The Dodge Challenger Message Board

I hope someone can help me because i'm going nuts. The other day I decided to put on new rubber brake line hoses, well, when I jacked up the car the front wheels would not spin freely. They would turn with great force or the weight of the car. I thought the rubber brake lines were bad so I replaced them. Same problem, so now I took off the calipers took them apart and cleaned them no major pits or rust inside. Same problem, so next I decided to replace the master cylinder and blow compressed air through all the lines while it was off, including the metering block and proportioning valve. Now it is better but not fixed completely, there is still force applied to the rotors. I can get about one revolution of the tire with a hard spin obviously this is not correct. Is the problem possibly in the metering valve or proportioning valve? Maybe I dislodged some dirt or debris with the compressed air which in turn partially fixed the problem but not completely. Please tell me where to look next. The car is a 70 Challenger R/T 440 factory power disc brakes. Thanks rick

You have done everything I would have done. Bit of a head scratcher that one.

did you check the slides on the calipers as well
cheers ian

The slides are geased and working properly.

When the brake is tight. Loosen the flex hose to that caliper to release any pressure and see if the brake comes free.

dave-r wrote:When the brake is tight. Loosen the flex hose to that caliper to release any pressure and see if the brake comes free.

that is a good idea,but perhaps you are right you may have some dirt in the proportioning valve not allowing it to release,you have doen everything i would have done,blow out the lines, r&r the calipers,master cylender,when you did the calipers did you replace the seals and o rings?

I did not replace the seals or o rings, they were in excellent shape. I just cleaned the piston bore and the seal grove and lightly oiled before reassembly.

The rear brakes probably have a residual pressure valve in the system somewhere. I can't remember how that works off the top of my head but I wonder if the front brake lines are getting residual pressure somehow?

Still can't remember but I have a feeling the early master cylinders had a residual pressure valve built into them for the rear brakes.

Is there a chance you have the brake lines going into the master cylinder the wrong way around?

Yes. I remember now. Sorry it takes me a while these days.

If it is an original master cylinder it has a valve in the outlet for the rear brakes which is the FRONT outlet on the master cylinder. Make sure you don't have the front brakes plumbed to this outlet.

dave-r wrote:The rear brakes probably have a residual pressure valve in the system somewhere. I can't remember how that works off the top of my head but I wonder if the front brake lines are getting residual pressure somehow?

yea that is right the drums have a different valve,that keeps the shoes close to the drum, the front have a valve that keep light pressure in the pads at all times,that is why serious drag racers prefer drums all the way around,so there is no drag, disc brakes always have some pressure on the pad but not so much it stops the wheel, i think there is a problem with the prop. valve

,but it is just a valve so if dirt is trapped in there the fluid will not flow back as easily,

this is kinda baffeling but brakes are simple but if there is air or dirt in the line there will be problems

,you know the calipers are good, the master cylinder is good,

man it has the be that valve,or something in the line that didnt get blown out,

yea a real head scratcher

Today I just ordered another new master cylinder because the one they gave me has two small reservoirs where mine had one large one for the front brakes and one small one for the rears. The box had the correct part number but I believe human error had lead to someone putting in the manual brake master cylinder. The part number is the same for the two parts except the manual one has an "m" at the end of the part number. It is made by A1 Cardone and very easy to mess this up. I hope this solves the problem but I still have a feeling it won't. The part should be in by the end of this week. so I was told. Thanks for the replies.

Today I just ordered another new master cylinder because the one they gave me has two small reservoirs where mine had one large one for the front brakes and one small one for the rears. The box had the correct part number but I believe human error had lead to someone putting in the manual brake master cylinder. The part number is the same for the two parts except the manual one has an "m" at the end of the part number. It is made by A1 Cardone and very easy to mess this up. I hope this solves the problem but I still have a feeling it won't. The part should be in by the end of this week. so I was told. Thanks for the replies.

R/T Rick wrote:Today I just ordered another new master cylinder because the one they gave me has two small reservoirs where mine had one large one for the front brakes and one small one for the rears. The box had the correct part number but I believe human error had lead to someone putting in the manual brake master cylinder. The part number is the same for the two parts except the manual one has an "m" at the end of the part number. It is made by A1 Cardone and very easy to mess this up. I hope this solves the problem but I still have a feeling it won't. The part should be in by the end of this week. so I was told. Thanks for the replies.

well i have found out that some brakes have the drum valving in the master cylinder, and some have the valve in the prop valve,you have the wrong master cyl. for sure, i have seen that happen before, it might make a difference, you have no choice try it and see, i bet it helps

Manual brakes my arse.
What they have given you is a master cylinder for drum brakes which is why it has two small resevoirs.
If it is a faithful reproduction of the original it will have a residual pressure valve in BOTH outlets. Hence your problem.

How long have you had this on the car? You made no mention of a new master cylinder in your original post so I take it you have been using it for some time?

dave-r wrote:Manual brakes my arse.
What they have given you is a master cylinder for drum brakes which is why it has two small resevoirs.
If it is a faithful reproduction of the original it will have a residual pressure valve in BOTH outlets. Hence your problem.

How long have you had this on the car? You made no mention of a new master cylinder in your original post so I take it you have been using it for some time?

I decided to replace the master cylinder,

he did ,but you got stuck with one of those knock offs,that most parts guys shove off and hope you wont notice,get the right one and it should fix the problem

Sorry took so long to reply, anyway it turned out I had to order a MC for a 71 I don't know why but it works and my problem is corrected Thanks for everyones help.

sweet!

R/T Rick wrote: I don't know why but it works and my problem is corrected Thanks for everyones help.

Rick well done on sorting the problem but does it not bug you that it caused all that grief and you dont know why??

You should try and find out why so it does not happen again and even better to know the fix for it if it does eh??

Find

I've already explained why and it has nothing to do with what model year you order. He sent you a drum brake master cylinder not a disc brake one.
He will not admit that of course so he has bullshit you about the model year.

I guess that guy owes you some eh Rick? Sounds like he dicked you around........