Jump to content

620 Land Speed Record


distributorguy

Recommended Posts

You can take any OD gear set out of any of these boxes and they interchange, correct?  Shaft size always stayed the same, and gear width was the same, right?  Anything I'm missing?  I'm also wondering if you can restack gears so 5th is 1:1, and you have 4 close ratio gears to use prior to that.  Feasible Mike?

Link to comment
  • Replies 870
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

I am 90% sure that all years OD gears are interchangeable.

 

I'm trying to remember how the Datsun Comp direct drive 5 spds were laid out. I don't think you can "restack" a normal Z or ZX 5spd, but Nissan did it, so I'm trying to remember how they differed inside. I do know that the DD 5spds used steel synchros and also the shift pattern was different, with first gear left and down.

 

Jamie Houseman used to make special gearsets for the DD 5 spd. I wonder if he still does. http://www.housemanautosport.com/

 

I like that big green Ford.

Link to comment

You should see "little green."   :thumbup:

'99 F150 4-door short box Cummins 4BT/Allison auto   400/700 at the wheels.  Big green only runs 47 psi boost so more like 700/1250.  My buddy John owns them.  He's now putting boost and FITech on a custom Exploder that looks like the new proto-type Bronco.  Shooting for a 500 hp 302.  

 

I think the only way I'll get a Datsun trans to work the way I want is to talk with Bob Sharp who probably has 1 left on the shelf.  Or hope the 240Z guy who ran Bonneville wants to upgrade to something else?  He has the close ratio 1:1 5-speed.  

Link to comment

Those DD 5 spds are worth their weight in gold. And parts for them are getting very scarce. I used to have a good stash of OEM DD parts, but I sold it all.

 

I'd love to come out to Bonneville and help you guys. When are you going? This year may be impossible with my current work load, but next year could happen if I plan ahead.

Link to comment

In the 71B 5 speeds 4th is not a gear at all but a direct coupling from clutch to tailshaft along the mainshaft.

 

ALL gears except 4th are engaged at all times. There is no 'gear changing' only the locking of the selected mainshaft gears to the mainshaft. 

 

On the bottom counter shaft 3, 2 and 1 (from front to back) are all cut on the same shaft and cannot be separated. These are in constant mesh with their mating gears (spinning freely) above it on the mainshaft. Reverse and 5th are at the very back and are removable.

 

 

 

My notes say the F5C71B was a dogleg pattern?

R..2..4

1..3..5

 

This is borne out by the fact that first gear countershaft is removable (just like 5th on a regular shift box is) that leaves 2, 3, 4 on the countershaft and direct coupling 5th on the mainshaft.

 

I have all kinds of gearing info for the 71A and 71B DD 5 speeds. Rally and Option 1, 2 and 3. 

Link to comment

That's right, the first gear has a separate shaft.

 

It's been a long time since I've had one of them apart, but I used to build a lot of them.

 

As I said earlier, parts for the DD 5spds are near impossible to source these days. The steel synchros were hard on shift sleeves. The sleeves and forks we're constantly wearing out, but I could fix them by welding them and re-machining them. The engagement teeth on the gears often needed replacing. Heck, even the shift rods wore out and needed to be repaired. The racers were not easy on these gearboxes.

 

At one time I had a batch of custom billet steel shift forks made, which were much more durable than the standard powdered metal variety. Those are all gone now too.

Link to comment

I found that listing of all the Datsun gear boxes and ratios long ago, and its printed out - stuffed into my service manual for reference.  

http://www.zhome.com/ZCMnL/tech/GearRatios.html

 

I don't know where the odd 5th gear came from that I have in the truck box.  Its barely noticeable as a 5th gear.  It feels identical to 4th, but rotating the shaft you can see there's less than 10% overdrive.  It needs to come apart after this winter to see what's going on.  

 

We scaled the truck again last night, now that its 99.9% ready for the trip.  It balanced at 49F/51R with me in the driver's seat.  That's with a full stack of ballast in the box.  We should be able to flip it to 51/49 without ballast, but since you need to keep your center of pressure forward of your center of gravity for stability, this should be a pretty safe baseline to tune from.  

 

Its raining all day today, so no tuning unless we get on the dyno???  I need to recheck the O-ring in the fuel pressure regulator to see if its swelling again.  It seems ot be acting up again.  Ughhh.  

Link to comment

Tonight will b e the last of the work on the Datsun before we leave.  Mount license plates (aero advantage), mount the GoPro so you can all live the experience on YouTube, and just a couple other little tidbits that need to be finished up.  Then pack up the shop and haul ass.  

 

This afternoon I learned how to rebuild the 620 door hinges.  I basically punched out the pin, drilled the hinges to 5/16", and used a piece of 5/16" rod to make a new pin, with threads on the bottom so I can tighten up a lock nut to add tension to the hinge.  Or you could simply buy a long bolt and cut the excess off at the bottom so the only threads are outside of the pivot areas.  

