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Old 11-06-2010, 11:35 PM
fastandyracing fastandyracing is offline
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Default Hydraulic T/O bearing brake fluid compatibility alert!!

Hey guys,

I had changed out my fox mustang to the dual master cylinder with hydraulic throw out bearing earlier this year, and have been loving it. The brakes are great, excellent feel, very adjustable, and the hydraulic clutch seemed to be much more consistant than the old clutch cable which seemed to stretch a little just about every race. The T/O bearing is from Ram, which cames with a new bearing retainer. The moving parts of the T.O bearing slide over the included bearing retainer, and a long stud replaces one of the retainer bolts and prevents rotation.

Anyway, on to my point.

A couple of weeks ago I was running a regional at the Sebring short course. In the second race, the clutch pedal started getting long, releasing closer and closer to the floor, I wasn't sure what exactly was causing it, so I backed off for a few laps, and the pedal seemed to come back. I finished the race, but when I went to load the car on the trailer, I had no pedal, and no fluid.

Checking it out, I found that the sliding part of the T/O bearing was leaking, not the hoses or fittings. There are just a couple of o-rings in there, so I called Ram to see how long it should be lasting, 5 or 6 weekends seemed to be a short life, and they asked if I was using synthetic brake fluid, since it could deteriorate the 0-rings.

I had used the Valvoline Dot 4 that I use in my street vehicles for the clutch, and sure enough it is synthetic. I had to go to a couple of auto parts stores to find "regular" brake fluid (that is how the bottle is labeled). When I took the T/O bearing out and pulled it apart tonight, sure enough one of the o-rings was deteriorated, not cut or worn out, just messed up, presumably from the synthetic fluid.

I have installed the new o-rings, and will be using "regular" fluid from here on out. I don't know if anyone has run into this or not, but I just thought I would put the word out, if you have a RAM hydaulic T/O bearing, be sure to use non synthetic brake fluid.


Andy,
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Old 11-07-2010, 07:09 AM
Walther
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Andy,
I've used Ram hydraulic t/o/b's before for several seasons with zero issues. However, I never used synthetic fluids either, just off-the-shelf brake fluid. I am surprised Ram is still using older technology o-rings considering what they told you. I wouldn't put thier o-rings back in, new or not.

It took me all of 5 seconds to find this link on Google. http://www.marcorubber.com/material_chart.htm Just a thought.
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Old 11-07-2010, 11:37 AM
fastandyracing fastandyracing is offline
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Mark,

That's the ironic thing, I wasn't trying to use a synthetic fluid, I was just using my usual street car brake fluid, I didn't even give it a second thought. At the local Advance Discount Auto parts, they don't even have any brake fluid that ISN'T synthetic. I had to go to Pep Boys to find some "extra cheap" brake fluid.

That is the first time I had to go looking for something cheaper to put in the race car!!

Andy
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Old 11-07-2010, 01:18 PM
Walther
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I had a fun experience with DOT 5 once.
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Old 11-08-2010, 11:10 PM
fairlane_68
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Has anyone considered using a slave cylinder to engage the clutch instead of a hydraulic throwout bearing?
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Old 11-09-2010, 07:37 AM
Walther
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Quote:
Originally Posted by fairlane_68 View Post
Has anyone considered using a slave cylinder to engage the clutch instead of a hydraulic throwout bearing?
I have!! It would be a lot easier to adjust/maintain.
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Old 11-09-2010, 12:38 PM
kbsmith1 kbsmith1 is offline
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Here's a picture of what John Rissberger built for a slave cylinder for
the Gen 4 camaro he is building. He asked me to post this for him:



It looks like a little fab work, but not too difficult.
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1993 Firebird AS #03 Oregon Region SCCA & ICSCC
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Old 11-09-2010, 01:08 PM
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wre46 wre46 is offline
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Nice job. Maybe he can share his measurements on what needed to be done to the fork.
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Old 11-09-2010, 02:29 PM
John Rissberger
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This is an easy fab.
Take by 1 inch bar stock drill and tap for a mounting block 3/8ths bolt.
Adjust the joint to half way on the push rod.
Cut the fork rod at about the opening in the bell housing.
Now hold in place and tack weld making sure the alignment of the push rod is straight back and not pushing up or down on the end of the fork.
Disassemble and finish welding the parts up.
I had to take the Transmission and Bell housing off a number of times to make sure the alignment was correct, so I would not want to do this in the car.

John Rissberger
# 10 Camaro Oregon
SCCA & ICSCC

Last edited by John Rissberger; 11-09-2010 at 04:24 PM. Reason: the bar stock is for the mounting block
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Old 11-09-2010, 04:09 PM
Dawson Motorsports
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Don't get me wrong guys, I think all the engineering is what this class is about. But, the whole problem started with synthetic brake fluid.
That being said, we had issues with Castrol SRF in Toms car. We were changing master cly's. every year or sooner. All because of the same issues with incompatibility of the rubber and fluid. It may not be the fluid, but something that is in the fluid, ie; one of the chemicals that are mixed in it.
We also had to bleed the brake system constantly.
We have switched brands of fluid and have had no issues.
Just throwing it out there, that's all.
Chuck
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