Confused about UN1 reverse set-up

[Danny]

I got a dismantled UN1 that seems to be a combination of a number of boxes. The crown is engraved with UN1-08 (Reno 25 V6t maybe) and there's also a UN1-21 alloy tag in my box of parts.

I've read everything about these boxes on this site and elsewhere, but my reverse gear arrangement is different. It looks like the idler is constantly driven and has it's own braking mechanism when beig engaged.

Can anybody shed any light on this as I'll being getting one of our local Albins gearsets made for it. Also undecided whether I have them do a conventional 1/2 syncro or their dog engagement. They can do either. The syncro change is not the fastest and can be fragile with missed shifts.

Thanks

 

[BruceA]

I believe some models had a form of syncromesh in reverse gear, and perhaps this is what it is. Im just trying to think of the model that had that .. just thinking it may have been the box that was installed in the Lotus V8's .. ??? hmmm hmmm
The -08 was indeed the V6 turbo box, but the -21 sure sounds like a Lotus number.

 

[Danny]

Thanks Bruce. I do have a new Esprit V8 crown and pinion for it.

When I get the new shaft made I would like to contine the same thickness for the fifth gear instead of it being necked down. Similar to the GTO and Bell configurations. I won't change the 5th syncro hub spine size though, unlike them. Being on the end of the shaft I don't think the shear loadings would break it. Certainly not with my motor (2.5tt).

Question: Do I need to have the sleeve for the 5th idler ground out to the new shaft thickness or can the gear itself be enlarged for a larger needle bearing?

 

[Dimi Terleckyj]

Danny

For what its worth I would not touch the gears with regard to machining out for larger bearings due to the problems you make for yourself if you break a gear and cannot just replace it with a standard gear without having it modified.

In the interest of reliability I have found that to run standard unmodified parts makes repair so much easier and cheaper than having to wait while specialty parts are made to order.

Dimi

 

[Danny]

Dimi thanks for that. It does make sense to keep things as simple as possible especially with difficult to obtain parts.

Here's a photo sample of what Albins can do. It's an "off the shelf" dog set in this case with a 3:1 first and 2:1 second. They have many of these parts already made due to the demand from the off-road racers.


You can see where the shaft is necked down on the LH side. That carries the sleeve for the 5th needle bearings . The sleeve would need to be ground if that part remained the same thickness. V8 Esprit's regularly break the shaft there. Typically coming off throttle and then powering back on.

Derek Bell designed his upgraded shaft around this weakness and grinds the sleeve to suit the shaft's new OD. They also remake the 5th syncro hub but I'd prefer to keep the original for the reasons you stated.

(PS How do I load my photos like everybody else?)

 

[BruceA]

Danny, I had my shaft made up to suit a few ideas I had along the way. You dont need to grind the bearing surfaces of the gears, they are big enough. What you do though is grind out the 'centre' of the shaft bearings, eg: the end thrust bearing and the front input shaft bearing. Take about 1mm out and you get an extra 2mm of shaft size. My shaft is now a minimum of 27 mm between the shaft bearings.

The 5th gear issue. I ground out the centre of the sleeve to suit the size of the shaft (27mm in this case - up from 15mm!) The idea of the necking down is to allow oil to flow to the 5th gear bearing. Durning production it was probably easier to slide the bearing on and not worry about anything else. I drilled the oil hole in the shaft, and it aligns with the hole in the sleeve. As the sleeve does not rotate, you dont have to worry about any hardening in the centre that will be removed from machining. You just have to make sure the shaft and sleeve oil holes are lined up when you assemble the shaft.

As for the 5th gear spline, mine is larger - same size as the shaft. This has no necking down, as it were. I had the centre of the 5th gear syncro hub spark eroded to the new size. You will also need to have a new nut made for the back of the shaft too - oh and bore out the large washer.

The issues you probably know about of teeth stripping on the 5th gear, well. Im going to have new gears made up that are 4mm wider. The gear will go from 18mm to 22mm, so hopefully this will give a bit of added strength. You will have to machine the 4mm or so from the shift hub, but I dont think this will affect it in any way.

Ive included a few photos of my shaft and what I had made up to suit.