If you let the pin rotate instead of being staked in like the original, it should last longer and not wear in the same precise spot where the load is applied.  The driver's door now operates like brand new.  

Link to comment

There are 3 gear sets for the 71B, generally. 

 

Wide with a..... 3.592 first

Mid with a........ 3.321 first

Close with a.... 3.062 first.

 

The counter gear sets can be rearranged by changing the two input gears top main and top counter sets. For example if you take the mid range input set and put on the wide ration transmission it becomes a mid ratio.

 

 

I counted gears on the '85 CCA18ET

 

The upper and lower input main and counter are 21/32 or 1.52

 

1st.... 3.591... 33/24 t

2nd... 2.057... 27/20 t

3rd... 1.359... 25/28 t

4th... 1.000

5th... 0.813...  24/45 t NOTE: the zx OD is 26/44 t

 

The mid ratio input gear set is 22/31 or 1.409 X the counter gear sets. If I were to put the 22/31 set in my 5 speed (above) becomes a mid ratio transmission...

 

1st.... 3.321

2nd... 1.902

3rd.... 1.25

4th.... 1.000

5th.... 0.750  see the NOTE above to explain the OD. my gears are different from the zx OD

 

 

 

 

If I was to swap the ZX input gears... 23/29 or 1.261 and multiply by the gear set on the turbo transmission I get...

 

1st....  2.972

2nd... 1.702... 42.8%

3rd.... 1.124... 34%

4th.... 1.000... 11.1% ????

5th.... 0.672... 32.8%

 

Wow this makes a serious close ratio 5 speed but the OD is useless for racing. If I also swap the ZX OD gears I then get 0.745 or 24.5% OD

 

For now this is as far as I can go. The OD isn't really changeable unless there is another gear set like 20/30 to give a .666 5th. With the zx inputs of 23/29 or 1.262 ... X .666 = 0.840 overdrive. That's about 16% so 5th would be usable.

Link to comment

Suggest taking a spare regulator, possibly of another brand......

 

I have 2 spare Holley regulators and a lower pressure Carter fuel pump already packed just in case.  Today I'll pull the valve assembly and check the O-ring.  I'll source several and change them daily if required.  That'll be easier than plumbing in a different regulator.  The valve assembly is a "fitting" per se - unscrew it and swap in a spare.  Change out the O-ring on the bench.  Who knows how it will respond to the crappy track fuel.  It may be less corrosive?  

Link to comment

For now this is as far as I can go. The OD isn't really changeable unless there is another gear set like 20/30 to give a .666 5th. With the zx inputs of 23/29 or 1.262 ... X .666 = 0.840 overdrive. That's about 16% so 5th would be usable.

 

I tore apart another 5 speed, (Z series truck) a mid ratio with a 3.321 first gear.

 

1st....  3.321... 33/14 t

2nd... 2.076... 28/19 t ... 37.5%

3rd.... 1.308... 26/28 t ... 37 % One tooth out corrected*

4th.... 1.000................... 20%

5th.... 0.863... 19/31 t ... 13.7%

 

 

The input gear set is 22/31 and the OD gears are 19/31 or .612 so on the zx transmission his only drops the OD to 22.8% Damn... big change makes little difference then little change makes huge difference but never the right way.. 

 

Hard to count teeth will confirm them again, again tomorrow.

 

Main and counter input gear sets...

22/31

22/32

23/29

 

OD gear sets...

19/31

26/44

Link to comment

I need to wrap my head around all that info Mike.  Thanks for all the ground work sorting through this.  I'm NOT a transmission guy - its the only area of a vehicle I have literally no hands-on experience.  Your ZX calculations would be excellent if there was a 5-8% OD gear available. 5th gear is almost impossible to use, unless its very slight.  The amount of horsepower it would take to be able to use a 16% OD at the air pressure of 125 mph is far more than you might expect.  Even having something very close to 4th - on either side of it - would be more beneficial than a real overdrive.  Hell, I'd even be willing to give up reverse for another forward gear that fits in the pack.  

Link to comment

The zx is 24.5% or twice that.

 

Most ODs are 12-18%.

 

 

I still have it apart so will count them again. (I did count them 3x each just to be sure but may have written down something wrong) A 37% to second and the a 39% drop into 3rd?  *was a tooth out in 3rd main gear corrected to 37% drop into third which is better. Seems like a big hole going into 3rd. I have heard this about most 5 speeds. This is why you are thinking of the 200sx transmission? I have a first year zx with 3.321 first and 37.5%, 37%, 23% 13.6% OD  With a 4.11 fifth pulls like another gear. This is the same ratios as the Nismo Wide ratio box.

