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Dog box manufacturing

Posted: Thu Mar 16, 2017 4:19 am
by german4inline
I´m thinking about machining the internals ( input shaft, gears, dogs, hubs…) of a dog engagement for my classis Renault Alpine. Unfortunately, most of you US guys are familiar with automatic trannies and not that with dog gearboxes. Probably there are some European guys with small engines which are interested in.
Most of you would probably recommend to source a dog gearbox from a supplier, but there are almost none. Some french guys are doing them, but the quality is unknown and they are relatively far away (1000 km is a lot for Germans ) so that I couldn´t visit them to check out the quality. Furthermore, my French knowledge is very limited.
Mostly the gearboxes which are offered are tinkered together with (weak?) components of the stock box, sometimes the gearwheels are turned off to keep the sychromesh toothing and shrinking a new gearwheel on the old bushing if the sychromesh style should be kept. Dog boxes are always straight cut and no one is accepting my requirements to make helical cut for less noise. The ratios are mostly unsuitable. Most customers maybe satisfied with those solutions maybe for lack of technical knowledge…..
When I digged in the internet I found Pfitzner performance gearboxes from Australia. They are producing maybe the best gearboxes worldwide or at least some of the best. There´s a where Pfitzner shows how easy his dog gearboxes are to change the gears even on public roads, when cruising with his Mitsubishi and he tells honestly that his gearboxes are suitable for daily use. According to common understanding, dog boxes are usually not recommended for daily use due to their harsh shifting behavior. I´ve had some contacts to Pfitzner but they have no suitable gearset for my requirements, but the contact was very gentle with some proposals, but rather no solution for my exotic car finally.
Pfitzner has a really clever design of his dog shape, very close to a “pentroof” design with nice and smooth rounded dog edges, not as sharp as others are. If an engagement is missed because to dogs are hitting together, the dog shape deflects them from each other and avoids a damaging of the dogs. In real life, the shifting seems to be alike synchromesh engagement unless really small clunking noise when the dogs are engaging. Furthermore, they also are offering helical gears, not just straight cut gears which are whining like a gas turbine.
Now I´m thinking about designing an own layout, it´s not that difficult. There are some companies in East Europe which are able to machine the parts for affordable costs, they have machines on west European standards.
Now I would like to find guys which are familiar with dog boxes, maybe ones which are rebuilding their own from Hewland, Quaife, Pfitzner, Sadev, a.s.o. and we can discuss about the pros and cons of the different designs. If someone is even as irradiated as me and is going to make an own gearbox, any help / thoughts / opinions / advices and pictures are kindly welcome !

Re: Dog box manufacturing

Posted: Thu Mar 16, 2017 1:50 pm
by mekilljoydammit
All right, an ambitious project you've started. I'll bite because I've been thinking on it too. And yes a lot of the traffic on this forum is drag stuff with its prevalence of automatics and the like... but not all.

First off, I'm not completely familiar... is this the A310 using the same UN1 transaxle that Lotus used?

Secondly, what are your goals - what power level are you at, what is the car being used for, and so on. What are you looking for in terms of gear ratios?

Thirdly, what are your capabilities? If having a reliable transmission design made were as easy as you make it sound, the price point would be a lot lower. Are you passionate about making a gearbox, or just about having one that works?

Part of the problem with dog engagement gearboxes is that everything is under impact loading. The reason dogboxes can shift faster is because unlike the involute splines that engage synchronized gearbox shift hubs with the gears, there's a lot of gap between the shift hub and the dogs - so a lot better chance of it finding a place to go when shifting. But because of that and the lack of the synchronizer ring to get everything up to speed gradually, there's an impact load between the shift hub and dogs every shift. How much depends on things - how well you match revs, how fast you shift, and so on. This is not just a matter of feeling unpleasant, it means that the dogs on the gear or shift hub will wear out or crack over time. The pent roof shape dogs helps the issue of getting into gear but not the impact loading issue. How fast depends on a lot of things, as I said.

