When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Problem: After car gets warm, couple of stops, brakes start tightening, car lags hard when letting off gas pedal, car wont coast , wont coast at idle, Stop the car leave in drive and you can get out of car and it wont move, lol.
Rotors obviously are very hot.
Let car cool down, or dont use brakes and it goes back to normal.
Bleeding brakes did nothing because it just repeats again.
Did a lot of reading and among all the possibilities, the master cylinder push rod play check stands out to me...possible not enough play. So I will check that first since it is a new booster.
Just wondering what others think.
Any help appreciated.
Original MC or new MC?
If new MC, did you bench bleed MC?
Original Brake Booster or new Brake Booster?
These symptoms began after you did an R&R of both the front & rear at the same time?
I was going to go onto a diatribe of B.S. regarding possibilities...instead, I opted to steal from CPP website.
Overheating or Dragging Brakes
•Improperly adjusted parking brake•See Rear Disc Brake and Parking Brake Adjustment
•Pre-loaded master cylinder or power booster•See Check Pedal Assembly
•See Check Booster Pushrod Adjustment
•Bad power booster•See Test Power Brake Booster
•Drum Brakes: Residual check valves•Remove residual check valve See The Right Valves
•Frozen parking brake cable•Replace parking brake cable
•Bad Calipers or wheel cylinders•Replace caliper
•Overfilled master cylinder•Fill to correct level for master cylinder, typically 1" from lip
•Drum Brakes: Drums out of adjustment•Drums may be adjusted too tight, readjust
Original MC or new MC? LIKE I SAID ABOVE, EVERYTHING NEW, EVERYTHING...INCL SS LINES, SS BRAKE LINES. COMPLETE FRAME OFF RESTO
If new MC, did you bench bleed MC? YES
Original Brake Booster or new Brake Booster? NEW
These symptoms began after you did an R&R of both the front & rear at the same time? BASICALLY...ACTUALLY CAR WAS BEING RESTORED FOR LONG TIME, LOTS OF DIFFERENT STAGES, NOT DRIVEN FOR LONG TIME DURING RESTO, SO NOT SURE WHEN IT STARTED DOING THIS, BUT DEFINITELY OVER PAST YEAR AS I STARTED DRIVING IT MORE AND AFTER R&R.
I was going to go onto a diatribe of B.S. regarding possibilities...instead, I opted to steal from CPP website.
👍👍
Overheating or Dragging Brakes
•Improperly adjusted parking brake•See Rear Disc Brake and Parking Brake Adjustment
•Pre-loaded master cylinder or power booster•See Check Pedal Assembly
•See Check Booster Pushrod Adjustment
•Bad power booster•See Test Power Brake Booster
•Drum Brakes: Residual check valves•Remove residual check valve See The Right Valves
•Frozen parking brake cable•Replace parking brake cable
•Bad Calipers or wheel cylinders•Replace caliper
•Overfilled master cylinder•Fill to correct level for master cylinder, typically 1" from lip
•Drum Brakes: Drums out of adjustment•Drums may be adjusted too tight, readjust
The pads and rotors are not getting grease on them, are they? I had an old Chevy van that had a small axle leak on the one rear drum that got the shoes wet. After a few stops, they got hot and swelled up and began to grab really bad when I stepped on the brake pedal, nearly locking up that one wheel. Once that started, it was dragging and got things really hot. I think the oil/grease causes the pads / shoes to expand much faster when used and results in dragging and overheating.
You just got to press the gas pedal harder, lol. They are really dragging, not actually stuck. But drag is so bad after it gets hot that you can leave it in drive and the car won't move at idle. That's why I'm thinking push rod adjustment might be the trick.
Brake pedal has play in it.
