I will run to auto parts store and get new bleeder screws again I guess
From what I see the MC is a different part number depending on if the brakes are “vacuum power brakes” or “hydraulic power brakes”. I don’t see any mention of a “police edition”. Also nothing implying the MC is different part number 2wd vs 4wd.
It appears nothing about the brakes is simple on this vehicle. The power steering pump is involved with braking in some configurations believe it or not (applies to the hydraulic brake booster system from what I can tell). Are you having any problems with the power steering?
So you get a good pedal when either of the front calipers is pinched off individually, right side or left side, but no-good when neither are pinched off? This is indeed a mystery. hmmmm … “brake proportional valve” is a possibility. But I see no mention of that part on your vehicle. There’s a reference to an EHCU or BPMV, both some type of brake modulating mechanisms, which could be some form of proportioning valve. If that valve is still in the hydraulic circuit, it could possibly be the problem. It’s also possible that by removing the ABS it now isn’t possible to bleed the brakes properly for some reason in that configuration. The instructions I’m seeing for brake bleeding, even using a gravity or manual method, still requires the automatic scan-tool brake bleed after the first manual bleed, then repeating the manual brake bleed.
The caliper bore size differs depending on the configuration, maybe you have too big of caliper bores somewhere. That could explain why you get a good pedal with either front pinched off, but not when both are open.
Another theory, maybe it’s a relativistic system, the brake fluid is moving into a 4th dimension?
from the MC the front brakes are piped directly… From the MC the rear goes through a wildwood manual proportioning valve in/out with an adjustable knob…
Correct on the pinching. I can pinch either side or both and the pedal is firm while running.
The scan tool only applies if the ABS system is in… other wise its futile…
MC Part # that’s in is Dorman # M390259…
yes ive adjusted the proportioning valve both ways…
4th dimension ? hmmmm possibly lol
We’re 100% sure the calipers are properly bled? If they weren’t bench bled before they were installed, that process can take a long time.
Is that picture above with the two screwdrivers your calipers or a picture similar to yours? Not clear based on
If it is not your calipers, please take and post a picture of your actual calipers.
I expect that’s the OP calipers in the photo. I suggested above – as an experiment to diagnose what’s going wrong – to place a spacer between the piston and the pads. Apparently the results of the experiment is that the spacer had no effect; i.e. when one or the other of the front calipers flexible hoses are pinched off the pedal is ok, but when both are open the pedal is low, spacer or no spacer. The OP has done about everything they can do diagnosis-wise. It seems like problem has to be from among these
- air remaining in the calipers
- faulty calipers
- incorrect caliper/pad/rotor combination for the vehicle
- faulty or incorrect use of the Wildwood aftermarket proportioning valve
This is a situation where ideally you’d have a manually operated hydraulic fluid pump you could hook up to each caliper independently as a testing fixture. A person could home-brew something like that using a spare master cylinder I suppose.
those are my calipers… the screw drivers are/were the spacers for that experiment you guys told me to do…
I took it to mechanic #5 to day, brought him up to speed, he suggested replacing these calipers… so im giving it a try… Why not ive bought 2 or more of everything else… just want to be consistant.lol ., Thanks George, Keith will keep you posted on the results
This would be a good problem for Hot Rod to the Rescue. Unfortunately it appears that feature has been discontinued (either temporarily or permanently) from Hot Rod Magazine.
If there is no air in the system, since you can’t pump them up, I’d say there isn’t any. The travel of the pedal will be long if you have the small bore master and should have the big bore booster. You never said if you have a vacuum power brake booster or hydroboost power brakes off the power steering pump. You did say the pedal drops when the engine is started. Both systems should do that.
This truck has huge caliper pistons from the start and requires a lot of fluid to move them. It is a poor design. I’d be putting in the big bore master, myself.
When I owned this gen truck, I’d manually adjust the rear drums every tire rotation so the pedal would not be so long. Did I say these brakes were a poor design?
vacuum booster , just replaced the new calipers again and still doesn’t improve…
Ive had it with this …. loading pics on craigslist to sell it… what a headache… thank you everyone for your help I really appreciate it … Randy
Sorry you couldn’t resolve this stubborn problem OP. Good idea to move the problem on to somebody else. Maybe they’ll be able to figure it out. Wasn’t for lack of trying, that’s for sure.
