rear tire skipping under hard braking

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Jeonsah
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rear tire skipping under hard braking

Postby Jeonsah » Mon Jan 29, 2018 9:56 am

Hey Guys,

I am having a problem with my AE86 GTS at the track when I do some very hard braking. The inside rear wheel will skip across the pavement when I start braking before a turn. I have also noticed that when I brake in general (even during cruising) that my steering wheel slightly turns to the left. I just regreased everything on the calipers. Not sure what else may cause this issue?

I have gotten in the habit of making sure all parts of the car are tightened down good before a race event. Is it possible that maybe the trailing arms are too tight? Here is some specs on the car:

whiteline rear sway bar on softest setting
T3 panhard bar
energy bushings for trailing arms
6kg swift rear springs
Tokiko HTS
T3 traction brackets
T3 panhard bar roll center adjuster


Thanks for any help

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totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Tue Jan 30, 2018 12:18 am

What happens under hard straight line braking:
Steering pull ?
Wheel locking?
Front diving ?
There are so many things that could make this happen, taking the steering out of the equation may help to diagnose the problem earlier.
Negative camber has a big effect on braking, reducing braking grip when going straight, in this scenario you would expect the wheels with the most camber (front) to lock before the rears. The normal driver fix for this is to wind on rear brake bias but in a turn the inside rear tyre gets unloaded and will easily lock and skip. Increasing rear rebound damping may help.

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Jeonsah
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Re: rear tire skipping under hard braking

Postby Jeonsah » Tue Jan 30, 2018 8:19 am

Straight line braking only causes the steering wheel to turn to the left slightly.
No wheels lock under braking in a straight line.
Front wheels are at -3.5 camber and rear is around 0.
I will try messing with rear strut settings. If I remember correctly, they were set to pretty stiff already but not near the maximum.

In terms of the steering wheel pulling to the left during braking. Does that mean a caliper on the driver side of the car is dragging on the rotor?

totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Tue Jan 30, 2018 10:02 am

If you suspect a side to side brake imbalance always check the non-working side, the side that it veers away from.
Can you not lock any wheels under hard straight line braking ?

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Jeonsah
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Re: rear tire skipping under hard braking

Postby Jeonsah » Tue Jan 30, 2018 11:05 am

totta crolla wrote:If you suspect a side to side brake imbalance always check the non-working side, the side that it veers away from.


Just to make sure I got this correct in my head. If i car turns to the left under braking, then I need to check the passenger side?

Yes, I can lock the brakes in straight line hard braking.

totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Tue Jan 30, 2018 11:18 am

Jeonsah wrote:
totta crolla wrote:If you suspect a side to side brake imbalance always check the non-working side, the side that it veers away from.


Just to make sure I got this correct in my head. If i car turns to the left under braking, then I need to check the passenger side?

Yes, I can lock the brakes in straight line hard braking.


If it turns left under braking you need to check the right hand side caliper, this is the least efficient caliper.
Do you have any way of adjusting brake bias front to rear ?

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Jeonsah
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Re: rear tire skipping under hard braking

Postby Jeonsah » Wed Jan 31, 2018 6:23 am

When you say right hand side, are you referring to the passenger side?

I am currently running the factory brake proportion valve. Is there one that bolts in nicely?

totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Wed Jan 31, 2018 8:29 am

Basically you need to check the opposite side to the way it's pulling.

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chohdog
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Re: rear tire skipping under hard braking

Postby chohdog » Wed Jan 31, 2018 4:48 pm

Good chance that side shock is blown.

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jondee86
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Re: rear tire skipping under hard braking

Postby jondee86 » Wed Jan 31, 2018 6:46 pm

chohdog wrote:Good chance that side shock is blown.

I second this opinion :) Reason: Commercials tell us that worn shocks are dangerous
because they increase the vehicles stopping distance. If so, the tire is not making such
a good contact with the road surface because the tire is no longer following the road
surface accurately. It is bobbling up and down over small surface irregularities instead
of maintaining a firm and constant contact patch.

So check to make sure your shocks are still working, and if they are, try a softer setting.
If that doesn't cure the problem there may an issue with the braking system. If the car
wants to pull to the left under braking during normal driving, there could be a pad not
seating properly.

Cheers... jondee86
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totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Thu Feb 01, 2018 3:18 am

A blown damper would show the particular corner effected 'dipping' under hard braking, especially at the front.
Under hard cornering the car would feel different when turning different directions.
The best test is to do as suggested above, soften the settings but do one damper at a time.
3.5° is a lot of negative camber and if the road is not perfectly flat you will get steering pull to the side which has the most tyre contact when loaded under the brakes.

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Re: rear tire skipping under hard braking

Postby CloudStrife » Thu Feb 01, 2018 10:28 am

Wow, almost -4 degrees camber. Are you running NRCAs?
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totta crolla
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Re: rear tire skipping under hard braking

Postby totta crolla » Fri Feb 02, 2018 2:31 am

So last night I jacked up the front of my car and turned the front wheels by hand and one side had noticeable drag and this was caused by the brake piston not returning correctly.
The OP might want to try the same test before doing all the other stuff stated above !

