Ultimate Backdating Thread

[techweenie]

Here's a preliminary shot of my (95% done) '85 Carrera backdate. Details to follow.

But if anyone needs any specifics, PM me! I did the whole job in my garage...

[drb930]

Originally Posted by techweenie

Here's a preliminary shot of my (95% done) '85 Carrera backdate. Details to follow.

But if anyone needs any specifics, PM me! I did the whole job in my garage...

How did you do the front fenders?

Thanks,
Dave

[techweenie]

How did you do the front fenders?



Thanks,


I lucked into a nice pair of longhood fenders for sale. That allowed me to sell off the later fenders and cut my costs. In fact, my net price on all the backdate parts was embarrassingly low.

[Joeaksa]

Originally Posted by drb930

How did you do the front fenders?

Thanks,
Dave

Dave,

I did the same thing years ago on my 1985 Targa. Looked for a long time for early model fenders and finally found a set.

Everyone I have talked with who did the "backdate" mod to the late model fenders said that it was more work than it was worth and to keep looking for early fenders.

[G450X]

I know most people like the bright trim, but I think the black trim looks great with most colors. I didn't think the lack of rocker trim would make that much difference, but with the before & after photos the difference is apparent (it looks very clean to me). Most people also blast the later ac vent dash, but it's functional and I honestly think it looks better than the correct (IMO hideously cheap looking) speaker grille dash.

The flag mirror is probably part of the "5%" left to back date, do you know if the base is similar to an early vintage mirror or will there be holes to fill?

The fact that it was done on a budget is the best part. I'm leaning toward a back date for my high mile '82, but parts/paint/prep/fitting will certainly not be cheap. I'm leaning toward a full TRE treatment for more weight loss - I've scoured CL looking for long hood parts for the past year and it's a tough search (unless you have deep pockets). I think the combination of weight loss (added performance) and the vintage look will be worth the effort though.

Be sure to post more pictures when you're finished. The latest Excellence had an interesting take on back dates, which I whole heartedly agree with. The current era of increased financial responsibility makes it almost prideful to say, "yep, it's a back date, I can't afford an original." "But.... it is a 911, and is faster, handles better, and won't rust like your original - and I can drive the ^%$#@! out of it without worry...." (stated with a big grin of course!)

[techweenie]

I know most people like the bright trim, but I think the black trim looks great with most colors. I didn't think the lack of rocker trim would make that much difference, but with the before & after photos the difference is apparent (it looks very clean to me). Most people also blast the later ac vent dash, but it's functional and I honestly think it looks better than the correct (IMO hideously cheap looking) speaker grille dash.



The flag mirror is probably part of the "5%" left to back date, do you know if the base is similar to an early vintage mirror or will there be holes to fill?



The fact that it was done on a budget is the best part. I'm leaning toward a back date for my high mile '82, but parts/paint/prep/fitting will certainly not be cheap. I'm leaning toward a full TRE treatment for more weight loss - I've scoured CL looking for long hood parts for the past year and it's a tough search (unless you have deep pockets). I think the combination of weight loss (added performance) and the vintage look will be worth the effort though.



Be sure to post more pictures when you're finished. The latest Excellence had an interesting take on back dates, which I whole heartedly agree with. The current era of increased financial responsibility makes it almost prideful to say, "yep, it's a back date, I can't afford an original." "But.... it is a 911, and is faster, handles better, and won't rust like your original - and I can drive the ^%$#@! out of it without worry...." (stated with a big grin of course!)

What's funny about your post is that I just went for a quick drive and the car died 2 miles from home. Had it really been a '73, I could have probably gotten it running. But in this case, I did not have a DME relay with me as I'd thought, nor a head temp. sensor. Not even a spare wire to short out the sensor lead. So much for thrashing it.

