Help reading Hewland pinion markings

[h00die]

All - I'm working to set up the depth and backlash on our mk9 (8:31 matched r/p, with webster side covers), and I'm not sure how to read these pinion head markings as they're not consistent with other measurements I'm seeing.



Is MD 3.537 supposed to be the same as "setting distance" (SD) to the differential carrier center line? If so, that doesn't make sense as I'd need a 1" shim to get there. If not, what is MD supposed to mean?

And is .020 the required backlash, or is .020 the gap-distance/offset-distance from the hewland setting-tool diameter (4.71") to the pinion head? .020 would make sense in EITHER scenario as that's in the ballpark of where I'm at, which is alarming.

Clarity on these would save me a lot of time and heartache as my paint-marks are close, but not perfect.

Any advise/suggestions welcomed.

[Lee Johnson]

All - I'm working to set up the depth and backlash on our mk9 (8:31 matched r/p, with webster side covers), and I'm not sure how to read these pinion head markings as they're not consistent with other measurements I'm seeing.

Is MD 3.537 supposed to be the same as "setting distance" (SD) to the differential carrier center line? If so, that doesn't make sense as I'd need a 1" shim to get there. If not, what is MD supposed to mean?

And is .020 the required backlash, or is .020 the gap-distance/offset-distance from the hewland setting-tool diameter (4.71") to the pinion head? .020 would make sense in EITHER scenario as that's in the ballpark of where I'm at, which is alarming.

Clarity on these would save me a lot of time and heartache as my paint-marks are close, but not perfect.

Any advise/suggestions welcomed.

h00die -- 3 years ago I had a helpful email exchange with Colin Reynolds @ Hewland Engineering on this very subject. In summary, the "MD" dimension is the distance from the 'back face' of the pinion (where the pinion bearing inner race seats against the gear) to the differential center line. Although I didn't perfectly clarify this point, I am pretty sure this would be interpreted as the distance perpendicular from the plane of that bearing seating face to the diff. center line. The .020" dimension on your pinion gear is the nominal space between the pinion setting fixture & the 'nose' of your pinion gear.

The Hewland Mk Gearbox manual has directions on how to set & check the pinion to ring gear backlash.

Lee Johnson

[h00die]

h00die -- 3 years ago I had a helpful email exchange with Colin Reynolds @ Hewland Engineering on this very subject. <...>

The Hewland Mk Gearbox manual has directions on how to set & check the pinion to ring gear backlash.

Lee - thanks a ton! THAT would make way more sense if it were to the back of the pinion head. Altho how that's helpful isn't really clear to me as that's a buggar of a dimension to try and get inside the case.

The .020 "gap" distance is more useful and what we're measuring to. I made my own setup tool using posts elsewhere on Apex, and that's been super helpful as well. I can post details if anyone is interested (uses mini cnc machine to make two face-centered discs out of HPDE, with a section of tubing to separate them and thus project the centerline to the center of the case).

On backlash, I do see the instructions in the various guides and manuals, but the hewland version unhelpfully says:

"<...how to set the dial indicator...> Minimum reading should be 0.005”. Refer to the Crownwheel and pinion setting label."

So, minimum .005, ok - but where is this mysterious setting label so I know nominal backlash?

Regardless tho, knowing my pinion depth is close is super helpful, as between chasing depth vs. backlash, it's super helpful to know at least one of your numbers is in the ballpark...which it is.

Thanks again!
Chris (aka. h00die)

[Fred Michael]

I would be worried about the pitting on the teeth

[Lee Johnson]

Lee - thanks a ton! THAT would make way more sense if it were to the back of the pinion head. Altho how that's helpful isn't really clear to me as that's a buggar of a dimension to try and get inside the case.

The .020 "gap" distance is more useful and what we're measuring to. I made my own setup tool using posts elsewhere on Apex, and that's been super helpful as well. I can post details if anyone is interested (uses mini cnc machine to make two face-centered discs out of HPDE, with a section of tubing to separate them and thus project the centerline to the center of the case).

On backlash, I do see the instructions in the various guides and manuals, but the hewland version unhelpfully says:

"<...how to set the dial indicator...> Minimum reading should be 0.005”. Refer to the Crownwheel and pinion setting label."

