Before I pull the gearbox...

[bash]

It seems like ages since I foudn the clutch problem, but work sometimes gets in the way of the TR6! I think I have a broken fork pin. I am about to start taking the gearbox out, but before I do I wanted to see if anyone had any ideas...

Before I worked on the clutch hydraulics I could engage gears. I have bled the rebuilt system many times and don't believe there is any air in there - I get over 1/2 inch of travel at the push rod. Now I can't engage gear with the engine running, though I can move the lever with the engine off, so I don't think messing with the lever is my problem.

With the engine off, I can easily push the car with it in gear and my wife pressing the clutch pedal, but wiht the pedal released I can't move it. This suggests to me that the clutch is working, though maybe it is not working well enough to operate with the engine running? Seems odd to me.

I have the interior out for new carpet and the gearbox cover is off to replace the crumbling cardboard with the TRF plastic one, so is there anything else I should be doing while I have access - even if I don't pull the gearbox. Also, what kind of grease should I use for the lever (if any)?

Looking at the nuts and bolts holding the gearbox to the engine, there are a few "missing" - Roger Williams' book seems to say that a couple of holes are supposed to be empty - is that true? If so how many and where are they supposed to be?

Any advice you can offer would be gratefully received - especially if it is telling me that I don't have to take the gearbox out!

Cheers
Alistair

Edit to add that I just tried starting in 1st gear with the clutch down and it started with only a minor movement of the car. Then I couldn't change gear... Not sure what that means, if anything.

 

[Guest]

If my memory serves me, there are a couple of locating studs or dowels at the top of the bell housing that locate the tranny for placement. But lately, my memory hasn't really been all that good. Otherwise, every nut and bolt should be there, 28 give or take.


Bill

 

[swift6]

Check the endfloat on your crankshaft too. If it is excessive it can reduce the clutch clearance.

/ubbthreads/images/graemlins/cheers.gif

 

[piman]

Hello Alistair,

if it is not already there, put the slave pushrod clevis pin through the upper hole in the cross shaft lever, this will give a little more release.
Also set your idle as slow as possible.

Alec

 

[Alan_Myers]

[ QUOTE ]
Hello Alistair,

...if it is not already there, put the slave pushrod clevis pin through the upper hole in the cross shaft lever, this will give a little more release....

Alec

[/ QUOTE ]

Hi,

Alec's suggestion is a good one. I'd suggest using as a test and not considering it a permanent solution. That's because the release mechanism *should* work when fitted to the center hole, not either of the other two. All TRs are supposed to be able to use the center hole. So, changing this just masks any deeper problem (if it works) and IMHO, is a temporary solution.

You should have 5/8" minimum movement of the shaft at the slave cylinder. If not (you said just over 1/2", but how carefully you are measuring it?) there's a problem in the hydraulics.

I also agree that the engine's thrust bearings are an important check. If they have worn and developed a lot of play, the movement of the crankshaft will use up part of the free play in the clutch mechanism, which already sounds to be minimal on your car.

You might be able to visually check if the fork pin is sheared off, by removing and looking inside the dust cover on the bottom of the bell housing. Remove the clevis pin and release shaft at the slave cyl. and slide a piece of pipe over the lever to allow you to move it a little by hand. Then look inside and see if there is a wink of movement between the clutch fork and the cross shaft. You'll probably need a small mechanic's mirror and some sort of light to get a clear view inside there.

Often the dreaded fork pin doesn't shear off cleanly, in which case it allows some movement, then catches and appear to function. The little bit of free rotation before the fork engages is enough to cause just the sort of problems you are seeing.

Overall, the TR6 clutch mechanism appears to not have enough margin for error and wear or any adjustability. It was redesigned (from the earlier, reliable mechanisms) to not require regular maintenance such as adjustment or greasing, and to give a softer pedal.

If you do find a problem with the pin, replace with a high quality hardened one and it would be wise to back it up with a grade 8 bolt.

It would also be useful to consider a larger bore master cylinder (.75", as opposed to the .70") that will make the pedal a little heavier but will cause more movement of the shaft at the slave. It's possible to have an existing master cyl. bored (or sleeved) to the larger size, but be sure to clearly mark it as such so that the next time it's rebuilt the correct kit is purchased and the right size seals are used on the piston.

And, there are kits to replace the push rod or shaft at the slave cylinder with an adjustable one, much like was used on earlier cars (and gave far less problems if tended to once a year or every 12K miles).

Other key, possible problem areas include:

Failure to use locating pins when aligning the bell housing with the engine (dowel pins were permanently installed on earlier cars, but were made removeable on TR6... a correct size drill bit can be used in place of a dowel pin). Even slight misalignment of the bell housing can cause clutch plate and TO bearing problems.

TO bearing installation must be done right, with the bearing being spun slowly while it's pressed onto its carrier. (Failure to do so causes different symptoms than you describe... usually early TO bearing failure signaled by noisy operation).

Check for wear in the linkage at the master cylinder, for example in the clevis pin attaching to the pedal. An elongated hole here will reduce the movement of the piston in the master cyl. and that in turn will reduce piston movement in the slave and at the release shaft.

