koby ,
good call!

Bruce, Drew,

There is a very interesting John Twist video on U tube: #158 clutch disk, which addresses a possible explanation to the no reverse issue. In the video it turns out that the aftermarket clutch disk is faulty in that the spines are not perpendicular to the clutch facings. The result being that the clutch does not completely disengage from the flywheel.
Check it out & see what you think.

Bill.

Bill.

Ohh Crap......but thanks.

Drew

Happy Fourth, everybody! Now go out and blow up something!

Problems shifting into reverse (a straight-cut non-syncro gear) is because of the input shaft of the transmission is still turning with the crankshaft. The syncro rings prevent you from noticing this in the forward gears. (And in truth you don't even need the clutch when shifting up. A lot of racers don't clutch when shifting up, only down.)

Causes:

1. Pilot Bush not letting input shaft turn independantly. Could be a tight fit, grease drying out (it will) or too much grease to start with.

2. Bad clutch. Dirty friction materials. Oil contaminated linings. Mis-aligned parts that don't allow driven plate to spin inside clutch when clamping pressure released.

3. Inadequate hydraulic system. Master cylinder is not moving enough fluid: bad seals, air not bled out (air is compressible so volume is insuficient under pressure), inlet valve not sealing; Slave cylinder is not moving enough: air not bled out.

4. Worn operating parts. To move the clutch far enough everything has to be in good condition and to original dimensions.

Think of all the parts in the system as being stacked on top of one another. If any are worn too much the total is not high enough. That includes the clutch master pushrod, clevis pin, the pinhole in the clutch pedal, the slave cylinder pushrod, the pushrod clevis pin, the clutch fork bushings and the throwout bearing. Even the ends of the clutch fork can wear as can the pivot pins on the throwout bearing.

Wear in the pedal, pushrod and it's clevis pin can reduce how far the master cylinder piston is moved.

Wear in the slave pushrod, it's clevis pin, the clutch fork and throwout bearing can change the position of the clutch slave cylinder piston enough that it is at the end of it's travel before the clutch is actually released.

This is why a longer pushrod may be needed, at least until the worn parts can be replaced. There needs to be some freeplay in the slave cylinder, but you only need about 0.100" of freeplay here. If you push the slave piston in to the bottom of the bore and pull back the clutch fork to where the throwout bearing is on the clutch and it is a lot more, your problem could be wear inside the bell housing.

C Ya,
Mark

Mark, thanks for your informative & always well thought out comments.

Koby, I tried your suggestion & guess what, my helper was able to select reverse with no grinding, I guess this confirms my problem is nothing more than a travel issue. In fact with everything reconnected & pushing the pedal extra hard into the carpet (& padding behind the carpet) for the first time I was able to select reverse several times with just a very slight grind.
I feel very encouraged that the lump will not have to come out after all.
Thanks to all, this is a great forum.

Drew, you might want to try Koby's test.

Bill

Thanks Bill and Koby....

Have all the clutch hydraulics out right now and hoping to have it all back together later on tonight.

Drew

Hi Bill,

You have just proved to me that a lot of the clutch problem is lack of slave piston travel which is what I thought many years ago (just more homework that the manufacturer of the gearbox and engine failed to do with the unfortunate MGC).

This is why I had the slave cylinder sleeved down to 15/16" to increase travel. I had tried extending the operating rod until I realised that this did nothing except push the piston into the cylinder by the amount of the 1/4" extension. There is plenty of movement possible within the cylinder.

When the car was new there was no problem until I replaced the driven plate after 51,000 miles.
On one rebuild I used a REPCO 9.5" driven plate (for a 3 litre FORD Capri, replacement part) and it worked wonderfully but if the car was put away hot and in humid weather and not used for two or more weeks the clutch would not disengage on start up. I used a socket to hold the withdrawal lever with full pedal then took another push of the pedal when the clutch then freed up. The problem was the REPCO plate grew onto the flywheel as there was none of the brass wire in the facings like the factory original plate. I drove the car around the suburb with full power on and off with the clutch pedal to the floor and it didn't free until I put the socket in and took another push on the pedal.

The Borg and Beck clutch now in (9" had MGC/Range Rover on the packaging and the wave spring between the facings was more wavy than the early MGC Borg & Beck driven plates. I recently bought an AP Automotive Products, incorporating Borg & Beck, MGC clutch kit and the driven plate in this kit also has the much more pronounced wave spring between the facings.

I think this may be the cause of our difficult reverse engagement problems, there is just not sufficient clearance with the factory clutch hydraulics to allow the driven plate to free easily.

Bruce.

Bruce,
I agree, it does appear like everything has to be perfect, it appears there was no reserve built into the design.
It's like the M/C is on the ragged edge in terms of its capacity. I suppose it would be possible to measure the amount of fluid moved per stroke of the clutch pedal & calculate the corresponding movement of the slave. It would be interesting to know what travel that equates to & if it meets the original specs. I measured my travel today & it's right at 3/8".
As you say, a longer pushrod does not achieve anything, the travel does not change.
Have you ever tried replacing the M/C?

