Mid 40's Mack Firetruck

[David Johnson]

I'm not sure where to start so I figured this is the best place as any.

I work for a City Municipality in the fleet department. They have a 1940's Mack Firetruck that they are wanting to use in parades and events. My boss says that hi is not happy with the performance of the factory 4 wheel drum brakes and wants to upgrade to a more modern braking system. I have no experience with these trucks but I can tell that will not happen with the current wheels and axles. I am thinking  that a modern axle swap would be the best route. What are the opinions on that?

if I do an axle swap, I think I would need to find a drop I beam for the front so that the ride height doesn't change or can I do a spring under solid front axle like out of a modern 1 ton truck? I also thought that if I could find modern knuckles that fit the 40's drop axle I could go that route. 

Any info would be greatly appreciated or if you just want to spitball ideas that would be awesome.

 

Thanks,

David

[alex g]

Not sure exactly what performance your boss is expecting to get out of a truck pushing 80 years old but before spending a Lot of time and money I would inspect your current brake system and service it. Drum brakes work fine for a parade truck. Your wheel cylinders are probably half seized and brake drums are probably rusty from sitting. If you get it working properly it will probably be good enough.

[David Johnson]

I'm not exactly sure what he is expecting either as far as performance. I do know this though, he wants to pull all plumbing, water pump, engine and trans and go back in with a fuel injected 350 with auto. I'm thinking we wants the look of vintage with it being more streetable. It is not going to get towed to locations but driven.

[David Johnson]

All 6 volt electrical will be pulled and 12 put in its place 

[Maddog13407]

might as well scrap it then. whats the sense? usually with projects like this, someone has all these ideas, truck gets torn apart, they lose interest and money and it gets parted out and scrapped. why not take some good advice, service the brakes, engine, rebuild the carb and see how she works out first. especially if its gonna be a parade truck driven three times a year

[kscarbel2]

For what you are describing, place the vintage body on a modern F-450/550 chassis.

[Maddog13407]

or an 80's-90's dodge 1 ton with a cummins and stick

[fxfymn]

What model truck is it? Please give us the chassis number as there is a substantial difference between an L model and an E model.

If you want to do a resto-mod then do what has been suggested here and go with a modern chassis and just move the sheet metal over. But, there are plenty of 40's era trucks running around that are perfectly functional and safe that are still using the OEM equipment.

The truck is already a 12v system, but it is positive ground. My $.02 is its not worth the hassle to change it to negative ground, but if that is what he wants to do "hit it Willy".

As for the current brakes; if they are functioning properly they will stop the truck as well as any other braking system. Properly adjusted and with a properly functioning vacuum booster they should lock the wheels up if that is what is desired.

No, they are not ABS and they do require an operator who knows how to use an older brake system, but they are perfectly safe as is with the possible exception of not having a dual master cylinder. If he is really anal about that than a dual MC can be fitted without a lot of hassle. Besides, if the driver doesn't know how to use drum brakes he/she probably can't drive a non-synchronous transmission either. (or maybe any standard tranny these days)

My guess is you are looking at the better part of a $100K bill to make a resto-mod. If you just need to repair the brakes and do some cosmetic work it is probably closer to $10K and the brakes alone should run around $2K.

 

[David Johnson]

Thanks for the advise everyone. I will get the Model number as soon as I can. I am new to the shop and just get bits and pieces of info. I am a heavy equipment tech but have no experience with vintage Mack stuff. I learned  today that the wheel cylinders and brakes have been replaced multiple time by previous techs. 

    I finally got a chance to crawl under it and I didn't even know it had a brake booster until I was looking at it. That would make total sense if the brake booster wasn't functioning properly. 

[David Johnson]

As a second thought, I kind of really like the modern engine and trans route. I think that would be really cool and unique.

[BillyT]

Everyone has good ideas, but what size truck is it? Is it a full sized pumper like 5 ton or bigger and running I think Fxfymm has the ticket the trucks of that era had "bone simple" brake systems,and if the wheel cylinders aren't gummed up from sitting and it's properly bled the booster would be a good thing to check! Probably the most expensive single component so the previous tech may have never replaced it! Good luck David!

[fxfymn]

1 hour ago, David Johnson said:

Thanks for the advise everyone. I will get the Model number as soon as I can. I am new to the shop and just get bits and pieces of info. I am a heavy equipment tech but have no experience with vintage Mack stuff. I learned  today that the wheel cylinders and brakes have been replaced multiple time by previous techs. 