 

[Stephane Goria]

Danny,

The UN1-08 gearbox went modified in 1988 (if I remember well) to handle a syncromesh reverse gear.

This is a good option that you would better keep. Also the primeshaft is a little bit more resistant to flexion because of the longer splines (reverse) on the primeshaft

So I would recommend to keep your config as it is.

UN1-08 is a 9x35 diff.

UN1-21 is the gearbox mounted on the Espace V6, it is a 9x35 with unfortunately a 0.82 5th ratio. Maybe not the best choice for speed but a good choice for autocross , even if a UN5, in this last case, would obviously be the best choice for autocross.

To add strength to the 5th gear, there are some kits available. One of them is the one on pics. Basically a plate to handle modified bearing and bringing less flexion capacities on the 5th gear shaft.

Sorry only 2 plates from the kits on my desk at the moment for a pic, but this would allow you to understand how it works.

Cheers

Stephane

 

[Danny]

Bruce, Stephane thanks for your advice. You've both given me a lot of new interesting stuff about these boxes.

Bruce that shaft looks very strong. What engine and car weight was it built for?

I'm thinking with my plans, 2.5tt currently 206kw but potentially capable of 300+, in a 1300kgs car I may be ok with Albins standard gearkits. Or perhaps just them to increase the 5th gear end of the shaft.

The bell housing I'll be using also has a bearing so the spigot shaft has a central support. In all there'll be four instead of three bearings for the mainshaft. Should help check any bending/vibrations/breakage of the spigot shaft.

I do like Stephane's rear plate. Did you make that yourself? Looks easy enough. And thanks for the advice on the reverse, I'll keep it now. It does look like it is always spinning but without any load if unengaged.

As for the .82 OD I shall stay with that since the engine can rev to a little over 7k and tyres will be around 245x45x17 or so. The diff will be 3.88.

Thanks for all the advice, this site is the best.

 

[Stephane Goria]

Hello Danny,

I was obviously kidding you with the 9x35 ratio. Comparing to 9x31, obviously 9x35 would be the best choice for street and hill climbs racing. 9x31 would be perfect for Lemans/Spa racing.

Yes the plate is a design of our own and is part of the set of improvments we engineered for our little team of rallye cars nothing of importance just sunday drivers doing some amateur racing. This setting fairly raise the resistance to flexion of the 5th gear shaft part. The main difficulty was to find a new combinations of bearings and unfortunately we had finally to have them purpose made to our specs.

In January, we have 2 UN1 gearboxes to rebuild for the winter season and if you are interested in the understanding I'll post pics of the whole set. At the moment, sets we had are already mounted and I just have some plates remaining because of the batch we machined , so no way to take pics...:thumbsdown:

I know this kind of ehancement is available from SADEV for the R5 GT and I guess they should have the same setup for UN gearboxes.

As you are rebuilding your gearbox, I recommend you to accurately check the clearance of your locking rings (3/4 and 5th), as they often look good but they are in reality not good to be reused in performance gearboxes.

Cheers

Stephane

 

[Danny]

Stephane yes I am interested in seeing photos of your rebuild when you do it.

Do you mean checking the brass syncros or the steel locking ring that slides over the lot? I usually check the brass rings for both sharpness of their serrations and how close they are to bottoming out on their corresponding gear.

Other than for a visual inspection of the steel locking slides I'm not aware of anything I should measure.

That strengthening plate of yours I take it doesn't work without different bearings, correct?

Cheers
Danny

 

[Stephane Goria]

Correct Danny,

I was talking about the brass locking ring. Even if Renault does not indicate any settings, my experience is to discard any locking ring under 1.40-1.50 mm when measuring from bottom on the conic gear.

The sliding hub has no specific measurements on it. Just the normal controls.

Our plate is made for special and specific bearings, we were unable to find the sets we needed in the existing refs on the manufacturers, unfortunately.

Ok, I will PM you to send you pics of the performance rebuild as soon as boxes are ready.

Cheers

Stephane

 

[PhillipM]

Stephane, do you do any work on the UN5 gearboxes that the Rallyes TT lads use for off-roading?
I'm trying to source a dog engagment setup, some sturdier bearings and a limited slip differential for ours, but getting nowhere at the moment.

