Spoke with Keith Crawford today, he is telling me that I don't need to do anything with my HT740 trans..
He said that the 740 locks up the tourq converter when you let go of the throttle..??..?? Is this true?
If not, that would explain why, I'm not feeling the Jakes as well as I should. I'm leaning towards what Brian Deihl has
enlightened me on with the external electric over hydraulic solenoid..
Anymore facts on this??
Thanks in advance
Nick-
Nick, The reports I have heard from various people indicate the HT series of transmissions all behave similarly, but each a little bit differently depending upon how the valve bodies were calibrated and the model of valve body. The best bet for you is to actually go experiment with your tranny on a steep hill and find out when it goes into lockup. It is very easy to tell when you are in lockup because when you press on the accelerator you get no increase in rpms if the road speed does not go up. Same on taking your foot of the accelerator. If your rpms drop without the road speed dropping then you're not in lockup. Many people have a hard time telling when lockup occurs because it happens during the shift into 2nd (on the 740, shift into 3rd on the 754). Other people have the lockup occur just before the shift to 2nd and therefore feel a distinct additional shift. You should be able to figure out how your tranny is setup by playing with these facts while driving.
Hi Brian,
When taking off from a stop, I feel 4 additional shifts in the trans. "feels like a 5 speed" but, I'm sure it's the lock-up.
And when at cruising speeds, when I let go of the peddle, the rpm's drop off.
Nick-
My 740 would drop out of lockup at about 15 mph. You could definitely tell as you immediately lost the action of the Jakes. I was in some mountains out west where I would have liked to have been able to keep it in lockup at a lower speed, but I never found anything east of the Mississippi where I would have needed it.
As I recall it was Brian that came up with the modification to keep it locked up and I think that would be an excellent mod to have.
Richard
Nick,if you want the hookup like Brian talks about you can get one off a fire truck at a wrecking yard as most had them,but regardless your Jake is going to release at the rpm where the man has it set where it is at 900 rpm or 600 rpm.mine is set at 700 rpm and you can down shift to keep the rpms up and the Jake engaged longer.
Nick- if your rpms are falling off when you take your foot off the accelerator at anything above about 30mph, then your lockup clutch is malfunctioning some how. Under normal circumstances, you should get lock up in the top end of 2nd gear. If you turn 2100 at 75 mph, then lockup should occur around 31mph and stayed locked up in 2,3,4. If your lockup clutch is not staying locked up like it should, your Jake brakes will do very little for you. Good Luck, TomC
I'm with Richard.If there is a modification to keep the Jakes on longer,I would like to know who to contact.I was in the MTS. in Ca. and nearly lost my brakes.I was in second gear with my 748 tranny and the Jakes would go out at 1300 rpm's about 15 to 20 mph.When I finally found a place to pull over my front brakes your smoking and the temp was about 405 degrees.I had to keep the tranny in reverse until I could block up the front tires.Needless to say if someone can help with this problem I would like to know.
Don
Don, you just need to adjust your buffer switch the Jakes shouldn,t release at 1300rpm it should be from 700 to 600 rpm
You should all remember that there are two different dropouts. One is tranny and the other is Jake.
The Jake buffer switch should be adjusted so that it opens up the Jake circuit at about 25 rpm above low idle. In other words if your engine is set at 550 rpm (mine was) then the buffer switch should be adjusted to open at 575 rpm. This disables the Jakes at very low rpm. As Tom indicated in an earlier post, this is more important in the four strokes than in the 2 strokes since the Jakes will continue operating on the four strokes right down to idle speed.
On the DD's, the oil pressure drops so low, generally, that in the 7-800 rpm range the Jakes will drop out due to there not being enough oil pressure to hold the exhaust valves open in the Jake system.
When descending very steep grades, with the gear selector in first gear, the 740 will not lock up until you get to about 10-15 mph in first gear. At that point, the Jakes will start working and will continue working as long as you do not slow down enough to drop out of lock up.
The other problem I experienced was that if the speed increased to about 25 mph then the tranny would shift to 2nd gear and of course that was not desirable because you lost a lot of the higher rpm Jake action. So I would have to use brakes to slow down until the the tranny would shift back down to 1st gear.