    I finally got a chance to crawl under it and I didn't even know it had a brake booster until I was looking at it. That would make total sense if the brake booster wasn't functioning properly. 

I'm thinking we are all going on the theory that the brakes are not functioning properly now. I'm also assuming you have driven it and tested the system yourself. Letting us know what it is actually doing would be helpful. 

Not to dis your co-workers, but I'm sure they have worked on very few, if any, hydraulic brake systems that use shoes. In other words, don't take someone else's word for what has been done and what is right or wrong with it. Go back over everything methodically and don't be ashamed to get out the books and follow them if you haven't worked on these before. Or even if you have and your memory is like mine. And remember that what is on there may not be correct since someone else has been into it. If the first guy did it wrong and everyone else has just put it back the way they found it, then that may be the story.

Like all trouble shooting problems I'd look at the simple stuff first. Brake adjustment, shoes on correctly (primary and secondary in the right place), glazed drums or shoes, brake bleeding, and vacuum to the booster all come to mind.

There is a filter in the vacuum line and the vacuum line probably runs to the pump as well, so I'd make sure the booster has vacuum before you remove it. The filter is located somewhere in the line, most often under or just behind the right front seat. The booster also has a vent that needs to be open. Mr. Mud Dauber may be in town, so you should check it. If the diaphragm is bad it will most likely blow blue smoke out the pipe from the brake fluid being pulled into the intake manifold.

My experience is they can be a bitch to bleed. They need to have the booster bled as well and I have found that doing that first works out best. I ended up using a pressure tank to force fluid through the system after trying conventional bleeding for the better part of an afternoon on mine.

I'm thinking the rear wheel cylinders are no longer available, especially if it is an E model. If so, I'd be pretty suspicious of the story that they have been replaced "multiple" times and if they have then they may be the wrong wheel cylinders. If it is an E model I have the PN if you need it. If it is an L model someone on here will have it.

[David Johnson]

Thank you fxffmn. I will get the model number tomorrow. Will it be on the plate on the body under the passenger seat?

[41chevy]

With all the good tips that FXFYMN mentioned 3  things can cause "poor" braking that I've come across with dozens of older vehicles that have passed through my doors, is the following

  When the systems get worn, the new relined shoes have a tendency NOT to get full contact, they  most times need to be "arced" to mach the drum. The old AMMCO Brake lathes have the set up to Arc the shoes to the drum radius  You place the shoe in the drum and see fit between lining and drum you may find minimal contact.

Many of the problems can also be to the lack of know how to properly adjust the brakes properly  (no inference to your skills) 

Look closely at the flex hoses, the OEM replacements until the mid 1960 when the aged  if they did not crack the would some times expand under braking and loss stopping power at the shoes.Some would get an internal crack that would either block the pressure to the wheel cylinders or stop the pressure from releasing to un apply the brakes. I've seen more to the first than the latter.

FYI I'm an ASE  Master Tech on Automotive and Heavy Truck for 34+ years    Paul

[fxfymn]

12 hours ago, David Johnson said:

Thank you fxffmn. I will get the model number tomorrow. Will it be on the plate on the body under the passenger seat?

It should be, but if it's not it should be on the front right frame horn. It will be something like 85L1001.

 

[BillyT]

41, forgot about "arcing"  New brake linings or older ones that aren't making full contact! When I was about 18 my buddy and I befriended an old German mechanic who had a private shop.His shop was in a wealthy area of Pittsburgh Pa.He showed us how to do a proper brake job! Remove and clean all the brake hardware replace any worn parts and lube everything! Also, and nobody including me does this anymore, put the linings in a vise and hand arc the linings with a rasp so they make full contact with the drums! He only worked on wealthy folks caddy's lincolns,and other expensive cars! This was in 1963 when only a few American cars had disc brakes (Lincoln was one) but if you got in a 1940 truck with perfectly functioning brakes and compared it with a modern truck of similar weight the 40s truck would feel like the brakes were defective! So for the old truck to stop adequately it would have to be in perfect order,hence arcing !the linings! My dad had a 1946 Chevy 1.5 ton flatbed and a 39 Diamond T 201 wrecker,both had straight hydraulic brakes with the master cylinder under the floor! You would be hard pressed to lock up the brakes on either one loaded! But most truck drivers of that era knew to maintain the proper following distance!