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Old 04-27-2016, 10:47 AM   #31
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There's not an access plug somewhere on the manifold to place the pyrometer?

I don't have an engine overheating problem. I've got a tranny that heats up pretty quickly and that's just on my way home from from grocery shopping. No problem on the highway but as soon as I hit the mountains my tranny temp goes up to a concerning level. That sounds like it could be an indicator of the condition of my transmission. Naturally I'd like one of those 5th generation transmission that only needs the TPS to run. Doesn't sound like it would go much faster but every little bit of speed helps.
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Old 04-27-2016, 10:55 AM   #32
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Maintaining the right tranny fluid temps is critical. It only takes a few minutes at too high a temp to virtually destroy the fluid. Then, the tranny suffers...badly. As I recall, Allison has a "never exceed" temp of something around 250 but recommends staying quite a bit lower.

Couldn't find the Allison chart but here is the same basic info regarding fluid longevity...

Transmission temperature/failure chart.
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Old 04-27-2016, 11:34 AM   #33
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Welcome GreyC..

Lots of great people on this site who have always been helpful to us.
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Old 04-27-2016, 11:38 AM   #34
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I start watching the temp gauge closely when it hits 200, although it's in centigrade on this gauge. What concerns me is that these hills that are making it hit these temps are quite short. The temp comes right back down as soon as I stop climbing, so I've avoided the big hills.
The most I know about these Allisons are the tranny number you guys have been flinging around. One of those six speed would be a lot more efficient at power delivery. I'll try a fluid change, and if that doesn't improve things I'll just have a professional evaluate it.
Thanks for the info.
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Old 04-27-2016, 11:40 AM   #35
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Transmission Temp Gauge?

Been a lot of discussion in this thread on transmission temp and monitoring the exhaust temp, but I do. Do most buses have a transmission temp gauge and if not how/where would you install one for the best temp reading?
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Old 04-27-2016, 12:09 PM   #36
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I would guess that it's optional when ordering a bus, but I lucked out again. Mine is centered in the side of the transmission pan on the drivers side. Looks like a fitting was welded in and the sensor placed in that. I've seen photos on here but I'll never remember where they are.
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Old 04-27-2016, 01:01 PM   #37
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I would guess that it's optional when ordering a bus, but I lucked out again. Mine is centered in the side of the transmission pan on the drivers side. Looks like a fitting was welded in and the sensor placed in that. I've seen photos on here but I'll never remember where they are.

most older busses do NOT have the gauge.. in fact I cant remember ever driving a bus that did.. some of the newer IC's I think do..

the Pyrometer spoken of is to monitor exhaust temperatures.. the reason for that is if you are pulling hard you can get tyhe CYLINDER temperatures way up.. .that really only happens on engines that are turned up...

like on a little DT360, it can be easily "turned up" to give it more horsepower in about 5 minutes.. you can get 20-30 this way.. however if you run Foot to the floor, in the right conditions you can over-temp the cylinders.. (your temp gauge measures coolant temperature).. over-temping cylinders can result in a blown up engine...

transmissions without a Lockup converter (AT545) are MORE likely to over-temp than a Lockup transmission (MT643, allison 1000s, allison 2000s).

the big problem with over-heating transmissions is it DESTROYS the fluid.. measning once you over-temp a transmission you need to replace that transmission fluid.. it will never recover back to its old-self.. thats where a lot of transmission damage comes from is the fluid is no longer properly lubricating...

the torque converter in your transmission is a fluid-form, of a clutch.. a Very inefficient one.. however it allows you to stop and not have your engine stall... the issue is that you are churning transmission fluid when you are going down the road.. that fluid heats up.. in a lockup transmission it locks-in like a clutch increasing power and efficiency... and because you arent churning fluid you tend to not get it as hot...

when we talk of swapping transmissions out to neweer models.. its often to gain top-end speed.. many of our busses will 'red-line' the RPM's yet only be travelling at 60 MPH or maybe 62 or 63.. these busses were mainly built to be driven on in-town school routes and not on the highway...

in laymans terms if I can replace my 4 speed transmission with a 6 speed i can gain the ability to travel faster.. if you think of how in your car, each time your transmission 'shifts' the RPM goes down and the speed stays the same.. as your speed increases so does the RPM then it shifts again dropping the RPM.. so adding 1 or 2 more "shifts' in your bus gives you the ability to travel faster at lower RPM...

this often leads to anbother issue which is that with more gears the engine may just not have the power to run the bus faster.. thus then the discussions start about "turning up" the engine.. to gain more power.. and why then pyrometers are important.. as yes you will make more power but you will make more heat too... esp since our diesel engines are turbo-charged...

-Christopher
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Old 04-27-2016, 01:12 PM   #38
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Thanks Cadillac. I'll get the transmission serviced and see if that helps. This fluid was burnt smelling when I got this bus. Good thing I'm actually driving on the valley floor most of the time on my recent short trips.

So what I'm gathering is that I don't need an extra transmission cooler, probably it's more like I've got a weak transmission or if I'm lucky if it's just the burnt fluid issue. That still leaves me wanting a 6 speed if I've got to replace the transmission. I'll just try to make this one last for a while until I find that other trans.
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Old 04-27-2016, 01:36 PM   #39
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Thanks Cadillac. I'll get the transmission serviced and see if that helps. This fluid was burnt smelling when I got this bus. Good thing I'm actually driving on the valley floor most of the time on my recent short trips.

So what I'm gathering is that I don't need an extra transmission cooler, probably it's more like I've got a weak transmission or if I'm lucky if it's just the burnt fluid issue. That still leaves me wanting a 6 speed if I've got to replace the transmission. I'll just try to make this one last for a while until I find that other trans.
if its already slipping then ts probably done for... if its not slipping.. but its acting. well like an AT545 does.. then its probably normal... if the fluid is burnt smelling and kind of brown then its a good ideato replace the fluid..

im with you on the 6 speed.. at some point I may do a swap out..

i'll run my bus for awhile first.. see where it really likes to hang.. and where I actually drive it the most...

a creative mind really has no idea where its going to lead me and my bus to go...

-Christopher
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Old 04-27-2016, 01:53 PM   #40
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Regarding the location for a trans temp gauge (a really good investment, BTW)...it should be located at the point where the fluid exits the tranny on it's way to the cooler. That will give you peak temp.

As for transmission fluid coolers, there are many types...air to air...air to water...in-line...radiator mounted...freestanding...remote...

Point is, there are plenty of options, combinations and mounting possibilities. Any of which will improve transmission performance and longevity by extending the functionality & performance of the fluid.

Your transmission will never be healthier than the fluid is. And as you will note from the chart linked above...it doesn't take too many trips into the hot zone to destroy it.
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