I just started troubleshooting this deeper today, I thought I had it fixed with the e-brake issue resolved. But I noticed it this morning when driving it longer than usual, which then made me realized it's been happening for at least the past few weeks ( Only drove it twice over that time, but only very briefly to check something else)
Feels like trans braking on it. And getting terrible gas mileage of course
If I think about your statement for a moment...brake pedal has play in it...and consider you changed both the MC & Brake Booster, AND...you did not make any adjustments to the brake pedal assembly, I’d suspect the Brake Booster push rod is too far engaged into the MC push rod. All things being equal, you’d expect the Brake Booster push rod to be ‘flush’ against the MC push rod, but now you have play in brake pedal. The ‘play’ is most likely the result of the brake pedal assembly not meeting the Brake Booster push rod because the Brake Booster push rod is pushed too far inward into the MC pushrod. Make the adjustment at the Brake Booster push rod so it’s just flush with the MC push rod.
I've read there should be 1/4" play at the pedal...otherwise I'm thinking its the push rod adjustment too. Wish I had that push rod measuring tool, but I will get er done and report back.
I've read there should be 1/16" play between booster push rod and M/C.
But why wouldnt push rod effect it when cold? With Car turned off it rolls so easily.
Also what about brake fluid, I've read leave 1" from top, but m/c is angled. So 1" is like 2" on the banked side. Just want to be sure brake fluid has room to expand when hot.
First, are your willwood calipers fixed or floating calipers in the front. When they start to drag, is it both fronts, both rears, all four or just one? You may have residual pressure drag, once the brakes warm up, they swell up a bit and it just gets worse. I'm not sure what kind of prop valve your running either. I"m pretty well schooled on brakes, I did a 10 year stint in R&D, 4 years of which was engineering level testing of brakes so the more you can tell me the more I can help you out. Kinda hard to hold the computer up to the car to figure out what's happening and causing it
I've read there should be 1/16" play between booster push rod and M/C.
Also what about brake fluid, I've read leave 1" from top, but m/c is angled. So 1" is like 2" on the banked side. Just want to be sure brake fluid has room to expand when hot.
But why wouldnt push rod effect it when cold? With Car turned off it rolls so easily.
That is correct. 1/16" is just about 'flush'.
Assuming you have the correctly sized brake booster vacuum line, you should have optimal vacuum to build vacuum into the forward side of the brake booster to set the initial vacuum and hold vacuum (contained within the diaphragm of the brake booster). The brake booster should be equalized (vacuum & atmospheric pressure equal inside brake booster - front & rear). IMO, you are 'preloading' the brake booster and engaging the MC because the brake booster has already engaged the MC and the pressure inside the brake booster has never been equal. The two-way valve inside the brake booster is not operating (positioned) optimally (dependent on both the vacuum and atmosphere pressure) because the valve bodies are preloaded - resulting in the inability to maintain equalization inside the brake booster.
Regarding overfilled brake fluid. It will have no effect on the braking. It only needs space above the fill line or anywhere between minimum & maximum to allow for expansion of the fluid as it heats up. That is all.
Last edited by Vintage Chief; May 1st, 2019 at 04:30 PM.
Reason: sp
I should have added to the above but hit the magic button too soon!
The push rod that actuates the master cylinder must be properly adjusted. Ideally there should be only slight clearance between the booster push rod and the master cylinder push rod. Interference will preload the master cylinder. When the system is preloaded, it builds pressure each time the pedal is pressed. Since the master cylinder is not allowed to fully release the pressure from the previous stroke, the system will eventually lock the wheels. Too much clearance will cause excessive free play in the pedal.
^^^This^^^ is your current condition. I took that from the link I already provided to you.
How close are the brake pieces from the exhaust? As the exhaust heats up fluid expands causing brake line pressure. Also double check the pushrod between the booster and the master cylinder,
If the booster pushrod length checks out OK , you may want to check the supplied slider pins for run-out and bushings.
How tight were the bushings on the supplied caliper bolts from wilwood ? You may have to lap them out a bit if they are a bit tight
76 Olds, just did that aspect couple months ago...the old grease had got sticky and calipers were sticking, even when cold. You could not push the car at all when in neutral and cold. Now it pushes with ease after redoing all the calipers, cleaning, regreasing pins, all metal on metal areas, etc. Calipers move freely now, and rolls so easy when cold and in neutral. But I will check them again anyways.
