Front Disk Brake Conversion not working ( UPDATE11/15)

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Well from the posts in this thread and some helpful pm's, I plan to buy a new disc brake proportioning block, lines, 70 Challenger calipers and hoses. I will retain the B spindles and switch sides so the caliper is front mounted. That should cure the interference issue and then I can tackle the lack of braking performance. Who knows, maybe by replacing all those parts, that problem may go away as well. We'll see...

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Look for a used one(proportioning valve), imo. I've read on here about too many problems with new one's.

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ON MY 70 challenger, originally drums, i have the 73a body set up using the stock distribution block and an adjustable valve in the rear line.
works exactly the same as my 74 cuda that has all stock disk brakes

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Well from the posts in this thread and some helpful pm's, I plan to buy a new disc brake proportioning block, lines, 70 Challenger calipers and hoses. I will retain the B spindles and switch sides so the caliper is front mounted. That should cure the interference issue and then I can tackle the lack of braking performance. Who knows, maybe by replacing all those parts, that problem may go away as well. We'll see...

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No. 70 Challenger calipers are pin mounted. So to run them you need pin type caliper adapters (used only) and pin hardware kit.

Sounds like you need 73-76 A-body slider calipers because of hose orientation?? Rick?

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In the first post he says that he has pin type calipers. So given that, he should be able to front hang the calipers and use factory E body hoses. Since it is a '70 model year, the anti-sway bar mounts should be in board on the LCA.

He is using the taller late B knuckle but that doesn't change the caliper position. Even the taller 11.75 rotor setup should still work with the factory hoses.

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Opps, my bad. I thought that 73 B-bodies had slider calipers and that was what he was using.

But his current situation is an easy fix with the correct banjo brake line. He needs to find the rubber one that doesn't have the 1" metal extension to it. There is an application for that. Like Aspen or Cordoba or something. Or run a custom braided line.

Here's rear mounted pin calipers with braided banjo line. The line is just routed in U shaped down from the banjo fitting and upward to the body fitting.

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Here's rear mounted pin calipers with braided banjo line. The line is just routed in U shaped down from the banjo fitting and upward to the body fitting.

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My knowledge of bump steer is this. You need to form a parallelogram with these 4 points. The lower control arm pivot. The inner tie rod pivot. The lower ball joint pivot. And the outer tie rod pivot. Can you explain how raising the upper ball joint pivot affects this? I don't see it.
Doug

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Maybe this will help you see... ;->



Rick

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So Rick which is it, the Chrysler engineers are brilliant or are they idiots?

In your articles of disc brake conversions you expound the virtues of the Chrysler engineers when it comes to the use of the taller knuckles on earlier models yet you chastise them because of the way they mounted the calipers?

You seem to forget you are dealing with Mopar owners that because the shading of reproduction hardware is off by one or 2 shades, do you really think they are going to move the brake line attachmant <sic> point and bend up their own lines ?

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I thought Dr.Diff came up with a solution to this by using GM brake hoses from a GTO Chevelle etc.

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It isn't impossible to have a decent setup with both ends of the hose on one side or the other (of the knuckle), you just need to really take the time to be 100% sure all parameters I've outlined are met, and be cognizant that hose life will be reduced (from the twisting).

Rick

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It's not idiot proof. You've got to think things out/

I run braided hose. The hose picture had been on the car from 1993 to 2010. It's been in 4 years of Iowa salty winters. It out lived: a broken K-member, bent steel rim/dimpled up shock tower hole/bent valance, and a few off race track surface "excursions", and about 80,000 miles

I only took it off because I changed some stuff. Hose was fine.

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Every time this topic comes up, it seems to feed on itself, ad infinitum.

The diagram isn't a Mopar, and may not be perfect. You asked for an explanation as to why moving the ball joint affects bumpsteer, and this does make that clear.

There's an old engineering axiom: Perfection is the enemy of good. At some point, you've gotta say "uncle", and get the pig into production. Lots of Mopars were pretty far from perfect. EG: fast-ratio E-bodies with lousy Ackermann (the engineer told me, basically: "it worked OK"...and it does. Most of the '80s-'90s FWD stuff with MacPherson struts, and the horrendous linkless swaybar setup. And, worst of all, F/J/M-body front suspension. Plot that curve! But, as was pointed out, nobody got killed. The cars just could'a been better. (A few Chrysler engineers did quit over the F/J/M suspension however).

