Yet another TR clutch issue

[BritBox]

Hi,

I guess it's my turn to have clutch issues with my TR250. It went from OK to pretty bad in just a few drives: initially had trouble with reverse, then getting into first from a dead stop. Bled the heck out of it and it is better, but reverse is still not really there. When I'm under there bleeding it I can see good action with the slave pushrod.

Some background: the car has about 20,000 miles on a pretty complete restoration. Motor internals are original. Gearbox totally rebuilt, flywheel lightly skimmed and balanced, Toyota Landcruiser throwout bearing, Sachs pressure plate, B&B friction disk. New fork and shaft, with second bolt pinning the fork. New slave cylinder, rebuilt master.

I had a similar problem about a year and a half ago. I ended up removing the "new" orange plastic flexible line between the master and slave, and replacing it with a nylon/stainless steel upgraded hose. Problem solved.

Question: In spite of what LOOKS like good hydraulic actuation, should I still suspect the master and/or slave? Or my new fancy flexible line? I'm sure I'd rather throw some parts at it before I bust the whole thing apart. Or should I suspect the dreaded fork pinch-bolt, even though I modded mine? I suppose that stranger things have happened. It "feels" fine to the foot, so to speak, for whatever that's worth. If the fork was broken it would be more consistently broken, wouldn't it?

If I pull it all out, I guess that's a good reason to finish the spare used motor with the fresh bearings and other new bits...

Any and all suggestions or comments welcome; thanks for reading this far!

Thanks,

 

[Keoke]

BritBox, I am not specificaly a TR man.However, based upon my experiences with LBC clutches you may just have too much variety in the car's clutch: "Toyota Land cruiser TO Bearing,SachsPressure plate,B&B Friction disk". Why all the variety??, arent TR replacement parts available.?? I Never miss match clutch parts;Covers and disks match by vendor.---Fwiw---Keoke?

 

[piman]

Hello BB,

a couple of things, which of the three holes are you connected to in the clutch cross shaft?, the top hole gives better release. Do you know if you have a 1" or a 7\8" slave cylinder, the latter will give more release as it travels further. (Smaller bore same volume from the M\C)
I have, for many years, thrown the nylon tube and used a solid line with just a short flexible, so your mod sounds OK. This swelling of the nylon line usually shows up only when the car is hot which is a give away to that particular problem.

Alec

 

[BritBox]

Hi Keoke,

It does sound schizophrenic, doesn't it? The parts are all common and popular upgrades to known weak spots in the TR250 and TR6 clutch. The components are the same as what The Roadster Factory sells as their "Magic Clutch" package.

For example, the standard replacement throwout bearing has been known to fail in 10,000 miles or less, although some people have no trouble with it at all.

Thanks and regards,

 

[Andy Blackley]

Mike: I had similar issues with my TR250 this past summer. In my case the culprit(s) were a missing clutch pedal return spring and extremely worn pedal shaft bushings. The slop and the failure of the MC to fully return prevented a full stroke of the pedal, resulting in the same problems. I also suspected that the MC cap wasn't vented properly. Three easy things to check, but since your car was fully restored these may not be your problems.
It seems most of the clutch problems are either due to the pin shearing as you mention or the TO bearing dragging on the input shaft cover. In most other LBCs the clutch is seldom a problem, too bad Triumph engineers didnt anticipate that a bunch of crazies would be still using their products long after the "planned obsolescence" date. /ubbthreads/images/graemlins/devilgrin.gif
Another good reason for considering the 5 speed conversion, IMHO.

 

[Alan_Myers]

Hi Mike,

Your problem does sound like insufficient clutch release action.

I thought maybe synchros, but you said the gearbox has been rebuilt and the problem also occurs with reverse, which isn't syncho'd.

I'd be curious what all was replaced in the gearbox when it was rebuilt. It's possible to get mismatched gearsets, if any needed replacement. There were a series of slightly different gearsets used over the course of TR production.

One other thing to check is the level of the oil in the gearbox, and what type oil is being used.

The braided stainless steel hose is about the best you can do in that respect.

You said the clutch master cylinder was rebuilt, but was that just a kit installed, or was it sleeved. Any flaws in the bore of the MC could eventually allow air into the system or might reduce the hydraulic pressure produced.

