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Geophilist · 10-05-2006, 11:48 AM

Chaplain Kent

Why don't you take Chummy back to the shop that did your old diesel and ask them to change your transmission filter?

Steve

Minnie's Mate · 10-05-2006, 02:41 PM

ChaplanKent, I remember when you had your engine replaced and have since bought my first diesel. I am by no means an expert on diesels, especially Airstream diesels, but what you described doesn't sound like it is all working right. No matter which side of the 55 MPH fence one falls on, from what I have read the Airstream Moho's were never speed demons and your expectations may fall at the limits of your motorhome's range. I don't know if it is a matter of brake size to weight ratio or what, but from what I remember about 60-65 is the max most people get with theirs regardless of length. However, my limited experience with my diesel and the reprogramming recall that Ford did earlier this year, your mileage is great, but you should be able to get more than 55 MPH out of your coach. I would expect more than that out of one of the longest that Airstream made; I believe they were 37' and on a totally different chasis and drive train that was essentially a city bus configuration that wasn't designed for highway speeds. Anyway, your turbo should indeed be kicking in. Mine will kick in at all speeds if I push the accelerator pedal too quickly. My truck will also reach speeds way faster than I want it too if I get too busy talking and not paying attention to the speedometer (recently pulling my 30' Safari I looked down and was doing 80, I immediately set the cruise at a lower speed).

With a newer engine, you probably have a computerized control system. It may be programmed for use in another vehicle, (I don't know what semi, tractor?) and need to be reprogrammed for its current use. I would go back to an Izuzu trained service center and have them do a diagnostic on the programming and reprogram it for use in a 15,000# motorhome and see if it makes a difference. It may just be programmed for a different transmission or different rear end and reprogramming may be all that is needed. Then I would look at other, more costly, options. You may want to contact the engineers at Izuzu for advise on what those options might be.

Chaplain Kent · 11-15-2006, 02:18 PM

I am still on my search for more speed and less RPM. A mechanic was crawling under Chummy and noticed that the passing gear was not connected. He stated that it may never have been connected. Does anyone else have a passing gear?

guy99 · 11-15-2006, 03:24 PM

I think 'passing gear' refers to the way an automatic transmission will downshift under heavy acceleration. This causes the engine to rev higher. Maybe that isn't a good idea with diesel's?

59toaster · 11-15-2006, 06:23 PM

First off....you folks are NUTS to run a 454 past 3k for extended runs. No wonder folks are popping motors at 80k. Its WAY to fast for a motor of its size. Yeah 4K to pull a short grade getting on the hwy but at 454 is happiest to cruise around 2600-2800 rpm. Past that it starts baking the oil out of it.

My 454 TH 400 suburban has temp gages on the oil and the transmission. with the 3.73 and 235x85x16/s I wont run the thing past 2800rpm even empty for any period of time.

I use to try to run it down the hwy at 75. I kept having issues of getting off the hwy and the engine temps stayed elevated. Even Thought I had a cooling problem. Added a tranny cooler thinking the tranny was raising the coolant temp, didn't fix it. Replaced the radiator....same problem. Put the temp sender in the pan and was SHOCKED at what I found. 2800 RPM or less the engine oil stays at around 250-280. 75 MPH it was up over 300f and hitting 350f on a long run.

My truck has a factory Oil cooler and it hits that.

Same deal with the transmission Even with the factory cooler and the AUX cooler Under 2800 RPM it stays under 180. Over 2800 with the elevated engine temps I am hitting 215f quick and thats hot enough to start ruining the seals.

Over drive is what you want. Keep your gearing for the hills and OD for the hwy. Its the best of both worlds.

I am a firm believer that the safest way to drive is with the flow of traffic. If you are running 55 in a 70mph zone you are causing idiots to stack behind you and start taking chances and possibly cause a wreck. It is safer even for the idiots if you can move at the posted speed limit.

I am looking at the Gear vendor or Bowtie OD.

overlander63 · 11-15-2006, 07:36 PM

Several forums members have had good luck with Gear Vendors overdrive units. My diesel tow vehicle with a 4.10 ratio, and a 3 speed automatic transmission has TWO of them. One on the back of the transmission, the other midway along the drivehaft. Total 40% reduction in RPMs while driving.
If you don't like that, our Isuzu FSR trucks with the same engine as Kent's motor home have Allison transmissions (4 speed). They run 2700 RPM at 65 mph in 4th gear...and 26,000 pounds.

