Outer Limits 4x4 Board

Ben, I would say that you are correct about using narrower gears in a 4 shaft portal, but of course you will have twice as many shafts, bearings and holes to make. I think it is still far simpler to flip the diffs, or while you are in Germany try to find some 404 Unimog portal boxes and send to England for 2 sets of KAM 3.00:1 Rover CWP's and slap it all together when you get back. Bill.

Thanks Bill, I will probably flip the diffs but I was just thinking about my options.

Yes I know it would be easier to just buy them, but Like you I have a huge pile of series stub axles and T-case parts. Oh well we will see what happens.

daddylonglegs wrote:I did read a couple of years ago that a bloke in the US whose Bronco was in the Top Truck Challenge ,changed from four wheel discs to four wheel drums. The drums were extensively drilled on the braking surface and he claimed they "stopped like glue" were far superior to his previous setup. I think that Bronco came second in the stopping test on that competition. I do have a spare set of six cylinder brake drums so i might try it one day. Bill.

Duuuude, this is a well known fact!

A drum brake can stop faster than a disc brake first time. The contact (pad surface area) is the important factor, a drum brake has significantly more pad touching under braking than discs from a similar sized vehicle.

Hence the drums will stop faster. The major reason people use discs is heat dissipation, weight savings, self cleaning and self adjusting, easier maintenance as well as some other favourable qualities that discs have over drums.

Once warm though a drum brake will not be as efficient as a disc brake. (this is based on two vehicle of the same weight with similar OEM braking capacities)

red90 wrote:12.7435

wTF?

BJ, Thanks but I am sure most of us are aware of the pros and cons of both brake designs but due to the unique design of the portal axles we are exploring ways of making a brake system that we are more or less stuck with work better Regards Bill.

So Bill, what is the major difference between volvo portals or your portals and the maxi-drive portals that mean they can use discs???

Ben. The differences between Mal Story's portals and Volvo's aside from design and construction ones are that Malcolm designed his to be easily fitted to an existing LandRover vehicle, hence the 4 shaft design to preclude flipping the diffs. he was also working with standard offset wheel rims in mind, this provides clearance for disc brake calipers.
In an effort to maintain a reasonable scrub radius, my vehicle and Volvos have non standard wheel rims with around 100% negative offset. This places the smallest diameter section of the rim where the caliper would be, so you would have to modify the rim to have a greater positive offset.
In most states of Australia you are not permitted to increase the wheel track by more than 2inches which by my calculations is not enough to fit disc brakes to Volvo axles. And as for myself, I was never that impressed when I had 4 wheel discs before I converted to portals to bother designing my drop boxes around them. Bill.

bj on roids wrote:wTF?

Sorry, I made an error, 12.7434

Ben, gear design involves separate processes. Design for strength (tooth as a cantilever beam) and design for wear (pitting resulting from hertzian stress between the curved tooth flanks in contact).

With planetary boxes, split drive systems with 2 or more pinions, or 4 gear portal boxes like maxidrive, the tooth load is reduced and the width can be reduced for strength. But wear on the the common gear wheel is increased, so the width has to go back up or you change the materials for the pinions and for the gear wheel.

Hi John, I have a question that is only slightly off topic but as we have your attention.
Can you explain why British manufacturers, Rover in particular, in designing geartrains, tend to lean toward high tooth counts with finer gear teeth and reduced core strength, whereas the Americans and Japanese go for a lower tooth count and big fat gear teeth that permit a good depth of case hardening for wear resistance as well as a thick ductile core?
I think the old Fairey overdrive gear wear problem demonstrates the failings of the British design. The early overdrives had a thin depth of case hardening and wore out very quickly, while the later ones had a thicker depth of case hardening on the same gear design to reduce wear,but they broke more easily due to a less ductile core. Regards Bill.

Bill,
I can't really answer your question, but consider the following:

Many years ago (more than 30 years) gear teeth were usually 14.5 deg PA (pressure angle). Considering the accuracy of the profile that was readily achievable then, this resulted in quieter gears and lower separating forces than with higher PA.

