UN1 13 Grinding when trying to shift

Have a problem with my newly installed Un1 13, it did work fine to begin with thoug selecting reverse has been a problem from day one, - tried different things, first off i use a 7/8 mastercylinder and original renault slave, when clutch is depressed it moves 12mm at the slave, tried bleeding it to see if this could be the problem but still 12mm movement, dont think this changed as pedal feels the same as when it worked(when it worked it did grind the gears in 1st a couple of times as stated below but didn´t really take any notice of it. Anyway took the car up on the lift today and thought i would try run it off the ground. Started it up -pressed the clutchpedal and selected 1st...no problem went in smoothely, then released and let the wheels roll while in gear -no problem, then pressed the clutch and now it wouldn´t completly disengage the clutch made a rattling sound and the wheels kept spinning as still in partly in gear - had to yank it out of gear, tried the other gears aswell and same thing hapens to some gears but not all the time?, tried reverse and wouldn´t go in at all. Have been told all sort of stories what it could be from "you need to bleed it" to a defective pilot bearing need to remove gearbox:shocked: am on the verge of breakdown here so i really hope some of you guys heard of this problem before and have a fix without me having to yank the box out, all input will be greatly appreciated.

Regards
Michael B
 
from my own experience you need more slave pin movement. I do not think 12mm is enough. You need to sleeve down the slave cylinder, which will give you more movement at the expense of harder clutch pedal. Speak to Frank Catt.
 
Might be easier to install a slightly bigger master cylinder? That would have the same affect on slave cylinder travel.
 
Thanks for the input guys, thought of this aswell, and did change it from a 3/4 to the 7/8 and made it a lot better than before, but the thing i find strange is that it has worked up until now, and i can still get it to engage most gears without any grinding or noise, the problem is once engaged then pressing the clutch wont disengage the gears which i only encountered a couple of times before, suddenly this just happens all the time?, if it was a cylinderproblem(size or lever not being pushed far enough) wouldn´t it be a problem selecting the gear in the first place? Corret me if i´m wrong but i would think i would be entirely unable to select gear..
 
Last edited:

Ian Anderson

Lifetime Supporter
Michael

I run a .75 master and Renault slave and get about 19 mm movement at the slave. I run a tilton pedal box.

As you get it to change sometimes and not others I would suspect air bubbles. They can be a pain to bleed out. I have heard some have success reverse bleeding by forcing fluid in at slave. And flowing it to master.

Last question what sort of pipe are you running? If it is flex all the way it can wear in time and expand when under pressure.

Ian
 
Hi Ian,

Thats the same thought i had but then again when it works it moves it the same 12 mm as when it dosn´t work, we tried it the other day when on the lift?. It might be that i´m just so close with the 12mm that its luck if it goes in or not, just found a place online where it states that it should be around 13mm to disengage the clutch but then again if you say yours move 19 inches with a 0.75 cylinder thats alot more compared to mine and i allready changed out my 0.75 it would only push it around 8 mm?, how far down do you need to press your clutch to get it to release? maybe if i could get you to measure the distance it needs on the slave just to release - then i can see if im way off on mine or if this really is the problem, also is the clutch slave on yours standard or sleeved down as mentioned above?

With regards to Pipe i´m running hard pipe all the way through, with only about 10" of stainlex flex on each end to connect the cylinders, so shouldn´t be any flex here.

Anyway will try and bleed again and see if i can do a reverse bleed as well.

Thanks and appreciate the help, its really a pain not to be able to get it out on the roads :).

