62 replies to this topic

[Alberto]

^No, was referring to the bolts that attach the U shaped brackets over the "rack" to the subframe.

 

Replaced front calipers this weekend at the track (thanks Ed Railton!).  That seemed to help the issue.  Then I switched to a set of RRs instead of my tired RA1s and the problem returned stronger than before.  New rear calipers and brake lines have been ordered.  Wish I had remembered to do this over the winter but had brain fart.  Was kicking myself all weekend at my terrible memory.  

[Ron Alan]

Welcome to middle age Alberto! You seemed to be faster last weekend...your issue didn't slow you down!

[fotostars]

Once you're done with all those "upgrades", you'll have to test them before your next "important race" for the points.

How about you come join us with NCRC March 21-22 ? Hint, hint! 

[Alberto]

Welcome to middle age Alberto! You seemed to be faster last weekend...your issue didn't slow you down!

 

 

Tell me about it...   I think I always had a mediocre memory though. Getting worse...

 

I did OK in quali getting a 2:13 on old RA1s from last season - or maybe it was the season before...  I forget when I got the tires.  I was fighting the car the whole time though.  My race was shit.  Managed to get one decent lap in the 2:13s but the car was behaving worse during the race than quali.  Still fun but frustrating.  I felt bad for the 2 guys behind me that were faster than me in the corners where my braking / handling issue slowed me down but they couldn't seem to get around me where it didn't.  Eventually, they got by when I made a bigger mistake.

 

I managed to get into 2:12s before my epic motor rebuild so I still have lots to improve before getting back to what the car and I am capable of.  Brandon is in the 2:11s in Sharpie.  He's my target but he's a more seasoned racer than I am.  He sure puts the work in to be a faster and have better race craft.

 

 

Richard, we'll see if I can make it there.  I could use the seat time.

[RazerX]

we will have lots of good mechanic types there to help your pulling issue

[Alberto]

Mysteries continue....

 

Got a pair of rear calipers from Mazda Comp and a set of brakes lines from Advanced Autosports.  Got them installed a few minutes ago and was doing a solo brake flush using my jack handle to hold the brake pedal down while I crack the bleeders. 

 

I noticed that I could easily turn the passenger rear rotor by hand while all the other corners took a lot more effort. 

 

I plan to do a 2 person bleed tomorrow once I replace the front brake lines but this seems odd.  Anyone got any thoughts?

[fotostars]

Hi Alberto,

The fact that you can easily turn the rotor is most likely because you didn't adjust the handbrake screw to bring the piston close to the rotor.

Adjust that first, Turn with a 4mm Allen (behind the 13mm plug) until snug and then take back 1/3 turn.

 

For the bleed, I replaced all my bleeder valves with "Speed Bleeder" ones. They have a ball inside, makes it an easy job by yourself...

[SaulSpeedwell]

This thread is so old, it is starting to stress me out!

 

"Pulling hard under braking" can't really be caused by the rear BRAKES.  The car trying to SPIN because of a locked rear is certainly possible - but rear brakes don't steer a car very effectively, unless you count skidding/spinning as "steering".

 

Even if you have only one FRONT brake working at all, the wheel will try to yank out of your hand - but you should be able to steer through that.  If the wheel is straight, the car should go straight, despite that it is tugging at your hands.

 

If the brakes are hot, they are working.  If one is way hotter than the others, it is working harder and should be considered suspicious.

 

If you can't steer through the "pull" with a straight wheel, it means one of your wheels is steering because of compliance ("flex" somewhere).  Front bushings and subframe would be the first place I would look - this assumes all of us Pro Commuter Car Cup drivers would already have found something as obvious as a sloppy tie rod end or balljoint. 

 

Like Wheeler said, a cracked front subframe will PULL - the harder you push the brakes, the more you'll have to countersteer - that is because the front wheel is being "peeled back" and steering on its own due to the braking force.  The good news if you keep it up, it will eventually completely fail.  I know because I had the pleasure of driving an NB that was fine, then started to tear, and then completely disconnected, all in one enduro.   The ones I've seen fail where the "pocket" attaches to the lower subframe, by cracking right around the weld.  The ones I see failed are the front pocket location.

 

Your front toe only matters in terms of total toe because you as the driver are "centering" the road wheels as necessary to go straight.  The two sides being different only matters as regards how straight your steering wheel would be.  So, 5 mm total toe out in front isn't ideal, but it isn't a huge deal.  It won't make the car undriveable or even very weird.  90% of drivers would never be able to tell.