Since then most gear teeth are cut more accurately and 20 deg PA is the norm. 25 deg PA is often used now when higher strength is important. Higher PA = stronger, but noiser and higher loads on support bearings (involute splines are 30 or 45 deg PA).

When I put maxi low range gears in a late model LT230, I was surprised that the rover gear teeth had a low PA. I mentioned this when I was speaking to Mal and he said they have varied the PA in LT230's over the years. The only conclusion is they have done so to reduce noise.

When the number of teeth is reduced below a certain number (depending on PA) the tooth profile starts to be undercut, reducing tooth strength (undercut teeth are thinner at the root where bending stresses are highest). At higher PA, a smaller number of teeth can be used before undercutting becomes a problem.

Undercutting can be reduced by using a larger addendum (addendum modification). Addendum is the height of the tooth above the reference circle, dedendum is depth below the reference circle (reference circle is pitch diameter with no addendum modification).

Sometimes it is necessary to modify the tooth profile near the tips of teeth to avoid interference near the root of the mating tooth due to deflection of the teeth. This is another process after the teeth are cut.

If everything else is the same (tooth size, material etc), increasing the number of teeth will increased the power rating.

I would say they use a larger number of teeth to avoid undercutting and other profile modifications and to get away with lower precision.

Gear design is fairly complex with many variables. I have used AGMA standard 218.01 for gear design, but this was supeceded by an ISO standard a few years ago. From what I understand, a computer program is essential to use the ISO standard.

Bill, I was looking back over this and have another question, given what you have said about Mal's portals and the need to upgrade the strength of the swivel housing bearings...

Since your axles (and it looks swivels) were flipped, the railko bush and steel pin would have been on the bottom. Did you make the pin any stronger, or machine a new one out of stronger material???

No Ben, I didn't flip the axle housing or the swivels. I merely welded up all the diff mounting stud holes and crownwheel clearance slots and redrilled the banjo so that the diff was upside down. I also cut the tin cover off the front of the banjo and rewelded that on upside down also. I decided not to use Railko pins or bushes because I think their design is incorrect. I think they should be tapered for proper adjustability.
Volvo's have spherical railko's which are also a great idea.
Bill.

So that means you are running a tapered roller bearing top and bottom in your swivels???

Yes Ben ,tapered rollers top and bottom. It may have something to do with the portals but I dont miss the additional damping that Railko's are supposed to provide. Bill.

It took me ages to find and retreive this thread from the back pages.
Can someone please explain the "Search" procedure that people often mention? Are the photos lost forever? if not how do I retreive them?
Thanks in advance.
Bill.

Bill,

What photos do you want - I copied some of them to my local drive.

Hi John. I was looking for the photos of the white 110 county on Volvos and my camo series2a on portals. I mistakenly believed that once photos and text were on the net they would be there forever, so I didnt save them in my computer files.
Regards Bill.

Don't suppose there is a bolt on adapter type kit for Rover diffs for these portals? For us non-engineering types......

I note that there was mention of Mal Storey making some?

Bill,

I have some of these. PM you e-mail address to me and I will send them to you.

up2nogood,
Yes Mal Storey makes them, but you probably don't want to know the price.

here are the ones u sent me bill

http://web.aanet.com.au/landyman/Bills%20Cars/

Thank you John and Landeyman. those are the ones I was looking for. A friend in Vietnam asked me to foward them on to him and I was dismayed to find they were no longer on this thread.
Regards Bill.

I wonder why no-one has bothered to produce portal axle conversions with disc brake assemblies. There'd have to be a market for them.

As long as you didn't have to spend 43 days making each set @ $60 per hour........

I know this subject has been discussed in detail (and a lot of the actual conversion speak is beyond my understanding from a bolt/weld on perspective) but wouldn't it be flash if they were readily available!

Want to set up a shed to build them in, Bill?

Well there would be a small market, but our restrictive vehicle modification regulations will mean most portal equipped vehicles will be unregistered competition trucks only. Maxidrive engineering have been making disc braked portals for Rovers for a few years now. I believe Marks 4wd Adaptors in Melbourne are contemplating doing the same for Toyotas and Nissans and other companies in the USA have prototype bolt on/weld on portals for their domestic 4x4's.
Bill.