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Author Topic: V730 Transmission top speed  (Read 3408 times)
PlumCrazy
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« on: June 30, 2007, 12:05:54 AM »

I got the bus title transfered to a Motorhome and got insurance on it today.
Took a test drive and again have come up with top end speed restrictions.

I absolutely expected this with the city transit bus I have used for my shell (1981 GMC fishbowl).
6V71 with V730 transmission combo with what I presume to be city gearing.

On the highway, I get 70kmh (sorry, Canadian Eh?) top speed downhill full throttle.
When I put the tranny in Neutral I roll and gain speed.
However, after I shift back to Drive I can get 85 - 90kmh on the flat with control.
Once I slow down to 70kmh or lower I am restricted to my 70kmh and cannot gain any more speed.

Last time I took the bus for a drive to the weigh scales a few weeks ago, I achieved 85-90kmh on the flat by just shifting to Drive from a standstill.

I do feel 2 gear shifts, into 3rd at about 50-55kmh.

Sorry for the long winded post, but I am a little confused.
I understand the real fix is to find out my gear ratio in the rear end and put in a highway gearset (or replace the whole drive train).

Any ideas what is going on here.

Thanx for any input.
Mike.
www.plumcrazy.ca
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1982 GMC T6H-5307
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« Reply #1 on: June 30, 2007, 02:51:43 AM »

Mike; 
     After reading your post, I took an RTS coach from work for a spin. These coaches have a v730. When the coach started to go I counted the surges. There were 3. First the torque converter locks up, then the shift to 2nd, then 3rd. That would feel like 3 gear changes, but in reality it's only 2. I wonder if you aren't getting 3rd gear. Or your torque converter isn't locking up. Also, for what it's worth, I was told that some city transit coaches, to keep their speed in check, didn't have or couldn't get 3rd gear.
     I hope this gives you a place to start.  Good luck;   Cable
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Sofar Sogood
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« Reply #2 on: June 30, 2007, 05:02:56 AM »

V-730 lockup is in second gear before 3rd gear sets in.

If you feel 3 shifts, You are fine. 1st gear you wouldn't feel because its all hydraulic, Then you would feel second kick in, then a bump as the torque converter locks and the final gear at about 40 to 45 mph.

The limiting factors are: 6V71 engine is a wimp @ about 190 hp. Governor is set low. Rear End ratio is set for city use. ( 5.36 , 5.13 , 4.56 or ?) As those were pretty standard. An RTS with a 5.36 rear will only do right at 54 mph and is great for drag racing but no speed.(empty) And that was with a 6V92TA that was pumped to 350 hp. It would tear off the line but putter along on the highway.

You can spend the approximate $3,500 for a gear change to 4.11 (4.10) but of you are lacking horsepower to push the bus, You will probably not change much except the top speed downhill with a 60 mph tail wind.

You could have a speed limiting governor that once you hit top gear limits you to about 50 mph. I saw that some transit agencies did that a while back. You need a mechanic familiar with the bus and setup to verify what you have.
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donnreeves
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« Reply #3 on: June 30, 2007, 05:33:48 AM »

One other problem you could have is that some V-730's are set to shift into 3rd at 2350 rpm. If you can't pull that in 2nd it won't shift to third. Mine is that way. When I changed from an 8V-71 to a 6V-92, the no load speed on the 6V-92 was set at 2150 and I couldn't get 3rd gear.After a week of crawling underneath and dropping vast amounts of trans oil on my face, I found all I had to do was adjust the governor.  Donn
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Buffalo SpaceShip
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« Reply #4 on: June 30, 2007, 06:31:41 AM »

Donn could be on to something here. And maybe you're fooling your modulator by shifting in and out of neutral at speed in order to get into 3rd lockup. But without a tach and some definite info on your final drive ratio, it's hard to know for certain.