 

The rear has 6-ish mm total toe-in, but thrusted "rightward" - meaning the car will dogtrack a bit, but again, this isn't a huge amount.  It  would cause the car to "hook" a little left under braking and into LHers, and "push" a little into RHers.  90% of drivers wouldn't be able to tell, and any of 6 other things could counterbalance this effect.

 

HOWEVER:  How are you measuring the X mm?  Front tape reading minus back tape reading using the strings at the wheel lip?  X mm at the wheel isn't X mm at the end of a toe plate.  This is why "angle" is really a better measurement, since 1/16" of "toe" on an old Mini Cooper with 8" wheels is 3 times more ANGLE than 1/16" of toe measured with 2 foot long toe plates!

[Alberto]

This thread is so old, it is starting to stress me out!

 

"Pulling hard under braking" can't really be caused by the rear BRAKES.  The car trying to SPIN because of a locked rear is certainly possible - but rear brakes don't steer a car very effectively, unless you count skidding/spinning as "steering".

 

Even if you have only one FRONT brake working at all, the wheel will try to yank out of your hand - but you should be able to steer through that.  If the wheel is straight, the car should go straight, despite that it is tugging at your hands.

 

If the brakes are hot, they are working.  If one is way hotter than the others, it is working harder and should be considered suspicious.

 

If you can't steer through the "pull" with a straight wheel, it means one of your wheels is steering because of compliance ("flex" somewhere).  Front bushings and subframe would be the first place I would look - this assumes all of us Pro Commuter Car Cup drivers would already have found something as obvious as a sloppy tie rod end or balljoint. 

 

Like Wheeler said, a cracked front subframe will PULL - the harder you push the brakes, the more you'll have to countersteer - that is because the front wheel is being "peeled back" and steering on its own due to the braking force.  The good news if you keep it up, it will eventually completely fail.  I know because I had the pleasure of driving an NB that was fine, then started to tear, and then completely disconnected, all in one enduro.   The ones I've seen fail where the "pocket" attaches to the lower subframe, by cracking right around the weld.  The ones I see failed are the front pocket location.

 

Your front toe only matters in terms of total toe because you as the driver are "centering" the road wheels as necessary to go straight.  The two sides being different only matters as regards how straight your steering wheel would be.  So, 5 mm total toe out in front isn't ideal, but it isn't a huge deal.  It won't make the car undriveable or even very weird.  90% of drivers would never be able to tell.

 

The rear has 6-ish mm total toe-in, but thrusted "rightward" - meaning the car will dogtrack a bit, but again, this isn't a huge amount.  It  would cause the car to "hook" a little left under braking and into LHers, and "push" a little into RHers.  90% of drivers wouldn't be able to tell, and any of 6 other things could counterbalance this effect.

 

HOWEVER:  How are you measuring the X mm?  Front tape reading minus back tape reading using the strings at the wheel lip?  X mm at the wheel isn't X mm at the end of a toe plate.  This is why "angle" is really a better measurement, since 1/16" of "toe" on an old Mini Cooper with 8" wheels is 3 times more ANGLE than 1/16" of toe measured with 2 foot long toe plates!

 

 

^Thanks

 

I was measuring toe to the wheel lip using the ruler supplied by Iron Canyon.  What said about a tape/ruler measurement vs angle makes sense.  Thanks for the education on that. 

 

The parts I highlighted are what I'm feeling out on track.  The steering wheel will pull hard and trying to brake in a straight line has me holding the wheel turned to the left 30-45 degrees.  Makes it rather challenging to negotiate a right hand turn like T3 at Thunderhill or T10 at Laguna. 

 

I haven't noticed any cracks in the front subframe but the force that I'm able to exert with my crowbar is nowhere near the force on track under load.  I've already checked the front end last year but will take it apart and probably replace parts.  Oddly enough, I have many spare controls arms but no front lower control arms...

[RazerX]

Alberto,  drive in the paddock in in the road behind sonoma / skid pad as Thill.  Just stab the brakes at 20 mph, if it pulls and turns the wheel, as noted in this thread it is likely a front brake issues.  the slower speed would lessen the pull/load for subframe/ball issue. But as noted check for ball joints and bushings and frankly that can be done just tugging on the top/bottom of the wheel for the issue you describe as pretty bad so the travel needs to be, 'large'.  Tie rod end and tie rod in general are quickly checked by jacking on front week /w the other on the pavement and seeing if you can freely turn  your steering wheel any travel, then swap the front tire on the ground and check the other side.   