I just started digging into this deeper today. All I know so far is what I've said above, and that driver side rotors were damn hot to the touch, ...and couldnt push car in neutral when hot, wouldnt roll when in drive unless give it some gas pedal...then coasted way to short.
Thx for all the replies. I appreciate everyones input. Will answer in detail later, and promise I will post progress and conclusions. But I need to eat something now, starving!
76 Olds, just did that aspect couple months ago...the old grease had got sticky and calipers were sticking, even when cold. You could not push the car at all when in neutral and cold. Now it pushes with ease after redoing all the calipers, cleaning, regreasing pins, all metal on metal areas, etc. Calipers move freely now, and rolls so easy when cold and in neutral. But I will check them again anyways.
Forgot to add that I did all four rotors but verified it was rear calipers that were causing the sticking due to sticky pins. Fronts spinned ok, rears would not. So I went ahead and did all four, and found front pins too were sticky. So I used higher end caliper grease, 2k° F type. All calipers and pins worked great as of 2 months ago, and car rolls fine everytime now when cold. So again, its definitely related to driving the car now at this point. That is good progress since then, but still something else going on. But I am curious about the pins too again. Thx.
My '68 did the same thing after doing a front disc conversion. It was fine cold but after driving it the brakes would drag to the point where I couldn't move the car when in neutral. I remembered that GM used to make an adjustable pushrod for just such a problem. They go over the procedure quite well in the service manual but you need some special service tools to set it up(special gauge blocks,etc) that are probably impossible to find these days. Since I suspected the pushrod I took the car out for a drive to get the brakes warmed up. Once I got back home(with the brakes dragging) I loosened the m/c nuts a bit & they freed right up. The aftermarket "Delco" booster I bought came with 2 pushrods(my car uses the short one) I cut down the long one to the same length as the short one minus about a 1/16th for a starting point. I kept taking a little bit off & trying it. The problem went away & the brakes have been great for the last 4 yrs.
^^This^^
As we’ve previously discussed several times above. What I’d do in your case either as a starting point or because you don’t have ‘the tool’ (let’s say), again if you have NOT made an adjustment to your brake pedal assembly (which you state is now loose and hopefully you realize why), remove the MC, dial/turn back the brake booster push rod until just touches your brake pedal assembly. That should remove the gap between the brake pedal assembly and the brake booster pushrod so they are flush - now allowing the MC push rod (piston) to slide back where it should be and remove your preload condition.
Question...are all 4 rotors getting hot or just the fronts?
I got to do what Rob said to find out, drive it again and go through the checks to figure this all out. (Thx Rob for input)
Guys, several have mention the same questions. I just really realized what was happening yesterday after 30 min drive, and I only quickly checked driver side front and rear rotors, and both were hot as hell. I couldn't spend anytime on it yesterday, so I parked car in garage and had to go...I will have to return to it probably this weekend.
And yes Chief, my own research indicated most likely need to do the pushrod adjustment, but wanted input from seasoned vets.
Thx for all the input, next step is to do push rod adjustment, hopefully that cures it. 👍
First, are your willwood calipers fixed or floating calipers in the front. When they start to drag, is it both fronts, both rears, all four or just one?
Green...they are floating version for GM A bodies. Really nice quality.
And not sure if all four yet, I checked driver said front and rear and both were way hot. Couldn't spend anymore time on it though. Had to put her back in the barn.
^^This^^
As we’ve previously discussed several times above. What I’d do in your case either as a starting point or because you don’t have ‘the tool’ (let’s say), again if you have NOT made an adjustment to your brake pedal assembly (which you state is now loose and hopefully you realize why), remove the MC, dial/turn back the brake booster push rod until just touches your brake pedal assembly. That should remove the gap between the brake pedal assembly and the brake booster pushrod so they are flush - now allowing the MC push rod (piston) to slide back where it should be and remove your preload condition.
** To clarify- I most likely, looking back, had 3 issues in brake system go wrong
1. Stupid e-brake issue with El Dorado ebrake setup. Very hard to get right for those that have done these. Temporarily e-brake preload not set to eliminate this issue for now.