Michael
 
Michael:
I agree with the other guys on going to a bigger master cyl. This will increase pedal effort somewhat but increase travel as you have found.
Two things about new clutches, one is that once you clean the "Fuzz" off the disc the pressure plate will close up that slight gap, and the clutch fingers will move slightly. It seems like a trivial bit, bit most clutches disengaged have only about .065- .070 clearance (roughly 1 1/2 to 1/3/4 MM, so having marginal travel on your original setup might mean when things break in you are not releasing sufficiently.
The other factor is heat and with a marginal release your disc may be dragging.
I would look up the manufacturer of that clutch and see what they recommend for release travel, make sure you have that travel available, and put a pedal stop on your clutch pedal to prevent over travel.
Good luck
Cheers
Phil
 
Phil - Hadn´t thought about the break in of the clutch but it does make sense thinking about it, think ill go for a 1" master or maybe get the slave sleeved down, does anyone know what bore size the slave is (its the pjn117) cant find anything on it online other than price and just want to make sure that i have at least a couple of mm more travel than now.

Also any recomendations to which brand to go for if i change the master, the one i have now is the 7/8 wilwood but thinking the 1" tilton would be the one to go for, anyway thanks for all your help and will let you all know how it turns out.

Michael
 

Mike Pass

Supporter
I had a similar problem and via a whole range of master and slave cylinders I ended up with a 0.75" master cylinder and and a sleeved down slave cylinder from Chris Cole. If you want one from him you will need o supply an old one as he only does them exchange as they are getting rare now. I also made up a new slave cylinder push rod from a suitable bolt to get the exact range of movement. You can make small adjustments by using small washers on the slave cylinder bolts. The Renault slave cylinder bolts are an odd size - 7mm thread. If you need longer bolts they can be obtained but not readily available. I got mine from a classic motorbike shop. When fitting a new push rod grind off the old Renault pin and use a suitable ht bolt. You can then change the rod easily. Mick Sollis at Southern GT does an adjustable push rod for the same purpose.
Another issue I have encountered is leakage at the slave cylinder which sucks in air on the return stroke and then you lose the full movement at the clutch. This is usually caused by the slave cylinder rubbers being "cooked" by the proximity of the very hot exhaust pipes which destroys them. Fit new seals and insulate the slave cylinder with suitable insulation and a reflective cover plate.

Cheers
Mike
 
Hi Mike,

Did some reading up online and found a bunch of stuff on this problem, especially the method of sleeving down the slave to 22mm. The push rod i had made to be adjustable allready and can actually be positioned pretty precisely and adjust movement either way, leaking shouldn´t be a problem its brand new. Now i went and disconnected my current master and found it to be a 3/4 master not a 7/8 - so no wonder i´m having problems. Now im thinking i really dont want to pull the slave out and send it out to UK and back, just to expensive, but im really interested in seing how much extra leverage i would give if i went with a 7/8 master or 15/16 and just left the slave alone, i´m not a wiz in hydraulics so if anyone can calculate how much more leverage it would give if i did that instead of sleeving the slave, so going from a 3/4 to a 7/8 or 15/16 and retain the 1.1/8 slave how much throw would it amount to in mm? compared to the old setup. Need to order a new one so if anyone has the answer please let me know :)

Michael
 
Ideally you need to know the stroke at the clutch pedal end then its master travel * (area of master / area of slave)^2 there is enough to go on though so you have a 1 1/8 slave and 3/4 master, that's 28.575mm and 19.05 giving a ratio of .4444

Using a 7/8 master instead is 22.225mm which is then a 0.6 ratio.

So to work back 12 at the slave divided by the ratio 0.44444 is 27mm clutch stroke, feeding that back in with a 0.6 gives 16.2mm at the slave.

A 22mm slave with the 3/4 would give you a 0.75 ratio so would result in 20mm travel.
 

Mike Pass

Supporter
The piston area of the 3/4" 0.75" master cylinder is 0.44sq"
The piston area of the 7/8" (0.875") master cylinder is 0.60sq"

The change in the amount of movement is the ratio of the two areas.

Changing from the 3/4" master cylinder to the 7/8" master cylinder will increase the movement at the slave cylinder by 0.60/0.44 or by a factor of 1.36 more.

If you need to sleeve down the slave to the diameter you want can be done by a good machining shop however you will need to locate a suitable rubber seal first and then sleeve and bore to the same diam as the cylinder the seal came from. A trawl through the parts catalogues should find you something suitable.

