K-7 GVW and Brakes


The old and reliable.

Golden Jubilee
Golden Jubilee

Posts: 5170

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Sun Oct 30, 2022 6:27 pm

K-7 GVW and Brakes

I have two K-7's one has a GVW 16500 and the other 21500, big difference!
On the one with the lighter GVW, it is a '42 and has all the hallmarks of being made for the Military, or had been used by the military. Has the military steering wheel, three bolt ball antenna mount and other things on the cab that make me think it was a war truck.
Interestingly it has 15x4 rear brakes and the small 1 3/8"x 11/16 hy-torque wheel cyl that are called for on the K-5 and K-6F or T and not the larger 15x 4.5" brakes and wheel cyl used on the K-6 and K-7. Everything else is K-7 (suspension which differs from both the K-5 and K-6).
It is possible someone swapped a K-6T axle in at some point but given everything else, I think it is as built.
There was no hydrovac mount under the pass door, but there was one on the frame that someone put there (flame cut bracket not purpose made). There was an unused bracket riveted under the pass door but it was too small and too far back for a hydrovac.
The guy I bought the truck from thought it had air brakes because there was a period looking air pressure gauge in the dash, but there are no other signs it ever had an air system, no brackets for compressor or pulley to drive a compressor. I doubt it ever had an air system.
Every K-7 I have seen has a hydrovac or air brakes, I have never seen one without a hydrovac and juice brakes.
Bearing were branded IHC, I don't know what timeframe they did that.
Looking for a return spring IHC #95-984H, Wagner number FC6785 NSN 5360-00-3533019
No luck anywhere. The Mil spec places show they have them, but when I try to buy they will not sell to end user. I know someone here found one of them that will sell to you but I don't know who it was or which site they used.

Golden Jubilee
Golden Jubilee

Posts: 5170

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Sun Nov 13, 2022 10:22 am

Re: K-7 GVW and Brakes

wagner box 2.jpg
Working further, I found I needed a brake piston. There are a few N.O.S. brake cyl on ebay right now but even if the bore's of the cyl match the casting numbers vary depending on what the application is. I can only conclude that to accommodate differing widths of shoes, different cyl were used even if they share bore diameter and general outline of shape.
I was able to come up with a N.O.S piston and my cyl honed out ok.
I was hoping to get all this brake work done before the cold weather closed in, no such luck, was 10 deg F this am and the past few days the windchill has remained stubbornly in the teens. Arthritis and general old age makes working outside with cold metal miserable in those conditions.
Sometimes opening the N.O.S. packaging seams like a crime, they sure knew how to package back then.

Golden Jubilee
Golden Jubilee

Posts: 5170

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Nov 24, 2022 3:28 pm

Re: K-7 GVW and Brakes

Ok, so I spent some time in my manual today, and think I have the answer to the hydrovac mystery on this truck.
Early K-7 were fitted with the 2nd series Hydrocvac's which are smaller in diameter than the 3rd series
6 3/4" tandem vs. 9 1/2"single. That would explain the too small bracket riveted under the pass door, and the piping to that point. So at some point the original hydrovac was replaced with the larger replacements that were used in later K-7s. Rather than change the mounts and modify the running boards to allow the bigger unit, they extended the hoses and mounted the hydovac behind the cab.
I was trying to figure out what was going on as the frame had the holes in it to run the brake lines for under the cab hydrovac.
I ended up just copying the install of my '48 K-7, modifying the running board and installing the hydrovac bracket with bolts.
It is great to have it back together and stopping.
Still curious about the low 16500lb GVW however, why get a K-7 when a -6 would cover that GVW?

Golden Jubilee
Golden Jubilee

Posts: 5170

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Thu Apr 06, 2023 7:15 pm

Re: K-7 GVW and Brakes

After the winter the RF wheel cyl started leaking. Not going to make the mistake of assuming it had what the parts book said it was supposed too, I pulled it down to find, sure enough, it didn't match the part book. Again the wheel cyl are smaller this time 1 3/8x 1. Book calls for 1 3/8x 1 1/8 on everything from the K-5 thru the K-7.
Wagner casting number of FC 2767.
I think Ford uses this cyl on some vehicle of the same vintage.
I would have guessed that someone put "Ford" cyl on the front because they couldn't find the IHC size if it were just the front that were odd. I may be wrong but I don't think Ford used the HI Torque rear brakes. With both front and rear being smaller and the GVW being lower than my other -7 I think this is as built.
Another oddity, one piston is aluminum and one steel?
Cups are coming soon and I think the cyl honed out well enough.
FC 2767 is still available new if I need to go that route.
Hard part is getting disassembled without breaking the bleeder or mounting bolts, or damaging the hose.
Brakes will plant your face on the steering wheel even with the cyl leaking. Only leaked when the temp changed (when it got cold at night).

Golden Jubilee
Golden Jubilee

Posts: 5170

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Sun Apr 16, 2023 9:44 am

Re: K-7 GVW and Brakes

Well I got both sides apart, honed and new cups installed, but I still have the same problem, the right side leaks when the temp drops. It was in the 80's now in the 30's and I have brake fluid on the wheel! Bummer. I think the right wheel cyl may have been honed out a few too many times. The casting looks more "weathered" than the left casting did. I am going to try one of the "Ford" cyl and see if it is a match. Available from "Dorman" as a W8265 for around $50. Casting is a direct interchange the question is: Are the pistons a direct interchange.? There are many kinds of pistons made for wheel cyl, some with "slots" for the shoe to contact, some with pins between the shoe and piston. Slots can be different widths, and pins can be attached or separate. Worse case I should be able to use my pistons in the new casting.
The "Ford" cyl and the cyl that is presently on my truck are not what the parts book calls for, The large piston is the same 1 3/8" but the small size is 1" vs. 1 1/8". Not a big enough difference to be a deal killer, and I don't know that mine didn't come out of the factory that way.
I'll post my results. It would be good to know that some sort of front cyl is available new. and worse case situation, if the casting fits and is correctly orientated, could have the small side bored to 1 1/8" and the original piston fitted to a K-6 or -7 with 1 1/8" small side cyl. Boring would be cheaper than bore and sleeve and could also be used when the original casting is damaged.
They were used on late 40's early 50's Fords and some Checker cabs, according to what I can find on the .net
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Golden Jubilee
Golden Jubilee

Posts: 4922

Joined: Thu Nov 29, 2012 11:47 am

Location: Bothell, Washington

Post Sat Apr 22, 2023 4:53 pm

Re: K-7 GVW and Brakes

a seller on eBay has new KB-6 and 7 Front and rear cylinders reproduced,

I bought fronts a few months ago, only issue I had was the groove in the cup is too narrow for the original shoes to fit all the way in, just had to grind thickness of end of the shoe, works great so far,
Gentle Men! you can't fight in here! This is the war room!

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