000+ for shoes to conform to drums in back . Suffering too with front discs and low pedal ..
Sent from my iPhone not by choice
I was wondering if anyone had any ideas that might help. The mechanic where I store my car was doing a few things for me prior to its spring release. I had mentioned that upon hard braking it seems a little soft. He observed the same, but hasn't come up with any solution yet.
This is a 413 with single Edelbrock carb. I have a disc conversion on the front and dual master using the SSBC kit. Also, last year I had the power booster reconditioned.
Thanks, Nigel
