No rear brakes - help please!

[CosMopar]

Hi,

I have an 1970 Chrysler 300 with front power disc brakes.
Today when testing the brakes I found out that I got zero stopping power from the rear brakes (front works perfectly). I just got the car so don't have any history of what could have happend .

First I tried to bleed the brakes but nothing happend. No air, no brake fluid came out. The brake pedal felt stiff as if I never opened the bleeder valve.
Could it be the proportioning valve that is stuck?
Maybe the rear brake hose that is clogged?
Any other ideas to try first?
One more question (searched everything on google but couldn't find any info about this part): Where the brake lines split up to each rear wheel is some sort of splitter with a knob on. The knob feels like it is spring loaded. What is that? Never seen it on any other car.
Hope someone can help me...

 

[traintech55]

Please post a picture of this "SPLITTER". Sounds like an adjustable valve, and it might be closed off. Need to see it to be sure.

 

[CosMopar]

Yes, that was my first thought as well. The knob was just spinning when I turned it. No resistance what so ever, and it sort of popped up when I pushed it down (as I said it felt spring loaded). Will get photos when I get to the garage tomorrow.

Got another idea. Next to oil pressure and water temp gauges (aftermarket ofc) is a switch that I never figured out what it does. Could maybe be a switch to turn on line lock?

 

[Davea Lux]

Yes, that was my first thought as well. The knob was just spinning when I turned it. No resistance what so ever, and it sort of popped up when I pushed it down (as I said it felt spring loaded). Will get photos when I get to the garage tomorrow.

Got another idea. Next to oil pressure and water temp gauges (aftermarket ofc) is a switch that I never figured out what it does. Could maybe be a switch to turn on line lock?

Unless there are wires running to the rear mounted valve, that is highly unlikely. Your 300 should have come with power disc brakes that were balanced at the factory for proper operation, so there would not have been any good reason to add an adjustable valve to the rear brakes. The rear brakes normally have a brass splitter block with a stud running thru it to anchor it to the rear axle. The stud is hollow and has a plastic or metal cap on in that serves as a rear axle vent. You should start by removing the defective adjusting valve and replace it with the factory brass block, this would also be a good time to replace the rear brake hose as well. www.manciniracing.com has the brake block with a new hose attached for about $30. I believe that www.inlinetube.com also supplies this part. I would suggest you again try to bleed the rear brakes after the new parts are installed and report back. Since you do not know how long the rear brakes have been inactive, you would want to do a thorough inspection of both rear brake assemblies, especially the wheel cylinders for signs of corrosion.

Dave

 

[live4theking]

I'm with Dave on getting rid of the adjustable block that is on the axle and replacing the flex hose.

 

[CosMopar]

Thanks! The brass splitter block looks original and that like it been there forever. So if the car has line-lock and I missed that some how it hasn't anything to do with it.
Found this on manciniracing. Looks exactly like the knob I referred to . Thought it had something to do with that splitter.
Axle Vent / Breather Bolt
Guess my plan is to first change the rear brake hose as it might be clogged.
Thanks again!

 

[Davea Lux]

Thanks! The brass splitter block looks original and that like it been there forever. So if the car has line-lock and I missed that some how it hasn't anything to do with it.
Found this on manciniracing. Looks exactly like the knob I referred to . Thought it had something to do with that splitter.
Axle Vent / Breather Bolt
Guess my plan is to first change the rear brake hose as it might be clogged.
Thanks again!

If that does not solve the problem, a bad master cylinder would be the next most likely culprit. You should get a "brake" idiot light when depressing the brake pedal if the master is bad. Might want to check to see if the idiot light still has a bulb in it as sellers have been known to remove the bulb to hide a defective brake warning. If the rear hose is bad, that would be a good indicator that it is time to replace the front ones as well as they are probably not far behind.

Dave

 

[Big_John]

A couple thoughts... First, are you sure the brakes aren't working? Even just a little? You know, jack up the rear and spin the wheels and have someone hit the brake pedal.

Second, try unscrewing the bleeder valve all the way out. I have seen them clogged or screwed up enough that they won't pass fluid through them.

Changing the rear hose is a good idea, although I might be a little surprised if that's the cause. There's nothing to wear out in that tee/vent bolt, so don't waste your time with that.

You mention "Line Lock"... Does the car have a Line Lock? If it does, is it in the rear brake line?

 

[CosMopar]

Yeah, will do that... atleast the brake light is working when the emergency brake is on (same bulb I guess), and the cable is connected to the proportioning valve.
Hopefully it's just a clogged rear brake hose, after all it looks fairly old and beaten up.

 

[Davea Lux]

Yeah, will do that... atleast the brake light is working when the emergency brake is on (same bulb I guess), and the cable is connected to the proportioning valve.
Hopefully it's just a clogged rear brake hose, after all it looks fairly old and beaten up.

Sometimes the inner liner of the brake hose will detach and clog the inlet on the brass splitter block. This usually happens when the brake fluid has become degraded for some reason and has started to break down the rubber in the hoses and wheel cylinders.

