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Brakes heavily biased towards the rear?


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Well now that my head gasket fiasco is done, I am ready to revisit this. I changed the front pads a couple weeks ago and it doesn't seem to have made a difference. The pads that I replaced still had a lot of life to them. Running EBC yellows all the way around now.

Again;

- No ABS errors.
- If it was a bleeding issue, I would have a mushy pedal correct? From what I understand, a mushy pedal would only show up for a front bleed issue and not a rear. Since no mushy pedal, it can't be a bleed issue with the front. Since the rear are working hard, not a bleed issue with the rear. Or??????
- Pump comes on a runs until the accumulator is full and then it stops.
- No pulling to one side or the other.
- Hand brake is not stuck (I can push the car easily with the hand brake off).
- All calipers move freely and do not appear to be stuck. They slide on their rails and I am able to retract the pistons when changing the pads.
- Front brakes are working, just seemingly not as strong as the rears, or the rears are working stronger than the they should be.
- I am just wearing out rear brake pads much quicker.

Other than disabling ABS completely by disconnecting the wheel sensors as Travis suggested, any other thoughts? I am leaning towards a complete flush, which it needs anyway, and saw the info posted here on hot to automate the process;

 

Has anyone actually flushed their Delco system with this process? has it been automated like Erik mentioned may be done? Otherwise is it just a matter of following the sequence with the same keystrokes and just keep topping up the reservoir? Am I right that you cycle each solenoid with the corresponding nipple open until you see clean fluid? I have searched and found reference to "or use the ‘Tech 1’ bleeding sequence" in the manual and articles but can't seem to find the actual procedure for bleeding/flushing using the Tech 1 tool. I can probably figure out how to use espritmon in place of the Tech 1 if I can find the actual procedure.

Hmmm, reading some other threads;

http://www.lotustalk.com/forums/f164/brakes-not-releasing-1995-esprit-304362/index3.html

and

http://www.lotustalk.com/forums/f164/help-brakes-sticking-delco-moraine-system-442562/

It made me remember something. I sometimes get a "jutter" or "pumping" feel when braking normally. To me it felt like a warped rotor. A good while back Travis (I believe) said it was unlikely a warped rotor and that it could be brake pad material stuck to the rotor from sitting still with the brakes on with a hot rotor and that a few back to back hard stops can remove the residue. Well, I have done that procedure and noted it fixed the issue. Perhaps this is actually the rears pulsing? I do not feel it in the steering wheel so this seems plausible. Now, this is during normal braking and not an ABS intervention, so that would rule out the proportioning valve correct? Possibly the rear solenoid? Or, does that point more towards the pressure coming from the master cylinder that is pulsing? AND if so, that would mean the spool valve or is that only active during ABS activation? Possibly my hard braking where I end up activating the ABS is clearing out the issue for awhile?

Sorry for all the outloud thinking here. Maybe it prodded some thoughts with someone more knowledgeable on the Delco system than me?

Yeah, a flush is coming up for sure as soon as I find the proper procedure using Espritmon.

Now, after reading this;

When the brake pedal is depressed, the
controller is alerted that the brakes have been
applied and monitors each wheel speed. If the
controller detects an impending wheel lockup or
determines that a wheel or wheels are not
decelerating equally, the controller will pulse the
corresponding solenoids on and off rapidly. This
activity can occur independently on each front
wheel and on the rear wheel that begins to lock up
first (select low)

It made me think about the fact that I have larger tires on the rear so during braking the system could be seeing the "slower" wheel rotations of the rear meaning it is locking up and pulsing the rears? Well, there goes that Idea because I monitored the abs system via espritmon during normal braking (no alerts) and then again in an ABS activation braking which did show the ABS notification. Hmmm

I think I will try this as a test tomorrow and see if there is still any pulsing and check the temps of the rotors.

http://www.voicecrystal.com/Esprit/ABS_Disable/

 

 

fronts.jpg

Edited by Techspy

John
94 S4

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During conversations I had with Pete at PNM reference Delco braking issues, he told me that he has stripped and cleaned master cylinders on four occasions. He said they had sludge in them, and having

I know exactly the bleed nipple you are talking about Danny. It is a right bugger to access.

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I enjoy and appreciate your recent posts and footage John. If anyone deserves a perfect Esprit currently then you would be one of a select few on the forum.

I recently upgrade my rear brakes, S3 to slightly larger rotors and Brembo calipers. It did worry me that I was affecting the balance braking between front and rear, particularly with most cars being forward bias. My test after upgrade was to slam the brakes on at circa 30mph and see which locked up and tyres left a mark on the road. Do your fronts lock up under hard braking?

