70 Cuda disc brakes very hot

[JohnnyMopar]

Hello! I just changed out the hubs, bearings, and calipers on my 70 cuda. Everything works fine, but the disc brakes get very hot after use. Hot enough that you only can touch them for a couple of seconds. They don't glow red or anything. 

The new calipers I bought came with new guide pins, but not new positioners. I heard that in 72 or so, they redesigned the pins so they didn't need positioners. Thinking this may be the problem, I kept one side using the old pins and positioners and the other side with the new pins and no positioners. No difference in temperature was noted.

In terms of bearings, I made sure the lock nut was hand tight, then backed it off a notch before putting the cotter pin in. There is just a slight bit of end play.

Any ideas, should they be this hot? The calipers are from Napa, and the hubs are Wagners. Thanks for any ideas. 
 

[Chryco Psycho]

What master cylinder are you using , the drum brake masters have a 10 PSI residual pressure valve built in that could be dragging the brakes

[JohnnyMopar]

Thanks!

The disc brakes are getting hot.  Were you thinking there was a problem with the rear drums?

[ksierens]

If the rears aren't doing their part, the fronts could be doing most of the work.  Also make sure the rear brakes are adjust properly.

[Chryco Psycho]

No , if the master is from a 4 wheel drum brake car / system the front brakes could be held on by the residual pressure valve causing them to get hot

[HP2]

More info is needed. Since the whole principle of brakes is the conversion of kinetic energy to heat, I'd say they are working just fine.

So, just saying they hot is a pretty open ended statement.  Hotter than before the caliper, rotor and bearing change, hotter than before the disc conversion (if you performed one before), hotter than your regular driver, hotter after stop and go driving, hotter after a trip to the grocery store, hotter after a pass down the track? We need some qualifications on the "hot" to dig into some potential issues.

[JayBee]

No , if the master is from a 4 wheel drum brake car / system the front brakes could be held on by the residual pressure valve causing them to get hot

I was thinking of doing this conversion too and a friend who had done it said I'd need a new proportioning valve AND master cylinder

[JohnnyMopar]

I see what you are saying about the master cylinder.  I haven't done anything with the brakes since buying the car.  So they could very well have been drums on the front originally.  When I jack the car up and spin the wheel it spins with little effort, but does drag a lot more than say my 05 Ram.

In terms of the disc brakes being hot, you can't hold your hand on the wheel, hub, rotor, or even the caliper for more than a few seconds comfortably.  They don't glow red or anything, but I do notice a bit of brake fade after a 10-15 mile cruise.

What is a good way to check and see if the master cylinder and/or proportioning valve are from a 4 wheel drum set-up?

Thanks!

[Chryco Psycho]

for $25 you can replace the master with a correct one for disc brakes
 or you can remove the brass insert with a drywall screw from where the line bolts into the master , if there is a rubber nipple in behind the brass insert you can remove it & re-install the brass piece & it should still seal to the line , the nipple is the residual pressure valve 

[farmboy70]

When you mounted the calipers was it difficult to install the pins? Most places are selling calipers for later models than the 1970 the calipers are different in 1970
Part number is 2944712-3 for 1970
3461964-5 for 1971 I have noticed that the pins can be forced into the later ones,compressing the rubber bushing. But it is a tight fit causing the bushing to fail.
This maybe why they run a little off causing extra heat.
Also in your post you hand tightened the bearings and then backed off some. They maybe too loose causing a slight run-out on the rotor. Slight rubbing of the pads.
I had a car once that the front hoses were collapsed inside allowing fluid to activate the brake but after the pedal was released the fluid slowly returned to the master cylinder causing the brakes to drag and over heat.
Just a few ideas
Dave

[JohnnyMopar]

Thanks for all the info!

I'm definetely going to check the master cylinder for the residual valve not knowing the history of the car!

How tight do you recommend on the lock nut?  Should there be any end play at all with the rotor/hub assembly?

In terms of the guide pins, I have tried several different combinations.  The new pins that came with the calipers did not have positioners (the metal clips).  After researching the subject, I Chrysler changed the pins in 72 to the new style that doesn't use positioners.  Just as you were pointing out in the part number difference after 70.  I left one caliper with the old pins/positioners and the other with just the new pins.  Same result in terms of ease of installation and heat generated!  In terms of tightness and how they fit with the bushings, they were snug, but went in fairly easy. 

[Chryco Psycho]

Basically the nut for the brgs should be finger tight , I overtighten it to make sure the brgs are seated then back it off & snug it , there should be virtually no play but no preload either

[73EStroker]

Also - please check the disc calipers. If they are older and do not return to rest position after brake application then they cause the disc pads to bind on the disc. This overheats the discs real quick. If they are ok when cold and do this after a few miles then this is most likely the problem. We are talking about the piston in the caliper retracting back about the width of a hacksaw blade or less which makes a big difference. I know this because I have replaced calipers on lots of vehicles in the past that gave me this same problem you describe.

[JohnnyMopar]

Thanks for the info!

[ShelbyDogg]

Is this power brakes?  It could be like the problem with CudaGuy's car. The Power brake booster adjusting rod was a little too long causing the front discs to not release all the way.   As soo as I felt the front wheels hotter than normal, I knew that would be the place to start.  You could always use a piece of Plastiguage in there to see how much clearance is there. I usually do it by feel.