So, minimum .005, ok - but where is this mysterious setting label so I know nominal backlash?

Regardless tho, knowing my pinion depth is close is super helpful, as between chasing depth vs. backlash, it's super helpful to know at least one of your numbers is in the ballpark...which it is.

Thanks again!
Chris (aka. h00die)

Chris--

Hopefully someone with more direct experience will pitch in. I think that once the nose depth is set correctly that tweaking the diff bearing spacing shims distribution from side to side (same total to retain proper diff bearing preload) will shift pinion to ring tooth contact pattern to that desired (while also changing pinion to ring backlash). Because of tolerances on pinion axis offset from differential axis, etc. from one gearbox to another, a precise backlash may not able to be specified. Hewland want to ensure there is at least some minimum backlash/clearance, while also having an acceptable tooth contact pattern.

I agree that for the user that MD dimension doesn't seem too useful. Likely it is used during manufacture including for inspection purposes.

Like another poster, I wondered about the apparent pitting in your picture...maybe it's really a bit of dirt/grease/packing material on the tooth surface(s)?

Lee

[h00die]

Like another poster, I wondered about the apparent pitting in your picture...maybe it's really a bit of dirt/grease/packing material on the tooth surface(s)?

Yes, I know about the pitting - I've run worse on the 901s I used to use. While I wouldn't recommend it, there's still some life in this one....but no, I'm not attached to it at this point as this was a cheap-enough 2nd hand unit.

This MK came from a formula car and is going into a production car, so I'm dropping from 10:31 to 8:31 due to wheel diameter. The spreadsheets say this is the right f/d for what I'm doing, but I won't know for sure till I run it. May get out there and find that I hate it. If that's the case, then I won't have spent good money on a r/p that only sees 20 minutes of use.

If it works well, then I'll keep an eye on it and eventually just replace it with a good one. I understand the 8:31s don't last long anyway, so I'm hoping that real world use tells me to go to a 9:31.

[Bobsy SR 6]

Chris

The mysterious label your referring to comes with each new crown wheel and pinion in the box. It specifies the recommended backlash as well as the gap to the shim tool. In a used gear set it is preferable to set the backlash back to the spec it was running at. The importance of this is to prevent starting a new wear pattern in the gears which will shorten the life of the gear set as well as more noise. This is why most seasoned transaxle specialists will take readings of the gear set prior to disassembly. For short term use however this probably is not a great concern.

Of greater importance is the dial indicator setup. The indicator rod must be placed correctly or erroneous readings will result. This is due to basic geometry. As the radius from the layshaft center line increases so will the apparent back lash reading. You must place the tip of the indicator on the flat of layshaft nut next to the point of the hex. This will give you the correct readout. For short term use some backlash is much better than none. You need room for the lubricant film between the gear teeth.

Best of luck

Tom

[scotty82]

You will take the MD . Subtract the Pinion head size , Than subtract you fixture radius of 2.355

The proper way to do back lash readings is off the 4/5 hub when all the hubs are stacked and tight on the pinion shaft
21 readings in 3 sets of seven , Each reading off of the 4/5 hub will be opposite each other .The low is the number you are looking for . The highs will of course be the run out . The pinion you have in the picture is very pitted
.You will slowly zero in on your back lash number.. And you will make a .002 change or so , and fall off what is called the hump . Meaning you have just fallen into the existing wear pattern , This is when you will start chasing your tail . I recomend a new ring and pinion .

[h00die]

And you will make a .002 change or so , and fall off what is called the hump . Meaning you have just fallen into the existing wear pattern , This is when you will start chasing your tail . I recomend a new ring and pinion .

Heh - yep. Figured that out. Spent a few hours tail chasing. But we learned some things, which is good...along with don't spend a lot of time on used-up hardware.

This r/p was 2nd hand and cheap, and we want to verify that tires, r/p, gear-ratios, engine power-band, all work well together as a package. If it does, then we'll definitely look at a new set. Pretty sure we could have set it up in half the time had these been new pieces.

Would have to get invested in new 8:31 only to find a 9:31 would work better. The calcs say 8:31, but you don't know till you drive it once and see if it works in reality.

Thx Scotty!