Two weeks ago I had the car gone through, new exhaust, one exhaust manifold, shocks, etc. and the left rear brake they put a new caliper on and bled it. I was out of town for a week so drove it little. Friday I sat it in the driveway in neutral with the e brake on for fifteen minutes. When I went to put it in the garage it acted like the e brake was still on but I muscled it in. The next morning it was fine even though I'd relaxed the cable the night before in the garage.

Tested it and Sat. took an 80 mile drive to Lightfoot for lunch. Ten miles from home had to stop by the roadside and left it in gear and off and came back and it was locked up tight with the left rear tire...tried to drive forward and back to loosen it and all I got was heat so the shop that did the work has an emergency wrecker so I called and Pops came and picked it up..grateful. When he winched it up the ramp that left rear tire rolled perfectly smoothly. It had released again.

We put it in the shop's garage with their two race cars and they'll look at it this week. Options seem to be....since emergency brake has worked well enough before that it may be the new caliper is hanging on and jamming a brake pad against the rotor or maybe it is the little shoe brakes in the drum which is the rotor.

Hopefully will know in next day or two. if it's the Caliper they put it on so wouldn't expect a bill.

glad I found out before taking it on the road track April 13.

Be curious to see what it turns out to actually be. I couldn't safely pull the wheel where I was stopped with traffic so it was a mystery.

Lance

 

Check for collapsed brake hose.

 

thanks...they have the car and they put new brake hoses on both rear wheel disks as well so they will be checking their own work. Once it went on the tow truck deck I gave the job to them though I am mightily curious. If it is something new then you have to wonder about suppliers of parts nowadays and quality. This shop uses top quality things as a general rule.

 

Wombyvette...

"Check for collapsed brake hose. " You sound like you might have experience. How would a collapsed brake hose create a frozen in place brake pad on the rotor?

 

I'll agree with Wombvette! It's a collapsed brake hose. Without going into the mechanics of how and why, I've been there and done that one.
Duane

 

Or if they changed rotors , they could have used a front on the rear and put the pads in a bind.

 

Basically the hose collapses internally and will let pressure be applied to the caliper but the fluid can't return so the pad remains pressed against the rotor.

 

I'd be willing to bet a bad original brake hose, too.
Not necessarily collapsed, they can also clog up with old, old moisture laden brake fluid.
I'd also be willing to bet they did NOT change any hoses, especially if they only changed the one caliper

 

I saw the new hoses when the mechanic showed me the car on the lift but they have it now so we'll find out. Could be trash in the hose too. I don't have as much faith in product suppliers nowadays as I once did. I still have one original caliper on it and the shop just called and the brakes locked up again getting it from one building to the other. The right rear is the last original caliper and it has, as expected, started to leak. Their conclusion is that the emergency brakes are fine and that it is likely the effects of the leaking caliper on one side and perhaps junk in the fluid on the other side so will replace the caliper which we were pretty sure needed doing before I took it to the track anyway. it was now the weakest link in the four brake system. they will check it and review the new driver's side and hoses as well as trash and a forced drain and flush of brake fluid if need be. Should know by later today if not by noon. When it happens, it releases naturally over a fairly brief time so is a puzzle if hose is not collapsed which was not the case when it just happened for them and immediately got it on a lift and looked at it.

 

They found a leaking right rear caliper and since the other three are new they changed that. They road tested it and thought it was okay. E brakes are fine. It did it again in the parking lot so they got it to do it two or three more times and quickly opened a bleed screw one rear wheel at a time and the pistons popped right back and releases on either wheel so no hangups of the pistons. Then they opened the bleed screw on the master cylinder and that released all. Their conclusion is that the original proportioning valve mounted on the frame rail down by the driver's side is the culprit and it is bad so they are getting a new one and will install, bleed, test it several times. You don't need a road test of more than 50' for what is happening so they are narrowing it down. The flex hoses are good, the calipers and pads are good, the lines are good, the Master Cylinder is good so it pretty much has to be the p. valve. We'll see.

 

Never seen one do that, but I guess it is possible.

 

from another forum poster: ".....I've had a proportioning valve go bad, symptom was that the front brakes would lock up tight the first time the pedal was pushed, and stay that way. Dont know if this helps or not, but is what happened to me.

JimK"

 

While the idea may be simple the actual valve has a number of gaskets and seals and parts....so, if mine is original which I believe it is, it's not out of the question that it is bad. We'll see.

 

I had a bad valve on my 74 I had in the 80's they would lock up tight wouldn't move till it bled down

 

The shop put a new proportioning valve on today and the brakes were fixed...however, the senser is bad on the new part so tomorrow they take it back, get another new one and hopefully the job is done. At least we know what caused the rear brake lock up and then slow bleed down! I was worried it was those lousy little shoe brakes inside the rotor that are the emergency brakes. Whew! Hope to have my Vette back by tomorrow night.

 

In your original post, you said the left rear wheel was locked up. If the right rear was not, then I don't believe your proportioning valve is the problem. It's been my understanding that the proportioning valve works to proportion pressures between the front and the rear systems and has nothing to do with the left from the right side of the car. But maybe I've been wrong all these years. (It's been known to happen. Just ask my wife.) If it was the valve, both rears should have been locked up together, not just one.
Duane

 

When sitting in the car I could only see that the left rear was locked up. When it repeated it in the shop parking lot they tested both and both were locked up so it was the proportioning valve and your undersanding is correct...as I understand it part of the valve's job is if the front brakes somehow get ruined without enough fluid the valve salvages some braking remaining with the rears and vice versa. With the new valve on even with the defective sensor the breaks worked perfectly again in the parking lot. Should get it back tomorrow subject to Zip having a part whose sensor works correctly. It did on the original one. These do have several o rings and there is movement inside and I suppose it is not illogical to say that a 35 year old valve could conceivable fail!

 

Nice to have little RoJo back with her best brake shoes on and working better than ever, one proportioning valve later! Hooray, she's back in the garage and will get washed in the morning. World always feels better when the Vette is back in her place in the garage to me.

 

[QUOTE=LancePearson;1576686101]Nice to have little RoJo back with her best brake shoes on and working better than ever, one proportioning valve later! Hooray, she's back in the garage and will get washed in the morning. World always feels better when the Vette is back in her place in the garage to me.[/QUOTE
Glad to hear it worked out..mine did the same thing..not a fun thing at all to deal with..it happened after I played with the brakes just like you..I took it apart and found a good bit of crud in there..easy fix though once you figure it out.

 

Thanks...when it happened I thought it was the e brakes and initially didn't know what a proportioning valve was or why so I learned something yet again. With me taking it for a day on a road racing track with 17 turns in April the brakes will get a workout so really must be in good shape. That is one of the things that one day event on the track really requires first of all by me, second of all by tech inspection and thirdly by common sense. i just love this car. It has a fairly good radio and speakers in it but I almost never turn them on preferring to hear and feel the car instead.

The other lesson to me in all this is when you fix one part of a system, like replace one caliper, rebuild pistons or put new pads on both front brakes, you have created strong centers in part of the system and then as you use the car, the other parts pf that connected system not dealt with become the weak parts of that system and with the age of the cars it's likely that the disparity will create leaks or failure so proactively fixing all of a system is more than likely the thing to do. I don't doubt that the valve had crud in it or the o rings had failed or both. I forgot to ask to see the old one. Just happy to have it back and enjoy such a nice ride on a 69 degree day in Virginia.

Good luck with all of our cars.