 

One item I don't recall be suspect is the brake portioning piece.  This is where four brake lines connect too and the master cylinder feeds its into it.  It's purpose is if there is rapid a brake fluid leaks is supposed to seal off part of the system to maintain some braking.  Think of a rock taking out a brake line.  Most cars i have worked on have the LF/RR on one system and RF/LF on the other and honestly I haven't delved into a miata's to know if that is their strategy.  However is that unit is defective or got partially engaged or broke it is possible that not all or equal force will be delivered to all calipers.  It it definitely an obscure suggestion, but i have had it twice in my life.  Once, not surprising, on a triumph...

[Alberto]

^ ball joints and tie rods are apparently fine when checked in that manner.  Even compared to a known good car in the pits.

 

stabbing the brakes in the pits around Thunderhill didn't reveal much.  Needed more speed and momentum to reproduce. 

 

I don't think the Miata proportioning valve works in the manner your described.  There is one hard line going to the subframe whereupon it slips off at the "junction box" at the pax side of the rear subframe.  The pax soft line attaches to the junction box.  Another hard line attaches to the junction box and goes to the driver side of the rear subframe.

[Bench Racer]

Also, the brake line for the front drivers side travels directly from the master cylinder to the caliper. The other front line travels to the nearest bottom connection on the proportioning valve. The rear line from the master cylinder travels to the other bottom connection on the proportioning valve. One top connection on the proportioning valve travels to the rear and the other top line travels to the right front. 

[Steve Scheifler]

Idid start at the beginning so not sure if it has been mentioned yet, but if this has been going on awhile and is related to brakes, you solid be able to tell by now just by the uneven pad wear.

[davew]

This problem has been going on a long time. You are not making any progress towards a cure. I think it may be time to admit this is beyond your capabilities as a mechanic. There are several good chassis guys in your area with expertise in Miatas. I would take the car to them and have it fixed right the first time. A few hundred buck$ spent to have the issue resolved will be less than an entry fee at your next race.

 

Just my opinion

dave

[Alberto]

This problem has been going on a long time. You are not making any progress towards a cure. I think it may be time to admit this is beyond your capabilities as a mechanic. There are several good chassis guys in your area with expertise in Miatas. I would take the car to them and have it fixed right the first time. A few hundred buck$ spent to have the issue resolved will be less than an entry fee at your next race.

 

Just my opinion

dave

 

I resigned myself to that a long time ago and took it to a shop.  Unfortunately, it did not yield any positive results so I'm back at it.  Talked to a couple of other shops where they would be following the same process as I am of replacing suspect parts.  Giving it one last shot with the front subframe and lower controls arms before trying another shop.

[Alberto]

Idid start at the beginning so not sure if it has been mentioned yet, but if this has been going on awhile and is related to brakes, you solid be able to tell by now just by the uneven pad wear.

 

Pad wear is actually even now but at this point I figured why not might as well do the rear calipers and lines just in case.

[Bench Racer]

6 months later and the right pull continues.     Back to basic square 1, after changing all the stuff you changed did you ever confirm that pressure to each front caliper was equal? If you do not have equal pressure everything else you do is wasted energy. Brake pad pressure kit $250.00, two pressure gauges and fittings for the bleeder fitting holes $100.00 or one pressure gauge and fittings $50.00, take the car to a shop that has either of the previously mentioned items $$$.

[tottepaab]

 Alberto

 

Did you ever find what was wrong  ?

 

Thanks

[SaulSpeedwell]

Toe equalizes when the vehicle moves and the slip angle of the tires do the same.  Toe will not cause a pull.  Toe not being equal on a front wheel will result in a crooked steering wheel while going straight.   Toe not being equal on rear wheels will result in the car operating at a thrust angle (dog tracking) and a crooked steering wheel while going straight.  The thrust angle will cause transitional changes to be different and for that reason should be minimized.

Do the following tests:

Measure wheel base left to right

Swap pads left to right and see if there is a direction change

Pulling in with hot brakes, leave the engine running and check for drag on all four wheels

 

I agree, but would add that camber split will cause pull in cars with something other than zero camber, and caster is (among other things) camber gain as a function of "toe" (or individual steering wheel angle) ….