1948 KB5 Railway Express


The place to put your K or KB "Build Off" story.

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Mon Aug 16, 2021 6:46 pm

Re: 1948 KB5 Railway Express

LOL, not going to say you are full of it. It may or may not have originally had the Hydrovac. When I got it, the rear brake line that went to the rear axle was 1 piece and rusted. The master cylinder bore is 1 1/4" used for standard brakes while the "power" master cylinder is 1 1/2". The truck also has the external brake fluid fill tank on the firewall and it was on the truck and appears period correct. That would suggest no hydrovac. My brake pedals appear to be original and do not have what appears to be needed linkages for the hydrovac, and there is only the single nipple on the intake manifold to pull vacuum off of and it goes to the distributor's vacuum advance. So from the physical appearances and parts I do have that came with the truck and if the info in the K & KB Service Manual is correct, the truck did not have the hydrovac system.

Does it mean that someone went to great lengths to swap out all the hydrovac parts and install a "standard" braking system, anything is possible in 70 years. The hydrovac appears to have been an option on the KB5 and I have enclosed a photo of one that is found on my brother's spare KB5 chassis. I could have added it, but felt it was not needed since the truck will only be for show, act as an advertising billboard, and sit most of the time. If needed, then it could be added in the future.

The addition of the check valve was done by myself and the lines are all new and also cut/flared/joined by me as you see it. So that is not anything factory, just an add-on I thought might pan out to be a good idea.

I honestly am not sure how it will stop, but road speeds are not going to be high, maybe 45 MPH, as it does not have overdrive, just the 4 gears and reverse. Being a truck driver, I know how to also use gearing to slow down as I am sure you do.

I am not sure IF these rear wheel cylinders are indeed the "mountain brakes?" The KB5, according to the Manual show the standard rear wheel cylinders as 1 3/8" x 11/16". The Manual also lists the "Special Wheel Cylinders" as the same 1 3/8" x 11/16" BUT the "Increased Capacity" brake shoes are listed as 15" x 4" x 3/8" and 15" drums. So is this a misprint if the "Standard" and "Special" rear wheel cylinders for the K-5 are the same? According to the Service Manual, and looking at the K-6 brakes, it seems that the "Increased Capacity" rear shoe is the same as the optional "Increased Capacity" rear shoe/drum for the K-5. Shouldn't the larger rear wheel cylinders also be part of the "Increased Capacity" brake shoe option?

So for arguments sake, lets say the "Mountain Brakes" were the optional 15" x 4" x 3/8" shoes and 15" drums. If you look at the rear wheel cylinder sizes, the K-5 uses the 1/3/8" x 11/16" and the "Special Wheel Cylinders" are listed exactly the same as 1 3/8" x 11/16". Then looking at the K-6 with the same optional brake shoes/drum (the "Increased Capacity") uses a larger rear wheel cylinder size of 1 1/2" x 3/4". The K-6 also uses a larger 1 1/2" bore Master Cylinder according to the Manual.

IF the photos of the rear brakes for the K4 - K11 Hydraulic brakes are correct, they all show the same style of rear wheel cylinders with the only difference being that there appears to be 2 different bore sizes, 1 3/8" x 11/16" versus 1 1/2" x 3/4".

With all that said, it is my guess that the "Mountain Brakes" on a K-5 would be the use of the larger 15" shoes/drums, and possibly the larger rear wheel cylinders.

Again, if the original rear cast brake shoes are correct for my truck and the rear axle has not been swapped out, from what I seem to come up with, and according to the Service Manual, it seems my KB5 has the "Standard" 14 1/8" x 3" x 3/8" shoes and the 14 1/8" drums and not the "Increased Capacity" or "Mountain Brakes."