My net cost for the transformation was $900 and 5 weeks of work (so far). I would like to backdate the mirrors, but that entails painting the doors. What I plan to do is some fine-tuning of gaps, elongated hood catch and doing something about the washer fluid bottle. The front panels need color sanding & blending into the doors a bit. I also need to revisit the rear bumper fit. But it definitely is a head-turner, especially sitting on a flatbed tow truck. LOL

[G450X]

I know that the Carrera Motronic is basically a better/more efficient system than MFI/CIS, but all those 25 year old electronics are a bit scary. I know you can minimize potential problems with multiple spares, but I think the older systems (MFI/CIS) electrical/mechanical set-up will usually still get you home most of the time (even if they run a bit rough) - a plus for the old systems I guess. If I ever switched to carbs over any type of injection, ease of maintenance & reliability would be my #1 reason - performance would be a distant 2nd.

A backdate on a budget - $900.00, I'm a bit jealous. I'm trying to save up at least $4k, but that includes paint.

Good Job, now get that rascal goin' and have some fun!

[techweenie]

I was very lucky to have gotten strong retail pricing on all the parts I took off and excellent prices on all the parts I picked up. A set of good fenders can run $1K if they don't need work.

I think I have spotted a problem with the secondary wires off the positive battery cable clamp. Looks like they are sparking, so are quite possibly the source of at least one of the problems. But you're right. Electronic systems are binary. No "limp home" alternative like the more mechanical systems. Generally the benefit of the Motronic is easy starting and smooth running cold, hot; whatever.

[Jens]

Looks lighter already.

[Joeaksa]

Originally Posted by G450X

The flag mirror is probably part of the "5%" left to back date, do you know if the base is similar to an early vintage mirror or will there be holes to fill?

The fact that it was done on a budget is the best part. I'm leaning toward a back date for my high mile '82, but parts/paint/prep/fitting will certainly not be cheap. I'm leaning toward a full TRE treatment for more weight loss - I've scoured CL looking for long hood parts for the past year and it's a tough search (unless you have deep pockets). I think the combination of weight loss (added performance) and the vintage look will be worth the effort though.

Be sure to post more pictures when you're finished. The latest Excellence had an interesting take on back dates, which I whole heartedly agree with. The current era of increased financial responsibility makes it almost prideful to say, "yep, it's a back date, I can't afford an original." "But.... it is a 911, and is faster, handles better, and won't rust like your original - and I can drive the ^%$#@! out of it without worry...." (stated with a big grin of course!)

I still have the flag mirrors on my backdated 85 model but have one Durant that is about ready to go on the car to make it look like it should.

One other thing about using an post-76 car is that they are zinc coated and thus less prone to rusting. I used to have a real 72 model and fought the battle with rust with it, so its not fun. This car eliminates this issue.

Joe A

[Joeaksa]

Originally Posted by Jens

Looks lighter already.

Jens,

I was thinking about going to stiffer T-bars on my car and in the end after driving it for a couple of years realize that its not really needed. Taking 3-400 pounds off of the car resulted in the car handling very well without it.

Also the same thing with the stock brakes. I have not needed anything stronger than the stock calipers so far, but then I do not race or track it either.

Joe A

[techweenie]

Originally Posted by Jens

Looks lighter already.

It's a little lighter. There are still chassis reinforcements for mounting bumper shocks that add weight, but the bumpers themselves, being at the extreme front & rear do add mass where you don't want it. This past weekend was my "shakedown" before Targa California, and the car feels ever so slightly better on the road. I'd like to pull out another couple hundred pounds, but lightness costs money, and this particular low budget car is about at the limit of what I'm willing to spend on it.

[AlexJ]

Originally Posted by rattlsnak

Tech, I'm doing a backdate on my 84 right now and am going the route of keeping my existing fenders and adding the turn signal housing fiberglass kit onto the bottom. Much cheaper this way. I haven't got to the bumper bracket issue yet but I am using the hood kit also.

hi, where did you buy the fiberglass housings?

What about the part on the flare (beside the turn signal to the end of the fender arch) that misses?

Is it sold by anyone?

[rattlsnak]

you can get them from rennspd.com and that part of the flair is included. see the pic in this thread.

Project 1984.. here we go again...!

[AlexJ]

Great! Thanks

[techweenie]

Here are some notes on backdating from a '74-89 rear bumper to the early style one piece RS type:

Steps for backdating the rear bumper (where it counts the most)

1. Remove rear bumper and shocks. Optionally, cut off the shock mounting brackets if you're okay with the backdate being irreversible. There's some weight in those reinforcements.

