Strongest Gearbox Possible

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Neil Jones
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Strongest Gearbox Possible

Postby Neil Jones » Wed Jan 21, 2009 2:25 pm

I'd like to put together a gearbox capable of handling 350 to 400hp that doesn't have to be treated like a baby. My application is street only. A few questions:

1. Is this possible?

2. Am I better off creating a 4 speed than a 5 speed?

3. Is the 4-speed Chillcast box 870423 still the strongest case available and are the best one's still only found in ’77-’79?

4. Can I adapt an 89-'90 box larger rear pinion bearing and stronger shift forks to an early 4-speed Chillcast box 870423?

5. Can I adapt the slimmed down profile of the 91-93 synchros and enlarged gear faces to an early 4-speed Chillcast box 870423? The pinion bearing and layshaft bearings were also enlarged on the 91-93 can the early 4-speed Chillcast box 870423 be modified to handle them?

6. Is the Saab Rally Rear steel diff cover the best available?

7. Is Jorgen Eriksson still in business? How do you get a hold of him? Does anyone have experience with his: Special selector rod, Steel selector fingers, Special selector 3/4th, Strengthened Primary Chains, Universal Joint on selector shaft, Special 4 chain primary gears with new chains?

8. Has anyone done this type of modification I mentinon in #7 above?

9. Adding a 4th row of gears and chain to the primaries and modifying them to accommodate an extra bearing on the upper primary as per the Works gearboxes?

10. Are 4 speed dog gears (38570Kr) still available? From who?

Any other recomendations or info greatly appreciated especially from those with actual hands on experience on making a Saab 900 gearbox last with this kind of horsepower.

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max
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Re: Strongest Gearbox Possible

Postby max » Wed Jan 21, 2009 5:29 pm

::Prepares for a long thread::

I dunno, what do you think guys, 10+ pages? :lol:
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Re: Strongest Gearbox Possible

Postby Crazyswede » Wed Jan 21, 2009 6:37 pm

could easily be 10 pages....in fact I think we already had a similar thread that went somewhere in the 10 page range.


350 - 400 hp in any abused gearbox is a big demand. Don't expect this miracle gearbox to be readily build able from off the shelf parts or particularly cheap. See if you can find on of the ultra rare saab 4 speeds with the factory rally diff, ring and pinion, gear set, 4 chain primary, reinforced case, diff cover, and custom inner drivers...Expect to pay someone $10,000 to part with it maybe more.

hard shifts and violent acceleration will try to force your gear shafts apart....case flex, chipped teeth, premature bearing failure, overheated oil are all things to worry about. Might as well get rid of the synchros and build a dog box. To give you an idea we looked into building a custom 4 speed gear set a year or two ago. The tooling alone was going to be about $8000....this was for a helical gear which is quieter and has more tooth contact area then a straight cut gear.

Most of us just learn to deal with the strongest stock box we can put together, run good oil, maybe an oil cooler and one piece inner drivers combined with steel covers and then modulate the throttle as required...or get real good at rebuilding. The latter option will help boost the economy.

Good luck, keep us posted and take lots of photos. :salute:
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Re: Strongest Gearbox Possible

Postby Neil Jones » Wed Jan 21, 2009 6:44 pm

Would you say that case flex is the biggest problem? If so, why hasn't someone thought about designing a new sand casting for a case that's more rigid? Where I use to work we machined numerous prototype sand castings for these guys:

http://www.mendeolatransaxles.com/homepage.php

Perhaps short runs might even be feasible hogging out a solid chuck of aluminum on a CNC machining center.

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Re: Strongest Gearbox Possible

Postby Crazyswede » Wed Jan 21, 2009 10:25 pm

Neil Jones wrote:Would you say that case flex is the biggest problem? If so, why hasn't someone thought about designing a new sand casting for a case that's more rigid? Where I use to work we machined numerous prototype sand castings for these guys:

http://www.mendeolatransaxles.com/homepage.php

Perhaps short runs might even be feasible hogging out a solid chuck of aluminum on a CNC machining center.



anything is possible with enough $$$$. Its just that most of us don't have a spare $50,000 laying around to pay for the material, machine time, and development work to build said gearbox. Several of us have learned how to make our reasonably stock gearboxes last without going crazy on expensive mods. A stock gearbox can take 300 hp as long as you drive it wisely.
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Re: Strongest Gearbox Possible

Postby Neil Jones » Wed Jan 21, 2009 10:46 pm

Crazyswede wrote:anything is possible with enough $$$$. Its just that most of us don't have a spare $50,000 laying around to pay for the material, machine time, and development work to build said gearbox.


