Grinding/buzzing and difficulty going into first?

[jlwdvm]

I took the transmission tech for a ride. I was able to consistently reproduce the grinding and difficulty downshifting into first when moving around 20mph.



His response: "Do you have the clutch all the way in?" "yes, I'm pressing it through the firewall".



"I has fresh high temp brake fluid it it" I said.


"Is it DOT 3?" he says.


"No, its is DOT 4" I said.


"Oh, that's the problem" he says.


"I have the same fluid in my Boss 302, GT350R, and '69 Firebird and have never had this problem", I said....as I proceed to heel-n-toe downshift to maybe convince him I'm not just some geek off the street.



We'll see what he comes up with.

[j o n]

At that point, I would have spoken with management. Tech doesn't know basic brake fluid technology. Get another one.

Dot 3 and Dot 4 are compatible.

The track prep sheet for the z/28 released by GM states:
Replace with a high-performance brake fluid that has
a dry boiling point greater than 279°C (534°F). After
conversion to the high-performance brake fluid, follow
the brake fluid service recommendations outlined by
the fluid manufacturer. Do not use silicone or DOT-5
brake fluids

[jlwdvm]

I sent him a screen shot of the Motul that states DOT4. I also asked him why I can't reproduce the problem in other gears if it is a Clutch-slave cylinder problem. Crickets.

[MiniBig]

After a full track day this summer, on the way home I had the same problem. I could not get it into first gear unless I forced it. I changed and bled the clutch and brake fluid. I haven't had a problem since.

[jlwdvm]

There is a GM bulletin that states that the use of a fluid with a boiling point over 446 should be flushed out after track use. Could I just bleed the slave somehow and keep the high temp fluid in the calipers? Suck the master down and fill with DOT 3, pump clutch repeatedly, repeat a few times to get the new fluid into the slave? Fluid recommendations?

[j o n]

This is that bulletin, I assume:
http://www.revbase.com/BBBMotor/TSb/...dPdf?id=200414

I would not read that as, DOT 4 needs flushed from the system after track use. That bulletin is 'save their ass' blanket for GM, all recommendation because they have no clue what fluid people will use or level of common sense of end users/mechanics.

I personally have used DOT 4 in numerous daily driven vehicles, brakes and clutch systems, no issues. DOT 3 and DOT 4 fluid are compatible.

Fully flush it and go from there.

A full flush is needed. Cannot cheat a brake/clutch system flush. It should be 100% consistant the same brake fluid in the system.

Again, if you want to seperate the clutch and brakes reservoirs use these:
Options for stand alone clutch reservoir
http://www.jdpmotorsports.com/jdp-mo...-zl1-jdp-c1001

http://www.jdpmotorsports.com/jdp-mo...-zl1-jdp-c1002

[pat_t]

Originally Posted by jlwdvm

There is a GM bulletin that states that the use of a fluid with a boiling point over 446 should be flushed out after track use. Could I just bleed the slave somehow and keep the high temp fluid in the calipers? Suck the master down and fill with DOT 3, pump clutch repeatedly, repeat a few times to get the new fluid into the slave? Fluid recommendations?

That won't work. Needs to be a full flush.

Motul RBF660 FTW

regardless of anything in there currently or any high spec racing fluid you put in, you should do a full flush of brake and clutch fluid once a year MINIMUM. Both Dot 3 and Dot 4 absorb water from vapour in the atmosphere. Once the water is in the fluid, the oxygen comes out as gas bubbles under temperature 1) lowering the overall boiling point 2) the gas bubbles are compressible ruining pedal feel and reducing slave cylinder travel/caliper piston travel for a given pedal travel.

Another reason never to fill with fluid from bottles on the shelf that have had the seal broken, however expensive and un-used the fluid was!

Still not betting against the clutch pressure plate requiring adjustment in your case though. A fluid flush is much easier to try first than pulling the transmission though.... Good luck, keep us updated

[jlwdvm]

Any DOT better than others? How much pumping to get the fluid swapped in the slave?

[jrob56]

When you say flush, you just mean put enough new fluid through the system bleeding it to be all new fluid, correct? Or is there actually a true flush procedure?

[Zslash28]

Your clutch needs bled? Try this, should fix your issue.

https://www.rangeracceleration.com/Clutch_Care.html

[jlwdvm]

I don't have a pedal issue and I wouldn't say that downshifting into first going 20mph is spirited driving (as mentioned in the article). The car has had Motul in it all summer with 3 track days under my belt. brakes were bled after each event.

[kramard]

Originally Posted by pat_t

I had some issues with the adjustment on my clutch being incorrect from new (massive clutch slip and difficulty engaging 1st at under 1000miles from new). Replaced it with new parts and now it's perfect even with 578rwhp

There is nothing actually wrong with the parts I removed, just the clutch pressure plate adjustment tabs are set wrong and would need re-setting before any re-fitment.

https://ls1tech.com/forums/manual-tr...djustment.html

That thread mentions there is a GM tech bulletin for setting the adjustment but I've not seen the document. Anyone know about it?

I'm interested in this too - I believe my adjustment is off. My car has less power then another z/28 (even though I have faster corner exit speed) and I occasionally grind going into 3 under braking.

Thanks,
Dave

[jlwdvm]

To top it all off, I went to get in the car at the dealer and noticed a nice paint nick just under the driver's window that i have to look at every time I get in the car. Then they made me stand there for almost an hour as they looked at video trying to prove that it wasn't them (which they couldn't). Now they have to pay to have the door repainted. What a "F"ing mess!

[jlwdvm]

If it is a brake fluid problem, wouldn't clutch performance be effected in all gears? Tempted to just take it to a different dealer (they sell a lot of corvettes, camaros, etc) with the Motul in it to see what they figure out.