I guess that you are worried that there is some underlying issue with your rear brakes that could materialise in a bigger problem later as changing the pads more often isn't your concern. It seems that your rear brakes are doing more of the work, so perhaps it is the fronts that need attention? 

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Thanks. Yeah there is definitely something wrong. This has not always been this way on my S4. It is heating the rotors too much and changing pads every month or so is just not good. It seems to be getting worse. I will be testing today and doing a flush as soon as I cam able to find the "Tech 1 bleed procedure".

John
94 S4

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During conversations I had with Pete at PNM reference Delco braking issues, he told me that he has stripped and cleaned master cylinders on four occasions. He said they had sludge in them, and having refitted them following the strip down, he hasn’t had any complaints from the owners. Clearly, it’s a complicated piece of kit, and as there’s no longer any parts available for them it could be a bit risky, but perhaps a disassembly and internal clean is something that might help?

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Margate Exotics.

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Thanks. Just tested with the rear solenoid fuse removed, and no difference. Getting ready to flush using Espritmon. I am guessing the procedure is to open the nipple on the corresponding caliper and follow the steps listed here from the espritmon thread while ensuring the reservoir stays topped up? Anyone with any additional info, advice appreciated.

1. lf release on,off

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24. rear hold and release on,off

EDIT: Not sure this is the correct procedure. I guess I can just use the manual stated way to bleed the brakes and just keep bleeding until new fluid flows.

Edited by Techspy

John
94 S4

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Ok, just completed the service manual procedures for bleeding. I suctioned out the reservoir just to the bottom and then topped up with clean fluid. Then bleed each caliper until it was obvious new fluid was coming out. After this I went for a drive. Pedal may feel a little better but hard to tell. I did notice that my front left pads squeaked a little on my first few slow stops. These are pads I put on about 200 miles ago that probably never seated because of this issue. Stopping seems a little different. Seems like less nose dive when braking. Maybe it is placebo. Anyway, after my drive the right side rotors were within a few degrees in temp, around 175 degree. The left front was about 150 and the left rear around 225. So, I am cautiously optimistic that this may have been the fix. I hope in a few more miles the front will be good and seated and the left temps will even out. If this is the fix, it must have been trash, really bad fluid or air in the fronts that needed bleeding. Wish me luck.

BTW, my rear rotors are getting a little grooved and after all this over heating I am thinking of replacing them. They are drilled rears from ramspott-brandt. Anyone have any other recommendation for drilled rear rotors? I am still recovering from the head gasket repair so a set a little cheaper would be great.

John
94 S4

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Can you not have the rear discs skimmed?

 

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Well a few years ago I asked about it at a local shop and they wouldn't do it. Actually after looking at the rears again, they aren't as bad as I recalled. I think I am good for now but may look for a dimpled set later as opposed to a drilled set.

John
94 S4

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I know exactly the bleed nipple you are talking about Danny. It is a right bugger to access.

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All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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Well after a good drive today it seems the issue is not better. Rears are much hotter. One was 325 while the front was 125! I think i am going to rebuild the calipers just to rule that out. I am sure they could use it anyway. And suggestions on where to get the rebuild kits? I am guessing it is just the seals and robber boot dust protector and mainly consists of cleaning any gunk out?

John
94 S4

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Have you replaced the front brake flexi hoses?

If you strip and clean the front calipers, and the problem still exists, then in my view it points to the Delco being at fault. 

Margate Exotics.

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I havn't changed anything from the stock setup. Why would you think the fronts are at fault?

As a test, I completely loosened the handbrake and made sure the lever on the calipers was as far released as it would go. Issue remained. Now I am wondering if the parking brake has been "over adjusted". I see where the proportioning valve is supposed to prevent that but wonder if it is not working correctly. but that doesn't make sense because the brakes don't drag. I am starting to wonder if when letting off the brake pedal that for some reason the rears don't release completely right away. I will probably jack the car up while running, use the brakes and see if the rears stay locked or release right away. Man I can't figure this thing out.

John
94 S4

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I was wondering if the front brake flexible pipes were causing a problem by not pulling up as hard as they should. If they're old, the could have deteriorated internally. Hence me asking if you'd replaced them. Rear caliper strip and overhaul is surely a good idea, though.

Also, there's no brake proportioning valve fitted with the Delco, that's governed by the master cylinder/ABS system.

Margate Exotics.