Dave

 

[CosMopar]

A couple thoughts... First, are you sure the brakes aren't working? Even just a little? You know, jack up the rear and spin the wheels and have someone hit the brake pedal.

Second, try unscrewing the bleeder valve all the way out. I have seen them clogged or screwed up enough that they won't pass fluid through them.

Changing the rear hose is a good idea, although I might be a little surprised if that's the cause. There's nothing to wear out in that tee/vent bolt, so don't waste your time with that.

You mention "Line Lock"... Does the car have a Line Lock? If it does, is it in the rear brake line?

I was at the car inspection and it was zero reading on the rear wheels. So no braking power at all.
Will try removing the bleeder valves fully, but usually some fluid will come out from the thread if it is clogged.

The line-lock was just a wild thought . Previous owner didn't mention it and I haven't found anything that speaks for it, except that switch next to oil pressure gauge that I haven't figured out what it does .

 

[traintech55]

Unless there are wires running to the rear mounted valve, that is highly unlikely. Your 300 should have come with power disc brakes that were balanced at the factory for proper operation, so there would not have been any good reason to add an adjustable valve to the rear brakes. The rear brakes normally have a brass splitter block with a stud running thru it to anchor it to the rear axle. The stud is hollow and has a plastic or metal cap on in that serves as a rear axle vent. You should start by removing the defective adjusting valve and replace it with the factory brass block, this would also be a good time to replace the rear brake hose as well. www.manciniracing.com has the brake block with a new hose attached for about $30. I believe that www.inlinetube.com also supplies this part. I would suggest you again try to bleed the rear brakes after the new parts are installed and report back. Since you do not know how long the rear brakes have been inactive, you would want to do a thorough inspection of both rear brake assemblies, especially the wheel cylinders for signs of corrosion.

Dave

Dave, if you were referring to my 1966 300, I converted it to disc brakes, changed the booster and master to the correct disc brake units. I also installed the dual brake system, and installed the adjustable prop valve to dial in the original rear drum brakes.

 

[Davea Lux]

Dave, if you were referring to my 1966 300, I converted it to disc brakes, changed the booster and master to the correct disc brake units. I also installed the dual brake system, and installed the adjustable prop valve to dial in the original rear drum brakes.

The OP has a '70 Chrysler 300, those should be discs from the factory. I agree that if a conversion from drums was made on '66 like yours, an adjustable valve is usually necessary. If memory serves me correctly, the 300 series mostly had discs from '68 forward on the big block cars and all from '70 on. Could be wrong though..

Dave

 

[Big_John]

The OP has a '70 Chrysler 300, those should be discs from the factory. I agree that if a conversion from drums was made on '66 like yours, an adjustable valve is usually necessary. If memory serves me correctly, the 300 series mostly had discs from '68 forward on the big block cars and all from '70 on. Could be wrong though..

Dave

1971 was the first year for standard disc brakes in the Chryslers.

In 1970, it was still optional. My '70 300 has discs, my Dad's '68 300, bought brand new, had drums.

 

[Davea Lux]

1971 was the first year for standard disc brakes in the Chryslers.

In 1970, it was still optional. My '70 300 has discs, my Dad's '68 300, bought brand new, had drums.

Thanks for the update.

Dave

 

[CosMopar]

Here is a photo of the brass block splitter and the rear axle vent.

Think I found the fault (at least one of them ;) ). When I released the rear brake hose at this brass block nothing came out. Even tried to brake bleed but it was the same as before. Then I disconnected at the other end (at brake line from the proportioning valve) and it started dripping brake fluid right away.
New rear brake hose ordered!
Thanks for all the help!

 

[Big_John]

Here is a photo of the brass block splitter and the rear axle vent.View attachment 180256

Think I found the fault (at least one of them ;) ). When I released the rear brake hose at this brass block nothing came out. Even tried to brake bleed but it was the same as before. Then I disconnected at the other end (at brake line from the proportioning valve) and it started dripping brake fluid right away.
New rear brake hose ordered!
Thanks for all the help!

Glad you found the trouble.

Just as a little info, you don't have a proportioning valve in your '70. You have a warning light switch and a metering valve in the front brake line.

From the 1970 FSM.

If you don't have one, download a copy of the FSM here: MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

This guy is a bit goofy, but he explains it.

 

[CosMopar]

Glad you found the trouble.

Just as a little info, you don't have a proportioning valve in your '70. You have a warning light switch and a metering valve in the front brake line.

From the 1970 FSM.

View attachment 180259

If you don't have one, download a copy of the FSM here: MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

This guy is a bit goofy, but he explains it.

Thanks for info!
Yeah, my bad. I actually watched this video the other night when I started this thread. The word proportioning valve seems to be missused alot (just like I did ;).

 

[ayilar]

@CosMopar -- it's been a long time since you last posted, is your 300 a convertible by any chance? You looked at several fusie 300 'verts before this thread, would be great to know.