 

[Stephane Goria]

Hello Philip,

I don't do any job on UN5 as we race with 9x35 & 9x31 final ratios. UN5 is a very good gearbox and even in its raw version includes some tricks, I'd like to see in basic UN1 as for example the input shaft with bearings to keep it perfectly straight, wich is more than a good idea...

Neverthless, and without any connections with them, I would recommend you to contact SADEV : Sadev - Conception de boîtes de vitesse - Gearbox conception. This company produces many ehancements for rallye & TT gearboxes

I know they have items for the UN5 as it is more than often used in TT cars.

Even if they are french, they are polite :thumbsup: and they speak english, so a quick email should have a quick and accurate answer.

Cheers

Stephane

 

[Danny]

Phillip

I'd also recommend Albins here in Australia. ttp://www.albinsgear.com.au/

They have been making shafts, gears, c/w and pinions for 20 years or more. Mainly for the off-road racing fraternity.

They can make up any combination and ratios you'd like. It's even possible for them to make a 5 speed c/r instead of 4+OD. Something with 5th being .96 and whatever you'd like for 1st through to 4th. Use this with a diff ratio that suits your usage.

The idea of a 5speed c/r gearset mated to the 3.44 diff appeals. Generally around $1k for the mainshaft and $500 a gear. If a dog change is selected they quoted me about $600 per hub and slider which serves a pair of gears which is only a little more than what the 1st and 2nd syncros will cost me. It was around $2.5k for their c/w pinions. (Those are aus dollars.)

They make dog gears like my earlier photo or a combination of dog and syncro which is something I'm considering.

They also have a kit to stabilize case distortion. Distortion can be a problem with the off-road racers here. It probably isn't necessary unless your vehicle is constantly leaping into the air and landing with lots of force for a few hours.

I found their engineer Steve Nicholson very helpful and willing to design new gears etc. He recently oversaw their first one piece shaft similar to the other heavy duty kits out there.

Here's another photo with some of what they can make, except for the second shaft down which is mine.

Cheers

 

[PhillipM]

Yes, we buy a fair few sequential gearboxes from Sadev, they do do parts, but it's for a budget car, so the gearbox would end up being half the car's value!

 

[PhillipM]

They also have a kit to stabilize case distortion. Distortion can be a problem with the off-road racers here. It probably isn't necessary unless your vehicle is constantly leaping into the air and landing with lots of force for a few hours.

That's exactly what we are doing, it's an off-road rally/safari vehicle, we've got phosphor bronze pads behind the crownwheel to stop the flex stripping the teeth off, and the case is strapped with shrink-fit steel banding to keep it from twisting.
$2.5K isn't too bad though, I'll have to get in touch and see what price a differential would add to it if they do one then.

 

[Danny]

I think you've got the same anti-distortion set-up as theirs.

Normally what ratios do you run and what size tyres and rev range?

 

[PhillipM]

We're on standard ratio's at the minute, using 255/70 R16's, 10krpm limiter.

1st gear is useless, 2nd's still a touch short really, but 3rd-5th could do with being a touch closer.

 

[Danny]

Would Albins 2.77 1st and something around 1.8 2nd work for you? Steve did tell me that once 1st gets to 2.77 or higher it can only be made with a dog change because the Reno syncros are too big to fit. Being able to do lightning changes in those two gears and then the usual syncros for 3-5th is a feature that intrigues me.

Only thing he told me from their experience, is that some drivers manage the dog change ok while others may ruin the slider and cog one or two times before they get the hang of it. Usually second "rounds off" requiring another slider and 2nd cog rebuild. Not too hard with these boxes though.

 

[PhillipM]

Nah, that won't worry us, we normal use sequentials in the other cars anyway.
To be honest, for what we do, if we could get 2nd a touch higher and bring the rest cloer together, we could do without 1st anyway, the car only weighs 700kg, so it doesn't struggle for bottom end even setting off in 2nd, it's got 80% of peak torque right from 3krpm to 9krpm, so the power band is fairly wide.