GlenCoombe · 11-15-2006, 08:06 PM

Kent, it's been some time since we last talked about your rig... is your turbo working now? I remember you stated it didn't kick in much.

59toaster I'm with you. My problem is that the GV route would likely mean I'd have to change my rear end ratio to find the sweat spot. At my present RPM's I'd be down into the lug range at 70 MPH in overdrive. If I could find 500 rpm of overdrive instead of 750 I'd be good to go..... then I'd have to find the $$$. Just agreed to drop $1800 on a new Honda EV6010 today.

overlander63 · 11-15-2006, 08:10 PM

Quote:

Originally Posted by GlenCoombe

59toaster I'm with you. My problem is that the GV route would likely mean I'd have to change my rear end ratio to find the sweat spot. At my present RPM's I'd be down into the lug range at 70 MPH in overdrive. If I could find 500 rpm of overdrive instead of 750 I'd be good to go..... then I'd have to find the $$$. Just agreed to drop $1800 on a new Honda EV6010 today.

Why not contact GV and see if they will build you a 10% overdrive, instead of the 20%? You would then be at 2700 RPM @60 mph.

ROBERTSUNRUS · 11-15-2006, 11:22 PM

Hi, I would, if I were you, either go with a Gear Vender unit or better yet just leave well enough alone until your three speed gives up then install a four speed overdrive transmission.

Bob

GlenCoombe · 11-16-2006, 06:11 AM

OL63, I'm actually doing better than that already. 55 mph = 2600 =205 engine temp prior to new T-stat.

60 = 2750, 65 = 2900, 70 = 3100 = 210. I'd like to have about 2600-2700 rpm at 70 so as I see it 500 rpm of relief. I think that once you get down into the 2400 range you're out of the power band and risk lugging the engine.
I had no idea you could spec a different final drive.
Anybody need some golf balls??

Just bought a new genset (EV6010) so I'm having to think about all the winter to do's I had planned. I'm still hot on a new floating inlaid wood floor.....

Chaplain Kent · 11-16-2006, 08:29 AM

Glen- the turbo is working fine, I just do not need it most of the time.
59 Toaster- The RPM is from a diesel engine not the 454 gasser.
Gear Vendors- I have spoken with them and they do not have a product for my Isuzu engine/ GM transmission.

cooperhawk · 01-05-2007, 04:10 PM

I was not aware that CK had a GM transmission. I was talking to the mechanic up the road from me. He has worked in shops that specialize in Isuzu in the past and now is farming and running his own shop. We discussed changing the ratio of the rear end and he says that it's quite simple to do it and he has the tools.

He also mentioned that a friend that he worked with specialized in installing an overdrive gear into the Allison Transmissions. I hadn't heard of that before. He' going to check on that for me.

dienst1 · 01-09-2007, 11:50 AM

I had the gear set in my US Gear box changed out to the overdrive from the PO's under drive. The difference is amazing. I had it done just before we left Ohio to come back to Southern California for the winter. I was getting 55 mph with a tach reading of 2900 rpm. Now I'm getting 60 mph at 2700 rpm. I have the 6BG1-T Isuzu engine (replaced the 6BD1 when it melted a piston) so it just loafs along at 60 mph. I'm still calculating trip mileage but I expect it will be 14+ mpg. I also had the SCS Frigette electronic cruise control installed at the same time. That really made the trip more enjoyable.

cooperhawk · 01-09-2007, 11:59 AM

You mentioned a US Gear box. I'm not familier with that. I have the four speed Allison Transmission with the 6bd1 engine with a turbo. I do however have the improved engine with all the upgrades. It seems to have plenty of power.

Chaplain Kent · 01-09-2007, 12:14 PM

Quote:

Originally Posted by cooperhawk

You mentioned a US Gear box. I'm not familiar with that. I have the four speed Allison Transmission with the 6bd1 engine with a turbo. I do however have the improved engine with all the upgrades. It seems to have plenty of power.

I am still searching and the US Gear over under gear box seems to be my only alternative. A four speed tranny would also be nice but mine is the old GM three speed. Chummy goes into the shop next week with a mechanic who is going to establish exactly what is going on now and what I am able to do.