Too much rear drum braking?

Problem: '67 Van 108, with original drum brakes (rebuilt several times) tends to lock up rear brakes on panic stops and then the van gets a bit tail happy.

The seller told me back in 2008 that he once spun the van around on the freeway in a panic stop.

He had the brakes redone after that - everything but the backing plates, which I found I had to replace after a year of ownership. From the looks of it, he had everything else replaced, including master cylinder, wheel cylinders, shoes, drums etc.

After my rebuild, in which I replaced backing plates, shoes, adjusters, the brakes work well, but like I said it does tend to lock up rear brakes on panic stops.

I'm wondering what kind of fixes I could do... different brand/quality rear shoes?

Since this is a 67 it comes with a dual master cylinder as well as a proportioning valve. Could the valving be off? Is it built into the master?

And yes, I know, I could do a disk brake conversion which likely would result in the front brakes doing nearly all the work (which they should anyway). But I'm not ready as yet to go that route. I figure the drum brakes can be made to work well, I just don't like the way they behave on panic stops.

Any ideas? Any recommendations for front/rear brake shoe brands/linings?

veefre a couple things I would check.
Is the master cylinder the correct one? drum/drum master ?
Check you parking brake cable ..I know this sounds crazy but it will effect how the pads release on the rears..
Did you grease the area were the rear pads touch the backing plates ..again this sounds insane to put grease anywhere near your brake system..but it is actually in the manual....the pads will hang hard on the backing plate once pressure is applied...

veefre,
Thinking a new proportioning valve will cure your issue. I had the same issue and even when I even hit a small bump while applying the brakes the rear would lock up. When you brake hard in these vans the weight not only shifts to the front, it causes the front axle to act as a pivot point lifting the rearend. Some models had a large weight installed next to the gas tank to help with this problem.

Find a "Adjustable" Proportioning valve. It will fix it. You have to play with setting it to your liking.

Dan

What Wopman said and what Dan said!

I would check what the others are sugesting. I
I think your original proportioning valve/distribution block may be hooped.
And I would install an adjustable proportioning valve, these vans have allways had rear lock up problems by original design. Even with the factory proportioning valve.
There is a way to test the original proportioning valve but you need moocho test gauges and alike.

Has the vans brake lines all been changed? maybe there is internal restricion in front lines due to corrosion?? Its more commun then people think. If the lines are more then 20 years old, replace them all!
Is it posible the original proportioning valve has been hooked up backwards? wouldn't be the first time I seen that.


Are the front brakes doing what they are suposed to under heavy braking?? does the front dip hard, hard enough to toss a pasanger without a seat belt? My new 12" rotor design on my 65 now has a rear proportioning problem but thats because I can almost lift the rear wheels off the ground on hard braking because the fronts grab so hard. The only thing I can do about that is put wieght in the back and bolt it down like your van is suposed to have just under the rear door frame behind the gas tank. 47 lb cast iron block on the 108s.
Are the rear brakes the original size?
Are the rear shoes installed bacwards?? there is a primay and a secondary shoe. backwards they will cause premature lock up.

M1D

Thanks.

Any ideas where I can find an "adjustable proportioning valve".

I've looked high and low but found nothing for this yaer and moel.

PS-the brake shoes brackets are lubed with grease in all the right places.

Not sure if the master cylinder is correct or not. It seems to be a bit larger than the stock one, since the throttle rod bumps up on it a bit at full throttle. No chance of it sticking at WOT, just that it never will get to WOT and with adjustment there is a bit too much lash in the accelerator pedal. Different issue, but it does point to the master perhaps not being an exact replacement.

The parking brake cable is fine... I went through that exercise when the repair bearing seals lubed the rear brake drums and I kept on adjusting the parking brake to try to keep the van in place. Since then I've fixed the leaky rear axle seal issue and the parking brake adjustment should be ok now.

Haven't checked the brake lines. Perhaps there is internal corrosion, don't know. It seems to brake straight and true, until the rear starts to skid and step out. I *think* the passenger side rear brake locks up first, but I couldn't swear by it.