FWIW, with my V730 and 4-1/8 rear end, I can get up to about 72mph (116kph) at 2100rpm. 2nd lockup to 3rd lockup occurs at about 45mph (72kph) and 2200rpm and is rpm-defendant, whereas the prior shifts are throttle-dependent.

If you have the R-N-D-2-1 shifter, you can play around with feeling the different gears and lockups. My favorite is 1st lockup, which doesn't ever occur in a standard shift sequence, but can be forced by waiting for second lockup in 2 and shifting into 1. It's great for climbing and descending steep hills. TomC taught me this trick.

HTH,
Brian Brown
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Brian Brown
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« Reply #5 on: June 30, 2007, 08:41:26 AM »

The mear fact that you can get 85-90kph after shifting from neutral to drive after coming down a hill tells me you're just flat out of horsepower (not a surprise with a 6V-71 non turbo).  You have enough power to maintain speed but not enough to get to that speed.  I would see if you have a vehicle limiting speed governor on the engine (usually another rod coming off the governor to a box).  You're engine governor maybe sticking at a lower than ideal rpm.  I would buy a hand held tachometer that you can push against the pulley on the front of the engine and see what the top governed speed it.  I bet it's set at 2150.  I would change that to around 2600 no load (Detroit made a 6-71 marine that was rated at 2500 full load) and see where that takes you.  I think in the future, once you get the bus converted with all the extra weight in it, you'll want more power.  Two ways of doing it-one you can turbo your 6V-71 to get an easy 300hp and 900lb/ft torque (you have 210hp and 550lb/ft if running 60 injectors), or just find another fishbowl with a 6V-92TA and swap the whole engine cradle-then you'll also have the correctly sized radiator.  Let us know what you find.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #6 on: June 30, 2007, 09:26:17 PM »

I'll have to do another higway run paying close attention, but I am sure I only feel 2 gear changes or surges.
Should I expect to feel 3 surges?

Acceleration speed seems quite acceptable from a standstill and speeding up from slow traffic, except when on a steep hill as is to be expected.

It is the inconsitency that bugs me here.  I can accept the limitations of power and speed, but want to make sure I know what I can safely expect to see.

Thanks for everyone's input.

Mike
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Cary and Don
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« Reply #7 on: June 30, 2007, 10:45:43 PM »

Hi,  We didn't feel three bumps in our V730 either.  Then we spent Christmas stuck in the middle of nowhere after the little gear on the transmission governor broke off and we only had first gear.   We now have three bumps. We suspect that something may have been wrong ever since we got the bus and just didn't know any better.  There were some of those governors on Ebay for about $15 and I bet they are still there.  We now have an extra.

Don and Cary
GMC 4107
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« Reply #8 on: July 01, 2007, 10:27:16 PM »

Quick update:

Took the bus for another run today. 
Changed fuel filters, topped up with fresh fuel.

Took her out on the highway and reached 95kmh without hesitation!
I thought I had it licked.
But, when I slowed down to under 70kmh, I could not exceed 70.

I pulled over, put the bus in 1st and drove to see how many shifts I felt.
I was intending to walk through a "manual" shift to count the lurches.
To my amazement, I felt 3 distinct shifts while still in 1st, the last at about 65 into 3rd and I reached my 95kmh once more.
When I am limited to my 70kmh I do not feel the third shift.

I thought back to my previous trips where I reached 3rd gear and top speeds and I realized that I had to reverse first, then shift into drive.

I think I may have a linkage problem.
I'll have a good look in the morning.

