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Tips
Tips

Having to pump pedal for pressure

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W

Winston

Jedi Trainee
Offline
Well I had a local import mechanic replace my clutch. Front to back. New cross shaft and bushings,the whole deal.
I'm having to pump two or three times out of first gear to get proper release pressure.
I rebuilt the master and slave cylinders prior to allowing him to do the job.I know they are done correctly. That sounds a bit haughty but they honed out fine and seals are fine under pressure.
I noticed he used a larger stock for the hydraulic pipe from the master to the slave.
He told me to put a couple of hundred miles on the clutch and bring it back for adjustment.
I did check and he attached the slave fork to the lowest hole and not the middle hole, that concerns me, an experienced mechanic on a TR4a should know better.
To his credit, the flywheel turned out beautiful, polished not a single groove . The main concern is what does he think he is going to adjust after two hundred miles.
The mechanic has his own TR4 as well as several other LBC's.
The shop has been in the family 52 years. Am I getting jerked around?
 
Sounds like air in the line to me.

JACK
 
Hi,

First I'd try putting the clevis pin in the middle hole... which is where it should be on all TRs. That will give more rotation of the clutch shaft with the same amount of slave cyl pushrod movement (but also a slightly heavier pedal). A doublecheck it to measure if the pushrod is moving at least 5/8" when the pedal is pressed.

Could be that the mech has a less-expert assistant or just had a brain f$*t himself and used the wrong hole on the lever. Or, maybe he knows something I don't and deliberately used that bottom hole of the lever. However doing so will usually just barely release the clutch, even under the best of circumstances. Thus, the extra pumping might be needed to get the max possible movement out of the SC pushrod. This could be exacerbated by some miles and wear and tear on the gearbox, expecially 1st gear synchro just getting a bit tired. Might be just fine, though, with full clutch motion.

Another thing that might help, is fresh oil in the gearbox. Personally I'd use 20w50 non-detergent *racing oil* in a non-OD gearbox or 30W to 40W *racing oil* in an OD gearbox (higher viscosity with higher mileage OD, lower with freshly rebuilt OD).

Pumping the pedal is also symptomatic to the system having some air in it and needing to be bled, assuming the hydraulics are otherwise good. Or, if there is any air leaking into the system, it will give the same symptoms.

I've had about 50% luck honing MCs and SCs over the years. Sometimes the slightest, overlooked flaw will cause problems, or honing increases the bore too much for the seals to be totally effective. Or, something happens during reassembly that damages the seals (I've been using Raybestoes hydraulic brake assembly lubricant the past few years and that helps a lot).

If you change the clevis pin location and still need to pump the pedal, I'd suggest re-bleeding the hydraulics to see if that helps. (Note: the bleed screw on the SC should be on top, if it's on the bottom, you'll struggle forever with it and never get all the air out.) Also check all the connections that there are no air leaks.

Not sure I understand about the size of the piping or hoses, but that shouldn't matter so long the system is totally sealed. (The relationship between MC and SC bore size, on the other hand, will make a difference in pushrod movement and pedal pressure.) FYI: the original braided hose from the pipe to SC on my TR4 was a large outside diameter, looked like AN-6 or -8, modern replacement I got from a vensor is a much smaller more like AN-3 or -4. But, again, this really shouldn't matter.

If you are using DOT5 fluid, it tends to trap air more easily and can be much harder to bleed than DOT3/4. One trick that helps is to stand a screwdriver upright in the MC reservoir and run the DOT5 down the blade, so that as little air as possible is introduced into the fluid when pouring it in.

Yes, the mechanic is right. It's important to go back and re-adjust a newly installed clutch after a short amount of use (when adjustment is even possible, i.e. on TRs up through TR4A or later cars that have wisely converted to an adjustable setup.) There will be some wear initially, as the parts bed in to each other. That's why the adjustment is needed in 200 miles. Even reinstalling a used clutch, it's likely to be needed, as parts settle in place. After that, check adjustment approx. every 12 months/12K miles.

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