I am open to comment if you can clarify any of this - just this 1 time. LOL

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Mon Aug 16, 2021 6:47 pm

Re: 1948 KB5 Railway Express

Picture of the KB5 chassis and Hydrovac.
Attachments
KB Hydrovac.jpg

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Mon Aug 16, 2021 8:03 pm

Re: 1948 KB5 Railway Express

You seam to have the mistaken impression that the hydro-vac connects to the brake pedal, it does not. There was a vacuum booster used on smaller trucks that did, but that is not a hydrovac, it is a simple vacuum booster.
I don't know how haveing a remote fill would preclude a hydrovac,
A master without power will have a RPC in the pressure outlet inside the master (rear end of the spring) and master for a hydrovac will have the RPC in the outlet of the hydrovac.
The picture you have of the K5 hydrovac will be obvious it has NO (mechanical)connection to the pedal or the master, it is controlled off hyd pressure. If you don't believe me, go out and look at that chassie
I have a K7 and a KB-7 the rear wheel cyl size and the GVW rating are different, the K-7 has the k-6 wheel cyl size and the lower GVW, but the rest of the truck is all -7. The -6 uses a different spring set up on the rear. Even the manual doesn't show this setup ( -7 with smaller rear wheel cyl), While it is possable that someone swapped a -6 axle and brakes onto a -7 suspension and truck, the difference in GVW would point to it being built with the lighter brakes.
WHat I am saying is the manual isn't gospel when comes to what has come out of the factory.
Drum brakes require a RPC in the system but can not have more than one in series. If your master has one, your added ones will result in the brakes not releasing fully and as the fluid temp increases the drag becomes greater, which heats the fluid more and can eventually lead to the brakes locking.
There are 3 sizes of the hi Tork wheel cyl you left out the 1 3/4 x 7/8. The larger SINGLE rear axle use the larger rear cyl while the tandem rear axle trucks use the smaller as they have 4 brakes stopping the load (in the rear) as opposed to just 2.
For some reason I thought yours had the 15" rear shoes, I don't know what lead me to that, so you may be right, it might not have had a booster, or it might. 70-80 years on it is hard to say. I am fortunate that at least one of my trucks, I am only the 2nd owner and KNOW nothing has bee changed.
Driving these trucks in the real world, I can tell you that the hydrovac makes a huge difference in stopping power. Grossing 18k a 269 low compression engines isn't going to slow the truck at all, a 233 isn't going to do any better with the lighter truck. You don't have the compression that a diesel has and you don't have the air to compress with a throttle closed.

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Tue Aug 17, 2021 8:32 pm

Re: 1948 KB5 Railway Express

OK, I got it. Apparently there were 3 types of power brake assist in the Manual, 1 - Power Vacuum Unit, 2- Second Series (B) Hydrovac, 3 - Third Series (C) Hydrovac. The Manual does not state year or truck type used.

I have included a picture of 1 & 3 for others to see. I was looking at #1 having the different brake pedal/rod connections when I posted. You are referring to picture #3, which looks like the photo of the chassis I included.

In #1 you can see the pedal/rod arrangement and how it connects to the vacuum canister. This set-up appears to be just that, a vacuum assist that aides the operation of the master cylinder when the pedal is depressed by additionally pulling back on the pedal. The master cylinder in the picture is the larger truck type which I removed from my truck as it was the replacement "777 1 3/4" bore" said to fit the KB5 when in fact it was too large of piston bore and not the original to my truck. The people the truck was purchased from had installed it along with the incorrect front wheel cylinders, new rubber hoses, and steel lines and said the truck had brakes. It took 2 feet to press the pedal and barely stopped the truck from a 2 MPH roll. So a little false advertising, but I did not know that 4 years ago.

In #3 this is called the "Hydrovac," not the "Power Vacuum Unit," so a different design, apparently a "B" and "C" design. I can see that it is not hooked up to the brake pedal as the power unit is. The line coming off the master cylinder connects to the unit and then uses the vacuum piston to apply force to the slave cylinder which then applies that pressure to the wheel cylinders. The "Residual Line Pressure Check Valve" is seen just before the outlet fitting for the line going to the wheel cylinders.