What type fluid are you using? DOT 4 or DOT 3 would probably be best. I've heard of DOT 5 giving problems.

With the extra pinning done on the cross shaft, I find it hard to believe that the dreaded taper pin has broken. However, there have been pretty bad junk pins sold in the past and they seldom shear off cleanly, usually allows only a little sloppiness in the rotation of the fork, which is enough to cause insufficient motion of the T.O. bearing and result in just the sort of problems you are seeing.

You might be able to feel or see if there is any problem with the pin by performing a test. Disconnect the slave cyl. pushrod, put a short piece of pipe over the lever and actuate it by hand. Even a little play would indicate the pin is likely broken and the backup bolt isn't doing it's job.

Also check the cross shaft for any lateral play at the bushings it rides in, that are pressed into either side of the bellhousing. Here's one place the older, TR4 style, with much longer, greasable bushings seems to be more durable and might be retrofitted (that means a new cross shaft that has been drilled and tapped for grease zerks, however).

I think Alec is onto something about the slave cylinder. 7/8" is a better choice, Triumph went to the larger one to give a softer pedal, and a lot of troubles started happening.

But, contrary to what Alec said, the center hole of the cross shaft lever is the correct one to use on all TRs, 2 through 6. The top one will give a heavier pedal and might overextend the T.O. bearing, the bottom one will give too little clutch motion.

Check that the hole in the shaft isn't oversize from wear and tear, too.

Another thing to consider is replacing the slave cylinder's pushrod with one from a TR4 or earlier. These are adjustable and have an external return spring (attaches to the mounting bracket at one end, and a little tab that slips onto the clevis pin at the other). I've seen someone selling a "kit" on eBay, which apparently was based upon some recommendations in Kas Kastner's book, but that's really is just a retrofit of TR4 pushrod parts to the later cars.


Somewhere I saw a dimension for how far the clutch slave cyl. needs to travel, minimum, but I don't rememeber where. ISTR it was about 5/8" minimum, but that might be incorrect. Hopefully someone will jump in if they can confirm or clarify this dimension.

I know a lot of people have experimented with mixing clutch parts, looking for an "ideal" setup, but I agree with Keoke that it might cause problems if any of those parts use slightly different dimensions.

Have you checked the thrust washers in the motor lately? Usually they give other problems before they would contribute enough movement for clutch problems, but if original they might have a lot of play. The action of the clutch always puts additional strain on them in the 6 cyl. cars. The way to check them is to reach in and push the fan mounting hub rearward, then put a dial micrometer at the front of the fan. Then have someone press the clutch in all the way, while you watch the dial micrometer for movement. Push the fan hub rearward again and repeat the test several times. I think the tolerance is .004-.008".

Let us know if you find anything.

 

[BritBox]

Hi Alec,

I'm pretty sure that I'm already connected to the top hole on the slave cylinder, I am familiar with the practice to which you refer. What I am not so sure about is the slave bore diameter, I'll check on that.

It seems like I could even shim the slave cylinder to move it closer to the clutch lever and improve throw, but that just seems like I'm sidestepping a fundamental problem.

Thanks and regards,

 

[piman]

Hello Mike,

moving the cylinder or an adjustable push rod is a red herring, as the slave cylinder is overlong, which is how it self adjusts. Unless the piston is virtually out of the cylinder when pressurisied that is not the problem, and if it is I'd look at the cross shaft. I know that the middle hole is 'correct' but if that were the only option then there would only be one hole.
Another quick check, what is the angle between the cross shaft lever and the push rod (at rest), it should be greater than 90 degrees, if 90 degrees or less then there is something wrong in the release mechanism.

Alec

 

[Geo Hahn]

Since you can get it into 1st and not reverse you are obviously right on the edge of it working.

Another thing to try... hold the clutch pedal down for a long time (minute or more) and see if things get much worse (i.e. you can no longer get it into 1st). That would suggest a problem with the seals or bore in the M/C.

BTW, I have encountered 2 types of rebuild kits recently. In one the big seal has a flared lip that is typical and has to be worked into the cylinder... on the other the flare is barely discernable and the piston goes in much more easily. Both work okay on my M/C but the latter may have less tolerance for a worn cylinder.

