Jetdriver69

I know there are many threads on this subject, but I would like a second opinion before I tear open the clutch master cylinder. My gear box is freshly rebuilt and installed about a week ago with all new synchos and shifted fine until today. Now it grinds in reverse no matter what you do and I have to start it in reverse to use the gear. I read that the clutch master is not giving me enough travel to fully disengage the clutch and the master plunger rod needs to be trimmed about 14mm to give me that travel. I also read not to forget to notch the end of cut plunger rod. What is the purpose of the notch? BTW the clutch slave cylinder is less than 4 years old and less than 3000 miles. Any more suggestions or am I looking at the wrong issue? Thanks!

BRB-83-911SC

A few questions, and thoughts....

Year of car?
Was the clutch hydraulic system opened during the tranny R&R?
Was the clutch master replaced?
Could you get reverse without grinding before the work?

If the master has not been changed, I would look at proper bleeding; if a dual disk clutch, I would look at Intermediate Plate adjustment. Either of those could have contributed to the demise of your synchros in the first place.

davek9

What year car please (is this a single disk)?
What has changed on the clutch side, you noted that you rebuilt the trans, why?
Does it work once you start in gear, if so than its working but dragging?

Ha ha.. i'm typing a bit slower than usual today

Jetdriver69

Sorry about the lack of relevant info. The car is a 82, multi disk clutch. Everything except intermediate plate is new, all synchos replaced with much machine work done by Greg B. The flywheel was removed and resurfaced. The car scratched in 2nd gear pretty bad prior to the rebuild. You couldn't get it into 1st unless you were at a dead stop and reverse was crunchy most of the time. The car is for my 16 year old son, so we wanted the box to be free of problems. The clutch master is less than 4 years old and was properly bled after the box was reinstalled. But the master may be bad, who knows? Other than the shifting being very tight after replacement , the box worked great. Today the reverse grinding began. If the master cylinder is not the problem, than the intermediate plate might need adjusting? It sounds to me that the clutch is not fully disengaging and if the clutch master had more travel by modifying the plunger rod, that might fix it. Comments, please as we are diving into the problem tomorrow. Thanks again.

Mrmerlin

the modification to the clutch MC is to remove about 4.5mm from the tip of the piston and slot it,
so the fluid can move through the orifice,
and remove about 2 to 3 winds of the spring so it wont go into coil bind

Also a good chance the release arm bushing has crumbled,
Inspect and the clutch clevis and yoke, these may may be worn at the pedal linkage.

If the flex hose is old replace it as they can swell and thus lose the ability to transfer the pressure

Jetdriver69

MrMerlin

So remove 4.5 mm not 14 mm from the plunger rod? I'm just reading from a previous thread that another guy modified. Thanks again.

Mrmerlin

You take the piston out of the MC bore and cut off 4.5 mm of the tip of the piston ,
this will let the piston push further into the bore,
also trim the new spring by 3 winds,
this so it wont go into coil bind.
follow above instructions for inspecting release arm bushing and clevis and pin wear , and flex hose

GregBBRD

The fact that it was fine and then started to grind points more to the actual clutch than the hydraulic system....but I always start from the hydraulic system and work from there....just like people are suggesting.

Those new syncros are hating life, right now. I'd suggest not driving the car, in this condition, until you solve the clutch release problem. Like I told you today...remove one of rubber plugs in the torque tube and watch the torque tube shaft, when someone pushes down on the clutch. It needs to quit spinning in a couple of seconds.....with the transmission in neutral.

Your old syncros were "beat" something fierce....from the low mileage that you indicated. The clutch not releasing is not a shock, to me.

The "early" transmissions (pre 1985) did not have a syncro in reverse...so it is pretty easy to monitor the clutch operation.....if it grinds going into reverse, the clutch is not releasing. The Borg Warner syncro design (1985 and later) gearboxes have a syncro in reverse and can "mask" a dragging clutch and thus make diagnostics a bit more difficult.

Jetdriver69

Before I dive into anything too complicated, should I bleed the clutch again? My son removed and painted the calipers and flushed and bleed the brakes right before the grinding in reverse began. Maybe some left over air in the system?

Mrmerlin

You could try the fluid bleed,
but at this point,
you should inspect the things I have suggested,
then order new parts if any of them are old or worn.

To answer the bleeding question no they are two separate systems fed from 2 different tanks in the same tank.
Hopefully you used ATE super blue fluid for the brakes

GlenL

Was the master replaced? I'd check for enough free play with the pedal up. There are two procedures for setting preload at the clevis on the clutch pedal. The new one can be too tight. You want a mm or two of slop so the master refills from the reservoir.

I don't think the kid could mess up the clutch working on the brakes. I don't deny determination, though.

Bleeding the clutch sounds good as it is easy to do compared to droppng the clutch pack. My trick is to unblots the slave and pull it out. Then push the rod all the way in and hold it there while you pump-bleed the clutch. Yeah, it take some coordination to open the bleeder when the assistant pushes the pedal down. Do a few cycles and try to tip the slave so the bleeder pointing up a bit.

If you're wondering about that, there is documentation from Porsche that describes bleeding the clutch system out of the car. "cool"

Jetdriver69

Yes the master, slave, reservoir tank and all hoses were replaced. We will try bleeding the system before removing parts. Thanks for all the comments!

Don Carter

Jet, Merlin's question about fluid is important. I just went through a lot of grief that resulted from adding Valvoline synthetic to a system with unknown fluid. The seals in the master and slave swelled up in a matter of weeks and caused the piston's to stick. Ended up replacing both master and slave and switching to the ATE Super Blue Racing fluid and have had no problems since.

Wish you were not on the other side of Houston or I'd swing by and lend a hand.

Jetdriver69

I believe Prestone DOT4 synthetic was used. Should I change it out for the ATE Super Blue fluid? BTW, it seems the reason the reverse was grinding was my son who is new to manuals was trying to shift into reverse after starting the engine almost immediately. If you wait two or three seconds after the start with the clutch depressed, the input shaft is completely stopped and shifts smoothly into reverse. The rest of the gears shift smoothly. We checked that the clutch fully releases and stops with the clutch pedal depressed in neutral in around 2 seconds, the pivot bushing, the clutch peal adjustment and both master, slave and all hoses are either brand new or less than 3 years/3000 miles. But I will change out the fluid if Prestone will be a problem.

Thanks!

Don Carter

I have no idea about the Prestone, it may be fine. There are posts here from Stan (MrMerlin) where he stated that he had seen cases where seals swelled when Valv. Snth. was mixed with other fluids, then it happened to me, so just wanted to pass that along. The blue fluid is 15.95/liter from Roger, and not available retail as far as I know.