Link to comment

The other 5-speed we have on the table, we would just not use first gear, unless we found an even higher rear gear ratio that the 3.89 we currently have installed, where it would be beneficial to get going from a stop, given our wild cam.  

 

4.2
2.49
1.66
1.24
1.00
 

 

Given that this gear ratio set you posted (below) would require a custom build, the trans above can be had for $300 or less in mass quantities.  I have a free one sitting in the shop.  It just needs some adaptation to make it work.  (Read as about 50 hours and a few hundred $$$ in parts.)   

 

1st....  2.972

2nd... 1.702... 42.8%

3rd.... 1.124... 34%

4th.... 1.000... 11.1% ????

5th.... 0.672... 32.8%

 

I think this truck will eventually get a custom box.  Ouch.  Maybe it would be cheaper for me to learn to cob gears and buy the machine...

Link to comment

A DD 5th would be best. Forth the best (strongest) in an OD 5 speed. Can you tailor your differential to run the truck in 4th?

 

3.89 with 24" diameter tires at 7k would be 128.5 in 4th

4.11 would be 7,393 RPM

4.375 would be 7,870 RPM

4.625 would be 8,320

Link to comment

Exactly.  The rules read "any transmission."

The rules also read, any rear axle/differential of the same type as original, meaning solid axle versus independent rear.  You see why I went with the 3.89.  It also puts us in the heart of our hp curve at 130, with room to climb.  But you can also imagine why I'd want a 5% overdrive as an option.  We need to stay between just shy of torque peak and our hp peak or the power band drops off significantly and we falter.  No room for error when there's only 3 miles to play with.  

Link to comment

Finally doing some hardcore Weber tuning.  Didn't get very far.  Got them balanced, and a couple runs down the driveway, only to find out the factory jetting is nowhere close to ideal.  I think the idle jets are slightly too rich, as are the emulsion tubes, messing with the main jets.  Then when the air correctors come in it goes radically lean.  I've dropped the main sizing, but it stays rich - likely due to the idle jets.  This is going to get expensive quick.  I need to run larger mains to keep the mixture above 4500 rpms from diving lean.  I hope the local VW shop has sets of 4 of everything on hand???  Otherwise I'm going to have to ship tons of parts to the hotel in Wendover and pray it'll work.  Never enough time. Its rained too much here to tune until now. Ugh...

Link to comment

Tuning is a bitch. You will need a good selection of jets, and other carb parts to get it spot on. Probably lots of seat time too, even with the dyno tuning.

 

I was talking with Frank Honsowetz many years ago and he was telling me that Mikunis were actually better suited to the L motor. They are definitely easier to tune than Webers, but I never knew what he meant about being a better choice.

 

If you were tuning Mikunis, I might be able to help you, but Webers are a different animal. I'm not familiar with all the emulsion tubes and accelerator pump adjustments that are unique to Webers.

Link to comment

Another problem with Weber, is that their numbering system for their jets is not linier.

A jet marked, say 220, is not necessarily larger then one marked 215.

 

Many are, but every once in a while they will throw you a curve ball, so you almost need Weber jet catalogue, that assigns bore size to the jet number,

or a set of pin gauges.

Link to comment

The local VW shop had everything I needed!  I switched to F11 emulsion tubes which were still a touch rich, so I soldered a couple of the lower holes closed and they work pretty well.  The richer I set the jets the better it runs.  I have a full precision pin set from .011" to .250", so I can drill and file jets to any size, including modifying crappy original Weber jets to a more consistent size.  

Duax - not only are the sizes not linear, they're not consistent either!  I buy 160's and drill them to fit since my new 160's were actually 160, 160, 161, and 163.  Probably because they were so inexpensive.   :poop:

 

I have another issue, and I haven't pinned it down yet.  Once in a while the acceleration goes completely to hell and it just spits and sputters, like its running out of fuel - usually right off a start.  The fuel pressure gauge stays consistent.  I think the crappy spring loaded balance bar between the two carbs is compressing, allowing the carbs to get out of balance.  Today I'll cut that out and install a solid adjustable stop.  Crossing my fingers.  

 

And last night we blew a tire making the last run up the driveway.  I'm not sure if it took a rock or what happened.  Now I need to get a new tire express shipped to the hotel, unless Ratpatrol66 comes through for me with the right size?  At this point I just need to go pick up the trailer and load it so we can leave VERY early tomorrow morning.  Today is one of those days that I have to remind myself this is fun...

  • Like 3
Link to comment

Fingers crossed - we hit the road within an hour.  

Bonneville or bust!   Bonneville and bust?  Bonneville either way.  I can't wait!  

 

If anyone wants to join us, you can just show up and wander through the pits until you see our blue/orange 620 or text me (I won't be answering many calls) if you're in the area.  It may be very difficult to find us among the 450 other vehicles spread over a mile's worth of pit lanes.  

612-804-554three

  • Like 2
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.