1980 Rabbit Diesel manual Project

[acidtonic]

Advanced the timing a bit and wow does it start easier and not want to die or miss now at low-load. Drivability has improved significantly. I think that was the bucking issue for the most part. Also not nearly as much smoke on a cold start. I'm really coming around to this car. Very fun to drive around in and absolutely simple to work on....

[acidtonic]

So I'm curious now how to best lower my final drive ratios and get the rpm down....

Seems like I'm in 4th gear after about 30-35mph and even going 50mph the rpm is very high. I can't imagine how much better the mileage would be if the engine wasn't screaming. I find it easy to take off from a stop in 2nd gear without using much throttle or having to lug the engine.

I have the factory 4 speed manual from 1980 on the 1.5.... am I just looking at a final drive swap or do I need a 5 speed? I could have swore I read somewhere that one of the best mileage transmissions was actually a 4 speed where 4th was higher than 5th.... wondering if that's the one I have or not? I'd love to lower RPM and I'm even willing to play with tires if a much taller tire will fit here.

Open to all suggestions on further MPG mods.

[TylerDurden]

Maybe post your tranny code, found at the bottom of the bellhousing. Here's some info on trannys & ratios. http://www.brokevw.com/020ratios.html

Taller tires can help a little, under-inflated tires can hurt a lot.

Fine tuning the engine with good compression, matched injector pressures and accurate timing helps a lot.

Driving slowly helps more than almost anything.

Plenty of aerodynamic modding info at ecomodder.com.

[ORCoaster]

If you have an 80 transmission and it is a 4 spd then your gear ratios are 1-4 as follows:  3.45  1.94  1.29  0.97  With a 3.89 final ratio

The FF or FN transmissions had these ratios for 1-5 gears with the same 3.89 final.  3.45  1.94  1.29  0.91  0.71  The jump for mileage is in the reduction from .91 to .71.  I think this is where you are thinking. 

Funny on the prices on these old FF or FN transmissions.  I just picked one up for 80 bucks and then noticed one for 650 on Craigslist in the local commuting area.  Hard to test these things on the bench without a heavy duty drill. 

[acidtonic]

So I'm looking for an FF or FN transmission then.... I definitely think this thing has too low of gearing for top gear.

Is the 5 spd swap just a matter of linkage and trans? Is this a well known swap? Having an 80 with a 1.5 makes it super hard to search when 90% of threads are about 1.6 or above.


I also was curious about turning down the fuel screw a bit since I feel like it has more power than I need. How far can I go with turning it down? That should help economy as well a bit too right? My goal is to go for pure highway fuel economy and use it for trips from Michigan to Illinois to visit family. 460 miles should be about a single tank or hopefully more.

I don't mind running around 55-60mph but I don't really want to go much faster until the revs can be lowered. I just know that it's not as efficient as it could be thus I don't like screaming the engine at 75-80mph.

I recently did a coast down test and at exactly 40mph when a certain signpost was "hit" I clutched-in and coasted to my street. In my other vehicles they would arrive at my street going approximately 10-15mph and my truck about 4mph. The Rabbit was surprisingly going around 26mph....Impressive!

I definitely want to find a 5 speed. Is the 4 speed I have desirable enough to be worth selling or trying to trade for a 5 speed? Or am I looking at just buying a 5 speed outright? Thanks again for all the traffic and interest in the thread guys

[ORCoaster]

Swap is just linkage and transmission.  Rather straight forward. 

Turn down the fuel screw a little bit at a time.  Like 1/8 turns.  You will know you are too lean when you try to take off uphill or with the car loaded and it just won't rev up, sort of bogs down and wants to die about the time you are putting the clutch to it.

Sorry your trip destinations sound terrible.  MI to IL?? Relies??  460 miles is 46 per gallon if you don't have an extended tank supply.  I often rode with the extra 1 gallon can in the car.  I was pushing a 450 mile round trip route and depending on how much running around in town I did I needed that last 1 gallon to get me to the pump without stalling out on the road 500 feet away.  Stupid STOP sign on a hill and lots of traffic at times.  Just ran the pump dry.   

Rabbits do Roll don't they.  Unless your brakes are dragging.
Some folks would like to have a good 4 spd transmission in place of a broken one so my guess is that you should be able to sell it.  The 5 spd will need the linkage and the shifter and some don't care for the extra work it takes to get that turned around.  Look to buy then look to sell.  You might find a swapper or exchange.

 

[TylerDurden]

Ja, that early GC tranny is worse total reduction than the eco-diesel AVX. An FN would be way better... lower your current revs by ~27%.

On stock tires, at only 60mph, that engine is turning about 3500rpm. An FN would bring that to 2550rpm. 

That could take the mpg from the mid thirties to the mid forties.

(23.5" tires could reduce rpm by another 100rpm. )

[acidtonic]

After a long session with the MityVac and troubleshooting vac-hoses; I was able to find and fix another vacuum leak. The hard plastic hose that goes into the vacuum distribution block was not holding vacuum or actuating the reciruclation-flap. So then I pulled the hose on the inside of the dash going to the distribution block and hooked the Mity-vac up to that and was able to build vacuum as well as for the first time hear the flaps actuate. Then I realized the leak must be the rubber elbow connection right off the hardline. Replaced that and BAM now the system holds vacuum right off the main vacuum pump line and I can move the lever around in the car and hear the flaps opening and closing as I switch from defrost to heat to A/C. It was too late to start the car after getting it back together due to noise but that should fix that issue. I'm curious if the A/C will turn on or not now.... I'll check tomorrow.