Knowledge, experience and creativity can often be a much better answer than throwing "$$$$" at the problem and hoping for good results. I've been a CNC machinist/CNC mill programmer for 15 years and I'd like to see if I can use my hard earned skills to benefit my Saab experience and perhaps help others in the process. You mentioned machine time. Machine time is not a factor for me. Neither is a CADCAM programming system or having the skill to use it. I program and machine harder parts every day at work and have for years.

Did you care to add any answers / specifics to the questions I asked in my first post?

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Re: Strongest Gearbox Possible

Postby Jordan » Thu Jan 22, 2009 9:26 am

From what I've gathered over the past years and what makes logical sense to me is that the major limiting factor in making bullet-proof transmissions is the relatively small gearset and maybe overall small proportions of the transmission itself. Other things like case deflection exacerbates the fact that gear to gear surface area is already too small and stripped gear teeth are common. Bearing failures tend to be a high mileage factor. Too much slop internally and load being transferred to parts not designed to take that load.

I don't know if I believe the 'chill cast' cases are really going to make that much of a difference in the end. Any case is going to need some reinforcement when we are talking about effectively tripling the power output that it was designed for.

The widest allowable gear faces is going to get you then best results. The 90+ 5-speeds have pushed the gear sizes to the limits in the space available while still having synchros . If you are going to make a custom gearset either, straight cut is going to give you the contact area you need in the same space, or you have to go dog engagment and use up that synchro space with gear face. Drop a gear to a 4 speed and you have more room to play with. Have you checked out the gearsets at speedparts.se?

Do some searches on this site ....there have been many discussions with good info in them.

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Re: Strongest Gearbox Possible

Postby Neil Jones » Thu Jan 22, 2009 12:58 pm

Jordan, based on the very limited information I have, I'm leaning toward building a 4 speed using the Chillcast 870423 case and using the biggest gears I can find as well as any significantly beefed up components I can find.

Has anyone else taken this approach and posted about the results?

Still have not found a way to contact Jorgen Eriksson about gearbox components he might have for sale.

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Re: Strongest Gearbox Possible

Postby sprokit_mk1 » Thu Jan 22, 2009 1:04 pm

saab 99 T16

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Re: Strongest Gearbox Possible

Postby Crazyswede » Thu Jan 22, 2009 4:21 pm

Neil Jones wrote:I'd like to put together a gearbox capable of handling 350 to 400hp that doesn't have to be treated like a baby. My application is street only. A few questions:

1. Is this possible?

As I said....anything is possible and it all comes down to how much time, energy, and money you have. The strongest factory rally boxes were 4 speeds...but then again they had not even built a 5 speed yet. The factory crash boxes had custom R&P sets, big gears, 4 chain primaries with additional bearing support, oil coolers etc. They are rare and expensive when found but they are supposedly indestructible. I believe that James has one or a variant of one. Also Jorgen in Sweden is a good resource for knowledge on strong gear boxes.

2. Am I better off creating a 4 speed than a 5 speed?
5 speeds are easier to find these days but 4 speeds can be found. It is debatable as to how much stronger the chill cast cases really are...as in it strong enough to handle another 20 hp?50?100?. Keep in mind that every 4 speed gear box out there is at least 25 to 35 years old and likely used. Airsweden was working on a 4 speed box built from a 5 speed case if I remember correctly. The later 5 speed boxes are built with bigger bearings and pinion bearings....but all cases should be modifiable to run a different bearing.


3. Is the 4-speed Chillcast box 870423 still the strongest case available and are the best one's still only found in ’77-’79?
see above....not sure on availability. We have looked at several boxes side by side and seen differences in all of them...chill cast or not. The chill cast box is probably stronger is some ways but again is it strong enough to withstand 400 hp or was it designed to hold up better to the "new" turbo engine.




4. Can I adapt an 89-'90 box larger rear pinion bearing and stronger shift forks to an early 4-speed Chillcast box 870423?

Yes I believe you can do so but I think you have to machine the 4 speed case.....though there might have been a lack of material issue there. Cannot remember.

5. Can I adapt the slimmed down profile of the 91-93 synchros and enlarged gear faces to an early 4-speed Chillcast box 870423? The pinion bearing and layshaft bearings were also enlarged on the 91-93 can the early 4-speed Chillcast box 870423 be modified to handle them?
If you want to build a strong box you are going to want a strong gearset...the only one readily available is from Speedparts in Sweden. I just checked and with the current exchange rate the cost of the set is $4700 without shipping. http://www.speedparts.se/shop/prod/sp_v ... 9-93.shtml.


