'93 VR4 State of the Union

[UTRacerX9]

Looks good Adam. Much better than the stock setup.

[FeaRpb]

Just saw your new FBM pump setup. Looks awesome man.

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[AdamVR4]

I've been battling a lightly dragging clutch, potentially forever, so yesterday I pulled the master cylinder to rebuild and this morning I pried out the clutch assist. I'll post pics later. I have the FSM, but is there anything else I should look for in the clutch assist? I know I've turned the threaded rod that goes through it in the past rather removing the pin and turning the bracket like I imagine you're supposed to.

[Chris@Rvengeperformance]

There is an adjustment on the booster rod on the engine side detailed in the manual.

[AdamVR4]

There is an adjustment on the booster rod on the engine side detailed in the manual.

Yup! That's where my attention is right now:

(from 3Si)

So after years of clutches subtly dragging, I've decided to get to the bottom of it. I've removed the master cylinder, clutch booster, and clutch pedal assembly.

Page 21-13 of the '93 FSM asks you to find dimensions B, C, & D to then determine the clearance (A) between the booster push rod and the master cylinder's piston.

In my case, (I've estimated tolerances on each measurement)

B (master cylinder end face to bottom of piston's receiving pocket) is ~.87" (+.010/-.000")

C (master cylinder end face to mounting flange) is .435" (+/-.003")

D (distance from pedal assy cage to booster push rod) is .425" (+/-.005"

So then, A = B - C - D

A nominal = .010"
A max = .028"
A min = .002"

Obviously the tolerance stack up is significant relative to the dimension.

When I lay the master cylinder on the back of the pedal cage, it's fairly obvious there's SOME clearance between the booster push rod and the master cylinder piston's receiving pocket. It could be as little as .001", but there's something there.

The real question is this: I believe the firewall sheet metal thickness must be included to determine the actual clearance. The FSM makes no mention of the firewall and the pictures indicate exactly what I've measured. Is this an error in the FSM?

If it is an error, what's the thickness of the firewall? I can just barely wrestle my calipers in there and it appears to be .05 to .06" ...

If we call the firewall thickness .050", that would mean the actual clearance between my booster and master cylinder is nominally .060", over .040" out of specification (.0082-.0181 inch).

Thoughts?

--------------------------

I extended the booster push rod .025 (changing dim D to .400") ... I was pretty shocked at how difficult it was to break loose and then move, but it gets easier as you extend it. It looks like Mitsu used an interference thread along with thread locker.

Anyway, now when I rest the master cylinder on the back of the cage, it doesn't sit flush, which gives me confidence in my original nominal dimension.

I will proceed assuming the firewall thickness is .050" and my original clearance was .060". After that 1st adjustment, my assumed total clearance is .035"...

I extended the booster push rod another .025 (changing dim D to .375") for a total change of .050"... Now, when I re-install this thing, the clearance should be about .010" to .020"

Final question -- how the hell should I stake the clutch booster push rod? I fear vibration + cyclical compression will slowly rotate it back to where it was. I don't REALLY want to fully remove it and try to clean the threads so I can reapply thread locker, but I also don't really want to just blob on some epoxy

[R/T93]

Loctite 290, it's green. It's light duty wicking loctite. Home Depot or Lowe's will have it. Meant for weld cracks and casting porosity.

Interesting read though, I have had a slightly dragging clutch for awhile now and it's not the cabin side rod.

[AdamVR4]

Loctite 290, it's green. It's light duty wicking loctite. Home Depot or Lowe's will have it. Meant for weld cracks and casting porosity.

Interesting read though, I have had a slightly dragging clutch for awhile now and it's not the cabin side rod.

Great suggestion, I'd forgotten about the green! 99% chance that's is what I apply before I throw it back together.

[AdamVR4]

Refined the measurements a bit.

Firewall thickness = .052 +/- .004
dim B = .863 +/- .002 (depth of receptacle on master cylinder)
dim C = .437 +/- .002 (master cylinder's flange depth)
dim D = .458 +/- .003
dim D (corrected, firewall t included) = .406+/-.007
dim A = .009 to .032 (.021 nominal) ... (target being .008 to .018)

I will err (ever so slightly ) on the loose side because I've removed a relatively huge .056" of clearance.

--------------------------

It's really nice to have this shit off the car. I've backed-out the upper clutch switch (this switch is depressed when your foot is off the pedal) about 2 full turns to maximize pedal throw, taken about .050" of slop out of my clutch booster (to maximize MC piston throw), and left myself with a few turns of additional adjustment at the primary under-dash adjustment point.

some pics..

Ready for minor surgery




booster in pedal assy




the push rod coming from the clutch booster. this thing stabs into the clutch master cylinder




after being adjusted and green thread locked




pedal assy sans booster




upper clutch switch backed out to maximize pedal throw




here's where i think the rod you can adjust below the dash will end up for maximum throw




...and we'll see if these adjustments have caused me to block off the bleeder valve in the MC.

[J-Groove]

Adam,

I'll be tackling a clutch booster swap here once I have some time. After all of the horror stories I've heard, is it really a pain as said? Many say you have to pull the dash, but looking at it I don't think you do. Is it exaggerated? :fingers crossed:

-John

[AdamVR4]

So I just pulled the slave and discovered a good amount of fluid in the boot (woohoo!). The slave looks a lot worse than I was expecting after ~12 years and ~5k miles. Starting to get optimistic that the clutch won't drag when I'm done here...

John -
Funny you should ask. I was able to pull the booster out of the pedal assembly while I was raging beneath the dash, but when I had the pedal assy and booster out of the car, I couldn't fit them back together... "the fuck?" ...I used an angle grinder with sanding disk to just barely clearance the sheet metal 'cage' of the pedal assy. In this image, 3 of the bends of the outer cage are fully visible. One has a sharpie 'mark' on it, and I ground that surface around that corner until I could reinstall the booster with minimal struggle.



It was daunting as shit, and there's some quadrant of hell where you spend all day searching for tools and getting in and out from under the dash of a 3000GT, but the pedal assy came out easier than I expected and wasn't hard to reinstall correctly. Your '99 may be very different and I don't have any HVAC so... lol