Now, people do drive dog boxes on the street anyway, but the people who are willing to do things like that are often the same sort of people who are willing to put up with straight cut gears.

So, consider if you are willing to put up with the internals of your transmission now being something that will periodically require maintenance and possibly part replacement. This will be true even for a professionally designed gearbox from a top manufacturer (XTrac, Emco, Hewland, Ricardo, Sadev and a few others... I wouldn't put Pfitzer in the top 5, incidentally, though they do make useful gear kits that fit in a lot of OEM transmissions)

Personally, I'd start off by figuring out if there's something that will fit your requirements off the shelf. Hewland, Sadev, and Elite Racing Transmissions have a range of lower cost transaxles (by which I mean thousands of dollars, not tens of thousands) that cover a wide range of power outputs, some of which are of roughly similar shape to the UN1. This will get you something proven, with available spare parts. You could also find a similar shaped production transaxle with a better availability of gear kits - Porsche or Audi transaxles, for example. Failing that, I'd try to design something that uses the stock transmission casing but with some commercially available racing gears that will fit onto custom designed shafts. This depends on the shaft center to center of the transaxle though, but means that when you wear out shift hubs and gear dogs you won't have to have more manufactured.

I would not go have gears made - I can practically guarantee that the price for a single set plus a few spares is going to be more than the entirety of a proven transmission. I wouldn't try modifying OEM gears either, as to me anyway, going with better gear ratios is more important than the method of engagement. If one was to do either of those things, I would use a design similar to how the Jerico and G-Force dog box transmissions work, where the shift dogs are splined to the gear rather than machined integral with the gear - this lets you not have to throw away the gear itself when the shift dogs wear out.

I would not design my own gearbox casing given reasonable alternatives, but if I did, I would design it to accept some commercially available racing gears. I would do that before I had someone machine custom gears. Remember, because of the shock loading, the dogs on the gears and the shift hubs will wear out! I would not want to have to deal with sitting on a large pile of spare parts, or waiting for the original manufacturer to have time to make more, or hoping some other manufacturer can do things perfectly compatible with the originals.