6. Is the Saab Rally Rear steel diff cover the best available?
If you are talking about the one that is available on this site then of course it is. It may not be the best one ever made...I don't think anyone has ever done a review of all the saab diff covers available....however there are not very many available. The one that we made was measured using a CMM machine, computer modeled, and cut on a water jet cutting system.


7. Is Jorgen Eriksson still in business? How do you get a hold of him? Does anyone have experience with his: Special selector rod, Steel selector fingers, Special selector 3/4th, Strengthened Primary Chains, Universal Joint on selector shaft, Special 4 chain primary gears with new chains?

Strengthened Primary chains....not sure about these....as I said in an earlier response the Saab rally boxes ran 4 chains and both ends of the shafts were supported in a bearing....vs the 2 or 3 chains found in the 4 speeds and 5 speeds where the gear is only supported on one side.

8. Has anyone done this type of modification I mentinon in #7 above?
yes someone has

9. Adding a 4th row of gears and chain to the primaries and modifying them to accommodate an extra bearing on the upper primary as per the Works gearboxes?
yes

10. Are 4 speed dog gears (38570Kr) still available? From who?
yes, speed parts ($4700 without shipping)

Any other recomendations or info greatly appreciated especially from those with actual hands on experience on making a Saab 900 gearbox last with this kind of horsepower.


.
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Re: Strongest Gearbox Possible

Postby Geoff » Fri Jan 23, 2009 2:51 pm

Eriksson Industries in CT used to make a "huge pinion housing" for pre '89 boxes (4 and 5spd). It was an enlarged housing and a "huge" pinion bearing. The pinion bearing was larger than the bearing that came with the 89+ boxes. Apparently this kit is no longer available. However that doesn't mean that someone with CNC access couldn't source a "huge" bearing and made a housing to fit it. ;)

The stronger primary chains are a stronger set made by the OEM supplier (JIWIS?) They are the same chains that the factory used before going to the 4 chain setup. Presumably they used them on the 4 chain setup as well. Jorgen can make you a 4 chain setup but doesn't seem to recommend it for most applications. Sorry, I can't find his contact info.

He has the special selector rod and selectors and u-joint on the selector shaft (external selector shaft) for better strength, wear resistance, and a better feel (which keeps people from missing shifts, slamming the box around, bending selector forks, etc.)

#6: Of course! :lol:
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Re: Strongest Gearbox Possible

Postby Neil Jones » Fri Jan 23, 2009 8:31 pm

Geoff wrote:Eriksson Industries in CT used to make a "huge pinion housing" for pre '89 boxes (4 and 5spd). It was an enlarged housing and a "huge" pinion bearing. The pinion bearing was larger than the bearing that came with the 89+ boxes. Apparently this kit is no longer available. However that doesn't mean that someone with CNC access couldn't source a "huge" bearing and made a housing to fit it. ;)


Probably no demand. When I spoke with Eriksson Industries in CT last week John said demand had really dropped off in the last few years. They don't even stock gearboxs for the 900 anymore and need a week to build one.

In any case, I took a good look at this picture that Pierre put up:

http://www.saabphotos.com/gallery/album571/ab5?full=1

I could model this part in SolidWorks / apply tool path in Mastercam and then machine it out of a chunk of 6061 on one of our Haas CNC machines. It's not a hard part to make. I thought I saw someone put up a post somewhere with the size you need to make the crush bearing because they are no longer available. I should have written it down. I'll have another look this evening.


Geoff wrote: The stronger primary chains are a stronger set made by the OEM supplier (JIWIS?) They are the same chains that the factory used before going to the 4 chain setup. Presumably they used them on the 4 chain setup as well. Jorgen can make you a 4 chain setup but doesn't seem to recommend it for most applications. Sorry, I can't find his contact info.


Found the IWIS website.

http://www.iwis.com/index.php?id=622

Geoff wrote:He has the special selector rod and selectors and u-joint on the selector shaft (external selector shaft) for better strength, wear resistance, and a better feel (which keeps people from missing shifts, slamming the box around, bending selector forks, etc.)


I wish he was easier to get a hold of/had a website with details and prices of what he sells.

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Re: Strongest Gearbox Possible

Postby Neil Jones » Sat Jan 24, 2009 1:02 pm

Crazyswede wrote: As I said....anything is possible and it all comes down to how much time, energy, and money you have.


A lot of it looks to me like having the connections to those in countries outside of the U.S. who know where to get the parts.

Crazyswede wrote: Also Jorgen in Sweden is a good resource for knowledge on strong gear boxes.


Certainly appears to be but I still have not found away to be able to reach him or find a web page on what he offers for sale.


