Shifting Trouble

[Matthew E. Herd]

Hello all,

I have a difficulty I am trying to resolve. I replaced an 8 month old slave cylinder on my 76 midget (engine and all was redone last summer). However, at mile 600ish (i'm now at 770 or so), it began to be extremely difficult to shift. With coercion, I can get it into 2nd at a stop, and 3rd and 4th when upshifting. However, 1st and (obviously) reverse will not go. I have determined that it does not disengage the clutch. I checked crank endfloat, and it is within what appear to be acceptable limits (I see slight movement, but no more than 20 thou if I were to guess). Upon inspection, I determined (yesterday) that my slave cylinder was leaking, and I replaced and bled it today. However, this still did not solve the problem. My master does not seem to leak, and seems to generate some reasonable pressure. Any advice to solve my problem?? I'm rapidly becoming frustrated

 

[aeronca65t]

These things can be a bugger to bleed (maybe because the bleed screw is in such an akward spot in a 1500). If the clutch "firms up" after you pump it a number of times, that's a givaway that there is still air in the system. Be sure that it's bleed *fully* before anything else. Use DOT 4 fluid or the proper Brit stuff and be sure it is always full each time you bleed it. Some of these cars use a plastic hydraulic line (from master to slave) that can fail sooner that a proper hydraulic flex line.

Also check the clevis pin and the hole at the top of the clutch pedal (that it fits through). A little loosness at the pin or hole creates a huge movement loss at the slave, making the pedal seem "low".

And be sure that the clutch slave is fully "home" in the trans hole with the pinch bolt tight.

We will all say a little prayer for you that the throughout arm or throughout bearing are not at fault.

I notice tha Rensselaer has a Formula SAE team. And a few years ago, Rensselaer brought an electric-powered sports racer to Lime Rock for a demo. It was pretty neat....someone up there like cars.

[ 03-11-2004: Message edited by: aeronca65t ]</p>

 

[Matthew E. Herd]

Yes, to my knowledge, there's no longer any electric powered projects ongoing. However, the FSAE team is pretty active. I am not on the team due to time constraints, but they do some pretty neat work. I find that the intake restrictor limits engine development (the dyno curves show linear increase up to about 5000 rpm, where they level off at 70 hp all the way up to 14,000 rpm), but they do extensive testing on their parts and have come up with some neat ideas. Personally, I don't think they're as wonderful as they do (I've had a few team members in my classes), but they are good with lathes and welders.

 

[Matthew E. Herd]

Also, on the clutch issue, the pedal does not firm up after pumping, I have the plastic line, so I checked it for bubbles with a flashlight (as it is the highest point in the system) and found none. I was not using dot4 fluid before, but am now ... supposedly the dot 3 destroys the seals? That seems fishy to me, but whatever. The old slave was DEFINITELY leaking, though, as fluid was all over the gearbox casing (and it was eating the paint, too. Makes hi-temp paint become soft and dull, as I discovered). However, it seems that the throw on the pedal isn't sufficient to generate the needed displacement, so perhaps I can figure out how to lengthen the stroke/tighten the pin. I have the pedal box open, and everything seems to be in working order ... we'll see. The old clutch was only slightly worn, but it seemed to disengage rather low down too, as I recall.

 

[Matthew E. Herd]

Alright, another thought occurred to me. I had the front wheels up on ramps. I believe it is possible that the air was collecting at the front of the cylinder, and not being pushed out. However, I have now raised the rear wheels above the fronts and am going to try my luck as soon as my assistant becomes available. Any other ideas?

 

[Matthew E. Herd]

Ok, I re-bled for the nth time, this time with the wheels up, however, it still does not work. No sign of air bubbles ... I'm at a loss. The pin connecting master to pedal is fine, the slave is installed happily ... what else could it be?

 

[Pat_Pattle]

Hi Matthew,
My only experiences of this type of fault are 1) where I had changed the cylinder complete with push rod, and the push rod was too short (wrong model), and 2) where there was an internal leak across the seals in the master cylinder causing insufficient pressure to move the slave piston.

Good luck!

 

[aeronca65t]

Try bleeding it at the clutch master cylinder. Pump it up and "just loosen" the hydraulic line until fluid squirts out from the fitting.

 

[piman]

Hello Mathew,
You mention a plastic pipe for the clutch. Triumph used a similar line on my 2000 sedan, and for years now I have regularly thrown it in the bin on all the cars I have owned and fashioned up a metal line with a conventional flex hose. The plastic pipe is a common cause of loss of slave pushrod travel as it expands with pressure especially when hot.
If you can substitute a metal line, forgetting the flex, as a trial. If it does alter the clutch, there's your problem.

Alec

 

[Matthew E. Herd]

Thank you,

Lets just say the new slave cyl worked worse than the original ... I couldn't even get it into gear

When driving it to my mechanic -(6 miles and 2 stoplights once in town, second gear only, and I couldn't stop the car or it would stall and I might not get it started), the only thing I have to say is BONZAI!!! It was an experience, all right. Also, I conclusively determined that the rebuilt is from a spitfire. I'll look to see if the pushrod was a different length. There is a possibility that the master does not function perfectly. All these things will be investigated. Thanks again for the help.