@Randy_Goodwin, Sorry you are giving up. Brakes can be fixed, they are not rocket science. Your problem is a bit confusing though, I think that it this time, if I were working on it, I’d put everything back original.
Some tips for the future though. You started this by tagging onto an old thread and them moved to a new thread, that it OK, new visitors often do this, but it would have helped to have inserted a link to the thread you originally started with as it has some important history.
Your problem started immediately after replacing the front calipers and rear wheel cylinders. At this point you should not have done anything to the rest of the brake system. First rule of mechanicing is if it fails right after you fixed it, you fixed it wrong. You may have gotten defective parts or a part that was not a direct replacement or something else went wrong. You go back over everything you did, you do not go looking for more bad parts.
BTW, looking at the picture of your calipers, the first thing I thought is they were not the correct calipers. That is why I asked if they were yours or just a stock picture you got from somewhere. I would go to a dealer with your VIN number and have them look up the correct calipers for your vehicle.
If you want to do it over the internet, go to https://www.gmpartscenter.net and enter your VIN. Then get the GM part number and cross reference it to the calipers from your supplier.
thank you… it started by changing the calipers and rear brake cylinders, true… then the shop said the abs is bad and the MC is bad… took it to the dealer, they also replaced the MC, checked, removed and tested the Calipers and then said abs is bad and is obsolete…and they gave up…then I removed the ABS, then another shop then another mechanic… then 2 days ago another shop and new calipers… but I did look at the calipers and yes its one big piston… I feel ive exhausted my efforts on this and have spent a lot of money at it along the way…Its still in the driveway lol……If your interested I can send detailed pic, firstname.lastname@example.org. Thank you very much Guys !!!
Very kind of each of you to respond and reach out to help… Thank you
So, after thousands of dollars and weeks of waiting for all manner of repairs the dealer advises that the ABS is faulty and obsolete and are unable to repair the tahoe. Again, my 30 year old Blazer looks MARVELOUS sitting out front ready to go with a firm brake pedal and a chilling AC. I’ll just have to ignore people turning up their noses at my fading paint.
lol …You got it lucky there RK, compared to me. Somebody in my neighborhood must not like the appearance of my truck parked on the street, thinking a 50 year old truck brings their property values down. They somehow convinced the local police to try to tow it away. The problem is the only way the police can get involved is if the truck is violating some law or the other, and the only possibility is the 48 hour parking limit. So the police started marking the tires nearly nearly every other day. I’d check daily, if I saw marks, I’d move the truck, no big deal. The surprising thing, this went on for 2 1/2 years!! They got very clever in the marking techniques too. It started as a thick yellow-crayon line on the street sides tires, from the top of the tire, down the hubcap, bottom side of the tire, and onto the road surface. Very easily seen. I guess they figured I was seeing the marks, so they moved on to more subtle marking techniques: rocks on top of the tires, marks on the street side rather than street side, tiny marks nearly impossible to see unless kneeling down by the tire. I’m not kidding!!
Then one day I was outside doing some garden chores and it starting pouring rain. So I moved underneath a tree, just standing there out of the rain drinking some coffee until the rain let up. What do you know, a squad car pulls up along side my truck, doesn’t see me, the officer puts on his rain-suit, doffs a plastic cover for his hat, gets out, walks to the sidewalk side of the truck and knees down to put nearly invisible marks on the tires. As he’s leaving I couldn’t help but to laugh. I mean he’s going to all this trouble, in the pouring rain ? For what?? … lol … The officer hears me laughing I guess, looks around, sees me standing there under the tree, weird look on his face, then hurries to the squad car & drives away. No more marks since.
that’s funny !!!
Ok so I just went to the auto parts store and ordered the bigger bore MC hahahaha I know but why not right ? Mine is the JB6 which is 1 1/8 " bore and the only bigger one is 1 1/4 " ….will post results soon
just bench bled and installed new 1 1/4" MC and bolted new lines up…I have not bled each wheel yet at all… started up motor and the pedal is hard when pushed down 3/4 of the way in fact I drove it and it will stop ubrutly… Cant wait to bleed each wheel then see but its just to hot today 98 degrees…will keep you posted with final results… thanks
Final results, Hard pedal when pedal is puched 2/3 --3/4 down then its very firm… I can live with that and feel safe when towing my toyhauler…… thank you everyone for getting to this point