Thread: Progress on the bus . . .

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Nice write up Johnboy! It's nice to see and hear you're getting so close to being done and can finally get to the best part. Enjoying it.

Originally Posted by 34_40

And we don't get photographed for the paper wearing leapord print suspenders either!

(Shrugs shoulders.)
Not a problem to me mate.
That's the way She Who Must Be Obeyed dresses me every morning.
It's who I am.

So if you have a problem with it, I would suggest that you're the one with the problem.
Not me.



(Just kidding ya...don't get septic... )

That's a nice writeup, Johnboy, and the bus is looking great. Also, good on ya' for the hair thing.
.

Originally Posted by johnboy

(Shrugs shoulders.)
Not a problem to me mate.
That's the way She Who Must Be Obeyed dresses me every morning.
It's who I am.

So if you have a problem with it, I would suggest that you're the one with the problem.
Not me.



(Just kidding ya...don't get septic... )

All smiles over here Boss! Just had to take a poke at the bear ya know?

We put a higher ratio diff (lower numbers,) 3.42:1 in the bus because at 90kph (55mph) the motor was revving way too high. (Being classed as an hgv 55mph is the fastest I'm supposed to be allowed to drive on NZ roads.)
Now, at 55 mph I'm revving around 12-1500rpm. Quite satisfactory; I'm happy with that.
But...I have inadvertently exaggerated/exacerbated the differences between 2nd and 3rd, and 3rd and 4th.
Revving too high in 2nd, change up, and too low in 3rd, too high in 3rd, change, and too low in 4th.
So...I decided to split the shifts with a Gear Vendors under/overdrive transmission in the driveshaft.

But; which transmission would suit my application?
So I went to their site:
https://www.gearvendors.com/cg2wdt.html
And decided that the NV4500 would appear to be the best bet for me.
But am I right in this assumption?
I'm not familiar with these things; and I'd hate to get it here (and paid for...ouch!) only to find it's just not right for what I want.
There are an awful lot of people on here who know an awful lot more than I do; and who's opinions I respect...so what do you fellas think?
Am I right?
Or am I wrong?

Help!

(Please?)

Originally Posted by johnboy

We put a higher ratio diff (lower numbers,) 3.42:1 in the bus because at 90kph (55mph) the motor was revving way too high. (Being classed as an hgv 55mph is the fastest I'm supposed to be allowed to drive on NZ roads.)
Now, at 55 mph I'm revving around 12-1500rpm. Quite satisfactory; I'm happy with that.
But...I have inadvertently exaggerated/exacerbated the differences between 2nd and 3rd, and 3rd and 4th.
Revving too high in 2nd, change up, and too low in 3rd, too high in 3rd, change, and too low in 4th.
So...I decided to split the shifts with a Gear Vendors under/overdrive transmission in the driveshaft.

But; which transmission would suit my application?
So I went to their site:
https://www.gearvendors.com/cg2wdt.html
And decided that the NV4500 would appear to be the best bet for me.
But am I right in this assumption?
I'm not familiar with these things; and I'd hate to get it here (and paid for...ouch!) only to find it's just not right for what I want.
There are an awful lot of people on here who know an awful lot more than I do; and who's opinions I respect...so what do you fellas think?
Am I right?
Or am I wrong?

Help!

(Please?)

Hi Johnboy! Remind me which engine/trans you have in there.....you did a chassis swap onto a Chevy truck of some kind didn't you? It sounds to me like you might have gone too far with your rear diff. gears. If you're only running 1200-1500rpms at 55mph pulling that kind of weight, it's probably lugging and has no power especially if you encounter any kind of grade change in the roadway. What were your original gears? What were the rpms that you considered too high revving? I read somewhere that the small block Ford engines, for example, cruise most efficiently between 2000 & 2200rpms. Maybe there's a similar optimum for your engine. Those GearVendor things aren't cheap. I'm wondering if it might be more cost effective to find a better compromise in the rear diff gears....

jb, I think that Randy's on target here, and just to clarify when we look at the Gearvendors site and run down their list in the various transmissions that they list we're selecting the right Gearvendors unit to match up with the tranny we have in the vehicle. Are you considering changing out the tranny, and then adding a Gearvendors unit behind it?$$$$$? I'm a bit confused with the options you're considering.

I'd think that your 6 liter Vortec would be a lot happier cruising at right around 2000rpm when at your desired cruising speed in 5th gear, plus you'll be up on your torque curve more where you'll have some power for the hills & curves without downshifting. Lugging it down to 1200-1500rpm is going to be hard on the lower end, and will tend to load up on you over time.

I've got a little spreadsheet that I built for my Tremec TKO that let me see the speeds in each gear across the rpm range, based on the tranny ratios, rear end gear, and tire circumference. The real test is what feels right in the vehicle, selecting your shift points, but it helped me to get a feeling for what I would experience based on the numbers, before spending a dime. Like Randy asked, what's your tranny, and also what's your tire circumference?

