Hi all, I recently swapped the original 8 lug drum brake Dana 44hd in my 73 W200 for the kingpin disk brake Dana 60 from a 1990 W350. I also swapped in the power brake booster and master cylinder from the W350 to replace my original booster and master. I did not change the pedals in the truck. When I first fired it up and hit the brakes it basically sucked the pedal in and the brakes stuck. The pedal could be pulled back out. The pedal pushrod was lengthened a little based on the advice of a local 4x4 shop. This made everything work, but it obviously isn't right. The brake pedal sits about an inch farther out than the clutch which makes it pretty uncomfortable to drive, especially in a regular cab since I can't move the seat back!

Any ideas what I'm missing? Do I need a different pedal length from a later truck?

Any other information I can provide to help figure it out?

Other than the location of the pedal the truck does stop really really well now which is a great improvement!

Thanks,
-Jon

Don't see how lengthening the pushrod could help.

Your problem is likely a stuck valve in the old booster. It could be the brake light switch was causing the pedal to stick the pushrod in and activate the booster but a longer pushrod would seem to make that worse.

Pedal assemblies shouldn't have to change.

Did you get the W350 proportioning valve to be compatible with the front discs? You're 4 wheel drum unit isn't correct.

Agreed on prop valve needed from donor truck.......was the older truck already power brake? If so try putting that booster back on......also is the brake light on now?

Unless the old booster was updated to a dual diaphragm, it won't provide enough assist with the disk brakes (BTDT).

Even though you shouldn't need to change the pushrod length, it sounds like it needs checked again. You want a tiny gap (0.020ish).

The drum brake distribution valve is 'empty' and doesn't provide any proportioning to the rear. If the rear locks up first then you should look at swapping the other one over.

Thanks for the input so far. Just for clarification:

I used a wilwood proportioning valve I had laying around. The brakes work very well right now with the fronts locking up just before the rears.

I am using the brake booster from the W350, not the original one from my W200. I am using the pushrod from the W350 also.

The power brake assist feels very strong, it's definitely not underboosted.

One other thing I noticed this morning. When you hold your foot down on the brake I can hear vacuum leaking out somewhere. The sound is only there when the pedal is held down a little bit like when sitting at a stop light.

-Jon

Bad booster!

BTW I was referring to pedal pushrod length, not master pushrod lenght. Opposite ends of the booster. Whozi is right about that gap.

I'm also assuming used parts.

Interesting, so a booster can fail in a way that makes it way overboosted? That would be a new one to me, but it would explain the symptons...

The booster is used, but I did put in a brand new master cylinder.

-Jon

Yep, the valve that controls the vacuum assist can stick and cause the booster to "drag" for lack of a better word. Btdt a couple times.

Yep, and if you're getting vacuum noise with your foot lightly on the brakes, I'd go ahead and replace it. Be sure to measure the pushrod length on the new one too.