2. Rear brake caliper drag caused by pin grease not allowing caliper to float correctly. Grease got hot and then sticky over the years causing this problem. Fixed by redoing all four caliper pins. Used much better Hi temp brake grease this time
3. M/C push rod issue (hopefully this is all it is). Probable cause of current issue that only shows up after driving car for a while or when car is warmed up.
I havent been driving car much because it's been under construction for so long, so many back to back projects, never really went on any medium to longer drives. So probably why it hasnt showed up before.
M/C push rod issue (hopefully this is all it is). Probable cause of current issue that only shows up after driving car for a while or when car is warmed up.
I would tend to disagree w/ your statement. Having the car "warmed up" should have nothing to do w/ your issue. The problem is most likely to arise when you begin applying your brakes. The MC piston cannot return to its normal position (and thereby relieve the pressure on the MC piston). Each time you push the brake pedal (as has been stated previously), the MC piston moves forward - it CANNOT move backwards relieving pressure because the MC piston has preload on it and it WILL NOT return to its normal position - it continually INCREASES in pressure, applying more & more pressure to your brakes. This has nothing to do w/ your car being warmed up - it has everything to do w/ applying brakes (which just happens to be the fact you're driving your car and it's warmed up from driving it).
If you drive it and get it stuck, what happens if the mc to booster nuts are loosened? Does it free up?
Not sure how your Post #9 has material regarding OCA# 38722, but had you done what DJS70cutlass suggested, you'd probably have found your issue. As well as what rob960 suggested later on>> Once I got back home (with the brakes dragging) I loosened the m/c nuts a bit & they freed right up.
You can immediately try two scenarios to validate:
(1) Loosen the MC nuts a modest distance so the MC has some distance from the brake booster (push rod). Take the car for a spin and apply the brakes numerous times. Chances are you won't find the brakes are heating up and bound;
(2) With the car "cold" (i.e. just started and not having loosened the MC nuts - the car just as it sits right now), start the car and in a very modest rolling forward condition, apply your brakes about 15-20 times. Chances are your brakes are going to lock up before your engine gets warm.
Chief - I get it thx. Applying brakes, M/C piston eventually cant release. Understood you from the first. I guess I got to be ultra exact with my words. I thought that was understood already.
And I will try both ideas just out of curiosity before I fix it, and post back. Actually home early today to hit it some. But its a rainy day today, so dont know if I will be able to try ideas.
But engine warm may still be cooking brake line, no? Took this pic today
Formulating a series of test in my mind, including Chiefs, to include most of the mentioned fixes/possibilities. One I already know is this problem does not happen with engine off, no matter how many times or how long brakes are applied.
Again, this is first time today, I've tried anything to fix this specific issue, or isolate what it is as I just found about yesterday after extended drive!..some of you please consider this, had no time to dig into it yesterday. Some questions here arent taking that into consideration. Thanks!
One I already know is this problem does not happen with engine off, no matter how many times or how long brakes are applied.
Can you please explain why that is? Thx.
You have any partial vacuum being applied to the brake booster when the engine is OFF?
You might do well to review how a brake booster and MC work together, what the one-way valve does, what the diaphragm does, and what the brake booster push rod does and think about this in terms of engine ON versus engine OFF in a "properly aligned" push rod scenario.
You might begin here>>>https://auto.howstuffworks.com/auto-...ower-brake.htm
There are plenty of videos and tutorials on the description of how both the MC & brake booster operate in tandem - when partial vacuum is applied to correctly positioned push rods.
Doesnt this mean its adjustable from inside the car? Threaded pushrod with locking nut.
Yes, that is the brake pedal side of the push rod. Admittedly, however, I do not know the manufacturer of either your MC or your brake booster; and, not that it would matter because many aftermarket MC and brake boosters are designed modestly 'different' - some w/ push rod adjustment(s) some require different sizes of push rods, and some (BEAR THIS IN MIND) have a locking nut on BOTHends of the brake booster push rod. Therefore, thinking you can adjust the brake booster push rod from the brake pedal assembly only might in fact create more damage. Again, there is often an adjustment on the end of the brake booster push rod which meets the MC. Don't assume the end which fastens to the brake pedal assembly adjusts the entire push rod - you could end up pushing both brake booster diaphragms apart and/or pushing the clever valve out of its assembled position. Didn't you get directions on making this adjustment from the manufacturers?