 

[powerwagontim]

Hi Britbox,
Can you explain, or direct me to a detail of the clutch fork extra bolt? I am about to redo the clutch shaft bushings and pin on a TR-4 OD tranny that is going into my 3a. Nows the time to make a change!
Thanks,
Tim

 

[BritBox]

Hi powerwagontim,

I'll start by saying that it's been about 5 years since I did the mod, so I don't remember a quick reference or link that I can direct you to. I'll dig around and see what I can come up with. The TR4 clutch is a little different, but I will try to explain how the mod works on a TR250 or TR6.

The clutch fork has a raised boss on the casting that is actually machined flat on the tip. It looks like it's just waiting to be drilled! You basically put the assembled fork and lever rod assembly on a drill press and drill through the fork at the boss and about two thirds through the lever shaft. Drill this hole to fit a 5/16" bolt that will be tapped and threaded through the fork casting ONLY. After you drill this first hole, disassemble the fork and drill the rod again, this time so that the 5/16" bolt can just fit easily into the shaft. Drill a small hole in the head of your 5/16" bolt so that you can safety wire it like the stock pinch bolt.

The idea here is that you have a second bolt to share the load with the questionable original pinchbolt. The new bolt (Grade 5 or 8) threads into the fork casting, but extends into the shaft. Sorry if I'm not describing the procedure very well; I'm sure that someone else can expand on or improve what I just said!

Regards,

 

[BritBox]

It's the people that make forums great

Hey,

Thanks to everyone on this forum who has offered advice and information so far! You guys have given me enough ideas to keep me busy all weekend. I will see what I can see!

Best regards,

 

[trboost]

This may help from a previous clutch topic.
https://www.britishcarforum.com/ubbthread...true#Post138106
I doubt the problem lies in the slave cylinder. The Toyota bearing although a beefier unit it had some size issues. The bearings contact surface was wider & pushed on the clutch fingers more outward of center compared to the factory unit. This & the fact that it had more drag caused it to score the spring fingers. This alone is not the cause but can be a quirk added to the operation of smooth clutch operation.

If the top hole of the arm has been used & first/reverse are difficult to shift in to my bet is going to be a broken fork pin. The design if this pin is definitly a weak point. The tricky part is the pin usually shears at one point creating the symtom you have now. The second half wedges in the top binding the fork to the shaft , enableing a slip & bind condition.

The attatchment will show you where to drill to remove the broken pin & where to install the secondary shaft pin.

Good luck & let us know what you find.

 

[Alan_Myers]

Re: extra bolt [was: Yet another TR clutch issue]

Hi Tim,

This is how I've always seen it done.

The extra bolt need only be 1/4" (or metric equiv.)

Get a good quality Grade 8, fine thread is probably best, and check that the dreaded taper pin is still in good shape and fitted properly. (Note: Always replace the tapered pin while the gearbox is out, when working on the T.O. bearing or clutch. And, when replacing the taper pin, try to get an "upgraded" or "hardened" one from a trusted vendor.)

For the secondary bolt, I simply use a hand drill and punched a hole through the fork and shaft, sort of "across from" or opposite where the taper pin is fitted. Really anywhere will do, that the fork rides on the shaft and has a relatively flat surface.

Slip the bolt in from behind and put a locknut/Locktite on it.

Just be sure to have a bolt with a long enough shank (unthreaded area) that goes the whole way through the fork and shaft, so that no bolt threads are inside the hole. If necessary, adjust with some plain washers and/or cut the bolt for length.

Also make sure the drilled hole is carefully sized to make for a nice snug fit.

 

[piman]

Re: extra bolt [was: Yet another TR clutch issue]

Hello all,

I do not like the idea of the second bolt, and don't believe that it is sound engineering to fit one. The problem with the taper bolt is ensuring that it is a snug fit in both sides of the release fork and the cross shaft. That done then it is unlikely to break. Adding a second parallel shank bolt, especially one substantially smaller in diameter than the taper pin cannot be effective. A snug fit is imposssible as the shank of the bolt is a smaller diameter than the thread, and as the thread has to pass through the shaft then the bolt shank will be loose in the cross shaft. It will serve no purpose unless the taper pin breaks (usually because it is incorrectly fitted) then the bolt will carry the load but will constantly rock and that too will eventually fail.
The only sound way to fit one is to have a proper sized shaft bolt and ream the holes to fit, in which case you might as well fit a dowel.

