4509 Rear end ratio 4.71 5/7 to 1? Or 4.11? 65mph with Allison 3 speed?

[busfan]

4.71 is what I pull up for the 3610 Hydraulic 2 speed.
The only tid-bit I could find is the 'transit models' 3610 Hydraulic 38 Passenger model and a late 40's coach, good chance that is a bit shorter than this 51 4509 35 footer Hydraulic 2 speed thou..

Hopefully fitting the 4509 with a 3 speed!

Any ideas on what I could expect as far as top speed on flat with a 3 speed and 4.71 ratio?

Looks like 4.11 would get me to 63ish while maintaining good economy.. Tire size is 9-20.   

[TomC]

Your 9.00-20 tube type tire is equal to a low pro 22.5, like a 275/80R-22.5. 517rpm (revs per mile). Allison V730 has a .875 overdrive in third. So with a 4.71 x .875 = 4.12 effective ratio x 517rpm = 2,130rpm at 60mph. If you cruised at 55 you'd be at 1952rpm. At 65 you'd be at 2307rpm-thee fastest I'd run a 71 series all day. Good Luck, TomC

[busfan]

At 65 you'd be at 2307rpm-thee fastest I'd run a 71 series all day. Good Luck, TomC

Thanks Tom! 

Guess she'll have to get used to the short haul, at that point just might as well leave in the 2 speed?   

Wondering if there different gear ratio's in the 4509 2 speed Hydromatic V drive transmissions?

Do you happen to know what the 4 speed spicer suburbans run for a rear end gear ratio?  I assume they are all the same knowing that there was about 4 different models/gear ratio's of manuals.

[Runcutter]

Since I drove 4509's and 4512's in service, please be aware of a big difference.  The 4509 is a spring ride, the 4512's were the first of the air rides.  Yes, the ride quality is different.  We did have a couple of 4512's (and a 4515) with four-speed sticks.  Fun to drive, even in transit service.  Occasionally, we'd have to use the 4512's and 4515's on the highway, in and out of Boston.  There was no problem with the sticks, but we were only on the highway for about 18-20 miles. 

So, my surmise is that, since they're essentially the same bus, the two-speed auto could probably be replaced with a stick.  (I think the autos were a VH-9, but could be a VS-2, my memory doesn't go back to that detail).  The straight 6-71 was a fine engine for both, but, remember, they were intended for transit service -- not speed nor highways (being designed before the Eisenhower Interstate System.) 

Do the GMC Old Looks (4509-4515) discussed here have much in common with the New Looks (Fishbowls), post 1961 or so, as to running gear?  Maybe, maybe not.  Do remember that they're different generations.  While the Old Looks had a straight 6-71, I think the Fishbowls started off with the 6V-71.  Might make a big difference on transmission compatibility, and the angle of the V-drive coming out of the transmission, going into the rear end.  All Fishbowls were air-rides, so swapping rear axles with an Old-Look spring ride might be a non-starter.     

I'd have a friendly argument with RJ, that while the 4106 may be the sports car of coaches, a 4512 with a stick is the sports car of transits.  I'd intentionally take one of the sticks when I worked Saturdays, the short day (only 10 hours).

But, in my opinion, the spring ride of the 4509 would be a deal-breaker.  Worth being aware of.

Arthur

[CrabbyMilton]

I wonder if anyone ever put a modern 4 stroke engine and automatic in one of those GM OLD LOOKS.
If not, an 8V-71 or 6V-92TA with a V730.

[buswarrior]

Might make a big difference on transmission compatibility, and the angle of the V-drive coming out of the transmission, going into the rear end. 

Arthur

This is your number one question.

On the highway side, 4104 rear angles are different from all that follow, and the V730 fits the followers.

Without a donor rear axle, it gets ugly quickly.

Which transit model/year marks the drive angle change?

happy coaching!
buswarrior

[TomC]

As far as 4 stroke engine changes-with the V730R (reverser gear), Detroit Series 50, Cummins ISL and ISM were used. S50 and ISL are about the same length, although S50 is much taller. I would go with a Cummins ISL can be turned up to 450hp and 1250lb/ft torque (RV version). Good Luck, TomC

[busfan]

Runcutter great stuff! wow lot's of information, so the VH-9 is the older tranny and likely has less top end speed?  I actually prefer the springs, hey the two captains chairs are air ride ..Just looking at the air bags on my fishbowl strains my nerves and wallet..

Tom thanks for the bit on the 4104, Bill up in Ontario with the 730VH2 mod told me that bit as well about the angle being different.. Weird as one would think 4104 would be same angle, is that something a spacer would fix?  I guess a spicer out of a 4104 would follow the same rule..dang those 730r's are cheap when they come up saw about 3 rebuilt for 100$ each..Not wanting to get that deep  

Now I'm thinking of different rims and taller tire options.