Mike
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« Reply #9 on: July 01, 2007, 10:42:51 PM »

One other problem you could have is that some V-730's are set to shift into 3rd at 2350 rpm. If you can't pull that in 2nd it won't shift to third. Mine is that way. When I changed from an 8V-71 to a 6V-92, the no load speed on the 6V-92 was set at 2150 and I couldn't get 3rd gear.After a week of crawling underneath and dropping vast amounts of trans oil on my face, I found all I had to do was adjust the governor.  Donn

Oh goody goody goody.. Now, How do you do that ?
My trans isnt coverd in my book. I have 3 little buttons for the Tranny. "Forward"  "Neutral"  "Reverse".. Thats it.. I have a Toggle switch on the panel to the left of D seat.  Its supposed to be like an Overdrive ?
Dont seem to do anything Huh

Paul...
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« Reply #10 on: July 01, 2007, 11:27:23 PM »

I have that red cover protected toggle switch too that doesn't seem to do anything.

I suppose it should be a mouse trap or emergency shut off, but in my case does nothing.

Mike.
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niles500
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« Reply #11 on: July 02, 2007, 08:29:01 AM »

Mike - you may want to check your Fluid level, Filter and Pump - in that order - HTH

*** that's Tranny Fluid, etc.
« Last Edit: July 02, 2007, 08:37:03 AM by niles500 » Logged

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« Reply #12 on: July 02, 2007, 05:37:39 PM »

59.03 Miles per hour... =  95 km/hr

I really hate having to convert speeds so that I can understand things.

That's downhill with a tailwind

Sounds like you have a 5.13 or 5.38 rear end ratio and probably 12R22.5 tires.

You can wind up but no top end power to maintain. Engine may be rev limited to 2150 or lower loaded
or just doesn't have the legs to run at top rpm for long. That is well past the power curve
for even a 6V92TA much less a non-turbo 6V71.

That shift at 70km/hr or ( 45 mph ) is the third gear lockup.

If your shifter is messed up you will no doubt kick the tranny into an unwanted gear and finish it off
in one big messy thud....

You answer is a re-power with a tuned up 6V92TA Silver (MUI) and a 4.11 Rear Ratio to get the power band back down to respectable.

I guess the question then is your bus worth dumping the better part of $10,000 into?
Half of that will just be the gears and getting them setup and installed.

A good used DD 6V92TA (MUI) will set you back a few pennies as will the stuff needed to operate and cool it. The radiator for the 6V71 will probably not handle the heat load.

You may want to find a whole cradle out of a FLXible (43 degree) or RTS (15 degree) depending on your layout. They usually have everything you need including the radiator and coolers. Might as well use/ replace the tranny while you are at it and a whole cradle is the best way to get everything.

Sorry I can't be much more help. I just kept thinking about what you were saying and based my response on info available.

Dave....
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« Reply #13 on: July 03, 2007, 04:58:41 PM »

Hello.

Strange report indeed.

Still using GM Fishbowls in transit service here in Toronto.

6V71 and V730

You feel three "shifts" in these, 1-2 hydraulic, 2 lockup,  2 lockup - 3 lockup.

the shift to 3rd is directly speed dependant.

Also, you won't get the shift to third if the transmission fluid is down.

Not unusual for one to ignore a manual selection for first gear. HT 740 will do the same. Tranny will upshift to protect itself from the inevitable over-rev by the momentum of the acceleration.

Definitly check the linkage, sometimes a bump to neutral is needed to achieve third if the linkage is off.

This set-up will roar along at the speeds you quote. With a light conversion, and a healthy engine, it will get you where you want to go. A V8 would make a nice upgrade, but may be scheduled as funds allow...

happy coaching!
buswarrior
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« Reply #14 on: July 05, 2007, 11:18:20 PM »

OK, problem of not getting 3rd gear is now solved.

Embarrassingly enough, it was the easiest thing that I should have checked first...  Low transmission fluid!

It was obviously low when I 1st drove the bus home after purchase but wasn't one of the things I checked, so I assumed there was a problem and I was looking for difficult solutions.

The bus drives and shifts smoothly and I am happy.
I am limited to 95kmh, but I am happy with that and it was a compromise I was willing to live with when I chose my city transit bus as a conversion shell.

This weekend is the bus's first official outing and I am looking forward to many fun filled adventures.

Thanks for everyone's input and help.
Mike.
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