Alec

 

[martx-5]

Re: extra bolt [was: Yet another TR clutch issue]

If the original pin setup was adequate, there wouldn't be all these failures. It's only prudent to install some sort of extra pin or bolt to ensure there won't be any problems down the road. Using a spring or roll type pin instead of a bolt will ensure a tight fit. Every trans that I have seen has had the problem with this pin. If it wasn't sheared off, it was starting to loosen and shear. It's a poor design. An extra pin installed can only help. It is in no way a detrement.

 

[piman]

Re: extra bolt [was: Yet another TR clutch issue]

Hello Mart,

I suppose i must have been lucky as I have been driving with this set up continually for over twenty years (different cars of the same range) and do not suffer pin problems. The bolt 'solution' as I said is not sound engineering practice, unless a fitted bolt is used.

Alec

 

[Alan_Myers]

Re: another possibility & extra bolt, revisited

Hi Mike,

Another thing occured to me. You might also check the two pins at the fork ends, that ride in and operate the T.O. bearing carrier. Over time these wear and flatten on the sides doing the work. This can add a lot of play to the mechanism (in turn reducing clutch release motion). The pins can be replaced individually, are pressed and peened in place in the fork ends, or the entire fork assembly can be replaced as a unit. A "cheap fix" is to grab the worn pins with vice grip pliers and turn them 90 degrees, so that unworn areas are now doing the work.

I don't think wear on these pins alone would usually be enough to cause the symptoms you describe. But, if severe or if in combination with other wear, etc., it might add up to the problems you are seeing.


Hi Alec,

The extra bolt method I mentioned has actually been a pretty common practice for some years now. Hey, I'm not a degreed engineer, so all I can say is that the modification works and has been proven. Many TR mechanics and enthusiasts do it, as a matter of course, any time the gearbox is pulled for any reason. No one wants to re-pull a gearbox every 5000 to 20000 miles, just to replace a $5 taper pin. (Or deal with more extensive repairs, thanks to this small item's failure that went undiagnosed for a while.)

The practice might have started with racers who were using upgraded, stronger clutches. Those began showing the inherent weaknesses of the release mechanism, which is probably marginally adequate for original specification. An alternative racer solution was simply to weld the fork to the cross shaft. But of course that means cutting and destroying the shaft the next time any work is needed in there.

For street cars, I think there are several reasons people started adding the extra bolt. Perhaps the most typical was in response to a glut of poor quality replacement taper pins that were widely sold a few years ago. Better quality and even upgraded taper pins are now offered by most good vendors.

In addition, it's well documented that replacement diaphragm-style clutch pressure plates sold in the not-too-distant-past for TR4A and later have required much higher release pressure than did the originals, due to stronger springs. That's because the manufacturers stopped making a plate specifically for TRs, and began supplying units that are used on a variety of models, i.e., some Volvo, etc. The stronger release springs put a lot of additional demand on throw out bearings, T.O. carriers, the fork, the taper pin and even possibly the slave cyl., master cyl. and pedal linkages.

The pressure plate situation has improved to some degree in recent years. Most knowledgeable vendors now offer plates that are closer to original strength. But, *all* currently available replacements still use moderately stronger springs. (Note: Anyone who happens to have an original TR diaphragm-style pressure plate might be encouraged to have it rebuilt instead of replacing it. Dunno about here in the US, but several TR specialists in England offer this service, on a strictly exchange basis since new units aren't available. TR4 and earlier used a different release plate that might appear a possibile solution, but unfortunately isn't because the plate is larger diameter, heavier, and uses a different mounting bolt pattern.)

Many folks working on TRs have continued doing the extra bolt modification for that added margin of safety, even though most vendors now offer higher quality taper pins and more reasonably sprung replacement pressure plates.

I don't know where you are buying your hardware, but the common bolts I've got in the garage have a larger diameter shank than threads. I just measured a standard 1/4" NF Grade 8, just like those I've personally used for the extra bolt modification we are discussing, and its shank is .246", while the threads are .244".

