Technical Overheating engine and stiff brakes at the same time

So I'm running a 56 Chrysler 331 hemi in a 52 dodge pickup, 700r4 trans and power brakes with a 7" diameter booster. I also have an electric pusher fan, supposedly rated for around 3000 cfms, because of little room in the engine compartment. Also have a big aftermarket aluminum radiator. 7 lbs cap. The fan is currently wired to be on all the time.

Everything was running fine until the last 25 mile trip, while doing 60mph the engine started to run super hot and at the same time the brakes became stiff, like I was applying the brakes ( the brake lights run off a pressure switch and my brakes lights stayed on)

How are these two things related? And where to start looking?

 

Problem likely related, engine overheated having to work against the brakes. Fix the brake problem and the overheating will remedy itself. Crack a wheel cylinder bleeder screw and the brakes should release.I'd start looking at the pushrod clearance in the master cylinder as the culprit.

 

Make sure that you do not have excessive rear shoe drag, that your brake pedal pushrod fully returns, with a little free play, and that the pushrod between the booster and master cylinder has a little clearance.

Do you have a brake pedal return spring?

 

check to make sure the exhaust, header or tail pipe isn't too close to a brake line or M.C.. Heat could cause them to expand. Maybe it took awhile for the heat to transfer and caused the problem

 

The too-long brake rod rears its ugly head once you've drove it long enough for the fluid to expand and not release the brakes. I would shorten it in 1/8" increments, or count how many threads you turn it. Best to keep track in case you go too far.

 

This is a very timely question for me. i had a very similar thing happen to me on Saturday.
i took the car on a long drive and my brake pedal became progressively more stiff with less and less travel.
the engine was not overheating and running at normal operating temp.
the pedal was getting to the point that i was concerned that i would not have emergency brake ability and the guy i was traveling with said my brake lights had been on for awhile (pressure switch off the back of the master)so i pulled off
and started checking around the car, the rear backing plates were extremely hot and the fronts were very warm.
after sitting for about a half hour the brake lights were out, i had pedal travel, and i was able to get home without incident. the exhaust pipe runs about 6-8 inches from the master cylinder before turning and exiting in front of the rear wheels.
this was the longest drive i have taken with the car, is it possible for heat alone to cause this stiff pedal problem?
Chappy

 

I had one line close to a header, the line turned cherry red and fluid seeped out of it, found it by tracing the steam cloud.

 

I think that 6-8" would be enough. You should check the pedal rod first while it is cold to see how much free play there is.

 

Thanks Bobss396 i will check it out this evening.

 

If the fluid expands from heat it will expand into the master cylinder, not build pressure in the system unless there is no pedal free play. The only way to have a pressure build up that turns the brake light pressure switch on is if the master cylinder can't return. The brakes can also apply if they are set up too tight on drum brakes. The shoes can expand with heat but the drum should expand a similar amount.

 

as always, this group is great! I'm glad to hear they're related and know what to focus on. Thanks for the tips and keep them coming. I'll look at the exhaust distance from the master/booster, pedal free play distance, leaking brakes, wheel cylinders and drag, and the rod distance between the master and booster. I'll report back.
Gimpyshotrods - I don't have a return spring on the pedal.

 

Are you still running the stock drum brakes? If so, you may want to find out if they are "center-plane" brakes which were common on Mopar vehicles around this time. It took a little extra "finessing" to adjust these brakes properly. I think a lot of the extra effort involved getting the shoes properly centered in the drums. They seemed to work OK but they just required a bit of extra effort to keep them adjusted properly.

 

Funny enough I was just about to reply with pointing out I have the original style drum on all 4. Those were rebuilt as well. But will check them.

So since the focus is on the brakes, attached is a pic (maybe not that great) of the booster and master. I forgot to mention that it's an under the floor set-up, but I think everyone figured that out. I crawled under this morning before work and remembered we routed the dual exhaust to the other side, so no heat source around. I also had to replace the booster check valve when installing the unit originally a couple years ago. As mentioned I'm running the original rebuilt drum brakes all the way around. Also have a remote reservoir on the fire wall feeding into the master.

