UN1 gearbox

#1
Whenever the gearbox gets hot the gear change deteriorates to the point where getting it into gear becomes difficult, it's okay when cold, it's been like this since installation, it's got the quaif gear set and I've changed oil from semi through fully synthetic and mineral oil and it's made no difference, clutch release is fine and but it won't go in gear when hot, any suggestions what could be the cause.
 

Ian Anderson

Lifetime Premier Supporter
#2
My guess would be that the gear change mechanism is stiffening up as it gets hot. It did on my first system and when the rods in the rod change warmed up they would go solid in the sliders.

I presumed it was a case if dissimilar metals expanding at different rates.

Ian
 
#3
My guess would be that the gear change mechanism is stiffening up as it gets hot. It did on my first system and when the rods in the rod change warmed up they would go solid in the sliders.

I presumed it was a case if dissimilar metals expanding at different rates.

Ian
Good point, it's pretty obvious, why didn't I think of that.
 
#4
Ian is correct, i remember when I had my rod gear-change made that where it passes through a rose joint, it needed to be made in solid bar as tube is never perfectly round.
Might be worth getting the car hot and removing the rear connection on the box and see if you can easily select gears with the arm on the gearbox.
 
#5
Ian is correct, i remember when I had my rod gear-change made that where it passes through a rose joint, it needed to be made in solid bar as tube is never perfectly round.
Might be worth getting the car hot and removing the rear connection on the box and see if you can easily select gears with the arm on the gearbox.
Still having difficulties, it’s not a pleasant gearchage at all, the disconnected rod shift works fine hot or cold, it’s definitely something to do with heat, pushed the car out of the garage this morning cold, the shift worked reasonably fine with engine off, left the car in the sun most of the day, it was 32C, started engine to put car back in garage and couldn’t get 1st or reverse gear, the other gears were very difficult, the slave cylinder is pushing out 15-17mm,could it heat generated in the hot gearbox transferring to the clutch and not allowing it to release properly, I guess I’ll not know until gearbox is removed, such a faff, it’s never been 100% since it was installed.
 

Mike Pass

Gold Supporter
#6
Not clear as to what the issue actually is. A bit hard to figure out with the info so far. Is the movement of the shift mech getting stiff when hot or is it just not selecting the gears. Are some gears more difficult than others? Is the clutch not releasing fully? What clutch, master and slave cylinder do you have? Whose rod change mech do you have? Does it have the lockable rotating adjuster? A few pics of the gearchange mech at the gearbox end would help to see what the issues might be.
With a bit more info the actual problem may be more evident. You are not too far away if all else fails. I have been over once before with Martin Gough when you were doing the painting of his red 40 - which is now my car!

Cheers
Mike
 
#7
Not clear as to what the issue actually is. A bit hard to figure out with the info so far. Is the movement of the shift mech getting stiff when hot or is it just not selecting the gears. Are some gears more difficult than others? Is the clutch not releasing fully? What clutch, master and slave cylinder do you have? Whose rod change mech do you have? Does it have the lockable rotating adjuster? A few pics of the gearchange mech at the gearbox end would help to see what the issues might be.
With a bit more info the actual problem may be more evident. You are not too far away if all else fails. I have been over once before with Martin Gough when you were doing the painting of his red 40 - which is now my car!

Hi Mike, good to hear from you, I remember the painting and it’s nice you’ve got Martin’s car, I’ve tried to contact him a few times but no reply, if you remember a few years back yourself and Martin took my car to Mick at Southern GT and he fitted the rod change amongst other things, the latest box is a new Chris Cole Renault Quaif upgrade, clutch is AP and without digging into my file I can’t this minute give you the details, 3/4” Girling master cylinder, not sure about the slave but if I remember that is 3/4”, to be honest it’s done very little mileage since this box was installed a couple of years back, the car is relatively OK when it’s moving in the upper gears but traffic is a no no with queues behind me as I try to get first gear, it’s certainly worst with this box...any help would be appreciated.

Cheers
John
 

Mike Pass

Gold Supporter
#8
Hi John,
I will send you a PM with Martin’s contact info as he has moved house and changed his phone and email etc.. He still has the painting on the lounge wall and very good it looks too.
I have a similar AP clutch set up from Mick and I had a lot of trials before I got the correct amount of movement and pedal load on the clutch. I have the same 3/4” master cylinder but I found that I needed a Renault slave cylinder sleeved down to 22mm that I got on exchange from Chris Cole. I also used his uprated release bearing and carrier. To get enough movement and keep the pedal force as low as possible I had to keep the free play to minimum so I changed the slave cylinder push rod to a custom one by removing the original Renault item and replacing with one made from a bolt and using an HT bolt instead of the riveted in Renault push rod pivot.. I believe that Mick Sollis does an adjustable push rod to get the free play to a minimum. The trick I found was to have some free play at the release bearing but to keep this to a minimum to maximise the movement at the clutch. I still however need to to fully depress the clutch to get a full release and the pedal load is reasonable.
You may need to adjust the gear linkage as you have issues with reverse and first gears which are in the same plane. You may not be getting enough rotation of the gearchange rod when everything is hot. Some rod changes have a rotation adjuster for this purpose.

Cheers
Mike
 
#9
Mike, thanks for Martin’s contact details, if you don’t mind can you PM me yours, your set up seems similar to mine, the clearance at the slave is as tight as I dare on mine, my instincts ,for what they are worth, are it’s the gearbox that’s at fault because when I disconnect the linkage at the rear and try to select gears using the drop arm for leverage connected to the shaft at the rear of the box it is very difficult to get the gears, it wasn’t like that with my previous standard UN1 box, probably not a true test but nevertheless it does make me wonder, even when the box is cold and I can select all the gears although it is a bit ‘clunky’, all my previous manual cars worked opposite to the way this box works ie got easier when hot.

I no longer have the facilities at home to take the box out so I’m a bit stuck at the moment.
 

Mike Pass

Gold Supporter
#10
It might be useful to give Chris Cole a call on 01952 416051 to see if he can think what the issue might be if it is inside the gearbox.
I have sent PM with my contact info.
Cheers
Mike
 
#11
I’ll give him a call tomorrow and thanks for your contact details, I replied with mine, not sure how forum systems work so let me know if you didn’t get it.
 
#13
John, we had a similar issue with my brother’s UN1 is his Esprit S4.

It turned out to be the clutch arm wasn’t properly engaged with the t/o bearing. The UN1 had been out recently for resealing by a supposed specialist but somehow the clutch arm ended up not properly engaged. When the box got warmed up the car wouldn’t shift right.

We took the box out and it became apparent pretty quickly what the problem was so we just reinstalled with the clutch arm properly engaged and the car then shifted beautifully.

Of course the “specialist” shop denied doing anything wrong....
 
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