I have cut some pretty fast lap times with the FWD stuff, and, on a smooth course, even the F/J/M stuff can work. Make the asphalt bumpy or undulating, though... ;->

Generally, all the later ('60-'62-up) longitudinal T-bar suspension designs (the ones with the adjuster in the LCA) were very, very good. I have the SAE papers that compare them to contemporary competitors, which looks like F1 vs. soap box racer. My point, therefore, is why, if the design is so very good, knowingly degrade it, when the parts to do it right are pretty easy to come by?

One the hose routing issue: I stand corrected, I was thinking "single piston caliper". But the point remains unchanged, on any non-OEM swap, be sure to check for stretch and abrasion as I outlined.

Rick

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Thanks Rick, question, is there a quality repop of the A,B,E spindle because are getting harder to come by?

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As I mentioned, somebody actually took the time to measure and plot this. If I can find the file or chart I will post it here. The toe change was approx. 3X on the '73-up B knuckle vs the correct one. (On a car originally equipped with the "short" knuckle).

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I looked and could not find the chart I saw. It showed the tall spindles toe change almost identical to the short one. I do agree camber change will change toe. Camber will change unless both upper and lower control arms are the same length. That's not going to happen.
Doug

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The chart in the post above is the one I saw. It shows the tall spindles toe change almost identical to the short one. <snip>

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I can feel the longer stroke on the pedal but the brakes don't catch until near the bottom of the stroke.

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I also did not touch the booster but if that was bad, it should show itself as almost having manual brakes, right?

I could also block off the rear brakes completely and try operating with just the fronts to see exactly how well they perform.

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(1) Yes I think pretty much so just like when you keep pressing them with the eng off. (2) Excellent idea to with a brass plug cap the rear brake port which'd be as you know the front port but I would cap both first. we gotta start somewhere to narrow this down

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Did I possibly get a bad distribution block? can they trap air?

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Rapid,

John- the distribution block I have now is a "supposed" good used. I bought a new one also but saw some threads about the new blocks having problems. I got the new block from Inline Tube, as well as the stainless lines.

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The big bore master is making the pedal uncomfortably stiff but the system seems to finally work.

Any comments on why the small bore master didn't work? Bad master? Should I try a different master?

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Sucess! (1) You'd think bad master but I'm not grasping how it was high and tight with the one (offending) side blocked off but spongy with it hookup up then a diff master made both front sides firm as you'd logically think there was still air in the bad side (2) To confirm (or deny) I'd get a diff one with a smaller bore and bleed it out since you're getting to be a bleeding pro and can do it in no time and the smaller bore will get the pedal feel where it is more comfortable for you

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When I would add in one side of the fronts I would get a good pedal, but more travel when pressing the pedal. When I added in the other front side, the pedal would almost go to the floor.

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One test will not find every gremlin,

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I read one of the brake conversion articles in a Mopar magazine that praised the conversion kit (one of the ones that uses a bearing spacer) because they had not had a single problem and had put over 5000 miles on them.

As a test engineer, I was torn between laughing or grimacing at such a paper-thin evaluation.

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Bottom line, use the right parts. Why would you use the 73+ spindles when the right stuff is available? There was an article in Mopar Muscle a while back, I no longer have the specs. They printed a chart with different variables between the earlier and later spindles and there were some differences, I think mostly with roll center. BUT, the test was not only skewed from the start with non-factory settings (lowered here, changed there, who knows if a stock setup would yield different results?), it also was very one dimensional - the factory ran these setups through simulations that measured everything seven ways from Sunday. One test will not find every gremlin, the same way that a standard alignment will not find issues beyond the basics.

The right parts are out there, use them.

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Sorry, should have clarified,

If I blocked one side of the front brake system ( didn't matter which side - after further tests ) I would have a decent pedal. When I hooked both sides into the distribution block is when I would get the overly long pedal travel.

I can't explain the results as fluid can't be compressed. How would the isolated rear brake system produce a great pedal, while adding the front lines would give me excessive travel? The signs point to trapped air but after switching masters, that theory is disproven.

I don't recall the actual bore size of the Ehrenberg Master but it is at least 1 1/8", possibly 1 1/4". ( Not 1 15/16" as I originally posted ). The Eberg master is what I have on the car now and is working but with an unnaturally hard pedal with only a little bit of travel.

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