Oops!
I wrote my previous post last night, had a beer or two, went to bed, and whilst awaiting sleep thought "Bugger! I didn't put enough information in that post!"
Tyre size is 225/75 R16.
Engine is Chev 400 ci Vortec, purchased as a new crate motor 2013.
Gearbox is 5 sp manual with electric speedometer. I've crawled under the bus, gone through my invoices, but can find nothing to actually identify it so that I could identify the ratios in it.

At those revs in top (5th) gear the engine isn't labouring and is very responsive, put the boot in and it launches instantly, there's absolutely no lag...it feels right.
For sure, I have to flick it between 5th and 4th fairly often; but that's not a problem, and at those revs in 5th I've got fuel economy.
So I'm happy with revs/ratios in top gear, it's 2nd/3rd, and 3rd/4th that is the worry.
That's the reasoning behind wishing to split those shifts, and still retain the lower revs in 5th.

Maybe give Coxy a ring and see if he can ID that tranny for you? Or maybe the fellow you bought the package from, assuming you got the crate engine & tranny together? Once you ID the tranny we can run some numbers on shift points vs rpm and see what works best for you.

I'd really be surprised if you didn't see an increase in your MPG by boosting your rpm up to the 1800 to 2000 range at cruise, and it would eliminate a lot of your downshifts, too.

I've been mullin' this over for a couple hours now... and if were mine, I'd probably track down a 2 speed rear end.

Not sure how popular they were down under.. but there's always another angle right!?!?

Johnboy, as far as I know, the chevy gas engines had NV4500's in them up until 2007 in a light truck. The diesels had a ZF6 behind them. Are you stuck on a manual trans? An Allison 1000 series 6 speed would be a nice trans for you. GM had them behind 8.1's in some motorhomes but they were mainly behind duramxes. The gear splits are nice on it and would fit your bus pretty nice I bet.

John,
I think Ryan is right about the NV4500. I pulled the ratios from Wikipedia for GM, '94 and later; and got your tire OD from Tire Rack. Running the numbers shows 1575 RPM at 55MPH in 5th, which is a bit low IMO, but may not be critically low.

What does come out is that your low gear is pretty much a Granny gear at 5.61 to 1, and second is still pretty low at 3.44 to 1.

If you say that 3500 is a good shift RPM you're only getting to 16mph in 1st, 26mph in 2nd, then taking it to 52mph in 3rd where you'd skip to 5th and drop down to 1575rpm.

If you went up to a 3.73 those shift point values would only drop a bit, to 15, 24, 48, 82, and top speed at 3500 of 112mph with no consideration for air resistance ; and your cruise rpm at 55mph would be 1717rpm.

With the GearVendors information we could plug in a 1.5, 2.5, 3.5, 4.5 and double OD for the Chevy tranny numbers if it would help. The ones that they quote are Dodge values - close, but not exact.

Originally Posted by 34_40

I've been mullin' this over for a couple hours now... and if were mine, I'd probably track down a 2 speed rear end.

Not sure how popular they were down under.. but there's always another angle right!?!?

Mike, the GearVendors unit is basically just an external 2 speed differential that fits between the tranny & the differential - lets you have an OD for every gear, but clutchless operation which is kind of a neat feature.

I also found out that ZF6's were put behind the 8.1's as well. The ZF6 has another gear between 3 and 4 with 5th being direct and 6th being OD. That 3-4 split on NV4500's is a big one on all the ones I've driven.

Originally Posted by rspears

Mike, the GearVendors unit is basically just an external 2 speed differential that fits between the tranny & the differential - lets you have an OD for every gear, but clutchless operation which is kind of a neat feature.

Yes, I know. I've driven many small trucks with a 2 spd rear axle. Most were small sized big block gas motors. And I never used a clutch unless at a stop sign or light.

Once proficient, gear selection happens with a "blip" of the throttle.

I also agree that Ryans selection is probably the most practical - and once in place easier than any other selection.

Originally Posted by 34_40

I've been mullin' this over for a couple hours now... and if were mine, I'd probably track down a 2 speed rear end.

Not sure how popular they were down under.. but there's always another angle right!?!?

I tried to reply to you lot this morning, but the little blue jelly-fish just went whizzy-whizzy around in circles and nothing happened...so I gave up after six or seven minutes. ( The time it takes me to have a ciggy.)
Two speed Eaton diffs were on pretty well every larger (over three or four tons,) truck I drove, with Road-Ranger 'type' three speed boxes on things getting up around the fifteen twenty ton (or more,) mark.
I drove milk-tankers (getting up around forty tons,) for more years than I care to remember, so yes; they're available in NZ, and that thought had occurred to me too.
The problem here is that if I fitted a new axle, I would also have to fit new (possibly larger,) rims.
That would require re-certification, as this vehicle, although only a Tonka toy of around three tons, is classified 'Heavy Goods Vehicle, (hgv) under NZTA rules, and any changes of that nature would require their involvement...and I don't want to get involved with those bastards ever again!