The reason the bolt modification works is because the stresses are distributed between two fasteners, rather than relying on a single one. A Grade 8 or better bolt is recommended for its higher tensile strength. I'd guess the taper pins are less than Grade 8, the replacement ones that broke so easily might have been ungraded entirely.

Anything much larger than 1/4" dia. bolt, or it's metric equivalent, is *not* recommended because that would remove too much material from the cross shaft itself, and might lead to shaft breakage.

I'll certainly agree that a drill press followed by careful honing of the hole to a precise size would be the very best way to make the modification. But, the modification can be done with a hand drill, being careful to center the hole and not make it oversize, without removing the fork/shaft from the bellhousing.

Yes, a dowel might be used instead of a bolt, as Martx suggested. While I've not heard of using a dowel, I have heard of approx. 1/4" roll pin being used. But, what worries me about this method is that there is no positive retention of either the dowel or the roll pin, so either might work loose and drop out, leaving us back at square one with only the taper pin holding things in place. In my opinion, a bolt with a self-locking nut is much safer.

Next chance, I'd like to try another alternative to *all* of the above: a co-axial hydraulic clutch release . Seems ideal since it not only makes for quicker shifts, it deletes all the troublesome parts: T.O. bearing and its carrier, cross shaft and its bushings, fork and its pins and the dreaded taper pin, and the slave cylinder and its linkage. Only the original master cylinder and hydraulic pipes and hoses remain. A bit pricey, yes, but if all those original parts needed to be replaced anyway, I suspect the end total wouldn't be a great deal more to go to this more modern release method.

My only concern about a co-axial release is that I'm uncertain how often adjustment might be needed. The only way I can see to do that is with shims under the mounting flange, which unfortunately means pulling the gearbox out of the car. If that was seldom needed, it would be a great solution, or an alternative or partial method of adjustment would be an adjustable pushrod at the master cylinder. TR-specific kits, like the one at the above link, don't seem to be available in the US, but "universal" co-axial units are made here (by 4 or 5 manufacturers, with varying reliability reports) and are much cheaper than in the UK. I'm still looking into this idea.

 

[71tr]

Re: another possibility & extra bolt, revisited

Alan,
I like the idea of disposing with all the mechanical systems and installing a hydraulic throw out bearing. Agreed the link you provided is a bit pricey. Maybe one should inquire of Herman Van Den Akker as his Toyota conversion kit includes a similar hydraulic bearing.

 

[piman]

Re: another possibility & extra bolt, revisited

Hello Alan,
I did a quick check myself on some 1\4" bolts that I have and some are a fraction up on the thread diameter and some are down, so it seems that I was not entirely accurate. I based my statement on the fact that the threads are rolled so a smaller diameter is required to get the correct thread diameter. The bolts I looked at were obviously double diameter before rolling, i.e. the threaded section is reduced to facilitate the thread forming action. I have, however, seen fasteners that were not made in such a fashion. (Also, of course, screws may be used instead of bolts by some people)
I still feel that it is not a good solution as it does not 'lock' the fork to shaft. A dowel, properly fitted would (although a roll pin won't to the same extent)
You mention a time of poor pins and that has probably given a bad name to the original system, which I maintain is OK, providing the pin is correctly fitted.
I went back to the technical notes of my Triumph car club (Triumph 2000 Register in the UK) and there is a mention of pins with too short a thread length, allowing the taper bolt to bottom on the head before the taper locks the fork to the shaft which is obviously unsatisfactory.
I do feel that people modify things to correct a fault which is caused by incorrect maintenace or assembly rather than identifying the fault and correcting that. I may add that I see this very often at the factory in which I work, 'mods' are made to correct a fault which is due to exactly what I refered to above.
The concentric release cylinder is the neatest hydraulic release mechanism, without doubt. Your reservations about adjustment can be met by making the cylinder (if space permits, and I think it does) with extra depth. This gives a self adjusting hydraulic mechanism, with the fluid doing the adjustment. (As is the case with the existing slave cylinder, it does not need an adjustable pushrod modification')
By the way my Triumph is my everday car and so needs to be reliable.

Alec