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
Isn't the 4905 a V drive if so a 740 won't work
good luck
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
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
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
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
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 (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
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
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.
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
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."
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
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
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
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
Bryan -
Let me clear up a few things in this thread:
The HT-700 series transmissions are for T-drive configuration powertrains. They will not fit in the V-drive GMC layout.
Until the newer "World" series of electronically controlled automatics, all the Allisons had a top gear ratio of 1:1, just like the manual gearbox. The major difference is in the bevel gear ratio used for the V-drive 730.
The stock bevel gear ratio for the Spicer 4-speed is 0.808:1, starting with the 4106s. Prior models used a 1:1 bevel gear ratio.
The stock bevel gear ratio for the V-730 Allison is 0.875:1.
The stock rear axle ratio for the 35-foot GMC highway bus models, starting with the 743, was 4.125:1.
The stock rear axle ratio for the 40-foot GMC highway bus was 4.375:1.
Coaches equipped with automatics do run slightly hotter than manual transmission models, but not to the point of overheating unless there are other issues with the cooling system, most of which are NOT transmission related.
All of the above is well documented in various places. What isn't as well documented is the following:
The optional bevel gear ratio in the V-730 was 1.04:1 (This is EXTREMELY rare, like new rear glass for a Scenicruiser.) Muni in San Francisco used these in their Fishbowls, but all of those coaches have long since been scrapped.
The optional automatic in the GMC was the VS series, up until 1977 or so, used with the stock rear axle.
The optional V-730 (using the stock bevel gear ratio), when installed in the 40-foot Buffalo, also included the 4.125:1 rear axle, in order to maintain performance relatively equal to the manual transmission.
The 4.375:1 rear axle was an option on the 35-foot Buffalos, but one that was rarely installed. (Primarily for mountain operators.)
Installing a V-730 into a 4-spd 40-foot Buffalo will lower your top speed by about 5%, and increase your fuel consumption by about the same. Without also installing the 4.125:1 axle, some of this can be regained by using 11R24.5 tires that turn 470 revs per mile.
All GM highway buses had their powertrains designed around tires that turn 495 revs per mile. When replacing tires, keep this number in mind to maintain stock performance.
There is a good calculator on Daris's site that allows you to play with all kinds of combinations. Click on the "MPH Calculator" in the LH window here:
http://www.thebouthilliers.com/4106/ (http://www.thebouthilliers.com/4106/)
Using Daris' calculator can give you a good idea as to why a stock 35-foot GM will "run away" from a stock 40-footer at any given rpm!
Finally, only about 235 4905s were built with the V-730 option during the last three years of production (1977 - 1980). I have a delivery roster with the VIN's of these somewhere in my files (still unpacked after my recent move).
FWIW & HTH. . .
Thanks RJ, that helps lay it all out. ::)
Bryan
I knew RJ would jump in and straighten us out. :)
RJ,
I did go to Daris calculator and plugged in my tire diameter and gear ratio. Tires are 12x22.5 and rear gear 4.375:1. It appears to be considerably off from what my actual is. Unless My Final Vehicle Record has the wrong gear ratio on it. I can run 75 MPH and it does not feel like I am close to 2100 RPM and seem to have alot left. Is the gear ratio on the axle stamped to a tag or something that I can verify?
Just when I thought it was all figured out :-\ LOL
Thanks,
Bryan
To get the MPH to show what I think the bus would top out at I think I must have an old Mopar 3.23 gear ratio! LOL! ;D :D :D.
Bryan
RJ,
If the reduced speed is only by 5% I should still be able to run 75 MPH if I chose to. Not that I want to all the time anyway. I know the ole girl will do 80 MPH with no problem on GPS. I have hit that speed going up a grade on my way to JV's place in Texas. Not purposely, just did not realize I was running that fast, oop's ::).
Bryan
Quote from: Lin on November 11, 2009, 03:27:54 PM
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."
I looked at my nameplate just out of curosity the numbers are as follows Serial # 0510015641
Part# 6882760 80 D 26
Model # V730 D
I don't know what the "D " is but it is after "A" and "B" so assuming there was a "C"
Interesting
Paso One,
I was refering to the rear axle ratio. Figured there must be an ID Tag that will list the ratio. But the V730 info may come in handy as well.
Thanks,
Bryan