Brimod Prototype Car

[Dadio]

Delighted , now don't do it again

[dinglem]

Whilst i put off stripping the diffs a little longer.... here's another interesting part to the story of this car.

It came with a selection of spares, including a completely different set of front hubs/turnbuckles (seem to use Optima Mid parts), spare Brimod driveshafts - which interestingly appear to be made out of different materials. I have pairs of each type so i can only presume one pair are hardened for use on the front?? Spare stub-axles to take dogbones, spare steering parts made out of nylon as opposed to the fibreglass ones as currently fitted to the car, and most interestingly of all, another spare set of gearboxes.

I have literally no idea how these gearboxes work or might fit and i haven't really sized them up against the chassis in order to figure it out yet either. They might even be for an entirely different prototype chassis set-up....

You will note they have sprockets on the outside to take a chain drive. Part of me is wondering whether this might somehow explain the two pinion position on the belt drive set-up as previously discussed? Or is this for a front wheel drive configuration?

Anyway - there are no out-drives on the rear gearbox as far as i can tell, but there is a very cool chain guide (which looks to show some use) a bit like the belt guide fitted to the belt set-up, and there is a Brimod gear adapter which for the moment i plan on switching over to the belt configuration for now.

I will get these gearboxes stripped to have a look as soon as i can (it is squeaky-bum time here at the minute as i have lost a bag en-route to my ship and of course, these two spare gearboxes were in the bag i lost!!!) If and when they eventually show up i will swap the spur gear adapter and have a nose inside the chain drive boxes.

[dinglem]

OK... so on to the front diff.

Totally unknown territory here, without any instructions, but it didn't take me too much effort to release the front-end of the car, with just a few screws requiring removal enough for me to be able to flare out the vertical chassis plates and to enable me to free up the front gearbox barrel.

I was expecting to find a ball diff, but it is actually kind of two out-drives over a central loose spline, and then these outdrives just tightly slip inside the main belt drive barrel which houses a couple of fairly large one-way bearings. It acts and behaves like it has front one-ways and drives going forward and freewheels as you would expect.

It behaves like a diff, without the diff! It is very much like the original SWB CAT front - end in fact. Quite a neat and very simple design, and of course, very well engineered. It has two fibreglass discs, what looks like a Tufnol(?) main belt drive gear and a nicely machined central barrel.

I just spruced it all up, lightly cleaned and oiled the bearings and put it all back together again after a few pictures.

[Dadio]

That's a nice solution for the one ways , keeps the up-sprung (or is it un-sprung , been drinkin and cant remember)mass low not having them in the knuckle or drive shaft , also keeps the muck out of them too .

[dinglem]

Yeah, it's quite well thought out and very well made. I just sat there for a while blinking and looking at it thinking 'how the bloody hell does that work?'.... Even when i put it all back together i sat there trying either wheel, then both wheels in both directions and trying to understand what happened. Really interesting.

It looks a lot better now it is clean, as the dull flat finish alloy on the diff barrel was really drawing my eyes..... it's all shiny like the rest of the car now! Just the rear diff to look at and tidy up. That's all dull too, but that will be a much more difficult undertaking to strip i imagine. Again, i am expecting a ball diff, but who knows with this car?!

Whilst stripping the front end i also noticed some lettering and numbers on the drive belt:-

'2520 MXL C5'

I have no idea what they mean, but when I Goodle'd that a belt that looked to be the same popped up, so for under a fiver i had a punt and ordered one. It says it is 640mm long, which seems about right. The original is 7mm wide so i just ordered the same.

Incidentally, the front and rear track on the car with just the alloys is around 245mm (should be spot on 250mm with tyres), so absolutely perfect.

Wheelbase is 268mm.

[Dadio]

MXL is a belt pitch very close to a GT2 , I can never remember witch is witch but one is a metric belt size and the other imperial , the long number is length and the short is width so the belt you ordered will be right I'd guess .

[dinglem]

Finally got around to having a go at the rear diff last night, and it was pretty much as i expected.