OK, got all that. Again, I don't feel my truck had this due in part to what was left of the rusted rear brake lines and the original type brake line distribution block where all the lines connected from the master cylinder - to include the larger steel line (5/16"?) that went into the brake line distribution block. I don't know where any holes in the frame might have been drilled to attach the Hydrovac or if all frames were drilled for the Hydrovac as an option when so ordered.

I decided to install the aftermarket RPC on my own as I know what their purpose is and thought it was a wise addition to the truck's braking. I did not know that the Hydrovac had this as part of the design.

My guess would also be that the Hydrovac has the longer and smaller bore slave cylinder that would also by design increase line pressure? I know that using a smaller bore MC will increase line pressure and use less pedal effort versus one that is larger, but the problem becomes that it also typically does not move the needed brake fluid and you can find the pedal going to the floor. The larger bore can move more fluid volume with less movement of the pedal, but requires much higher pedal effort to push the pedal. So MC bore, wheel cyl. bore, and pedal fulcrum ratio all have to match for a good braking system.

I will see how well the truck stops as is. I have a number of options I can do if needed, from the Hydrovac on the spare KB5 chassis to hydroboost if I wanted to go modern. My goal here was/is to keep the truck as close to factory as original since it was/is very complete and in such good shape. I wish it had not been and then I would have upgraded it to a V8/automatic, late model axle/front discs, late model rear end, and late model braking. Probably would have been much easier and already driving and on the road by now.
Attachments
kb5 -Power Vacuum.jpg
kb5 - Hydrovac.jpg
Last edited by mrjim2017 on Wed Aug 18, 2021 6:28 pm, edited 1 time in total.

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Wed Aug 18, 2021 8:06 am

Re: 1948 KB5 Railway Express

Hydrovac's were used from the get-go on the larger series K's and were in continual use up until most medium/heavy trucks moved to diesel and air brakes became more common
To be honest I don't think I have ever seen the vacuum cyl on the brake pedal set up on a truck, only in the books, but I deal mainly in the heavier trucks and not the lightest. They have proved to be incredibly reliable and I have several 80 year old units working. I much prefer them to hydro boost but require a vacuum source. They only can boost pressure not volume, like any assist so the master provides all the volume of the fluid, the hydro-vac increases line pressure.

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Wed Aug 18, 2021 7:15 pm

Re: 1948 KB5 Railway Express

OK, edited my previous post. My images were too large and I resized them smaller.

Again, not 100% sure what trucks used what power options. Going by the Manual, it says "IHC Models Using Hydrovac (Standard) - the various models from K-6 thru K-10". Then on the side bar it lists those models having the Hydrovac as an option, "K-5, KS-5, KR-11, and KS-11."

Air Brakes appear to be a Special option on the K-7 thru KR-12F

The K-1 thru K-3M only show the standard hydraulic brakes only, no power option.

The K-4/KS-4 and K-5 Models available with the Optional "R-66 Vacuum Power Cylinder" having a 6 3/4" diameter vacuum cylinder. The Manual lists different vacuum power cylinder sizes, but this may be generic info from Bendix who made the units available.

The K-6/KS-6 and K-7/KS-7 are standard with the "R-66 Vacuum Power Cylinder."

The K-6-T/KS-6T/K-6F is shown using the R-76 Vacuum Reaction brakes with a 7 3/4" diameter vacuum cylinder (which seems to the model number given the "B" Hydrovac system)

The larger "C" Hydrovac system used a 9 1/2" diameter vacuum cylinder and was standard on the K-8T models, K-8F, and K-11F/KR-11T models.

So back to the KB-5, the brake options were a standard hydraulic system (which mine has), and Optional "R-66 Vacuum Power Cylinder" (which is the first drawing from above), or the Optional "Hydrovac" (which is the second drawing from above).

The chassis/trucks get bigger, the Vacuum Power Cylinder and Hydrovac become standard while the Air Brakes are an option.

Along with the options above, you also have those larger brake drum/shoes of the "Mountain Brake" options.

I think that covers it, but I am no expert, just going y what is printed in the Service Manual - 1940 1/2-1949.