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Jeonsah
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Re: rear tire skipping under hard braking

Postby Jeonsah » Fri Feb 02, 2018 5:38 am

totta crolla wrote:So last night I jacked up the front of my car and turned the front wheels by hand and one side had noticeable drag and this was caused by the brake piston not returning correctly.
The OP might want to try the same test before doing all the other stuff stated above !


will do, thank you.


CloudStrife - no nrca's here. :)

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Re: rear tire skipping under hard braking

Postby CloudStrife » Fri Feb 02, 2018 11:32 am

Lol, you should get them.

And brake drag is a pretty common problem as most people either:

A., change rotors, pads, and fluid but never rebuild the actual piston cylinder parts (which are getting 30+ years old now).
Or
B., Purchase re-man calipers from a site that has poor quality control (Rockauto, Autoz, etc. etc.). In my experience re-man caliper companies just don't do a quality inspection before sending them out. Sure, the piston will engage, but one side could be more recessed than the other, parts were not properly torqued/ coated with anti-sieze, etc. etc.

Rebuilding a caliper proper takes time and dedication for sure.

You can also have rub/rotor resistance. The hub has to allow the rotor to spin just right, and spinning either side usually shows different resistance.

The good news is it's not your diff :)
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matt dunn
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Re: rear tire skipping under hard braking

Postby matt dunn » Sat Feb 10, 2018 12:51 am

I had an issue with the rear skipping under braking in my race car, KE70 so similar setup to AE86.
Found the problem a few days later when pulling apart that the top shock mounts were loose,
(cant remember why now, but they had been out and put back in by someone else)
The harder you braked the worse the problem was, but as I run a locked diff there was no pull to one side,
but you also could not start to turn into the corner while the back was skipping.

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Re: rear tire skipping under hard braking

Postby jinx » Sat Feb 10, 2018 1:09 am

rubber brake line can collapse internally, causing caliper to stick
caliper sliding pins can b frozen stuck also

CloudStrife
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Re: rear tire skipping under hard braking

Postby CloudStrife » Sat Feb 10, 2018 9:36 pm

matt dunn wrote:I had an issue with the rear skipping under braking in my race car, KE70 so similar setup to AE86.
Found the problem a few days later when pulling apart that the top shock mounts were loose,
(cant remember why now, but they had been out and put back in by someone else)
The harder you braked the worse the problem was, but as I run a locked diff there was no pull to one side,
but you also could not start to turn into the corner while the back was skipping.


Do you mean the nut that holds everything together at the top?

Because it is a pain to torque down proper. I stripped the threads on one side.
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matt dunn
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Re: rear tire skipping under hard braking

Postby matt dunn » Thu Feb 22, 2018 2:57 am

CloudStrife wrote:
Do you mean the nut that holds everything together at the top?

Because it is a pain to torque down proper. I stripped the threads on one side.


Yes that is the one.

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Re: rear tire skipping under hard braking

Postby Nick94tt » Tue Mar 13, 2018 9:15 pm

CloudStrife wrote:Rebuilding a caliper proper takes time and dedication for sure.


The fronts are very simple (and the rebuild kits - snap ring, boot for the piston, and piston seal - are diet cheap. I redid mine over an hour or two.

Pulled each one separately so incould use the brakenpedal to pump the piston free. Degreaser in a bucket and some qualit6 time with a brass wire brush to clean out the oxidation.

Rent a brake caliper cylinder hone from advance/autozone/etc if youy need to clean up the bore. Scotchbrite/metal polish to clean up the piston as needed.

Assembly is tricky at first, just order an extra kit or two for spares. I used 3 to do the front calpiers. (Tore a boot)

The amount of loose rust waiting for you inside the calipers will likely make your head spin.

All this assumes it's the brakes. The tears are definitely more involved. Waiting on the SST to redo those.

Super detailed videos on YouTube cover the steps.

Hope it helps. ^_^

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Re: rear tire skipping under hard braking

Postby CloudStrife » Tue Mar 20, 2018 5:36 pm

Just to let you know, we didn't end up needing that SST.. I forget the part call out, but whatever that weird tool attachment was, we didn't need it. The fronts were rebuilt and powder coated.

I was following the Brazilian guy's write up on YT.
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Re: rear tire skipping under hard braking

Postby Nick94tt » Wed Mar 21, 2018 12:37 pm

CloudStrife wrote:Just to let you know, we didn't end up needing that SST.. I forget the part call out, but whatever that weird tool attachment was, we didn't need it. The fronts were rebuilt and powder coated.

I was following the Brazilian guy's write up on YT.


I did the same for the fronts. Very helpful. I'm set to take a shot at the rears without the sst, just got caught by a random snowstorm. Made the first run around town with no front swaybar and an open rear pretty entertaining.

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Re: rear tire skipping under hard braking

Postby CloudStrife » Thu Mar 22, 2018 8:49 pm

Hahaha, bro old school driving! Just make sure you don't take off the rear spring on that.. You'll never get it back on lol.
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