20 replies to this topic

[CNano8]

Hello all I’m having a problem with my brakes after doing some maintenance work to my nb1 Miata. At my last event I had a front wheel bearing start growling so while I was in there for the hub (changed both fronts because why not) I rebuilt all 4 brakes as well.

I’ve read that leaving the ebrake adjuster assembly in place could be detrimental to lap times if it drags so I deleted the entire ebrake assembly. While I was rebuilding the rear calipers (new boots, seals etc) I removed the adjuster assembly from the caliper piston (the part with the “hotdog”) and reassembled.

Got the car back together and bled the brakes. I noticed the pedal was very spongy, borderline no pedal feel at all. So I decided to bleed them again just in case there was any trapped air bubbles in the lines. No bubbles came out on the second bleed but the pedal is still spongy. Started the car thinking maybe if the booster had a vacuum source maybe it would stiffen up but nothing. I’m at a loss for what to look at next besides replacing the entire master cylinder. There is no visible leaks anywhere and my fluid is still at the same level. As a side note the brakes were 100% fine before I rebuilt them and I use a Motive power bleeder. Thanks

[Tom Sager]

Did you also have the fronts apart?  One thing you could look for is that all 8 pads are properly seated in the caliper brackets.  If 1 pad isn't installed correctly (because it fell out of it's spot with piston pushed all the way back) it can cause that. 

[callumhay]

Experienced a similar issue with the rear e brake self adjuster delete. Long pedal, spongy but was still able to slow the car. Tapping the pedal before the corners helped to set the pads and improved it.
I suspect some of the differences in feel of length of travel is normal. I did not like it and went back to the non gutted calipers

If you can’t find the cause you can try putting a non gutted set back on and see if that changes it which may be the only way to know…

[Steve Scheifler]

Removing the adjuster correctly should not make them softer at rest. Double-check that everything is in place as Tom noted. Then bleed in the correct sequence but always end with an extra quick bleed or two on the LR. Whether it was sticky bias valves or something else I never proved, but we had two cars that always felt spongy in the shop if we finished on the front. Repeating the LR solved it. Speaking of the bias valve, it’s an unlikely source of your issue but not impossible, perhaps during all the rebuilds some contaminants got in it. But since 90% of the time it’s the last thing you messed with, go back over everything you took apart and be sure there isn’t an internal leak or air trapped somewhere.

[CNano8]

Did you also have the fronts apart?  One thing you could look for is that all 8 pads are properly seated in the caliper brackets.  If 1 pad isn't installed correctly (because it fell out of it's spot with piston pushed all the way back) it can cause that. 

Yes I did have the fronts apart. I will recheck all 4 corners to see how everything is seated. I did notice during install that the rear pads on both sides were a little loose in the caliper which I thought was a bit odd. When I seen this I figured it was due to what you mentioned, the piston being fully retracted in the caliper. I thought after I bled them the piston would naturally tighten up against the pads to hold them in place against the rotor but that doesn't seem to be the case.

 

Experienced a similar issue with the rear e brake self adjuster delete. Long pedal, spongy but was still able to slow the car. Tapping the pedal before the corners helped to set the pads and improved it.
I suspect some of the differences in feel of length of travel is normal. I did not like it and went back to the non gutted calipers

If you can’t find the cause you can try putting a non gutted set back on and see if that changes it which may be the only way to know…

Interesting that you had a similar issue. Yes the feeling is as you described, a long pedal but spongy still able to slow the car though. I just dont know if this is normal as to what the pedal is going to feel like with this modification done. I do have a new set of untouched calipers for my new, under construction, SM. I will chase a few more things down but I agree a sure check would be to put a known good caliper on to see if the pedal feel returns.

 

Removing the adjuster correctly should not make them softer at rest. Double-check that everything is in place as Tom noted. Then bleed in the correct sequence but always end with an extra quick bleed or two on the LR. Whether it was sticky bias valves or something else I never proved, but we had two cars that always felt spongy in the shop if we finished on the front. Repeating the LR solved it. Speaking of the bias valve, it’s an unlikely source of your issue but not impossible, perhaps during all the rebuilds some contaminants got in it. But since 90% of the time it’s the last thing you messed with, go back over everything you took apart and be sure there isn’t an internal leak or air trapped somewhere.

Thanks for the reply I will recheck and rebleed again. If all else fails Ill put on another set of calipers to see if that does the trick. The bleed order I do is LR, RR, RF, LF which I believe is correct. This particular car is a TT car not a SM so I am running a Wilwood prop valve with the in cabin adjuster. I tried cranking the rear bias to see if that would help at all but unfortunately it did not. 

[Steve Scheifler]

Ah well, with non-stock bias valve never mind that part, they are a different design from what you have.

[ChrisA]

When you rebuild the brakes a lot of air needs to be purged and the rears, especially, have little nooks for air to catch in. The Motive Pressure bleeder does not provide the fluid flow force needed to force out those little trapped bubbles, it's too slow for that. Get a helper and bleed the brakes with the traditional Open/Close method, i.e; Close >Pressure >Open >Peddle-down >Close >Release >Repeat. Also, get a soft dead-blow hammer to smack the calipers a couple times during the process to dislodge the air bubbles. And, mind that reservoir, much too easy to let it run dry, which leads to .

[Alberto]

Double check that you don't have any leaks at odd places like the brake bleeders and the area where the grenade used to be.  The last caliper that I blew had brake fluid seeping and then fully spewing out of the area where the grenade / adjuster is.