Re: Dog box manufacturing

Posted: Sat Mar 18, 2017 4:56 pm
by german4inline
First thank for your big statement – lot of questions…here we go:
My car is a A 110, not a A 310. The car is more fragile looking, much lighter and has a 4 inline engine from Renault 5 Alpine. Basically 1,4 L / 93 hp, my engine is in progress , bored/stroked to almost 1,8 L, estimated 200 hp with all steal internals, big head /valves , ITBs and all the stuff as you know supposedly.
My gearbox ist the 330 4 speed, can be converted to 353/ 5 speed, but the stock ratios are too short and the steps are poor, as well the gears and the diff too weak. In Germany/France usually this typ of boxes will be upgraded with the internals of the NG5-gearbox from R5Alpine. The gears and diff is much stronger, but the ratios are even worse as the stock box. The ratios are 3,81/ 2,17/1,41/1,03/0,86, final drive 3,77. My layout is 2,63 / 1,68 / 1,28 and 3+4 can accepted with 1,03 /0,86. Of course, I need only the internals such as in/output shaft, gearwheels, hubs, dog rings etc., I can use the stock gear housing and maybe the forks and selectors, maybe that they have to be replaced to stronger ones. Further, I would
keep the main shaft with the pinion and crown wheel which is strong enough.
My engine with a spec.output of 113 hp/L will pull strong just over 4000 rpm, and I need close ratios and a long first gear what I can use as a really drive gear. I intend to use my car mainly as a trackdays / slalom car, just for pleasure, no daily driver. But I don´t do any serious competitions. For me it´s also important to be able to go on a German Autobahn ( freeway) with 100 miles without getting mad due to excessive rpms. The target is 3000 rpm and 100 km/h (62 mph) in 5. gear. Currently, in 4. ( last) gear the stock gear of my car makes 70 km/h with 3000 rpm, you are going to go crazy when cruising.
Due to the relationship between car layout and power, it´s impossible to make max speed with this car and 200 hp, because it would be theoretically be appr. 280 km/h ( 175 mph). With this speed, the car would take off like a plane. The power can only used for accelerating, max. speed maybe 220 with really big balls.
Your 3. question:
I´m an engineer, but no designer. My profession is engine development, and I was in the past involved in German DTM and later as well in even much higher revving engines with 10 cyl. ;-)
I`m no gearbox specialist, but due to my experiences I trust myself to make a working layout. I know how dog boxes are working. I have some possibilities to machine parts, but not good enough to produce those internals for a dog box. To make this professionell, you need CAD/CAM design tools and a CNC turning machine, CNC milling and compagnies with special toothing machines. A friend of mine who is designer did my constructions together with me , unfortunatly he´s got seriously sick some weeks ago and I don´t know if he gets ok again at all.
Basically, it´s absolutly necessary to source a compagny which is prepared and interested to make the parts. I`ve had some contacts here in Germany and I first intended to pre-turn all shafts and wheels by myself and let the toothing procedures and the case hardening make by order of the particular shop, but in Germany, we have very high labor costs and the charge just for all toothing work and grinding would be around 4000 €, and yet I would have to bring the turning parts too.
So I have looked around and I found a shop in east Europe where the labor costs are just a fracture of the germans and the quality is top level, some german race shops let their work do there. I had some contacts to them via Email and they invited me to talk about my plans, but as told, I have no drawings or CAD models currently available.
Your concerns about the load of the dogs are not as critical as you are worried about. Every motorbike has a dog box and they are working some 10000 km without troubles. Of course I admit that the loads of a bike are notably lower due to smaller torque and less weight oft he vehicle. But the loads on the dogs doesn´t cause breaking out of the dogs if the are dimensionally correct designed and hardened. The bigger risk is inappropriate gearchanges by people without dog box practice. Then the edges oft he dogs are crumbling, especially if they are poor designed and hardened. If you do firm, quick gearchanges, a dogbox can live many years.
Your intension with the splined dog toothing at the gearwheels was as well my consideration to avoid the changing oft he gearwheel itself if the toothing is worn. But honestly: The manufacturing of such an assembling with gearwheel and toothing, add spline tooting on the gearwheel itself, add inner spline toothing on the shift dog, add flat grinding of the gearwheel and the shift dog… summary you have much more effort and costs as to change just the integral gearwheel. Furthermore, you can save space to make the gearwheel wider – and definitly less costs. The toothing of a gearwheel is very expensive if you make one unique part – if you make more, they are almost free. My toothing specialist adviced me to find some other guys to make 3 or 4 part sets, they would be a fracture of costs. If one gearwheel is 350 €, I would get another 5 ones for 30 € each !!! So you can make the spare parts straightaway together with the inital order. The big costs are set-up costs.
To use inner parts of another gearbox mostly fails due tot he different shaft distance. On my gearbox is it 70 mm. You proposed as well to use approved parts of reputed suppliers such as Quaife, Sadev, X-Trac a.s.o. None of them have suitable parts for me, and if they would fit, they even are offering only straight cut gears which are noisy for public traffic what I wouldn´t accept at all.

Re: Dog box manufacturing

Posted: Sat Mar 18, 2017 5:04 pm
by german4inline
I forgot:
My car has a swing rear axle ( yes really), which is mechanicly coupled to the gearbox. There´s a pivot housing involved where the axle halves are swinging around. Thats the reason why I can´t use a simple transaxle gearbox of hewland or others to match on my car. I also wouldn´t swap my rear axle to a double wishbone o.s. to overcome this problem, hence I had to knock down the whole car.

Re: Dog box manufacturing

Posted: Sat Mar 18, 2017 11:03 pm
by mekilljoydammit
Ohh, the A110, those I have seen before over here. Beautiful little things.