I got in this morning and pumped the brakes, the pedal did get a bit harder but still have about 1-2 inches of play. Then while holding the peddle I started the truck and the pedal went down but not till the floor.

No visible leaking along the lines or back side of the wheels. Tonight I'll jack it up and spin the tires for drag. and take the drums off to inspect the wheel cylinders.

 

You for sure need a return spring with the under floor master cylinder. The weight of the pedal will keep the brake piston from returning all the way and every time you push the pedal it holds a bit more fluid back in the cylinder just as it would when you pump and hold the brakes.

 

Had a similar problem ( with a hydraulic clutch on a newer car) had replaced the slave unit, put in the wrong number DOT brake fluid. When the engine warmed (about 45 min) the fluid under the hood it would expand and disengage the clutch.
Let the car cool and it worked fine again until warmed up.
The car dealer and they told me to flush the system and only use DOT #4 or DOT #5, worked fine after that.

Master may be getting cooked expanding the fluid.

 

If your drum brakes need some adjustment, your pedal will pump up higher, it has nothing to do with a leak. Even with front discs, my pedal is improved with the rear drums properly adjusted. With a booster, it should drop like you describe, but with the drums adjusted, it will drop less. It never hurts to pull off a drum and look things over. Look at the rear of the backing plates first, anything looks funny, pull that one first.

 

Thanks, also I'm an idiot, forgot to also mention I installed a adjustable proportioning valve.

I'll check to see what brake fluid I have in the system, I think I still have a partial bottle.

I'll look inside the cab to see where and how I can connect a return spring.

 

Dot 5 is the silicon brake fluid. Dot 3, Dot 4 and (rather confusingly) Dot 5.5 are the non silicon variants. Dot 5 doesn't play with the others nicely and can have an adverse effect on rubber components.

Chris

 

***uming all rubber is new(hose's)?

 

Good to know, thanks Chris. I'll check tonight.

 

Yes all new rubber and solid brake lines

 

Although I will double check all connections as well.

 

Ok, got home late from work, I removed the check valve and it's bad AGAIN. Why would this go out twice. I picked up a new one and true vacuum line hose, I used fuel line currently. I'm also thinking of adding a vacuum canister for good measure. Tonight I'll find the half bottle of brake fluid to see the DOT and jack it up to inspect drag and wheel cylinders. I'll also look for a way to mount a return spring.

 

Has the engine backfired, ever?

 

Funny enough, yes as a matter of fact it did last year thru the carb, but none during this last trip. I checked the timing and adjusted the carb to a more rich mix and it ran much better but not great. I also had a hunt Magneto look-a-like distributor and running a rebuilt '56 generator. I sent the hunt distributor out to get modified to an external coil and I replaced the generator with an alternator and it hasn't done the backfire since and ran great. Great power and gets up to 60 pretty quick and decelerates just as smooth.

 

As an update, the brake fluid used was DOT 3. No dragging when I jack up the truck and manually spin the tires.

 

This is a problem I ran into this spring.

https://www.jalopyjournal.com/forum...asing-pressure-after-running-vehicle.1104102/

 

Thanks Petejoe and others that pointed out the booster pin adjustment issue. I crawled underneath late last night after work and did see that the booster pin had no clearance with the master cylinder. So I adjusted that out. Maybe tonight I'll hook up the vacuum canister and take her out tomorrow for a spin and see what happens.

 

That's your problem... no holes for the fluid to p*** thru...

 

That's the problem I had. I adjusted the booster pin correctly when installing new, but since my booster was ch***is mounted it was getting very warm/hot from engine/header heat. I finally figured out that the rubber diaphragm was becoming "more pliable" for lack of better words and the engine vacuum was applying the brakes.
A little extra clearance and problem solved.