TheSamba.com :: View topic - Automatic gas transmission in a diesel VW

Mon Jan 09, 2006 10:55 am

I would like to convert my diesel Jetta to an automatic for my wife to drive but diesel automatic transmissions are quite hard to find. Would there be any problem using a gas automatic transmission instead? (Since I already have one)

Mon Jan 09, 2006 6:14 pm

What year Jetta is this?

Wed Jan 11, 2006 3:42 pm

I should have mentioned that. It's a 1989. I know that everything will bolt up. My main worry is that the gear ratios will be wrong and that they make their power at such different rpm's.

Wed Jan 11, 2006 5:04 pm

I wish I could help, but I've never drove an automatic Diesel, that I knew of at least, that had the wrong tranny in it. I've mixed and matched 4 and 5 speed Diesel/Gas trannies that worked out OK. But I think you are right, on automatic diesel, drivability may suffer, I don't know how badly though. I don't have the gear ratio specs for those handy to compare, but I'm sure the diesel would be geared taller to keep the RPMs down at higher road speeds. If you were to make such a change, and you didn't like how it ran, perhaps running taller tires on there might help gear it up taller. (I do that already on my 85 5-speed Golf, wanting more ground clearance plus taller gearing for better gas milage. I run 175/80R13 snows in winter and 185/70R13 the rest of the year. - I've found this makes my speedometer read low by about 14.5% and my odometer read low by about 10.5%)

Sat Jan 14, 2006 8:17 pm

just teach your wife to drive stick, took a couple months for my x to get it but I converted her before we had been married a year, women like control too once they get that feeling of control they never want to let go of the shifter

Sun Jan 15, 2006 7:43 am

I tried that first but after she crashed it I figured it would be easier to get an automatic. It looks like I'm going to have to go with my original plan of finishing up the GLI I started in the fall. I took out the 16V and replaced it with an 8V and switched it over to an automatic. I'm just not a big fan of gas powered watercooled VW's. I've had lots of Rabbits and always had lots of fuel injection problems and the fuel injection on the GLI looks a lot like the Rabbit fuel injection. I've had my Diesel for 10 years now and put over 320 000 km on it so far with hardly any trouble at all (It had 360 000 km on it when I bought it) so I really don't want to switch back to a gas if I don't have to. I'm concerned about the fuel economy too since I used to get terrible mileage with the Rabbits. It looks like I'm going to have to tolerate it until she gets a bit more comfortable driving and then maybe I can convince her to drive a stick.

Sun Jan 15, 2006 9:16 am

I guess it depends on the car. I know there are some cars with problematic CIS Fuel Injection out there, I've worked on some of them, but I think a lot of problems are due to neglect or letting the car sit parked for a long time and getting the fuel distributor full of nasty varnishy gas.

I had a few minor FI problems on my 85 Golf when I first bought it, but that was mostly because it had sat a while before I got it. After I started driving it reguarly, those problems worked themselves out. (Biggest problem was the tendancy for such systems to not run very smoothly upon startup until you've revved up the engine a few times, to get even flow to all 4 injectors, a problem that is completly gone now) My car is up to around 240K now and I changed the injectors out around 190K, and i've owned it since around 170K. But other than the injectors, a fuel pump relay, and the in-tank transfer pump, (which only have about a 10 year lifespan), and other normal things like the fuel filter and air filter, I have changed nothing else in the system out.

I do think the CIS-E setup I have on the 85 is better than the CIS+frequency valve setup they used in 80-84. But the pre-oxy-sensor systems from 77-79, I've seen some of those that ran like a "raped ape" - surprisingly strong.

Now, the GLI/GTI 16V with the CIS-E Motronic system, electronic ignition advance and all that, the shop I used to work for had a few of them that were troubleshooting nightmares. I think they tried to get do too much wiht the CIS-E system sometimes when they should have gone to fully electronic FI. Having said that, when the 16V's run, they can scream, I remember a 16V Scirocco I took on a test drive once and it was very fast.

So how bad gas milage are you talking about? The 1.8 in my 85 Golf gives me about 29-32 MPG in warm weather, that's almost all highway driving, but usually with 2 passengers in a carpool in windy and hilly terrain at 65+ MPH and about 130 mile round trips. This winter I've gotten from 26-31MPG. Definately not Diesel figures, but I'm happy with the mix of power and economy I'm getting.

-Andy

Sun Jan 15, 2006 11:22 am

I had a 1980 Rabbit that gave me 34 mpg and I was happy with that but I had an 81 and an 82 that only gave me 17 - 19 mpg and that was after new platinum plugs, new wires, new filters etc. I even replaced the injectors in the 82 and the only benefit was that it started better. The local VW mechanic even adjusted the CO setting on the fuel distributor with no gain in fuel economy. By the way, I'm using the fuel injection from the 85 Jetta that I got the motor and transmission from.

Sun Jan 15, 2006 12:52 pm

damm my bug does 25 or better in all conditions28-31 on the freeway, ya'll are turning me off further to getting a newer car, my vans don't even drop down as low as 16

Sun Jan 15, 2006 3:36 pm

by the way, those milage figures I listed above for my 85 Golf - when I drive my bugs out to work, my 1600DP baja gets anywhere from 5-8 MPG less, and there are some hills I can't maintain 65MPH on. Add wind to that and it's worse. My big bore 40HP 62 bug, that one is even slower, gets slightly less or about the same MPG as the Golf. Plus neither of them are very fun for carpooling when the weather is cold.

Okay, the 85 Jetta FI - that may very well be the older frequency-valve/warm up regulator type of CIS and not the more refined electronic differential pressure regulator/coolant temperature sensor variety that the US-made models were using in 85, like in my Golf. I've seen many early A2 Jettas that still retained the older system.

That 16-17MPG average is just awful. There was something wrong, somewhere in that car. CO adjustement "by ear" is different than dialing it in on an exhaust gas analyzer, by the way. So it depends on how it was done. And don't use single-terminal Bosch Platinum plugs, they have a reputation for poor running. Myself, I use the three-terminal copper core W7DTC plugs.

-Andy