I hope you'll excuse the questions - I've heard a lot of people bring up a lot of ambitious ideas without having any idea what they were getting into. Sounds like with your background you have a pretty good idea; I apologize if I caused offense there. I'm an engineer too, also in the profession of engine development, though for small generators and things like that, nothing as interesting as you've been involved with. I'm working on setting up my own ambitious projects on my free time. ;)

The difference between wear on motorbike dogs vs racing cars might be down to the greater inertia of everything in the driveline of cars and not just the greater torque. But as you point out, you're not intending on using it every day. There are a lot of variables in dog wear - some drivers just seem harder on equipment than others, and with limited use it's certainly possible to get some years of life out of shift dogs.

70mm is annoying - I tend to think in terms of Hewland gears because they're commonly available, but the Mk5/9 and LD200 gears are about 65mm center to center, and the FT gears are about 75mm. I do wonder if you could the pivot housing you mention to a Hewland, but that doesn't solve the issue with the straight cut gears that you want to avoid.

I race Mazda RX-7s in the United States - I have some friends who modified the stock transmission to accept Hewland gears with some success, and I have a 1980s vintage dog box conversion with custom gears that is long out of production, and I am currently trying to figure out what to do after I use up my stock of spare parts, which is part of why I'm being cautious about the idea of going with too many custom components. I have some thoughts of making a front engine RWD transmission based off Hewland FT components, but I have more important things to work on first.

Re: Dog box manufacturing

Posted: Sun Mar 19, 2017 5:06 pm
by german4inline
No bother, your questioning about my background is completly ok, might be indeed I`m a dreamer without any experience.
I´m not even consequently focused on a dog engagement. If I would find a shop what realises parts for a synchro engagement, I would agree immediately. But the manufacturing of well working snchro internals might be more critical as dog ones. With a close ratio layout, even a synchro box will be provide a very quick gearchange due to the low rev differences which have to be matched to each other.
You might oppose that I could use the stock sliders / hubs ( of the sliders) , sychro rings etc., that would make sense. The problem with my gearbox is that to realise my required 1.+2. ratio, the gearwheel dia of the 1.+2. gear of the main shaft has to decrease significantly ( whilst the diameters on the input shaft increases). Stupidly, the diameter of the stock synchro ring is very big and needs the dia of the stock gearwheels. That is the reason why no gearbox builder to my knowledge offers a longer 1+2. gear – not enough space for stock synchro rings and the whole synchro assembly.
I know an hungarian guy who is very busy with gearboxes since about 2 years and I know him personally ( he has nothing to do with the compagny what I contacted as I told). I talked to him about my plans and my required ratios and made a calculation with useful ratios , geartooth numbers and moduls what he grasped willingly. Then I didn´t heard about him any more. Half a year later, funny, I found „my“ gearbox on a well-known auction portal with exactly the ratios I provided him. He realised them by using a completely different synchro arrangement from another Renault gearbox which is smaller in dia and it looks nice on the pics. This solution was his own idea, very good – if it´s working…
Unfourtunatly, this guys refuses to tell me other customers which did experience his boxes already and I know some other simple conversions of him which he sold a friend of mine. On these boxes there were some irregulations in quality what limits my confidention. If I would know that the synchro box is working, I would it order already today. It´s very difficult to get a commitment with him, his german is limited and my hungarian and his english not existent…..
If I would go on with a own synchro gearbox, I should source a comparable box from what I could use the synchro arrangement with sliders, rings and hubs to use them or at least as a sample to copy the dimensiones to make new matched parts. Making these parts all new, I´m worried I´m not related to Mr. Gates….

Re: Dog box manufacturing

Posted: Mon Mar 20, 2017 10:22 am
by mekilljoydammit
Ha, I timed my post perfectly with the server backup. Oh well, redoing from memory.

I have seen examples where the engagement splines for a synchronized gearbox are larger diameter than the gears and it worked without problem, but I see your point about not wanting to have to remake everything from scratch.

