Help: un1 gear changes

[stuart]

hi all.
i have a renault un1 gearbox mated to a ford cosworth engine 2l turbo its mid mounted and gear changes via 2 cables.
the box is in the car and works fine,
it is easy to change gear slowly but when i try to do it quickly it never engages the gear properly resulting in grinding and staying in neutral.

i have the box apart at the mo and cant find anything wrong with it.
what i have noticed is its very hard to change gear easily or smoothly by hand.
i have found that the springs that push the metal ball bearings into the selector forks/rods, are very strong.
i thought that as this box was designed to have a metal rod connected directly to it then the strong springs would be fine, but as im using cables that are 8' long, and have a shorter throw, this could be causing me problems.

so im going to change the springs to ones that are the same length but softer, making it easier for the ball bearing to move out of its notches.

has any1 else done this?
or any 1 else had trouble changing gear quickly with a cable setup? how did you fix it??

thanks
stu

 

[Erik]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

Stu, while I do not have any personal experience with the UN1 gearbox I would advice caution in changing out the internals with something that was not designed for it. You may find that will do the trick, but then again, it may cause other unforeseen issues. It sounds to me like you might have a couple of issues going on here. It sounds to me like you may simply have some issues with the synchronizers in the gearbox being a bit worn. While they may still look good, they may indeed need replacement. This would explain why you do not have an issue with slower shifting, but do when you try to power through the shift gates. When you try to shift a gearbox quickly you ask the synchronizers to work much harder, as such when they wear, they become unable to meet the demand, and you get a gearing grind.

I would recommend doing a comprehensive rebuild of the gearbox and check your linkage to ensure that you do not have any slop in there. If this does not rectify the issue, then perhaps look at re-engineering it. Just my .01 1/2 cents on this though, and I wish you the best of luck with your project.

Erik Johnson
GBox Performance Transaxles
(303) 440-8899 work
(303) 895-4828 cell

 

[Stephane Goria]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

Hello,

The box is dismantled.

It happens on every gear? Check the dog teeth and hubs.

Cheers

Stzephane

 

[stuart]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

thanks guys,
i know its not a problem with the linkage, thats all tight and working well.

the box is in pieces at the moment and i am going to a gearbox specialist in the morning for them to look at the synchros.
i dont know what is worn out/every day wear and tear.
the baulk rings do have some wear on them to, but again i dont know how much is too much.

i was also advised that changing the cetent springs to softer ones could cause it to jump out of gear if they are not held in tight enough, so i will leave them alone.

i will let you know how i get on with the gearbox shop tomorow.


he also told me that vaxhaul/gm have a little trick for helping with shifts, by adding a weight onto the swing arm.
i might make a bolt on weight to try help, it will give the change more momentum.


also is there any way of telling exactly what gearbox i have? i know its a un1 but dunno exactly wich 1.
theres no tag on the outside.
inside its got a mechanical speedo drive, yellow plastic.
with a 7500rev limit, 245 40 17 tyres, it runs 44mph in 1st and 77in 2nd.
any1 know what exact box it is? so i know i order the correct synchro if needed.

 

[Stephane Goria]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

To know wich UN1 it is :

How many teeth on crown diff?

Mechanical speedo or sensor on the gearbox?

How many teeth to the 4th gear pinion?

How many teeth to the 5th gear pinion?

Cheers

 

[stuart]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

thank you,
i will count them tonight.

 

[Simon]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

Stuart,

I'm sure that a query Chris Cole could help you with.

Simon

 

[Frank Catt]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

The problem is most likely not in the box at all, check your hydraulic clutch operation for clearances first. Frank

 

[stuart]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

I have spoken to quite a few people about this, and every1 has different opinions.
I was told it's just a slow changing box I have to live with,
synchros,
wrong oil
bad gear linkage
dodgy clutch.

The oil used is silkolene pro race.
Gear linkage is fine, all adjusted up with plenty of reach.
Clutch hydraulics are Renault 21 slave and girling 0.75 master, both new and pressure bled, clutch parts ap cover and 6 paddle centre plates

so I'm lookin at a gearbox problem. I will get the synchros checked by the gearbox specialist today and go from there but don't know what else it could be?

 

[Frank Catt]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

Stuart, you will probably need to sleeve the slave down to 22mm from the standard 28mm, or upsize the master cylinder to 7/8 or 15/16 in bore.

 

[stuart]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

5th gear has 33 teeth
4th has 35 teeth
I will count the diff tonight, I don't have it with me.

 

[stuart]

Re: help with un1 gear changes. hard to do at speed but easy at slow speed changes.

I need to change the master so will fit the biggest I can get.
How do I sleeve the slave down?

 

[stuart]

Will this master be ok?
Girling 0.813 or 13/16
a .75 is 12/16 so not a lot different but it's the biggest I can find?

Any1 know where I can get bigger?

Professional Motorsport Parts, Spares & Rally Equipment from Rally Design

 

[Frank Catt]

Tilton do MC to 1.125in, should try 15/16 if can, but will make pedal effort heavier.

 

[stuart]

Just found a 5/8 but it's not a direct replacement so will have to see if it fits my pedal box

MASTER CYLINDER KIT 1 MAK1

will look for the tilton one.

 

[stuart]

Right I have
35 teeth on the diff
35 on 4th
and 33 on 5th gear.
Does any1 know what box this is?


Also I went to the gearbox place tonight and they said the synchros were worn but it's nit excessive and not to change them, but the springs under the synchros felt very soft, so I have ordered new ones from Renault, £3 each so a bargin.

Then hope that a bigger master cylinder and a tweak on the cables will sort it?

 

[stuart]

little update,

i have rebuilt the box with new stronger synchro springs, grinded the detent springs down a little,
moved a bracket the holds the gear cable inplace a bit better
grinded the clutch fork for more clearance on the bellhousing
new longer rod that goes between the slave and fork

once its all back together i will try it with the current clutch master cylinder but if i still have issues i am going to up it to the next size.

will let you know how i get on

 

[Erik]

So what happened with this? Were you able to get it to work correctly?

Erik Johnson

 

[stuart]

i got it back together and with the detent spings a bit shorter it is a lot easier to get in gear,
as in you have to use less force on the gearstick to get it into the gear.
this is especially noticable when changing into 5th,
i didnt change the detent spring for 5th gear, and it requires a lot more force to get it into 5th over the other 4 gears.

clutch wise, im still waiting for my slave cylinder to be returned,
i sent it to wealdon engineering to be sleeved.

once its back on the car i will update how its all going.

 

[stuart]

right, update.
it been a while but ive had other bits to sort out, and had to wait a long time for the slave to come back.

now its all fitted and...
its no better.
the pedal is heavier, and it looks like the fork is moving further, but it is still really bad from 1st-2nd and not great from 2nd-3rd and 3rd-2nd

im still using a 0.75 master with the sleeved down slave thats 22mm.
is this ok or do i need to up the size of the master?
is there anything else i can do to improve the change????

it is really pisses me off when trying to go fast and having such bad gear changes i have to watch every1 pull away from me, even tho i know i would be infront if the gear change was working properly.


any ideas?