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Aug 19, 2021 7:48 am

Re: 1948 KB5 Railway Express

Close, The R66 is a hydro vac, the same one used on the single rear -6,-7. I can't find any reference to what uses the pedal connected vacuum chamber. It MIGHT have been used on the early COE trucks, there is little info on them. A -5 with power brakes would most likely have the hydrovac, but may have had the pedal cyl, I just have never seen one in all the old trucks I have been around.
Again, it comes down to what is written in the manual is not what always turns up on the trucks. The manual covers a lot, but seams to be inaccurate as what came with what, there was more mixing of parts than the manual indicates. As in later years, where you could spec a Loadstar with a higher GVW than a Fleetstar, although the Fleetstar line was a "heavy truck" and the Loadstar a medium truck. It just depends how it was ordered.

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Sat Aug 21, 2021 8:53 am

Re: 1948 KB5 Railway Express

Further research turned up a 1944 Military Training Manual for the Bendix "Power Vacuum Unit" and the "Hydrovac."

The R66 & R76 are shown to be the Power Vacuum Unit, not the R66 Hydrovac as you have said or the R76 as I had thought. Maybe the designation was changed post war?

There is also a 1st Series Hydrovac and 2nd Series Hydrovac shown in the manual. There is no 3rd Series, but this may be due to the date of the training manual - 1944.

Here are the pics of the various units. You can click on each pic to make it larger if needed.
Attachments
01  Power Vacuum Unit.JPG
02  Power Vacuum Unit.JPG
03  Hydrovac 1st Series.JPG
04  Hydrovac 1st Series.JPG
05  Hydrovac 2nd Series.JPG

Golden Jubilee
Golden Jubilee

Posts: 5171

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Sat Aug 21, 2021 10:27 am

Re: 1948 KB5 Railway Express

All I can tell you is what I have seen both in person and in my IHC manual.
Never seen a -6 or larger with anything but a hydrovac
Manual list R-66 for -6 and -7 execpt R-76 for tandem -6
The list a RP-66 for -7 COE trucks. No info on what the RP is but pedal type?
The CTS-8 doesn't list any truck using the pedal type, or call out where they were used.
Without any documentation to the contrary, and my observation, I can only conclude that R66 is the std hydrovac seen on the -6 and -7
There is no cross reference between R numbers and hydrovac numbers. the same can be said for the pedal type, no cross reference.
I will note that the R number corresponds to the diameter in inches and 1/8ths of an inch (first digit 6= 6" 2nd digit 6 = 6/8") and that holds true for all hydrovac's and vacuum assist cans. (R76 is 7 3/4" R94= 9 1/2")
The power cans seam to be the same in the hydrovac and the assist can, just how it is controlled and how the assist is applied to the system is different.
Give all that, I think RP is safe to assume that is a pedal unit and the plain R are hydrovac's.
Admittedly the manual doesn't call it out specifically, but given real world exeriance, it is a safe bet.

Rusty Driver
Rusty Driver

Posts: 195

Joined: Mon Sep 04, 2017 6:22 pm

Post Sun Aug 22, 2021 7:54 am

Re: 1948 KB5 Railway Express

OK, more info. Yes, seems the First letter designations on the assorted units is what identifies them. "H" is hydrovac and therefore H66 is the Hydrovac version.

There is also the Slide Valve unit "RP60."

Then there is the "PDL" Pull Unit.

And the "RXL" valve used for tractor trailer applications.

Hopefully this may add to the discussion and clarify the brake differences. As you point out, the actual factory manuals would most likely provide better answers as to truck type and application. And, seeing some of these applications were war and post war, what was supposed to be used and what was actually supplied could easily be different due to lack of parts or available assemblies.
Attachments
Hydrovac 1st Series.JPG
Hydrovac 2nd Series -01.JPG
Hydrovac 2nd Series -02.JPG
Hydrovac 2nd Series -03.JPG
Slide Valve -01.JPG
Slide Type Valve -02.JPG
PDL - Pull Cylinders.JPG
RXL Valve -01.JPG
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