HT740 in 4905

[bryanhes]

I have searched the archives first before asking this and did not find what I was looking for so here is my question.

I have the 8V-71 w/ Spicer 4 speed. I would like to have the Allison Auto but from the folks that have converted to this from the 4-speed seem to have an issue with engine heating up on a warm day and highway speed being reduced considerably because of the loss of the 4th gear.

My question is can an HT740 be installed to the 4905 w 8V-71? Reason for thinking this is that it is a 4 speed auto and thought I might be able to keep from some of the issues I have heard of. I do not really know what the differences are between the two other than 3 to 4 speed. What are the good, bad and ugly thoughts? 

Thanks,
Bryan

[luvrbus]

Isn't the 4905 a V drive if so a 740 won't work     



good luck

[Don Fairchild]

Clifford;

you beat me to it. Most run the V730 in the 4905's but if you wanted to get trick you could run the RTS V drive.
I think it is either a ZF or Voeth (Not spelled right).

Don

[RickB]

Bryan,

I have a good used 730 out of my old 4905 sitting in storage that you can have. I wouldn't make the switch to an automatic until you have dealt with your overheating issues though, even with a tranny cooler these transmissions will exacerbate any cooling issues on hot days and long pulls.

My 4905's 6V92 was consistently coolable after I had the radiator recored. Unfortunately, there are alot of other things  that can go wrong with the GM's cooling system. The hydraulic fan, stats, water pump etc.

I am not sure where you are but I am Minneapolis/St. Paul and would be happy to givce you my old transmission.

No guarantees of course...
Thanks,
Rick

[bryanhes]

Rick,

I don't have an overheating problem. I was told by a couple of people that have converted from a Spicer to a V730 that they experience the engine running warmer which is probably due to trying to run the same highway speeds that the bus was able to run with the 4 speed in a 3 speed. I'm sure it is because higher RPM's to try and maintain the same highway speed as with a 4 speed.

I do not want to give up my ability to cruise at 70-73 mph in the heat of the summer for the convenience of an automatic. My temp will stay at 180 in 95 degree weather all day long running the factory air. I was not sure if the HT740 would even work. I was just thinking if I could go with a 4 speed auto I would not lose anything but gain the convenience of the auto.

Bryan

[bryanhes]

Rick,

Let me do some more checking into this if I can figure out a way to not lose highway gearing and cooling ability I would take you up on the transmission. My other thought was can the rear end be geared differently to accomodate for losing the fourth gear in my spicer.

Thanks all,
Bryan

[bryanhes]

On another note if anyone has a need for HT740's there are several lots of five for sale on a government liquidation site. They thought they were all rebuilt. Here is a link. http://www.govliquidation.com/auction/view?auctionId=2776509&categoryId=e4897

These seem to be going pretty cheap for a lot and there looks to be several lots.

Bryan

[RickB]

Bryan,

I apologize I just skimmed your original post and thought that you were the one with the overheating issues.

On the gearing issue, I'm sure there are people here who can confirm or deny my advice here but I am under the impression that all the Allsion's in high gear are in a 1 to 1 ratio. Meaning that once you are in converter lock up top gear in a 6 speed or a 3 speed you are in a one to one ration between the engine and transmission. Your top end RPM's would not change a bit from what I understand, althought there most certainly guys here that know one heck of alot more about this than I do.

So the overheating issues that your friends are experiencing may have nothing to do with gearing (now rearend gears are a whole different subject) and may be due to the fact that if you have a less than optimum operating cooling system and then you take another component that generates heat and add it to the cooling system it may be the last straw and put you into an overheating situation.

my 2 cents worth and good luck

[Lin]

The top gear is not 1:1 on all Allison transmissions.  There are over-drive units.  However, third gear in a 730 is 1:1, which is the same as 4th in the Spicer.  Any additional heat issues could only come from the cooling needed for the transmission.  If you could find a way to do that without making more demands on your radiator, you should be fine.

[bryanhes]

I would habe to look back into my manual but I think if a 4905 came from the factory with an automatic it had a different rearend gear ratio than what a Spicer 4 speed had. I think 

Just reading Lin's post as I was typing. If that is true than why would it seem that people I have talked to that have converted would experience higher RPM at the same speeds with an Allison 3 speed auto than what they did with the Spicer 4 speed? As I said to begin with I thought the rear end ratio is different based on what the factory installed. 

As for cooling issue. I would think with a good tranny cooler and possibly a larger radiator (not sure how much larger would fit in the space) would take care of any additional heat generated from the Allison.

Bryan

[Lin]

Well, I stand corrected.  4th in a V730 was usually an overdrive with a .88:1 ratio.  Does that confuse things more?  The following is taken from pardo.net:

"A typical V730 had a 15% overdrive giving a 0.875:1 highest overall ratio. Some were built with different bevel gear ratios, giving a 1.04:1 overhall highest ratio. The lower-ratio units were mostly used with smaller (e.g, DD 6v71) engines and in steeper hills. By 1990 the sales brochure only showed the overdrive unit. See the assembly number found on the transmission nameplate. Look up the assembly number in the Allison parts manual, which will list it as an A or B group code. Group code A is the 0.875:1 ratio and group code B is the 1.04:1 ratio."

[bryanhes]

I just confirmed with my manual and a friend I consider to be A GMC guru that the factory 4 speed had a gear ratio of 4-3/8:1 and the automatic had a 4-1/8:1. It appears that some of the earlier GMC's had an option of 4-1/8:1 on some 4 speed models. Unfortunately my Coach Final Vehicle Record shows it was ordered with a 4-3/8:1.  Which means I could deal with running a higher RPM and just add a tranny cooler with a temp sensor activated fan and tie it into a heat exchanger. I think this should work fine 

Bryan

[wildbob24]

Bryan,

To the best of my knowledge, the 4905 came with the 4 3/8:1 ratio gear with the 4 speed or the automatic. The optional automatic used then was the VS2-8, which is a 2 speed transmission. As far as I know, the V730 was only installed at the factory during the final year of manufacture(1980). Any other 4905 with a V730 has been converted.

The reason the V730 is a little slower than the Spicer is the ratio of the bevel gears are different. The V730 is, as Lin stated, .875:1. The Spicer is .808:1. So, with the V730 you lose a little top end. Some people(like me) get most of it back by changing to 11x24.5" tires.

Bob

[bryanhes]

Actually my manual shows 4-1/8:1 as standard in 4107-4903 and 4905 up to 1970 anyway. For some reason mine was ordered with 4-3/8:1. I don't know why the difference. This is in Maintenance Manual X-6814.

Bryan

[TomC]

Even though the Allison V730 is just a three speed, it will out perform the 4 speed manual since with the automatics torque converter, 1st, and second on the manual is taken care of by 1st gear with the torque converter on the automatic.  I have the V730 on my transit.  With 4.56 gears and 11R-24.5 rubber, I turn 1850rpm at 58 or just over 2100rpm at 65-which is fast enough for me.  Granted, there is more heat rejection with the automatic, and the fuel mileage is not as good, but once you drive one, you'll never want to go back.  Good Luck, TomC