Great info all, Thanks! George

[Runcutter]

I wouldn't hang my hat on my recollection of which automatic transmission was where, when.  

I just pulled out a 4512-4515 maintenance manual, and the TDM's (Transit, Diesel, Manual vs. TDH, Transit, Diesel, Hydraulic) had a Spicer model 7141 transmission.  Angle drive 1 to 1.  Ratios, First, 3.86 to 1, 2.50 to 1, 1.50 to 1, and fourth (direct) 1 to 1.  Reverse 3.29 to 1.  Manual refers to a separate Hydraulic Transmission book, which I probably don't have.

Fishbowls (New Looks) started with TDH 4516 model number.  I do have a later maintenance manual.  At least post-TDH/TDM 4523, sticks had a Spicer 7145VK. However, sticks were mostly for Suburban models, (SDM), with higher ratios (4.28:1 First, but then the same 2.50:1, 1:50 to 1, and 1 to 1).  Higher reverse, at 3.56 to 1.  Interesting, maybe the higher first ratio worked differently with a different rear end, or worked because the bus was lighter.  May not mean anything.

So, a possible point of research might be the specs, and angles of a 7141 Transmission vs. a 7145.  Don't know what the VK meant.

My belief is that Old Looks, at least post- World War II, had basically the same running gear.  But, that's my belief, not documented.  The main point is the Old Looks had straight 6 engines, Fishbowls had V-6.  Total change in engine compartment, because it was an entirely new model, new type of vehicle.  Most likely, that would have changed the angles.  Similar suspensions, but the question could be whether a Fishbowl rear axle and transmission might work.  More likely, though, the issue there would be the mating of the engine and transmission (in-line versus V-drive).  

Of course, different angles could also result in cutting a new hole in the engine bulkhead.  Don't know about old-looks, but the bulkhead was a weak spot in the earlier Fishbowls, the way you spotted a cracked bulkhead was to look at the builder's plate,  If it said 4517 or 4519 (maybe up to and including the 4521), it likely had a cracked bulkhead.

For anyone not aware, the old GMC numbering was T (Transit), S (Suburban), P (Parlor -- coach); D (diesel) or G (gas), M (manual transmission, H (hydraulic transmission).  Next two numbers were seating capacity, (37, 45, 51), last two were theoretically the model in the series -- but with some inconsistencies.  At some point, even/odd referred to 96 inch wide (odd), or 102 inch wide (even) bodies.  

Arthur

[chessie4905]

After installing the hydra-shift in our 4104, we decided to try a 4:55 rear for better starting out. We got one from an old look and one from a new look or fishbowl. We didn't know about different angles in those days, but the new look rear wouldn't work because, at least, the stud holes were, if I recall smaller and would have needed enlarged. At that point, we used the old look rear. Bolted right up and made starting out and backing up a breeze, and with the Hydra-shift, in overdrive would still top out a little over 85. Only issue was that ring and pinion were severely pitted and made a growling noise. We went back to the 4:12, as with no internet back then, no resources to find a good one.

[busfan]

After installing the hydra-shift in our 4104, we decided to try a 4:55 rear for better starting out. We got one from an old look and one from a new look or fishbowl. We didn't know about different angles in those days, but the new look rear wouldn't work because, at least, the stud holes were, if I recall smaller and would have needed enlarged. At that point, we used the old look rear. Bolted right up and made starting out and backing up a breeze, and with the Hydra-shift, in overdrive would still top out a little over 85.

Was the Old Look 4:55 too?  Wow Dunno if I need to go 85, sounds like the perfect ratio for highway cruising thou!

[chessie4905]

Yes, but that was a special addition that GM made to  regular transmission giving an overdrive in each gear. Top speed in your situation would be about 60 to 62 mph. If you installed 4:12 rear from a 4104, your top speed would be 68 or 69 against the governor.

[TomC]

With 11R-24.5, 4.56 rear end, V730, I cruise at 60mph @ 1,900.

[Paso One]

Going way back when my fishbowl first hit the road the 6V71 was coupled to the VH9 and a 5:31 rear end. Top speed was 48 MPH.
I got a 4:10 rear end from Luke and a 4:11 from Loren at Dreamliner coach.
I put the 4:10 rear end in and kept the 2 speed VH9 transmission while i looked for a V730 top speed was 56 MPH.

When I got the V730 installed with the 4:10 I was able to cruise at 64 MPH

I bought a parts bus from Colorado with a 8V71 and a VS2-8 transmission  and a 5:31 rear end that bus cruised at 73 MPH (according to chase vehicle)
This was a factory fishbowl  set up sold to Seatle transit c/w jakes.

[busfan]

Looking at a 69' parts book I found that SM(suburban manual) models were only sold with 4-1/ 9 1 ratio and 4-5/ 7 1 ratio rear.. Should help to narrow it down.

Thanks Ches Tom and Peso all good stuff, guess I will plan my future slow driving accordingly ..