The numerous red light cameras have caused me to change my driving habits. When I see a yellow, I brake... hard... which is oik in a modern car but in the van it gets very interesting. I don't need another $550 ticket!

Holly crap man for $550 you put disc brakes and much more on that van.

Theres not much chance of a "wrong" master causing the problem. any master applies the same presure out put for the rear as it does for the front. regardless of wether its a 1" bore or a 1.125" bore the output presures are equal from its two ports unless it does have an internal problem, but not likely or you would feel a low or sinking pedal.

If the pasanger side locks first you could look at tire traction. drum diameter (should be within .010 of each other), shoe adjustment.

There is a real posobility of pluging lines if they are old.

equally as important for even braking side to side is the rteturn springs all have the same strenght. Best to make them all new (spring kit) if in dought.

The adjustable proportioning valve I was talking about is like this
http://www.wilwood.com/MasterCylinders/MasterCylinderValves.aspx

I'm thinking I need to go to a proportioning valve with an anti dive valve , and I want to go with the hydraulicly actuated brake light switch because I have replaced my factory one thre times and stil lasts about three months then acts up again.

What about your factory proportioning valve? That might be the source of the problem.

M1D

sorry I didn't realise the 2nd gen was without a proportioning valve. I guess I confuse that with the 3rd gen one I see on other 2nd gen vans.
The factory style combonation valve would not be appropriate for a drum/drum set up but if all else is correct then the adjustable unit wil likely fix the problem. But you do have to make sure all else is right otherwise your just adding a bandaid.

M1D

As I recall, the rear drums shoes are more narrow than the front brake shoes, yes.

I didn't measure the rear wheel cylinders, though. That sounds however like it might be the problem. I will have to check that out.

The return springs are all in good condition, no worries there.

I suspect it wouldn't hurt to install an adjustable proportioning valve in this van even it has drum-drum brakes. And of course it would prepare it for the eventual (I admit) conversion to front disc brakes.

Although because it currently has no proportioning valve, it would involve cutting and double flaring cut ends of existing lines, no?

Drums appear to be in good shape. They were new not too many miles ago.

The knockouts are nowhere near to being ion a state where they could be knocked out.

Drilled and mill slotted out, maybe.

I don't think it's possible to put the shoes on backwards, but next time I have the drums off I'll check that as well. I took photos before tearing down the brakes for the first time... and as I recall I posted photos of the powder coated results a couple years ago here.

OK, here is a shot of the left (driver's side) front brake assembly. The shorter shoe is clearly in the forward position...

Drums appear never to have been turned. Don't know if they are Chinese. There are knockout stamps on them, but the stamping just isn't deep enough to be able to knock them out (I tried with one).

When I first put the new shoes in (after repairing leaky axle bearings) the rear brakes caused the rear tires to skid even when ice cold. After a while they seemed to bed in and didn't grab as much, but in a panic stop they often will.

If anything the drums have too much meat on them. It was a chore getting the front drums on because of the new shoes. But those shoes have also bedded in and the drums are easier to pull/install now.

I adjusted the brakes by backing out the adjuster until the drum wouldn't go on, and then backed off a bit. There was some rubbing going on for a while, but it went away after the shoes bedded in. Both fronts spin easily now with brakes not applied. When the shoes did drag, it was even, not cyclic as one would expect with out of round condition.

Tires are relatively new (2008) and good quality (Goodrich Premier). Plenty of tread, good traction rating, etc.

How can I tell if the rear wheel cylinders are oversized? Without taking them apart an measuring the bores, that is...

All good suggestions.

I'll see if I can try them next time I have the van up on stilts.

All of the above could be the problem. Also, before I install new shoes I take a flat file and angle off the front and back edges of brake pads--don't breath that stuff. Sometimes new shoes on old drums (almost always out of round) bind up if not prepped first. Sure hope it's something simple. Good luck and happy motoring!