Drew, let us know how you make out.

Bill.

All back together...all new from master to slave....bleeding tomorrow.

Drew

Hi Drew,

Yesterday I jacked the "Truck" up at the rear so that the outlet line at the master cylinder was at the highest point then removed the slave cylinder and used a 4 inch G clamp to hold the piston in the fully in position and with the bleeder (automatic bleeder nipple this time)at the highest position we bled the system using full strokes.
A lot of air came through the bleeder tube. After flushing through 3 times, with no bubbles at all, I tried the pedal half an inch of free play them solid pedal, no movement possible.
With the slave back on the bell housing there is 1 inch of travel before the clutch takes up exactly the same as the brake pedal. So if the clutch still gives problems with reverse it will be within the clutch.

Time will tell when we get home next Thursday after a 2 day Mid-Week run.

Bruce.

Hi Guys....

Renewed all of the hydraulics from master to slave and this afternoon I tried something different. With the slave removed and hanging from the feed line with the bleed nipple up I filled the reservoir on the master and then used my "Mitty-Vac" to pull fluid down from the master. In order to keep the slave piston fully in the "back" postion I put an old push rod in the slave and strap locked it in place using the mounting holes of the slave. After several refils of the master and much pulling of brake fluid through with the Mitty Vac the fluid was clear of air bubbles so I locked up the nipple for the last time and put the slave back in place.

I have not driven it yet as it is up in the air and we still have to bleed the brakes but the pedal feels really stiff and good.... hopefully we may have beaten it this time. Brakes and on her feet tomorrow so I will report out then.....

By the way...if this works I may have to take back all the bad things I have said about my Mitty Vac...

Bruce....hope yours has worked too and it is not in your clutch itself...!!!!!

Cheers, Drew

Hi Drew,

I think we may be on the right track, at last, I now have 12mm slave piston travel up from 10mm (20% better), the clue seems to be jacking up the rear so the clutch line is at the highest point (I bled the rear brakes with the rear raised while it was up)and then bleeding with the slave off and piston fully in with bleed nipple uppermost. A 4 inch 'G' Clamp works a treat to hold the piston in then you can apply real pressure to the pedal.

I found my 6mm shredded rubber insulation and the black yukky hard board behind the carpet stopped the pedal going fully down so I have relieved my insulation and cut away, around the clutch pedal this hard backing. now the pedal goes hard down onto my 6mm insulation plus the carpet which seems to be it's maximum travel.

Like you I have just fully flushed out the brake fluid and I will test tomorrow.

Bruce.

Clutch exactly the same as before.....

Drew,

Sorry to hear that after all that effort, very disheartening.

You should try Koby's test I.e. Cro bar on clutch release lever. It will help to identify if the problem is with the hydraulics or the clutch itself.

Bill.

Yup Bill, is the next step....taking a break away from it for a bit....

Drew

Hi Drew and others,

I think I have had success with the "Dreaded" clutch.

On a mountain test run today it performed like when it was a new car, much easier gear changes and NO problem (other than the normal balking) with reverse.

I will report after out 2 day Mid-Week run this week.

Bruce.

Tried Bruce's "C" clamp process and achieved a bit better clutch operation and feel to get any better than this we are looking at pulling the engine and checking to see what the release bearing and clutch fork look like.....a winter project....!!!! For now it is more than driveable and it is time to enjoy it. Thanks to all who offered up thoughts and possible solutions.

Clutch and brakes were bled....carbs set up and it was off to the Northern Indiana Lakes British Motor Club July meeting last night......beautiful night for a late evening, top down drive home through the countryside......

Drew

Hi Drew,

I have just returned from a 300 mile run and the clutch cold worked perfectly as did ease of use of the gearbox. Cold reverse can be selected over and over at 2,000 rpm but when hot sometimes easy and quiet and occasionally graunching gear cogs.
Also clutch judder comes and goes so there is something happening with the clutch itself.
The hydraulics with 12mm travel seem perfect. Bill Murray measured his slave piston travel for me and he also has 12mm with everything working perfectly.

Today on start up reverse could be selected easily at over 1,500 rpm over and over and on returning home reverse went quietly straight in. Yet at lunch yesterday graunching and judder. Something is causing the driven plate to catch intermittently.
I don't think the pilot bush would cause this after being good for 47,000 miles with the current clutch, and never being a problem before.

Bruce.

Hi Bruce....

Hope you had a great trip. For me... I never get grinding upon trying to select reverse just engaging a tad low upon releasing the clutch in either 1st or reverse. Had my wife depress the clutch while I measured finding movement exactly the same as yours. Going to drive it through this season and further investigate during the winter months.

Cheers, Drew

Hi Drew,

As the clutch problem started 2 years ago, very intermittently and has been happening at random lately, I am starting to wonder if something has happened to one of the driven plate facings, cracked segment etc. that caused the drag as the segment moves out of place.

The only long term solution is going to be to pull the "Bloody Great Green Lump" out, but I want to delay it until next year if I can. Too busy to do it now and we are having a cold wet winter completely out of context for out usual lovely winter weather.

Bruce.