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Who can tell me more about this ratio? That’s what I have in a MK6 case with MK5 gears. I have the notes fromTRE refresh under previous owner indicating this combo. I have an old gear ratio chart from PBS Engineering that lists this ratio but other than that I can find no other reference that these parts existed. Curious more than anything else. New at this and just want to learn.
thanks
Just a guess, but I wonder if they were used back in the day when tires were taller and skinnier than now, and a super-low diff was used to give acceptable acceleration?
Also from days of standing starts, and winding "real" race engines tight....10K up.. narrow power band...Quote:
Originally Posted by Lotus7
Bob L.
If it's a Hewland MK6 then the ring and pinion is VW beetle based and hence 8/33 which is available from a VW bug
Are you saying actual Beetle R&P can be fit to a MK box?Quote:
Originally Posted by kevskisps
Only if you replace a bunch of other parts as well... all of the gear hubs are different (Stack and key into each other), and I would assume the diff is also not the same as a mk8/9
Of course it can, since that is what it came out of in the first place. The problem is that it cannot be used with any of the Hewland parts, since they are all very different.Quote:
Originally Posted by Ducman
Quote:
Originally Posted by R. Pare
Well almost anything can always be made to work with anything else....that was not the point of my original post. Somewhere along the way an 8:33 ratio was available from Hewland or for Hewland MK series transmissions. I have one and as I mentioned the ratio shows up in this PBS tech document....as well as an 8:35.
I just haven't seen any other mention or reference so thought I'd ask if anyone happen to know....maybe not
https://www.apexspeed.com/forums/att...d=101576&stc=1
As I was referring to in my post, the earlier mk series (4/6/7) used the VW r&p but different pinion shaft gear hubs. A friend had a mk6 in his March and was a bit odd (gearbox and friend!). Only one of the gear hubs is splined to mate with the VW pinion shaft, all others slide on and are ‘keyed’ at the end faces to lock into the next hub.. it is critical that the pinion shaft torque is enough or the stack will shift in loading and unloading the engine.. since the ring would be VW based and not Hewland (I believe the dimensions are based the on a British Ford diff), the matching diff would also need to be sourced (and bearings, etc).. the later mk5/8/9 design is far superior and stronger than the VW design.
it is interesting that the gear sets and dog rings are the same parts. You can find mk6 gear hubs for sale on occasion at a decent price since they aren’t in high demand
https://www.apexspeed.com/forums/blo...4-3087da8086a1
https://www.apexspeed.com/forums/blo...3-d67edca2b747
Indeed, some of the early FF's had Hewland MK6s boxes with with a stock VW 8:33 ringgear Pinion. For instance, The '68 Bobsy FF (aka the Pizza-Pizzq Car) which I restored several years ago had the original tranny in it, I'm pretty sure. It was Hewland Mk6 with the 8:33 ring/gear pinion. Here's details on that restoration. Frames 19-23 show the work on the diff carrier and the ring gear which you might find of interest.
On the MK6 both pinion and lay-shaft nuts are right hand thread, unlike later MK series Hewland s where the pinion shalt has a left hand threaded nut. And as mentioned earlier in this thread the MK6 used different hubs because the splines on the VW pinion were not the entire length of the shaft. Rather the hubs interlocked with each other with lugs rather to the Pinion as with later Hewlands with splines going the entire length of the pinion shaft. Both, however, both use the same Mk 6-8-9 gear sets.
Yes, an 8:33 is a stump puller which might work well for auto-crossing. But it is easy enough to simply gear it taller for road racing. Where I'd run a 24-27 top gear with a 9:31, top gear, the 8:33 was a One-0ver (Yes) 26-25 top gear. Works out to about the same top speed/RPM at the top end. Other three gears also correspondingly taller taller for the same rps and "splits."
If you get into this box and the diff carrier has pressed on roller bearings (rather than taper bearings with removable races), it's a bit of adventure (!!!) getting the side plates off to access the diff carrier, the side plate seals, and set up preload. I'd highly recommend you get in touch with Scott Young. He saved my bacon by providing substitute Tapered Oller Bearings (thus the races stay in the side plates.) WAY MO' BETTER for setting up pre-load, etc.
Cheers,
Bob Alder
Thanks all - this is starting to make sense for me. I ended up finding a Hewland parts book that listed the 8:33 r&p along with 8:35 and 9:31. At this point is looks like it's no more complicated than that is what was available before the MK8 came about - at which time they must of decided it was too crowded and went instead with the 8:31 and 7:31
https://www.apexspeed.com/forums/att...d=101588&stc=1
Also I can confirm as both Robert and John indicated, my pinion shaft is not splined it's entire length. So this does mean I have the earlier pinion shaft. But I have the MK5 layshaft and gears.
Also per Roberts comment on the diff carrier I found in the build sheet from TRE that tapered roller bearing were installed (along with required side plate modifications) in place of stock
This may very well be the case. I JUST had my MK9 rebuilt by Scott Young Enterprises where they replaced the old VW R&P 8:31 with a modern 8:31. Could have installed an 8:33 instead at a much lower cost. But, it would mean changing my gear inventory. :greenflag:Quote:
Originally Posted by kevskisps
Just had my MK9 rebuilt and this was certainly the case.Quote:
Originally Posted by scorp997
Scotty Young can answer all of your questions on these gearboxes. :thumbsup:
Ducman, you don’t happen to own the yellow March 729 that was posted for sale here recently, do you? If so, that is the car I mentioned above. It has a mk6 gear hub set, a 9:31 Hewland mk6 shaft, mk9 side plates and axles are adapted to rubber donuts. An odd combination if you don’t know Hewlands.
No doubt, but to me part of the fun is exploring and learning. This is my first Hewland so I'm facinated. Box is fine for now. It has zero hours on it since Taylor did a complete rebuild, recondition, and update 10 years ago....Scott may have done it (he would have been there at that time right?)Quote:
Originally Posted by Ralph Z.
Nope - 8:33 with MK5 gears - this is in a TC FB that some of you may recognize from another member's project:Quote:
Originally Posted by scorp997
https://www.apexspeed.com/forums/att...d=101590&stc=1
Understood. :thumbsup:Quote:
Originally Posted by Ducman
John,Quote:
Originally Posted by scorp997
That March 729 is in SoCal now. I'm not sure where that gearbox came from but my 1971 March 719 has a Mk8, which I confirmed with Hewland Classic to be one of the 3 sent to March in the winter of 1970-71.
Garey, I knew you’d know where it was... pass that info on to the new owner if it still has the ‘box in it. Some of the mods are very obvious, like the bolt on mk9 to rubber donut adapters. I’m sure it wasn’t the original gearbox and a previous owner built what he could and met the rubber donut requirement of the time.