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W126 short body OM606
WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
W126 short body OM606
Hello diesel fans.

I have been browsing this forum for quite some time and figure it is time to give back with some information about my latest Mercedes project.

Here I will document the build of a replacement for my current daily driver, a 1983 W126 with om617. That car's chassis has in the neighborhood of 700k miles and has seen abuse no other car could handle. I initially started refreshing that body but have continued to find more and more damage that isn't worth the time to restore, so decided to find a good example generation II short body. I'll make another thread someday about the build I did in 2005 on the '83, but for now I'll focus on the new car.  I found a 1991 350SD which had a blown engine and excellent interior with minor paintwork needs, then drove 2600 miles to pick it up.

The car will have the following specs:
7.5mm Dieselmeken pump
BW S200 from the DPUK guys
722.6 from S55
2.46 LSD

Here it is after loading with come-along in Portland, ready for the journey back. Towing Jeep has a om642/722.6 and rear airbags so was not a problem capacity wise:

[Image: 20180206090705.jpg]

However, along the way the trailer blew two tires at different times in the trip:

[Image: 20180208110421.jpg]

Then I get close to home and run through the carwash to get all of the magnesium chloride off, very excited to get home:

[Image: 20180208155828.jpg]

Shortly after leaving the carwash I look in my rear view and see a shower of sparks and smoke once again...
[Image: 20180208173727.jpg]

This time it had to get a flatbed ride on a medium truck the rest of the way home, rental trailer rusted out leaf spring shackles couldn't take any more. Car was right at the rated weight of that trailer.

Here it is with the '83:

[Image: DSC03956.jpg]

Here is the unmolested interior, best w126 I have seen in awhile:
[Image: 20180520144911.jpg]

I started stripping down the old car, here are photos of the original configuration of the IP in case anybody ever needs to see that:
[Image: 20180211151331.jpg]
[Image: 20180211151317.jpg]
[Image: 20180211151303.jpg]

And the stripped om603 with it's replacement:
[Image: 20180312181227.jpg]

I sent the mechanical pump off to Dieselmeken for 7.5mm rebuild:
[Image: 20180220115554.jpg]

The OM603 suffered failure from the oil pan baffle washers being ingested by the oil pump.

Here you can see the impacts on the oil pump gears and washer:
[Image: DSC03959.jpg]
[Image: 20180213082005.jpg]
This sheared the oil pump sprocket bolt in half, and blew out the front of the timing cover:
[Image: 20180213081958.jpg]
[Image: DSC03961.jpg]
The previous owner said they shut it down immediately, but not soon enough:
[Image: 20180508092400.jpg]
Damage was worst from front to rear of the crank. Pistons were trashed, no reason to try and save this engine.
[Image: 20180507202054.jpg]
[Image: 20180507211559.jpg]

I have been collecting parts from the junkyard for the W126 build for the last 15 years or so, and had originally selected a 2002 S500 transmission since the output flange is the same dimension as the one on the 350SD driveshaft.

I have piles of W126 crap that needs to be sorted one of these years:
[Image: 20170808124149.jpg]
[Image: 20170808124117.jpg]

About the time I got the S500 and 722.3 transmissions out of storage I happened across a 2002 S55 in the pull it yourself yard:
[Image: 20180311140859.jpg]
I grabbed the transmission and a few other goodies, including the S320 alternator and transmission cooler lines from the W140 in the picture:
[Image: 20180311172050.jpg]
[Image: 20180319164318.jpg]
I'll find out in the near future how that AMG muffler flows with the OM606.

I think the OM606 may have come from a flood car, I picked it up in Houston after the hurricane for very cheap. The only problem I found was heavy corrosion in the injector wells.

I cut a tarp and sandblasted the wells in a similar fashion to intake valve cleaning on the BMW diesels:
[Image: 20180429163733.jpg]
[Image: 20180429163741.jpg]
[Image: 20180429172317.jpg]
The lines kept the media out of the injectors.

Once the corrosion was removed, I pulled the injectors and sent them out for rebuild with 150 bar pop pressure. This left cleaning the carbon out of the glow plug and injector holes:
[Image: 20180501113823.jpg]
[Image: 20180501111337.jpg]
[Image: 20180501111404.jpg]
[Image: 20180501111414.jpg]
Scotch pad on a shaft:
[Image: 20180501142914.jpg]
[Image: 20180517113928.jpg]
I ground down some drill bits to use to clean out the injector holes (by hand), they worked perfectly in place of a reamer.
[Image: 20180501111326.jpg]

I tapped out the water pump housing for the bypass hose:
[Image: 20180415131709.jpg]
There was some additional drilling and tapping needed for the older style RPM sensor. This is a 18mm drill hole size for the sensor, and I used m6x1 for the attaching screw:
[Image: 20180517111057.jpg]
[Image: 20180517143456.jpg]
[Image: 20180517143507.jpg]

More to come soon...
06-25-2018, 08:43 PM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
RE: W126 short body OM606
Sorry about some of these images, the hosting site I used has some autorotation that can't be changed apparently.