I also tested my vac-pump by hooking my Mityvac up to where the plastic hard-line went and with the engine running it was bouncing off 15-psi at idle. This was lower than I expected but I still had the brake booster connected and was only Teeing into the connection. Perhaps my brake booster is leaking as well....  I couldn't get the brake booster line off the plastic fitting with the other vacuum lines so I couldn't directly test it.

All in all I think I'm getting closer. After pulling the rain tray I realized I'm not able to get to the Heater Blower unless I remove what appears to bolts coming up front the inside of the dash. I can't spot any blown fuses so I think the fan-resistor is probably the culprit but I couldn't get to it to find out. I really don't want to pull the dash so hopefully I can get that blower-cover removed without going through all that effort.

More to come....

[acidtonic]

Confirmed that the vacuum actuation lever on the HVAC now works. Looks like the wiring in the dash was really hacked apart by someone who tried to rewire it. I'm thinking I may just pull the molex for the blower-fan and try to manually wire it up to see if it still works. I think I just have a wiring problem at the moment. I'll take some pics tonight.

[acidtonic]

I'm really upset with the wiring situation here. There's multiple spliced wires and dangling connectors to the point I can't trust it. I'm going to directly bypass that and aim for the fan over the next day or two with the time off. Here's some photos and hopefully if any of those connectors are recognized please let me know. I assume some of that is for the missing radio but I bought the car without one and have no idea what the connections on the back should be.

I also can see a single plastic-slot grounded(verified with meter) wire hanging below the dash near the shifter and a bit farther up in there is an identical but red wire that has no current that I can detect hitting it. Neither are plugged in to anything. I also see what appears to be a variable resistor which was definitely just screwed in under the dash and not stock and wired into some wires running to the drivers kick panel.

My gut feeling says that some part of the blower-circuit failed (like the grounds I read about here) and the person perhaps wired the variable resistor as a fan-speed controller? Otherwise what use is there for a variable resistor under the dash like that? I can get more photos but I'm going to need some help figuring that part out. Excuse the photos, it's below 20 degrees out and it's just too cold to hold the camera steady.

[TylerDurden]

No worries, dude. All that rat's nest is radio wiring (Blaupunkt, methinks). The pot is a front/rear fader.

[acidtonic]

No worries, dude. All that rat's nest is radio wiring (Blaupunkt, methinks). The pot is a front/rear fader.

I was hoping that was all radio wiring but the spliced stuff worried me. I was under the dash on my back with a flashlight and I think the molex is *way* up there in a spot that's going to be difficult to reach. I may get a coat-hanger and try to fish it up there to avoid pulling the dash which is so cracked and old I'm sure to break it.

I also noticed a very very slight residue of dampness when on the passenger side floor specifically right at the kick panel where the carpet kinda flaps over with velcro. Car did see rain about 3 or 4 days ago now. Yet the area seems free of water damage or surface rust when I peeled back the carpet a bit. I did notice there was some glue holding the carpet on that I didn't remember seeing on the drivers side. I wonder if that's a sign of a previous water related repair like a seal or something.

[TylerDurden]

MK1s are notorious for windshield leaks at the lower corners. That and missing/cracked raintray over the fresh air inlet.  I'd ensure the drains in the cowl are clear of debris that can back up water. Even the sealant in the cowl/firewall areas can shrink and leak.

[acidtonic]

Ok good news! I was able to manually power up the fan although it did sound a little rough as it first spun up for about 1 second then cleared up. I ran it on the highest speed for about 20 seconds.

What I found was odd is that I must have the strange switched-ground setup because I first was thinking I'd jumper the 4-speed fan switch with 12v like I've been reading here. As soon as I started getting close with the probe end I saw a small spark and backed off quickly. Upon testing I have ground being switched by the fan switch and then when I pulled the heater fan molex I noticed it was black and not white.

So I figured I'd reverse the instructions for trying to hotwire the fan and I decided to use 12v on the black/red wire and then ground to one of the other pins. Sure as hell it fired up!

Now I think I know exactly what the problem has to be.... I'll just run a dedicated 12v wire through the firewall with a 16amp fuse and tie it directly into the other side of the molex that mates up the the Black/Red cable on the blower-side of the molex. That should cure my issues and still let me use the fan switch on the dash without being too janky.

I'll also get some pics of the rain tray whenever I get the time.

[TylerDurden]

.... I'll just run a dedicated 12v wire through the firewall with a 16amp fuse and tie it directly into the other side of the molex that mates up the the Black/Red cable on the blower-side of the molex. That should cure my issues and still let me use the fan switch on the dash without being too janky.

Keep in mind, the original supply of 12V to the fan is switched through the accessory feed and the load reduction relay... so, I'd be careful to not backfeed the switched accessory bus, and of course remember to turn off the fan or put the dedicated 12V line on a switched relay to avoid killing the battery when the engine is not running.