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Hi folks,
Quick question as I don't have my reference materials here at work...
When doing a gearset change on a Hewland Mk9, outside of gear lube and hylomar, are there any other components that should be replaced during the process such as cotter pins or clips?
Thanks,
Erik
definitely use new cotter pins. shouldn't need anything else. While it is apart, check for fresh wear in the dogs on the gears and the other internal parts. Also check for unusual amount of metal filings in the gear lube that might indicate alignment issues or rough tratment by the driver. (no offense meant there).
Use new quart of gear whatever gear lube you normally use. Some folks mat state their preferences here.. some use 50w oil, some use redline gear lube etc.
Dear Rick and Shep,
The maximum wear on the dog lugs, both on gear and dog ring is 25% the height of the dog. IE when the rounding of the dog exceeds about .040", the dog lug is worn out.
One caution on oils for MK9, or any transaxle using spiral bevel final drive gears; Never use engine oil! The spiral bevel gears require an Extreme Pressure additive to prevent galling of the gear teeth. Extreme pressure oils are labled either "EP" or GL5.
For Formua Ford a good qualtiy 75W90 oil , synthetic or natual is just fine. We prefer synthetic, either Redline or Valvoline, as they tend to yield better shifting.
For more information on wear limits and torque values, see our website at http://www.taylor-race.com/pdf/MK9numbers.pdf
If you have any questions, please contact me at craig@taylor-race.com, or Scotty at scotty@taylor-race.com.
I hope that this will prove useful.
Craig
Thanks Rick,
How many cotter pins, what size (obviously, I haven't done my first change yet...)
As for metal filings - no offense taken - after the painful sounding grinding noises I was making at Nelson last year (mis-adjusted linkage, newbie driver), I'd be surprised to find any dogs left at all...
Awesome! Thanks Craig!
(I plan on using the Redline Lightweight Shockproof gear oil)
2 pins, 3/16" x 1.5" or longer (trim to fit).
Have at least one new roll of paper towels and a fresh can of brakeclean handy. I don't recommend using brakeclean on the gears themselves -- just wipe the oil off and let the leftover film of oil help prevent corrosion while in storage. For that matter, don't spray brakeclean in the bearing carrier or main case. Spray it on a paper towel and wipe the oil off the mating surfaces.
Also be prepared for nuts and washers (and studs) that should be replaced. The rear cover uses 1/4" nuts, and the bearing carrier uses 8mm nuts. Replacing these now will minimize damage and make future changes easier. I've seen cars that use a hodgepodge of nylock nuts and jetnuts on the rear cover -- requiring two different wrenches! Any studs that pull out should be cleaned up or discarded, and fresh studs loctited in.
when changing the gears, the top shaft stays in the trans. Hence, the gear cluster has a tendency to fall out in a pile. Very intimidating when changing gears for the first time.
I use a 16" or so length of 1" pvc placed like an extension of the top shaft when withdrawing the rear carrier. That way the gears, bearings, dog rings, and spacers slide on to the pvc rather than dump out on the floor.
Also, have a large (14-16") circular pan placed under the rear of the trans after the oil has drained, to catch remaining oil & use as a place to put the gear carrier & new gearsets for reassembly. you do not have to buy the $50 version from suppliers, just use a pizza pan.
Thanks Craig---
Shep: Pay attention to what he says, he is the main gear man!
not a consumable but darn smart things to have are magnet oil filler plugs....call craig taylor for 'em. one for the side of the case and one for the top.
That's a good point -- the filler plugs do get chewed up after a few years, and they're relatively cheap to replace with a magnet version ($19.99, our part #1410-C03, in stock).
A pipe thread sealant such as Loctite (our #3374) on the filler plug makes removal easier as well. You don't have to gronk it in so hard to stop it leaking, and it acts as an anti-seize so it will come out easier, too.
I really recommend a stand for the rear carrier so that it can rest firmly upright in the tray. I made one but they are available for those that don't have metal working tendancies.
you can double check the thrust clearance on the main shaft, which is set by a shim washer at the pinion bearing end, by assembling all of the gears on the main shaft and installing without the layshaft. Snug up the nuts on several of the main case studs and then you can stick your finger in to wiggle top gear. It should have about .008" of float, but you can easily see if there is too little clearance (it won't turn) or get a feel for if it has way too much clearance - it slides forward and back with excess float. I had one box that for some odd reason needed almost .080" of shim to get correct end float - with the shim missing (the way the box came back from a re-build) the dog ring couldn't engage top gear. Very tricky problem to find.
Questions: I always have used a 1 5/16" socket to take off the main and lay shaft nuts. Went to help out a friend this weekend and found that his gearbox (late Mk9 it looked like, on the back of a 86 Van Diemen) had a 1 1/4" nut set. What's up with that?
Is there a good fix for a worn out upper drain plug hole? Mine has had so much use that the plug now threads way too far in. I have thought of re-tapping to the next larger size but is there a clever fix?
Thanks, Brian
Brian,
Your idea of measuring the 5th gear end float is right on. A properly bent feeler gage can actually be used to measure the float.
However, simply shimming at the front, between the main pinion bearing and the 1st/reverse hub might not be the entire answer. Keep in mind that changing the shim at the front of the stack moves the entire gear stack. This will require that the shift forks be readjusted to keep the dog rings centered.
However, if it is just the 5th gear endfoat that is a problem, and the shift forks are properly adjusted for the shim and hubs that you have, a thicker thrust washer can be fitted to bring the 5th gear endfloat to the required .008". We stock over thick washers for exactly this purpose. They are simply machined to the thickness required for endfloat.
The 1 5/16 nuts were used on the early Hewland gearboxes, and are still used on the Formula Mazda gearboxes. Later gearboxes are equipped with 1 1/4" hex. We have the 1 1/4" hex nuts in the 7/8" x 20 (extra fine thread) both in left and right hand thread. We also have the 1 5/16" nuts in 7/8 x 20 (extra fine thread) in left hand thread for the pinion shaft, and in 7/8 x 14 (UNF fine thread - the thread that is coarser than the pinion shaft thread.) So now you can have anything you would like.
Hope this helps.
Craig