Just my experience. It may not be the same for everybody.
Richard
Quote from: luvrbus on August 06, 2007, 04:07:18 PM
Nick,if you want the hookup like Brian talks about you can get one off a fire truck at a wrecking yard as most had them,but regardless your Jake is going to release at the rpm where the man has it set where it is at 900 rpm or 600 rpm.mine is set at 700 rpm and you can down shift to keep the rpms up and the Jake engaged longer.
Hi Luvrbus,
Brian is sending me his.. Nice Guy! Huh..
Nick-
Brian, Tom, Richard,
Brian said, Other people have the lockup occur just before the shift to 2nd and therefore feel a distinct additional shift.
Is this the distint bang into 2nd gear I have when not heavy on the throttle?
Thanks
Nick-
Nick, i sure Brian told you to disengage the over ride before you stop because it will tear the flexplate if you forget
Would it help to tye the selonoid into the buffer switch?
This way it would release when the jakes do.
??
Nick-
I know little about jakes.I will be headed to the Twin Cities by Maple Groves for a few weeks if any one knows of a good shop.I have a 85 Prevost with an 8v92.
Thanks
Don
Quote from: rip on August 06, 2007, 07:28:48 PM
I know little about jakes.I will be headed to the Twin Cities by Maple Groves for a few weeks if any one knows of a good shop.I have a 85 Prevost with an 8v92.
Best bus repair shop in the Twin Cities is C&J Bus Repair in Bloomigton at 952-881-0034.
Quote from: Nick Badame Refrig. Co. on August 06, 2007, 07:23:36 PM
Would it help to tye the selonoid into the buffer switch?
This way it would release when the jakes do.
??
Nick-
Sure sounds like a smart idea to me. That way there is no way to forget it.
Richard
Nick,you can get the bang as you called it out of the 740 with new trimmer springs take it to someone that knows Allisions ,not a dealer because they will install factory springs.i have a 740 in my Eagle and you can not feel any shift points it took me awhile but it shifts smooth now
Common sense will tell you no matter what other variables there are in play - the Jakes will cease to function when the tranny goes out of 'lock up' whether that is at 500 rpm, 1200 rpm, or any other rpm (as DML has stated) - if you have a AT that locks in 2nd, chances are it down shifts at 1100 to 1400 rpm (2 stroke and 4 stoke are different) - so you should never see 600 to 800 rpm on an Allison in 2nd or above (unless you have a tranny that lets you select lock in 1st,2nd as some have shown) - the manual tranny guys have other options - FWIW
On my V730, the shift from first to second is always smooth, no matter the pedal position. What does cause a definite bump, is on easy acceleration, it shifts from 1st to 2nd then when it goes to 2nd lockup, can be a much stronger bump or lurch. Very hard to adjust on a mechanical transmission. Good Luck, TomC
Seems like there should be an way to rig up an indicator light to indicate whether one is in lockup or not.
Hi Nusa,
Now, that is a brilliant idea....
Any clues as to how??
Thanks
Nick-
While discussing Jakes, there is one more item that should be discussed, and that is exhaust valve clearance adjustment.
The Jake manual indicates either .059 or .063 inches (if my memory serves me correctly) clearance, depending on the style of engine.
When I had mine adjusted properly at .059 inches I found that I had good Jakes when the engine was still cold but the braking action diminished as the engine warmed up.
I then changed my valve clearance to .055 inches and it was almost unbelievable the improvement in braking action with this change.
I do not recall if this adjustment was with the engine hot or cold, but it would have been the condition of the engine when adjusting to .059 as directed by the Jake manual.
Richard
Seems like there should be an way to rig up an indicator light to indicate whether one is in lockup or not.
A while back, I looked this up in my Allison manual. There is a lock-up test port on the transmission. You could install a pressure switch in this port and connect it to a light in the dash. This is one one the ports that is used if you install a solenoid to keep the transmission in lock-up mode. If I rememer correctly, lock-up pressure is within 15 PSI of main pressure. Main pressure at full rpm is 175-200 PSI.
When I started running the wire on our bus for the Jakes, we added an indicator light on the dash that is connected to the input to the Jake solenoids. This light only lights when the jakes are activated. Jack