 

[littlecars]

Just one more possibility make sure the diameters are the same. Alarger diameter will not move as far as one with a smaller diameter, thus not disengauging the disc.

 

[Matthew E. Herd]

Ok, more fun on this subject. Just got back home and brought the Herd Rod out of the garage. Sure enough, the supposedly fixed clutch issue has reappeared. Symptoms are as follows: When initially running, the car wouldn't shift into gear (nothing new, but I didn't expect to still have this problem). So, I started the car in first gear. It runs fine and does not seem to affect idle measurably. Still runs at about 550 RPM, just as it did 30 seconds before I shut it off to put it into gear. Also, it would actually start with the car in gear and wouldn't lurch (clutch depressed). When driving it I discovered that the car upshifted beautifully (as well as ran beautifully -- that's a relief!), but would not go into gear without some forcing. Once home, I had to stop it and restart it again to get it into gear and at that time, the car would now roll forward on its own when the brake wasn't depressed. I seemed to detect a sqeaking or something to that effect when the car was running and the clutch was depressed (out of gear).

I find it a little difficult to believe that air leaked into the system (once again, the slave is brand new and has fewer than 15 miles/6 weeks on it) when the reservoir is still topped up and I detect no leakage down the pedal. Since the old slave had a bad seal and was most likely leaking onto the clutch, is it probable that the clutch swelled up since it was last driven. If so, what is a suitable course of action? Shall I leave the car in gear, running, with clutch depressed and heat it up? Also, I hear tell of using tilton master cylinders on the speedwell page and a few assorted other places. Would this be a direct fit replacement and displace a greater volume than my existing cylinder. Or, has anyone found a replacement that would displace more than my master cylinder does?

 

[Dave Russell]

I'm beginning to like my old fashioned mechanical clutch linkage more & more.
D

 

[aeronca65t]

OK...we'll assume that you have bled the system fully (it sounds like you have).
We also have to assume that your plastic line to the clutch slave cylinder is OK (I'm still running one too, but as Alec has implied, these things are a weak point in the system and should really be replaced).
If your clutch pedal has become soft over time, you may have a clutch master cylinder that is leaking internally. This means that the fluid on the pressure side is leaking past the seal back into the reservoir. If this happens, you won't see an external leak, but the pedal will loose firmness with time. I'm not sure why the DOT 3 fluid is not OK, but it may have caused this problem.
My clutch pedal hydraulic system has worked fine for at least five years, but one thing I do almost every year is:
Fill the fluid reservoir, crack the bleeder (without touching the pedal) and let the system "drip" for a while (10 minutes) to purge some of the old fluid out of the system. Brake fluid absorbs water, so this tends to flush some of it out. Be sure the reservoir is maintained full while doing this.

 

[Matthew E. Herd]

Thanks, I'm taking it to the mechanic today, as I never actually drove it when it was fixed (supposedly) so I have no way to judge about pedal firmness. It may be as you say and the master is leaking internally, however, I checked the reservoir and it was topped up, so no more than 1 ml could have leaked (in my opinion). Do you think that would have caused the harm?

 

[aeronca65t]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Matthew E. Herd:
so no more than 1 ml could have leaked (in my opinion). Do you think that would have caused the harm?<hr></blockquote>

No. As long as you can see some fluid, the system should function.

 

[Matthew E. Herd]

Well, as the clutch play has been completely eliminated (or as much as is possible) and I now have just enough pedal to disengage the clutch, but not shift gears, I have decided that the master must be faulty. I hear what I believe to be a slight squishing sound, so perhaps there is a seal that isn't quite doing the job. At any rate, I've already ordered rebuild kits and hope that this will indeed solve the problem. Other problems have cropped up which I will revive another old topic on ... valves ... to cover that one.

Thanks for all the help on this subject, however.

 

[Matthew E. Herd]

At last, the solution to my problems! (and probably the cause). I suspect that the fluid leaking from the faulty slave seals caused the clutch plates to expand. To that end, I fabricated a new clutch master cylinder pushrod as follows: I measured the length of the old pushrod. I then chopped the U shaped piece holding the clevis pin from the shaft. I then drilled and tapped the back side of the U shaped piece, and threaded in a length of 5/16 by 24 threaded rod. This was then screwed in as far as possible (while still clearing the pedal when fully shortened), and an arbitrary length cut from the rod (mine was approx 37mm measured from the center of the clevis hole to the end). Another lenth of the remaining portion of the original pushrod was then cut, with the sum being equal to the original length (plus or minus 1--ended up at 34.5mm). These two parts were welded together and a jam nut installed to secure the threaded rod to the U shaped portion of the pushrod. This then allowed for adjustment from about 71mm to 80mm, with the original length being 73mm as measured from the end of the rod to the center of the clevis pin hole. Once installed in the pedal box (this part requires removal of the master cylinder, unless you're very tricky), I found, by trial and error, that I could adjust it until the car would shift again. At roughly full extension, the car now drives and shifts like a champ, but the pedal engages about an inch off the floor. I expect to prove my theory about swelled clutch plates after I have driven it for a few hundred miles and the plate is dried out a bit.

If you're having similar problems, or could not visualize my rough description of the extended pushrod, just email me at herdm@rpi.edu and I'll help as best as I can!