This video shows at least (aside from the tool) how the brake booster push rod is adjusted to meet the MC push rod piston.
Did conversion 5 or so years ago. I don't remember now where I got booster or m/c (maybe Summit?), probably have instructions in huge pile of saved stuff. But I don't remember having this issue back then at all.
I got a small window of no rain between squalls.
Went through all the test. First 15-20 minutes couldnt reproduce. Final 5 minutes driving up to garage it happened. Opened hood, loosened m/c maybe less than 2 turns and it released. Could coast again, and be able to push it easily in neutral. So now on to adjustment. 👍👍
Turns out my booster is a Delco Moraine NON-adjustable pushrod type. So looks like I have to shim the M/C.
Spun my wheels researching it as there is nothing to adjust on the pushrod. So checked a General booster installation pdf from Jegs and it states to shim it if non adjustable Delco type. So I guess I will start there with the shims.
Turns out my booster is a Delco Moraine NON-adjustable pushrod type. So looks like I have to shim the M/C.
Spun my wheels researching it as there is nothing to adjust on the pushrod. So checked a General booster installation pdf from Jegs and it states to shim it if non adjustable Delco type. So I guess I will start there with the shims.
------------
Good to hear you have nailed down what you thought could have been the problem in your first post. I have difficulty trying to remember how I adjusted things from last spring haha.
I couldn't imagine having to re-think something after 5 years. However, with a little more insight here, you already knew the key elements in what to suspect and check .
That's the thing I enjoy most about this site, even thou I know what the problem could be, its nice to know we can come to our forum and get some confidence and re-assurance to keep our projects moving forward and performing their best.
I've had Wilwwod D52's on the front of my 76 for about 3-4 years now and they still work great.
They aren't cheap but a good investment for the performance they deliver. I had a problem with the supplied fittings and hardware initially myself.
I don't think the brake line in the picture will pose and issues with overheating the fluid. Mine front line running across is very close to my headers as well, haven't had any issues. The brake fluid can take some serious heat before boiling or expanding to cause any issues, even with the line in the picture shown to be close to your headers.
Happy to hear you found the problem, and most of all, the updates to how your progress is. This will help so many others going forward since some members don't take the time to update.
Your Olds came a long way since your Day 1 pictures, Happy to have you with us, I love the car and all the effort you have put into bringing it back to the community to share it with us.
Cheers'
Eric
Thanks Eric! Really appreciate the positive thoughts and words. Kind of made my day👍
I know the basics of most things, but brakes are a bit magical! Press the pedal and presto, car stops. Ive never had to diagnose anything like this before. I like a good test, brain storming exercise, but brakes are always a bit over my head on how they actually work.
(Actually restoring this car has been amazing, gut wrenching, literal blood sweat and tears experience. So far I've done everything myself, except set the backlash on the rear end. I got a least a 2 yr degree in hours wrenching and research for sure, probably more like 4 year!)
I watched a few vids that chief sent, and then the magic of YouTube, couple hours later I watched 25 videos and many blogs on brakes! lol.
Yes, this site is gold. Gives you confidence to dive in and DIY.
Good to hear about brake lines and headers, whew...cant take much more tweaking!
Yes D52s are what I have. Quality part. Very happy with them.
And yeah, I want to always follow up and post results. I know how it is when people leave the thread hanging with no results posted, no follow up. Not right man!
Shimmed it with 1mm SS washers for starts. I read another guy who went up to 3mm, but thought 1mm worked best for his setup. I basically just cracked the nuts barely, and it immediately released. So I hope 1mm does it. If not will add 1mm at a time. Also will bring wrench with me to slightly crack nuts again if it happens again out on road, to get her back home again without her feet on fire.
Will test tomorrow, and post results. Have a great weekend guys.
May 1st, 2019, 09:46 AM