The oil filter housing from the om603 has some clearance issues:

[Image: 20180325141955.jpg]

This was alleviated by removing material from the intake tube and housing with a belt sander:
[Image: 20180325144752.jpg]
[Image: 20180325144628.jpg]
Now the oil cap can be removed without pulling the intake! Will have to see if I went too thin on the lid though.

A little support is needed to be welded to the OM606 cooling tube to make it work with this housing:
[Image: 20180506204550.jpg]
[Image: 20180507184013.jpg]

Injection pump timed, installed along with a new metal impeller water pump:
[Image: 20180506113619.jpg]
Here you can see how far 8 was from the original setting ~14 in the viewing hole:
[Image: 20180506113542.jpg]
[Image: 20180506144246.jpg]
[Image: 20180429110441.jpg]
The thermostat housings are different, and to use the original hoses I had to use the original smaller om603 one:
[Image: 20180424160903.jpg]

I wanted to retain the original Nippon AC pump from the 350SD. I left it charged and hanging in the engine bay. The base plates for the alternator and AC pump have slight differences between engines:
[Image: 20180508195457.jpg]
Note how one of the alternator plates has clearance on the back for the crank pulley on the OM606. The OM603 version would need slight modification.
[Image: 20180429110144.jpg]
6031550735 right, 6031550435 middle, 6052140239 left . The compressor mounting holes between the E300 and 350SD have different dimensions .
[Image: 20180429110113.jpg]
[Image: 20180424173623.jpg]

Here you can see the different nose length on the 2002 S500  V8 alternator vs the late 90s W140 S320 I6 alternator, I6 on the left:
[Image: 20180311172105.jpg]

The S55 transmission took a beating in its accident, but damage appears to be limited to the pan:
[Image: 20180311184846.jpg]
With the E320 bellhousing and new intermediate plate (seal) and better pan installed:
[Image: 20180507175946.jpg]
The output flange on the AMG transmission is 4 finger, while the 2002 V8 version has an exact match 3 finger dimension to the 91 350SD driveshaft.

Here we have some side-by sides of various transmissions:
90s E320 I6 next to original from 350SD and S500:
[Image: 20180213103600.jpg]
[Image: 20180304145759.jpg]
300SD -> 350SD -> E320
[Image: 20180311172146.jpg]
300SD ->350SD -> E320 -> S500 -> S55
[Image: 20180311172050.jpg]

For now I just used the torque converter from the E320, hopefully it isn't fried. The S55 had very low miles, pink fluid.
Here are S55 AMG left and S500 flanges:
[Image: 20180514120825.jpg]
The S500 flange is not the same as the E320, this one is much smaller than the 350SD and S500.

Here are the turbos I had out of storage next to each other:
E300 left, 350SD right
[Image: 20180508103713.jpg]
E300 top, S200 bottom
[Image: 20180508103729.jpg]

The pile in the garage is getting excessive:
[Image: 20180319164359.jpg]
Time to pull the body in:
[Image: 20180306123044.jpg]

And now we find out how far off everything is:
[Image: 20180517173319.jpg]

[Image: 20180517173330.jpg]

To my amazement, everything lined up like it was designed for this combination.

[Image: 20180517180237.jpg]
[Image: 20180517180245.jpg]
Will have to reroute the heater core lines a bit:
[Image: 20180517195433.jpg]
Perfect, that is the 99 E300 pan in the W126
[Image: 20180528173418.jpg]
[Image: 20180528173426.jpg]
The DPUK adapter
[Image: 20180612152303.jpg]
Cleaned out the original oil cooler
[Image: 20180528173444.jpg]
And the biggest question of the day, the driveshaft. It fits perfectly with the original flex discs.
Now if these start to fail to frequently, the S500 has much thicker discs that can be used but will require a couple CM removed from the overall shaft length. Time will tell...
[Image: 20180528173343.jpg]

I got lucky and found a 125k mile LSD from a 560SEL at the pull it yourself yard:
[Image: 20180520131814.jpg]
[Image: 20180520152521.jpg]

And now there is a company making full aluminum replacement radiators for the gen II W126 diesels:
[Image: 20180403152504.jpg]
[Image: 20180528173305.jpg]

The belt is not the same size due to the different accessories. I used a 2153 mm belt for now as it was the closest fit, but a few mm shorter may be needed. The main vacuum tube bolted directly up to the vacuum pump like it was original.