2. Remove rear reflector -- carefully. There's market value in this piece if not damaged. The clips that hold the "plugs" in are not meant to release, so you will have to pull, pry and persuade them to release. Better to cut or break the clips than the reflector. Don't be distressed if some of the gray mounting blocks separate from the reflector. They just glue back on.

3. When the reflector is off, you should cut off the boxed metal support. I used a Sawzall. You can leave the welded flanges on the rear panel, because they will be covered. But clean off both ends (inside of tail light openings) with a grinder.

4. Test fit your rear bumper. Assuming a one-piece fiberglass RS type bumper, plan on attaching it with bolts run through the lower flange of the rear light openings and through the seals. You will also use bolts through the rear quarter flange. I recommend running all bolts through the rubber seal. Beware of putting any stress on the rear bumper. Engine heat will make it distort, and if there's stress, the distortion may not be to your liking. Note that most RS one-piece rear bumpers are very poor fitting and may need a lot of fiberglass work. Allow yourself time to test fit and rework the 'glass. before finalizing the mounting.

5. 4-5 mounting points along both 'side pieces' of the rear bumper will carry it. There's no easy way to support the license panel, but you could attach a flange to the rear body and 'hang' the top of the panel on it, if you like. An aluminum angle piece from the local home improvement store will work. But in truth, you don't need it. The challenge in attaching the bumper is the mounting bolts adjacent to the oil tank. You may want to drop the other side of the bumper to get these bolts in place. The preferred fastener is a 25 to 30mm long bolt with 4-5mm thread. I recommend welding or brazing a small rod across the head of the bolt in a 'T' shape in order to allow assembly/disassembly with one tool. Use locking nuts for this. You can use conventional pan head bolts inside the tail light opening in order to clear the tail light housing. You will want to monitor how tightly you fasten those bolts. You don't want to compress the seal too much. For the truly meticulous, a sleeve inside the hole through the bumper seal will allow you to cinch the fastener tight without squashing the seal.

[techweenie]

I revisited the rear bumper mounting now that the bumper has 'seasoned' and heat cycled a bit. I don't know the original application of this bumper, but it was too wide for 9" flares and not wide enough for 11."

Clamping it to the quarters stressed the bumper (thick GT Racing street weight piece) and caused some warping. I spent a couple months watching the bumper reshape (warp) itself and then took action.

Noting where the inner edges of the tail light lenses were, I drilled holes into the vertical outer sides of the molded bumperettes just out of sight and used a plastic saw to cut backward from the forward edge of the bumperette to the drilled hole. I wanted stress relief to reshape the bumper, and hopefully, the round hole will stop the tendency of the area to crack. Too early to see if I'm right.

This is how the right side of the bumper fit when first attached:



You can see the stress of pulling in the bumper end caused the mid-portion of the bumper to gap away from the quarter.

Here's how it looks today:



Better.

Here's how I did the final attachment of the fiberglass bumper. First, I drilled holes in the tail light housing openings and dropped panhead bolts through (panheads better cleared the housings).

Then, I used the three holes in the Carrera's quarter panels as guides to drill corresponding holes in the bumper.



I had T-bolts welded up, bought nylon stand-offs from the local electronics store and drilled them to fit the T-bolts, cut them to the height of the seals, and then cut holes in the bumper seals big enough to accommodate the nylon stand-offs.








Hope this is all clear. Although you can use longer sheet metal screws to re-use the speed nuts on the quarters, I popped off the speed nuts in favor of locknuts so that all the fasteners are the same. The ones next to the oil tank are somewhat of a challenge, demanding a 'wobbler' fitting for your socket drive.

Not sure how well the photos convey it, but the bumper warping was almost completely eliminated by the T-bolt and spacer solution.

[Jens]

Clever solution. Nice werk.

[Joeaksa]

TW,

What did you use for the rubber buffer inbetween the two pieces?

Joe

[Jens]

Joe, I think it's the early stock rubber fender-to-bumper gasket. The white backing paper is supposed to be removed so that it self adheres to the fender to keep in place and not squeeze out. In a normal situation, that is. Here there is a pre-tension problem that needed this creative solution.