I posted recently about using thread sealant on the brake bleeders to help fix an issue where they were seeping slightly.

[CNano8]

When you rebuild the brakes a lot of air needs to be purged and the rears, especially, have little nooks for air to catch in. The Motive Pressure bleeder does not provide the fluid flow force needed to force out those little trapped bubbles, it's too slow for that. Get a helper and bleed the brakes with the traditional Open/Close method, i.e; Close >Pressure >Open >Peddle-down >Close >Release >Repeat. Also, get a soft dead-blow hammer to smack the calipers a couple times during the process to dislodge the air bubbles. And, mind that reservoir, much too easy to let it run dry, which leads to .

Good idea ill do a traditional pedal bleed when I rebleed. Hoping to get to this tomorrow. Tonight ill be hanging out with some pals at SCCA track night    

 

Double check that you don't have any leaks at odd places like the brake bleeders and the area where the grenade used to be.  The last caliper that I blew had brake fluid seeping and then fully spewing out of the area where the grenade / adjuster is.

I posted recently about using thread sealant on the brake bleeders to help fix an issue where they were seeping slightly.

Will do good to know, im going to check over the whole system. I dont want to fool around with something like brakes.

[infamousjim]

Yes the feeling is as you described, a long pedal but spongy still able to slow the car though. I just dont know if this is normal as to what the pedal is going to feel like with this modification done.

My feet may be half blind but I didn't notice any change in pedal feel when I gutted my calipers. 

[callumhay]

My feet may be half blind but I didn't notice any change in pedal feel when I gutted my calipers.

I see that your car is a 1996. OP was 99 and mine same year.

Don’t know if that makes a difference in year of car or if the issue is due to some type of error as others have said or a non issue for those that have race/ car know how

[CNano8]

I was finally able to get at the brakes this afternoon. I think they're ok, well as good as they will be. First I rechecked the hardware and assembly. I then rebled them using the traditional pedal method, tapped the calipers with a rubber mallet and double bled the LR caliper. The pedal is definitely much firmer than what it was before. I attribute that to some air bubbles that did end up being bled out. There are no leaks anywhere in the system which is I was happy to see. Overall the pedal feel is still different than before but to be expected with this mod although I wouldn't call it "bad". It will take some getting used to. If I really dont like it I wouldn't mind going back to adjuster calipers and keeping an eye on them after a session out on track. Im atleast confident at this point there are no hardware issues with the brakes and I wont suffer brake failure on track as I test drove the car after this process to confirm. Thanks all for the help it is much appreciated.

[Alberto]

fwiw, I did not notice any difference in pedal feel from regular reman calipers to Drago's fancy, gutted calipers (in the rear).

Suggest you bleed again after the first session.  

Good luck

[CNano8]

fwiw, I did not notice any difference in pedal feel from regular reman calipers to Drago's fancy, gutted calipers (in the rear).

Suggest you bleed again after the first session.  

Good luck

Will do thanks

[RWP80000]

For what it is worth, with the gutted e-brake rear calipers, there will not be any take-up of the 4mm socket screw behind the 14mm access screw next to the e-brake bracket mounting bolt.  As a result, as the brake pads wear down, there is nothing to keep the rear brake pads adjusted for the wear.  I always remove this access plug before each race weekend and tighten the screw to where the pads are firmly against the rotor and then back the screw off 1/4 to 1/2 turn.  This prevents excessive pad knock back in the rears.

 

Rich Powers

[Sphinx]

Dumb question, but did you also happen to change brake compounds?  Unwittingly, I did that a few years ago when I went to the the "flavor of the month" pad and spent years chasing the soft pedal.  Changed pads to something more aggressive - problem solved!

[Ron Alan]

For what it is worth, with the gutted e-brake rear calipers, there will not be any take-up of the 4mm socket screw behind the 14mm access screw next to the e-brake bracket mounting bolt.  As a result, as the brake pads wear down, there is nothing to keep the rear brake pads adjusted for the wear.  I always remove this access plug before each race weekend and tighten the screw to where the pads are firmly against the rotor and then back the screw off 1/4 to 1/2 turn.  This prevents excessive pad knock back in the rears.

 

Rich Powers

There are different methods...But for what it is worth if you take out the piece(hand grenade)that is in the middle of the piston...and ONLY this piece(touch NOTHING else)you now have a front caliper with nothing every to adjust!!

[SaulSpeedwell]

One of few certain facts:  If you run full thickness rotors and pads (and/or make shims such that the pistons on all 4 corners are fully "bottomed"), you can absolutely eliminate "knockback" as a cause.  Supremely useful as a diagnostic, and also useful for saving brake money and being faster, depending on the class and how you elect to implement this concept.

[CNano8]

Dumb question, but did you also happen to change brake compounds?  Unwittingly, I did that a few years ago when I went to the the "flavor of the month" pad and spent years chasing the soft pedal.  Changed pads to something more aggressive - problem solved!

Good idea but I was still running the same Carbotech XP10/XP8 combo. 

[CNano8]

I had a chance to drive a 99 E Production miata on track last weekend. What a great experience that was but anyways they eliminated the prop valve completely and used a couple unions to bridge the hard lines. It had an amazing pedal feel, rock hard and very grabby (I believe HT10 pads all around) I had to really pay attention to my brake pressure until I got used to it after a couple laps.