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Ah ok. I am leaning towards the front working ok but the rears "over working". When checking the temps, the front seem to be around 100-150f after a normal drive with normal braking while the rears get up to 225-325f. So if I am stopping aggressively and need "stopping power" and have to rely on the rears to stop me within a certain distance, yeah, I could see that. But just coasting to stops with minimum braking and the rears getting that hot seems to point to "over use" of the rears IMHO. I could be completely wrong however :)

Actually there is a pressure proportioning valve on this system (see page 47 of section JF) however it doesn't work in the conventional way.

"Pressure Prooortionina Valve (TMC/Bendix  brakes only)
If the brakes are vigorously operated when the accumulator is charged and the vehicle is stationary
(at which time the ABS does not operate to control brake line pressure), the very high pressures produced
in the boost chamber and rear brake circuit .could  result in the rear brakes being applied with a force
sufficient to overadjust the parking brake mechanism contained within the caliper piston. In order to
prevent this possibility, and the consequent brake drag and pad wear, a pressure proportioning valve is
fitted into the rear brake circuit, and is located at the right hand front of the engine bay"

So, if it is bad the hand brake could be "over adjusted" but I don't see any evidence of that. Just wondering if it could be defective and prevent the rear line pressure from releasing immediately.

John
94 S4

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Sorry, I hadn't clocked the fact you had the earlier TMC brakes.

In that case, I think it's definitely worth changing the limiting valve. Lets face it, it's 28 years old, and it's an easy option. Well, easier than rear caliper overhauls, anyway.

Margate Exotics.

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I actually just checked and after releasing the brakes, the tears spin freely immediately. There goes that idea. Next I am going to jack the rear up with cool brakes and idle in 1st gear and check the temps. I can spin easily by hand but there is a very slight drag which I understand is normal. Just want to see how much they heat up with no brake action.

John
94 S4

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Thanks for the link.

I just jacked the rear up, put it in 1st and let it spin the rear wheels for awhile. Only a couple degrees increase in temps. So it seems the issue is only happening during the actual application of the brake pedal. No dragging after brakes applied or in general. At this point I can only think that the issue is within the master cylinder. Maybe the spool valve.

John
94 S4

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On 30/03/2018 at 08:57, Techspy said:

Ok, just completed the service manual procedures for bleeding..

Did you also bleed the two nipples on the master cylinder and cycle the solenoid valves?

DanR

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On 4/3/2018 at 18:57, Techspy said:

 So it seems the issue is only happening during the actual application of the brake pedal. 

In the UK for the annual MOT test the car is put on the brake tester which shows the actual efficiency of each disk while braking.

A brake test maybe of help. :thumbup:

Edited by jonwat

Cheers,

John W

http://jonwatkins.co.uk

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5 hours ago, Techspy said:

Actually no. I didn't identify any evidence of air on the system and did the bleed to flush out old fluid. Any thoughts that being neccessary?

I just did some brake bleeding last Friday after replacing the front rotors and pads. I bled the master cylinder driver-side and got a lot of air out. When I did the passenger-side, there were some fine bubbles that appeared the other reservoir. So I think the passenger side bleed point on the master cylinder goes to the rear brakes.  Definitely worth trying to bleed the MC.

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It's actually really easy in my opinion (and I rarely claim any service on an Esprit to be "easy"). Bleeding the MC is the same as you normally would (with 2 people).  Depressurize the accumulator (manual says to pump like 40 times, but mine needs about 50 to feel the pedal go soft).  I use a 24 inch 1/4"  diameter clear tube and run it into a plastic peanut jar with a hole cut into the middle of the lid. For the driver-side, you just have the 2nd person pump while you open and close the bleed nipple. For the passenger-side, you turn the ignition to Accessory and then have the 2nd person hold the brake down 1/2 way to activate the ABS pump. 

Pro Tips:  Put thick paper towels under to master cylinder to prevent brake fluid drips onto the paint (It's much harder to get your hand under there to try and wipe up anything once it does dribble under there). Then for added protection, I use a thin bungee cord to wrap and hold a terry cloth towel around the neck of the reservoir. Keep a few spare towels handy for quick access.  Also make sure the person pressing the pedal doesn't press fast or else it'll shoot the fluid outside of the reservoir.

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  • 1 month later...

Well, after flushing the system with new fluid and at the same time bleeding all 4 corners, it seems the issue is now fixed. Possibly I had some debris in there or maybe the fluid was just too old? I am ashamed to admit that it was way too long since I changed the fluid. Also, when parking now I don't use the parking brake but just put it in gear (unless on a really steep incline). This has prevented the "shimmy" that has developed in the past from the rear pads baking onto a hot rotor. Hopefully this has fixed the issue.

John
94 S4

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