Cheers
Mike
 

Mike Pass

Supporter
Area of the15/16" master cylinder piston is 0.69sq"
Calculate accordingly if you use this master cylinder.
Cheers
Mike
 
Right...school is in:shy:

Thanks for the explanation to both Dave and Mike appreciate it very much...just one thing i was wondering was, what benefit would there be to sleeve down the slave instead of just upsising the master?, as i can see i would get an approx. throw of 18.6mm if using the 15/16 master so almost the same as if i do the slave, reason i´m asking is i have no idea as to whom would rebuild the slave here in denmark tried asking our local machineshop and they wouldn´t touch it, tried the local brakeshop that mainly does cylinders and calipers and neither would they, However if getting it sleeved offers any significant benefit like softer pedal(Am a little worried the clutch will be too heavy if going to a 15/16) or the like i would be willing to send it to the UK to have done even thoug it would be more expensive than to buy the larger master.

Thanks again

Michael
 

Ian Anderson

Lifetime Supporter
Reason some people sleeve as opposed to going larger master cylinder is because

Larger master means more fluid has too move to the slave and this take a finate period of time for the fluid to flow the length of the car.

If you go for a larger master cylider and to avoid clutch "drag" when you release the pedal you should also increase the diameter of the pipeworl from 3/16 to 1/4 or bigger. Larger pipe ismakes it easier for the fluid to move

Ian
 

Mike Pass

Supporter
Sleeving the slave and increasing the master cylinder have the same effect. Changes in master cylinder diameter are quite big steps. Sleeving the slave gives you the option of smaller steps so you can fine tune the action so you get just enough movement with the lowest pedal pressure. It took a lot of changes to get mine just so.
Costwise the sleeved slave was about £130 exchange from Chris Cole. I use an AP Ferrari 355 cover plate and an AP driven plate with Renault UN1 splines (both from Southern GT). I also use Chris Cole's stronger clutch release bearing and holder.
Cheers
Mike
 
Allright Ian makes perfect sense, as it is i allready have 6mm or 1/4 hardpipe running through the car so if i have that i should be able to use a larger master and still have a resonable return rate, as for changing the slave and get it sleeved would set me back considerably if its 130 exchange, just posting from here is another 30 and back a tenner or so, thats 170£ and i can order a new master from 85£ wouldn´t that be a better solution now that i do have the bigger pipes?

Mike when you say it took alot of changes in you system to get it just right and to finetune it, did you start out like me changing masters or did you get it sleeved more than once(seems a very expensive method to finetune if thats the case). What i´m leaning towards now is going with the 7/8 master and try it out, if it gives me an extra 4 mm throw at the lever i would assume it would clear completely when its allready close as it is now, the 15/16 would increase leveraction by 6.5 mm which i would guess is more than i need or would it be better to go a little larger to be on the safe side, what do you reckon?

Cheers
Michael
 

Mike Pass

Supporter
I firstly juggled the master cylinders and the feed pipe diameters to get an idea of which one would be in the right range. I use a 1/4" pipe to give a good flow in the pipe. The best one did not have quite the right amount of movement at the slave (not enough) with the standard slave cylinder. So I tried the sleeved one and this gave just enough movement to work the clutch properly. The last bit was fine tuning the length of the push rod and again when the clutch had bedded down.
Cheers
Mike
 
:thumbsup: Allright i´m with you, still thinking about wether to go 7/8 or if its a safer bet with the larger 15/16 especially now you say that the best one you tried wasn´t good enough(what size was that?)since you had the same slave as i do, clutch setup isn´t far off from mine aswell .

Michael
 

Mike Pass

Supporter
With my set up I ended up with a 3/4" master cylinder and a sleeved down slave cylinder It works the clutch OK and with an acceptable pedal weight. I suppose you just have to try one or two and see. I ended up with 3 "spare" master cylinders! You have to find the set up which releases the clutch properly and then put up with the weight of the clutch action.
Cheers
Mike
 
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