I think the Hewland Mk-series sliders might be about right - versions of that gearbox are sold with up to 240hp, but Hewland stuff mostly has the ring and pinion being the weak point. I think they deliberately make the slider rings softer than the gears as well, so that they wear out first, and it would probably save you trouble to have that commercially available. I have some sitting around in my shop that I could use to make some rough drawings so you can see if they would work, as you obviously know the dimensions of everything in the Alpine gearbox better than I do. I could also measure some Mazda MX-5 parts to see those might be helpful to you.

Re: Dog box manufacturing

Posted: Mon Mar 20, 2017 2:00 pm
by german4inline
The problem of the synchro ring is not just the diameter. The friction face of the synchro ring is on the outside, not inside - sorry, I didn´t mention that. And the opposite face for the synchro is inside of the 1. and 2. gearwheel, it´s inside turned out . So I would need the friction face inside the gearwheel as Long as I wouldn´t change the design, an thats definitly not possible with longer gears.

Sounds perfect that you could forward me some drawings of Hewland and as well Mazda MX5. I know the Mazda has a brilliant gearbox, easy to change the gears. Probably I could transfer some assemblies to mine.....How is the Mazda synchro designed? Usual layout?

Another information what I would be interested in would be the shaft centerline distance of several gearboxes, but it´s very difficult to get them. Most people doesn´t even know what is meant.....On the Renault gearbox, it´s 70 mm. I´m curious what you can show me...

Re: Dog box manufacturing

Posted: Mon Mar 20, 2017 2:11 pm
by mekilljoydammit
Not exactly sure what you mean by "the usual layout" - the Mazda has a male cone on the gear as the friction face that the brass synchronizer ring mates to, and the hub that is fixed to the output shaft overlaps both.

I have a couple gearboxes sitting around I can measure shaft centerlines on, and yes it's very hard to find that information... something like 3 different Mazda designs, Hewland Mk-series, and VW Rabbit of some vintage.

Re: Dog box manufacturing

Posted: Mon Mar 20, 2017 3:41 pm
by BigBlocksOnTop2
Check out Zero Shift.

Re: Dog box manufacturing

Posted: Tue Mar 21, 2017 6:54 am
by german4inline
Yes, what you describe is that what I mean with "usual layout". It´s like the old Ford / Opel a.s.o., hat is working fine without being advanced.
Mazda + Hewland would be interesting, I´m curious to see.....

Thanks a lot =D>

@BigBlocksOntop2: What is Zero shift?

Re: Dog box manufacturing

Posted: Tue Mar 21, 2017 3:39 pm
by BigBlocksOnTop2
Google Zero Shift. They are in England. Some what new technology in clutchless wide open throttle shifting.

Re: Dog box manufacturing

Posted: Tue Mar 21, 2017 4:58 pm
by mekilljoydammit
The Zeroshift ideas are not something to pursue if you want to keep the number of custom manufactured parts down.

Re: Dog box manufacturing

Posted: Wed Mar 22, 2017 7:37 am
by german4inline
I didn´t know Zero shift at all and had a look to the side. It´s fascinating, although I don´t understand the last detail. I´m not yet sure if you could make gearshifting without any electronic support just by mechanic movements to suit the travel of both forks in the right way. If I would make all dog parts from scratch on new by myself, the more expense compared to a common dog style would be worth the effort at least if i would enjoy the function of this system. No backlash, smooth shifting sounds perfect. But supposedly, the devil is in the details....probably not enough space within the gearcase for the forks and selector shafts. Looking forward to your Miata measurements :wink:

Re: Dog box manufacturing

Posted: Wed Mar 22, 2017 11:36 am
by mekilljoydammit
Yep, sorry some stuff came up, should be able to get measurements posted Friday at least in terms of "photo with dimensioned lines", and possibly some drawings.

I know I'm still posting on here, but I can't go dig through the home shop while I'm running tests at work. ;)