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Posted by: dmilzoff Aug 23 2003, 01:31 PM

Am I getting too fanatical or is this a real problem?
On my 914-6, I have 911 brakes up front and original rear brakes. I found the right rear brake dragging (smoking!). After opeining the vent clearance and oiling the emergency brake linkage, I took the car out for a 4 mile ride.
Rotor temperatures using a infrared temp probe was
Left Front 145 deg. F.
Right Front 150
Left Rear 180
Right Rear 225

Question 1: Shouldn't the front rotors be hotter? Should I remove the brake proportioning valve or replace it with a new one to correct this?
Question 2: Is the right rear too hot for such a short ride?

Posted by: VegasRacer Aug 23 2003, 02:52 PM

Those numbers do seem a bit strange.
My suggestion is to remove the proportioning valve.
This easy fix has worked well for me.

Posted by: dmilzoff Aug 23 2003, 03:05 PM

Should I just replace it with a tee? Is this a easy to find part?

Posted by: redshift Aug 23 2003, 03:15 PM

I have the same problem with a car, sometimes. It's apart right now, but I plan on T'ing it.

Why always the right side?


M

Posted by: kdfoust Aug 23 2003, 03:28 PM

That doesn't sound like a prop valve to me. When rubber brakes lines fail (after being really, really old, like 30 years old) sometimes the inside of the line will deteriorate partially blocking fluid flow causing the caliper pistons to fail to retract completely. If you don't have relatively new rubber lines on the car I'd take a good look at them - or just replace them, they're only like $8.

Good luck,
Kevin

Posted by: Brad Roberts Aug 23 2003, 03:32 PM

A balanced brake system will only have about a 15-20 degree spread between the front and rear (fronts hotter).

I'm going to guess your rear calipers are sticking (pistons sticking in the bore).

It could be the prop valve but both sides would show equal temps if the prop valve was crap.

Kevin is dead on with the brake line thoughts...

I'm glad to see somebody actually using their infrared temp gun...

You should see the brake temps from a factory GT3RS (400-500 degree range)


B

Posted by: dmilzoff Aug 23 2003, 03:41 PM

OK. So I will replace the brake lines. If that doesn't help, I guess BOTH rear calipers should be rebuilt or replaced. - ? Are they worth rebuilding or should I replace/upgrade?

Posted by: VegasRacer Aug 23 2003, 03:42 PM

Because it is the farthest away.

I agree that the problem sounds like there is more going on that a bad proportioning valve. If you're gonna replace the lines, rubber is cheaper but why not consider SS ?! If you really want to go fancy you could add an adjustable proportioning valve.
(it sure is easy to spend somebody elses $$$'s)


Attached image(s)

Posted by: Brad Roberts Aug 23 2003, 03:44 PM

While doing the lines.. go ahead and install the 9$ Tee. That way you only have to bleed the brakes once.

I would go ahead and rebuild your brake calipers (they are not exactly easy)..

If you dont need an Ebrake... install stock 914 calipers on the rear.



B

Posted by: Brad Roberts Aug 23 2003, 03:45 PM

I still havent installed a prop valve that I DIDNT run wide open. I can think of 2 turns at 2 tracks that I would need less brake pressure at.. I just deal with the car squirming a little from 100+ down to 60.


B

Posted by: dmilzoff Aug 23 2003, 03:49 PM

I do need the emergency brake because the car is used for the street (and track). It seems that I should
1. Replace the brake lines and replace the prop valve with a tee.
and, if temps are not within 15 - 20 deg front/rear
2. Rebuild the calipers.
Oh joy.

Posted by: Brad Roberts Aug 23 2003, 03:51 PM

I'm betting you have one piston hanging up on each rear caliper.

Honestly.. replacing those rear brake lines with the engine in the car is more of a pain than rebuilding the rear calipers.

Getting to the top bolt on the prop valve with the engine in the car is also a chore...


B

Posted by: dmilzoff Aug 23 2003, 03:53 PM

Correction. I forgot that the brake lines were replaced with SS years ago. I guess a Tee and caliper rebuild is in order.
You guys don't make this easy.

Posted by: Brad Roberts Aug 23 2003, 03:55 PM

Ha ha.. easy.. would be me coming over and doing it for you...LOL


B

Posted by: dmilzoff Aug 23 2003, 03:59 PM

Would you (or anyone else) be interested in rebuilding both rear calipers if I sent them to you? Really.

Posted by: Brad Roberts Aug 23 2003, 04:06 PM

I would rebuild a core set I have here and send them to you.. then ask for yours in return.

I'm about a week away from being in my shop full time.


B

Posted by: redshift Aug 23 2003, 04:19 PM

Hey Brad, how much? What's the turn around?


Miles

Posted by: Brad Roberts Aug 23 2003, 04:21 PM

I dont know the "amount" until I start pulling them apart. Some go quickly...some take forever (depending on how bad they are).

A high number would be 150$ a caliper exchange.



B

Posted by: dmilzoff Aug 23 2003, 04:22 PM

Hey. Me first. How much? What's the turn around?

Posted by: Brad Roberts Aug 23 2003, 04:23 PM

Turn around time would depend on parts availabilty. Some times you can get the rear rebuild kits.. some times you cant.

I would just buy some kits and rebuild calipers I have sitting here collecting dust. Then send them off.

I'm at least a week away from starting them.


B

Posted by: Dave_Darling Aug 24 2003, 05:25 PM

Let's think about the T thing for a minute. The T will allow more pressure to go to the rear brakes, right? Because the stock proportioning valve limits the pressure that goes to the rear.

So adding the T will let the rears work more. Which will increase the rotor temperatures, not decrease them.

I think the T is a red herring in this case. (Doesn't mean that you shouldn't do it, just that it doesn't have any bearing on the symptoms.)

--DD

Posted by: dmilzoff Aug 24 2003, 05:50 PM

Good point. Thanx. First order of business is rebuilding both rear calipers. Then I will retest temperatures again before any other changes.

Posted by: airsix Aug 24 2003, 09:37 PM

Everybody seemed to forget that the fronts are vented and the rears are solid rotors. That would seem to explain why the fronts are running cooler.
-Ben M.