Crazyswede wrote: Strengthened Primary chains....not sure about these....as I said in an earlier response the Saab rally boxes ran 4 chains and both ends of the shafts were supported in a bearing....vs the 2 or 3 chains found in the 4 speeds and 5 speeds where the gear is only supported on one side.


Do you know of any picture or diagram that shows how this works? I'm having a difficult time visualizing this.

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Re: Strongest Gearbox Possible

Postby Neil Jones » Sat Jan 24, 2009 1:04 pm

Neil Jones wrote:
Crazyswede wrote: As I said....anything is possible and it all comes down to how much time, energy, and money you have.


A lot of it looks to me like having the connections to those in countries outside of the U.S. who know where to get the parts.

Crazyswede wrote: Also Jorgen in Sweden is a good resource for knowledge on strong gear boxes.


Certainly appears to be but I still have not found a way to be able to reach him or find a web page on what he offers for sale.


Crazyswede wrote: Strengthened Primary chains....not sure about these....as I said in an earlier response the Saab rally boxes ran 4 chains and both ends of the shafts were supported in a bearing....vs the 2 or 3 chains found in the 4 speeds and 5 speeds where the gear is only supported on one side.


Do you know of any picture or diagram that shows how this works? I'm having a difficult time visualizing this.

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Re: Strongest Gearbox Possible

Postby DrewP » Sat Jan 24, 2009 3:04 pm

Neil,

I'm glad that you are persuing this. I had aspirations when I started at engineering school here in Chicago to do some work to strengthen the 99/C900 boxes too. I've also got a good bit of CNC and modeling experience, but don't have too much free time right now, I spend it all working on our Formula SAE car.

However, I highly suggest you pick up the cheapest extra C900 box you can get your hands on, broken or not (unless you have one already) and tear it down (unless you have done that already).

There is a good thread on here from a year ago or so like was mentioned that lists and discusses the general failure modes of these boxes. They seem to be bearing failure (sometimes leading to increased shaft center-to-center distance, which cleans the teeth off the gears), the primary chains or sprockets having issues, the case splitting around the diff bearing carrier flanges from the thrust force of the ring gear and output pinion trying to lever themselves apart. Then there's the gears that are either overloaded, ran without enough oil and got brittle, or are just getting along in their fatigue lifespan that fail at the roots of the teeth. Boxes that have been sitting a long time could have corrosion cracking issues where parts were not well coated in oil as they sat.

In taking mine apart, I made several observations that contradict the accepted failure modes, particularly about the case flexing and allowing the shafts to separate from each other.

The case actually looks extremely rigid, and the input and output shafts are supported through pretty helfty buklheads at the front where the input, or primary housing bolts to the main case, and at the rear where the pinion bearing housing bolts to. The only way that 'case flex' could allow the shafts to actually spread apart, is if the bearing bores for the two shafts pushed hard enough apart to shift the shaft centers away from each other. On the box I took apart, an '82 5-speed turbo box, the front bulkhead was about 0.5" thick and ribbed, it looked pretty hefty compared to what I was expecting to see after hearing for years about how compliant the cases are. The rear bulkhead is beefy.

Image

The input shaft has gears 1-4 cast right onto the shaft, and is hollow in the center and rides on a stationary layshaft that is retained in a bore in the front buklhead of the primary housing, and rides in a bearing at the back bulkhead where the pinion bearing housing bolts. At the front it rides on the layshaft with a small collared needle cartridge between them. As the needle bearing wears, and as the radial surface of the layshaft where the radial loading is centered wears is allows the layshaft to shift away from the output shaft, which is what widens the gear spacing.

Image

Image

Image

New layshafts and needle rollers are still available, or if you can't get a new layshaft, you can index the old one 180 degrees, to put the fresh side up, and re-grind the locking notch in the end.

I have a photo gallery of my teardown here, so you can see the internals. This box was pretty worn when I took it apart, but it worked and didn't make any terrible noises, and look how much wear there is on the 4th gear end of the lay cluster bearing support area, on the layshaft and the needle bearing.

5-speed teardown gallery

The diff support bearing end could benefit from stiffening, this the heftier rear diff cover, to stabilize the left and right flanges, there have been people who make an external girdle that integrates with the diff cover and wraps around the sides and bottom with bolt flanges to go onto the inner driver bearing housing bolts, the guy in Iceland with the photo gallery of his hasn't been around in a while though, and his photos are down. Maybe someone saved them?



Sorry that was so long, I think I got most of my thoughts, will be following where this goes.

Best,
Drew
Last edited by DrewP on Sat Jan 24, 2009 3:17 pm, edited 1 time in total.
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