Check for wear at the slave cyl. clevis pin and release lever. If the hole is worn oblong, it will introduce extra play and reduce movement of the mechanism to release the clutch properly.

I seem to recall the TR6 clutch slave cyl. uses an internal spring to retract the shaft and piston back in when pedal pressure is released. Earlier cars used an external spring from a little washer-like attachment at the clevis fork, anchored on the slave cyl. mounting bracket. I don't know that the internal spring is a problem. But, at the very least, the external spring is easily checked visually for any breakage, stretching or damage.

Be sure the slave cylinder is correctly mounted on its bracket. Look at illustrations in the various manuals to confirm. I'm not certain about the 6-cylinder cars, but on the earlier 4-cylinder cars it's easy to get it wrong, which will cause the slave cyl. push rod to come up short and fail to release the clutch.

Check for wear in the two bushings either side of the bellhousing, in which the cross shaft rides. Again, extra play can waste some of the mechanism's motion and reduce release movement at the clutch. Later cars used non-greasable bushings here that were about half the length of the earlier, greasable ones. It means replacing the cross shaft, too, but there's an argument for retrofitting with the earlier style bushings and giving them a shot of grease once a year at the same time the release shaft is being adjusted. The earlier, greasable setup seldom gave any problem.

Hope I did't miss anything... and this helps!

/ubbthreads/images/graemlins/cheers.gif

 

[machinemd]

Bash,
I just finished pulling my tranny and the bolt count is 17. Two of them tho are either 3/8" locating pins or shouldered bolts and as Alan indicated are real important for proper alignment. Looking from the tranny side they're at 2 o'clock & 8:30. Mine are a light press fit into the bell housing and I just leave em there for help on the reinstall. For Nelson Reidels real interesting write up on both the locating pins and fork pins go to https://home.comcast.net/~v.navarrette/
Steve

 

[swift6]

[ QUOTE ]
You might be able to visually check if the fork pin is sheared off, by removing and looking inside the dust cover on the bottom of the bell housing.

[/ QUOTE ]

I don't recall TR6 trannies having the inspection port with dust cover. I have three of 'em including the one in my car and the only way to look inside the bellhousing is to remove the transmission. I have seen them on TR4 trannies, along with the longer input shafts.

/ubbthreads/images/graemlins/cheers.gif

 

[bash]

Thanks for the thoughts, guys - much appreciated! A special thanks to Alan for that excellent advice - it is printed and in my TR6 folder!!

I think I have been kidding myself that I don't need to pull the gearbox out since I found the push rod had been lengthened. I really don't know why I am so worried about it - it seems to be something of a rite of passage for a TR6 owner!

Thanks again
Alistair

 

[grossgo]

Well
if you have the carpet out and the cover off, you're halfway there /ubbthreads/images/graemlins/yesnod.gif. Don't stop now.
Al gave some great advice, but I know I don't have a dust cover on my '74 transmission. The ONLY way to see inside is to take it apart /ubbthreads/images/graemlins/eek.gif.
GT

 

[bash]

Now I am trying to pull the gearbox...

I am back again... I am now trying to get the gearbox out, on my own. Can anyone tell me how to unfasten the nuts and bolts holding the engine and gearbox together? Even if I had a helper it looks like I would need to move a lot of stuff in the engine bay to get to the bolt heads. Is there a secret?

Also, after removing the nuts and bolts at the prop shaft, I can find no easy way to separate the flanges. Does this just come apart when lifting out or do I need a hammer? If so how hard can I hit it before I break something!

Thanks in advance for any advice.
Alistair

 

[Guest]

Re: Now I am trying to pull the gearbox...

Alistair,
You can get to each and every nut and bolt holding the transmission bell housing to the engine plate by yourself. Just use a open spanner wrench in the engine compartment and a very long extension on your socket from the interior. Usually what happens is the spanner wrench will start to turn with the bolt/nut and jamb itself somewhere in the engine compartment so you can finish unbolting the rest from the inside. I have found that a compressor driven air ratchet works best here but hand powered ratchet does the job. Take them all out (you do know the starter and slave cylinder have to come out first) and the tranny won't fall; it is resting on the top studs. You will have to separate the rear flange with a blow or two or three from a hammer. Some have resorted to driving a sharp tool between them. Be careful doing that. (you did remove the four bolts) You can slide the drive shaft back a bit as it is two-piece. After everything is loose, get under the car (should be up in the air to where you can comfortably get underneath and benchpress 100 1bs.) Usually lifting the tail will break the tranny off the engine plate. (You DID support the engine to the garage floor. I used a sharpened 2x4 that jambed nicely between the oil pan and the engine plate. Some have jacked off the pan. Never did like jacking off a pan unless some padding is used.) Will have to bump and wiggle rearward a bit to clear the studs on the engine plate. Slide back with tail lifted slightly and benchpress up onto the passengers floorboard (no seats, right?) You are home free. How's you back feel now???


Bill