Once i eventually managed to extract it (not as straightforward as it appeared), i found the usual ball diff set up with an allen key adjusting screw in one of the out-drives. The diff action was very smooth indeed, and the entire unit was particularly clean apart from a light coating of grease and dust. I must admit i was loathed to strip it when i knew it was probably set to the optimum having only been built for what was presumably light testing. As it all felt so smooth i opted to leave it as it was and replace it back into the car. Looking through the gears and inner out-drives i could see the diff plates pressed up against the sides of the main drive gear. Both that gear and the belt drive appeared to be made of the same dark brown material as the front diff. Hard to tell whether it is Tufnol or some fort of Bakelite material? I have read up on Phenolic Resin Laminated Bakelite gears which are supposedly very tough and silent running, and they do look very similar in appearance to these, so perhaps that is what they are. Would be good to get some spares anyway. At the moment they have zero wear. The same round fibreglass belt guides were present as seen on the front, and the entire unit is firmly clamped together with the three small screws as also seen on the front.

It also has a pair of lovely machined alloy bearing holders which mate into the round cut-outs in the vertical chassis plates when installed. All in all it is another lovely piece of engineering.

I took the opportunity to count the gears whilst it was out. The small drive pinion on one of the outdrives has 17teeth, and the main diff gear has 47teeth. I though that info might be of use later on should i try to work out the final drive ratio. The only thing which is twisting my melon currently is that I don't have any small allen keys out here with me, and that drive pinion which mates up to the final diff drive gear is very slightly offset to one side - will have to adjust that to get a full mesh when i get off ship.

In other news... my luggage has turned up in-country so it seems as though the spare gearboxes are not lost afterall! Hopefully they should make it out to me in the next few days so i will be able to look at those shortly. It also means I will be able to fit the correct Brimod spur gear adapter to this current set up. Then..... on to the electrics.

I have also settled upon a bodyshell for this car. Nobody really knows what it was built with.... no pictures or details of this car actually exist. It has been run and there is evidence of servo tape on the chassis to suggest radio gear was installed at some point, so you presume it was driven a little. I will add more on the shell once it arrives and i can trial-fit it, as at this stage it is a little bit of guesswork.

[Dadio]

The diff parts do look more like Tufnol than Bakerlite , looks like it has a weave to it and Bakerlite is usually more natural plus the colour looks more Tufnol , this kind of component is the best argument for getting a 3D printer , you run off a copy in carbon nylon that's expendable and save that utterly unique part in pristine condition .

[dinglem]

My father is proper into his plastics and so on - they were his job for his entire career, so he can ID materials such as these no problem. I am sure he will be all over it once I get it home and he can give it a look over. I did do a bit of research into what it might be which is how I came up with that Bakelite option. These gears seem much darker than the Tufnol gears I used to run, and I did see some of those Phenolic Resin laminated example gears online earlier which looked very much like the ones in these diffs. Could be wrong though.

I agree with you however - if they cannot be replaced then I need to have a good think about my options. The belt was my main priority for replacements, but that rear main drive gear is also something I need to have in duplicate really.

[jwscab]

Tufnol bakelite, phenolic, resin etc is all under a larger group of composite materials. It could be paper, glass, pulp, teflon, kevlar etc. So it's all kinda the same material with different fillers.

[dinglem]

Tufnol bakelite, phenolic, resin etc is all under a larger group of composite materials. It could be paper, glass, pulp, teflon, kevlar etc. So it's all kinda the same material with different fillers.

Well hopefully I can find one of the above in 32DP with 47 teeth so I have some sort of spares back up! I doubt the belt pulley ones will be an issue but there is all sorts of potential for stripping that main rear drive gear....

The chain drive gearboxes should be arriving here with me in the next couple of days so I will give those a look over next.

[jwscab]

Yep I'd bet your dad could modify a pan car gear or two to fit properly. Wonder if 47t is a common size

[Dadio]

Is the rear diff gear and pulley all one part or are they separate , it looks like one piece .
For belts and pulleys have a look at "Belting online " I've used them and they have a fairly comprehensive catalogue .

[dinglem]

Yep I'd bet your dad could modify a pan car gear or two to fit properly. Wonder if 47t is a common size

Yes, i am 100% certain my father will be able to sort something. Good call regarding the pan car gear too. I am starting to look for 47tooth 32dp gears online now, but not coming up with much so far.

[dinglem]

Is the rear diff gear and pulley all one part or are they separate , it looks like one piece .
For belts and pulleys have a look at "Belting online " I've used them and they have a fairly comprehensive catalogue .

They are separate parts. If you look closely you can see there is a fibreglass disc belt guide between the two parts. The whole unit is held together with 3 screws as per the front unit. The outdrives and diff plates are then pressed against the balls in the rear drive gear and tightened via an allen key screw through one outdrive as per most other ball diff examples.

Thanks for the belting online link also