6X6 brake ideas?

[Overkill6x6]

Im putting a pair of 14 bolts under the back of my 90 cclb. I'll be leaving the drum brakes on it. Does anyone know if I can take a master cylinder off of a newer truck with hydro boost and 4 wheel disc with the push rod and make it work? Will a rear disc master be able to run four wheel cylinders on the rear circuit?

 

[dremu]

This is something I wanted to do with my old crewcab and didn't have the space/time/justification. I'm jealous One of the Fast & Furry movies had a six wheel crewcab with a flatbed, soooo sexy.

Some thoughts: I looked for but never found a slave cylinder, to slave the tandem axle to the middle one.

Failing that, you could certainly tee the rear brakes together. Discs take more volume to activate, if memory serves, so a disc/disc master might flow enough to do four wheel cylinders. It might also generate enough pressure to send them to Guam, so an adjustable inline valve for the rear circuit is probably a good idea. You might also want to bump up the rear hardline one size (if factory is 1/4", go to 5/16" or 3/8".)

I suspect you'll do a lot of Googling and prolly find better results on hot rod sites, as they're the people doing totally custom brake setups and mixing and matching parts.

Oh, speaking of switching to hydroboost, I've done it on multiple trucks. Well worth it, but you do have to swap a bunch of parts (brake pedal, booster with pushrod, and the master, regardless of disc/disc or disc/drum, has to be for a hydroboost and not vacuum as the mating is different.) Lots of good info in this thread https://ck5.com/forums/threads/illustrated-hydroboost-swap.306221/

Wondering how you're doing the suspension? Leaf springs for both, one set inboard of the frame, maybe? Links? Inverted leaves like the semis?

Also curious how you plan to drive the tandem -- divorced 205 or the like?

-- A

 

[Overkill6x6]

Trucks already hydro boost, forgot to include that. To complicate it further I'm seriously considering cutting brakes for the rear as well (need all the help I can get in the turning radius department).

Yes it'll be leaf suspension with the rear most inboarded. The tails of the leaves will be mounted on a cantilever. Similar to multidrive.com.au. I've got a 205 on the back of the 465 then there will be a jack shaft to a Dana 24 turned backwards for the dual outputs

 

[dremu]

For disc-disc, your best bet to find a compatible master cylinder would be for a P30 van. Some of them came with disc/disc and hydroboost. Note there's MANY variations, so they also came with disc/drum.

There was a member here years back had a custom tandem axle made up with a stub shaft through the R&P. Donno if he ever put together the truck Trying to remember the axle, it had D70 outers, which are basically the same as the 14BFF, so it coulda been a helluva thing.

Anyway, keep us posted. I suppose you could put the truck up on stands and video the wheels as you brake, see which end stops first. Obviously that doesn't take into account weight loading in real-world conditions, but it'd give you an idea of the abilities of the hydraulic system. Plus it would look cool

Oh, and good call on keeping the drums. 14BFF drums, either SRW or DRW, are quite good at stopping, simple to work on, and have a decent parking brake. Come to think, with some clever cable work, you could have all four parking brakes working.

-- A

 

[Overkill6x6]

Good thinking! We have a p30 on the farm with hydroboost, totally forgot it had it (they still drive it so I can't steal parts but it'll be easy to check the difference).

Truck is srw and I figured four drums would be easier to figure out. I thought of linking the parking brakes with the same bracket they use to split left and right, now just behind the factory bracket. Might have to take out the extension in the factory cable and move it all forward to get enough room to tie it together.

I'll be putting a build thread together once I get it back in the garage. The holidays kinda killed the momentum.

 

[dremu]

You'll also want an adjustment between the front and rear parking brakes, a piece of threaded rod or something. Or do two loops, each with its own adjustment ..shrug..

Fortunate on having a P30 handy. I had to make multiple runs to the parts house, they got tired of seeing me

-- A

 

[diesel4me]

I could be wrong but I think disc brake master cylinders dont have a residual check valve built in, that drum master cylinders have--that keeps a slight "pressure" on the wheel cylinders to prevent having to pump the pedal to get full braking action..

There are some good reads online about master cylinder swapping regarding this...and other potential issues you may encounter..

 

[FOR MUD]

Do you really need both axles braking? A disc setup on a std two axle truck can stop a ton of weight.

 

[campfire]

I could be wrong but I think disc brake master cylinders dont have a residual check valve built in, that drum master cylinders have--that keeps a slight "pressure" on the wheel cylinders to prevent having to pump the pedal to get full braking action..

There are some good reads online about master cylinder swapping regarding this...and other potential issues you may encounter..

I think the residual check valve is combined with the proportioning valve on these rigs.

 

[campfire]

If possible I highly recommend the G3500 axles with removable brake drums. Much easier to work on than the older style of 10.5" axle.

 

[Overkill6x6]

Do you really need both axles braking? A disc setup on a std two axle truck can stop a ton of weight.

Probably not. But I had thought not having an inter axle diff that if I try to lock them up at speed with brakes on only one axle that it would torque the rear driveshafts and Dana 24 pretty good?