The Stovebolt Site Forums The Parking Lot Big Bolts Bendix or Midland Brake Booster

Need some advice or suggestions for which brake booster I should focus work on.

I presently have a Midland C3388 (AKA: C462, 518026, RV46201x, B7034) it appears to be the only booster ever installed on the truck, can't guarantee it though. It needs rebuilt - mostly due to a tear in the main power diaphragm, second there are internal fluid leaks.

I also have what should be the factory correct Bendix 374000 (AKA: 518028, B7027, 2208488) at least has a problem with the control valve leaking/admitting atmosphere to the rear of the can or not admitting vacuum, when installed and hooked up brakes are on hard.

Finding a complete unit on the shelf isn't happening. I'd prefer to rebuild one of them, or second, send one in for rebuild.

First, which one is more powerful (my guess is the Midland)?

Second, which one will I have highest chance of success in rebuilding (I'm leaning towards the Midland again)?

So my plan is to try getting the Midland fixed for the two reasons above. However, if I can easily figure out the problem in the Bendix, I'll use it, because documentation says its what should be on there anyways and I can be back on the road sooner, maybe cheaper.

I've had the Bendix all torn down and inspected and replaced some parts from a similar kit, the interior of the can is a bit rough. The hydraulic brake piston and bore is reasonable. The control valve hydraulic piston and cylinder also seem acceptable. Leads me to think there is a problem with the control diaphragm (not the original, maybe its too long), springs or poppet (not original either) being pushed or held open.

The power is going to be a function of the vacuum piston diameter and the bore of the fluid cylinder. The bigger the vacuum piston and/or the smaller the diameter of the fluid bore, the more boost will be produced. If those dimensions are the same, both units will have the same amount of boost. NAPA stores usually have a selection of new or rebuilt boosters that would probably be less hassle and/or expense than trying to repair what you've got. The tricky part will be finding an old geezer who can still use a paper catalog!
Jerry

asilverblazer Seems like you could find a rebuilder in your city that could advise you what way to go. My 2 boosters on a 51 6400 and a 48 2-ton have both had service in the form of hydraulic jack oil,like the service book says,2 oz.twice a year. They work fine at around 70 yrs. old.

asilverblazer One other thing ,found a rebuilder thru my local Fisher parts store in Evansville Indiana,seemed sharp he said if your truck gets rid of brake fluid every day come back to me Iknow what to do for that. The rebuilder is in Evansville,I am in Illinois about 100 miles away. Anyway that has been my experiance with boosters. Carter's told me to use hydraulic jack oil,book says bendix vacuum cylinder oil,I tried it on rubber cylinder cups didn't hurt the rubber.

Update: I finally got my brakes sorted out.

As noted above I was really leaning towards rebuilding my Midland booster, getting parts for it was just not working out. Lead times were crazy long or the price was crazy high. Went back to original plan of rebuilding the Bendix.

I got a rebuild kit installed and everything seemed well and good - except that same as before - installed on truck and brakes are on full stop.

I ended up having a few diaphragms for the control body and decided to shorten the rod that inserts into the control valve cylinder. Deciphering the wizardry inside the control valve well enough to type how I decided to do this is beyond me - but it DID WORK. Brakes are working like they should.

Other thoughts, I do think the Midland had a better pedal feel, maybe it produced more boost. Also ran a new hydraulic line from master cylinder to booster with new double flare fittings.

asilverblazer My 51 6400 Bendix booster will slide the front tires if you climb on it,solid feel so can't ask for much more .Now the 48 2-ton sets too much so brakes are not as good but will stop.

I could probably get a slight improvement by tweaking on the shoe adjustments. The right rear is a smidge tighter than the others, it locks first. Otherwise, they are working better than ever except for the two weeks the midland was working right.

I found rebuilt HydroVacs at a place called Reman, Inc. Reasonable prices, they ship to Alaska (which is rare) parts are in stock and the people who answer the phone actually speak English and are very knowledgible, both qualities are rare nowadays! Highly recommended!