Thats as far as I am now, I still have to do the following:
Build 3" exhaust
Mock up intercooler size and order
Wire everything and install shifter - will be using the Ole controller for the transmission
Extend heater core hoses to their new homes
Build transmission cross member for the 722.6 mount
Boost hoses, gauge, and EGT gauge
Fuel system - I pulled the pumps from the 560SEL and am going to try to use one of them with a external adjustable regulator in the stock gasser location. If that doesn't do a 044.

Right now I am saving up for a new welder as the china welder I have gave up the ghost on the oil filter housing coolant tube. I'll update the thread when I make some more progress...
(This post was last modified: 06-25-2018, 11:40 PM by WSchotty.)
06-25-2018, 10:18 PM
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Sotvisp Offline

Posts: 40
Joined: Jun 2013
Location: Sweden
RE: W126 short body OM606
Fantastic post good work !!
Diesel Power
06-26-2018, 01:23 AM
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awsrock Offline
300SDL / HX30 / 90cc

Posts: 176
Joined: Oct 2009
Location: Illinois
RE: W126 short body OM606
Heck yeah, blazing speed progress! I have a mild 300SDL with a 603 and am planning on one day putting a 606 in there, so this thread will prove most helpful.

I also have a 722.6 sitting in the garage waiting for me to have some time to put it in. Good to know the stock flex disc works perfectly. 
Do you have any concerns about the low 2.46 LSD? With the overdive, your rpms are going to be super low. I got the "small" 722.6 hoping the smaller first and second gear would help with off line performance. Will be interested to see how it works for you, if I need to upgrade to a bigger rear axle I may look for a ....350SDL model? Perhaps we will need to talk about that if you don't need your old one.

Pretty much nobody mods these 126s but that front bumper is gold for putting in an intercooler. Right now I have a 27x9 stuffed in there with no problem. I just had to grind off maybe half an inch of the plastic on the inside. I could probably get up to a 27x12 without it sticking out from the top or bottom too much. Consider boring out the two holes in the engine bay that have a rubber part in them, they are good routes for IC piping.

Attached Files Image(s)
(This post was last modified: 06-27-2018, 09:10 AM by awsrock.)
06-27-2018, 09:07 AM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
RE: W126 short body OM606
Thank you Sotvisp.


Glad to hear there is somebody else out there building W126s.

I'm interested to see how the 2.47 runs with the OD transmission. The extra power with that diff will probably be fine, I'm not drag racing this one. I've had a 380SE 2.47 in the om617 83 W126 since around 2002 and it is a whole different car. Given that the car usually started in second and was essentially a 3 speed most of the time the 2.47 made it a excellent highway cruiser, and the shift points make the approximate speed ranges 1st ~20mph | 2nd~ 40mph | 3rd~60mph | 4th~have hit 120+. This actually improved the mountain driving too, most of this car's life has been DD at 5000-9600ft above sea level running mountain roads, it really doesn't do too bad for a 100hp car.

The 350SD 2.82 diff is the same case size as the 2.47, so I will probably keep that if the gearing is wrong for that 722.6. I also have a 2.88 small case diff from a 87SDL in case I need to go even higher, but will lose LSD in that case. I am kicking myself for letting a 350SD diff and driveshaft slip through the junkyard a couple years ago, I never anticipated actually owning one of these. They use a 3 piece driveshaft rather than the 2 piece. I have an extra SDL 2 piece if you need one of those.

The intercooler does have plenty of room, I am probably going to go with 28x12x3 or 3.5. What width did you use? I also found one that flows 7 or 800 cfm that will fit completely in the lower part of the bumper, but I'd rather have excess capacity due to the long uphill pulls this engine will see. I need to make a cardboard version for test fit before I order.

Here are W126 ratios in case anybody wants them:
1st Generation w126
Years,Model, Engine, Differential Ratio, Differential Case Size
1981-1984, 300 SD, OM617.951 3.0L I5, 3.07,
1985, 300 SD, OM617.951 3.0L I5, 2.88, 1.1 Liter (California from 10.1984 in California: 2.88, 1.1 Lite
1984-1985, 380 SE+SEL, M116.963 3.8L V8, 3.27,  from 1981-10, 2.47, 1.3 Liter
1982-1983, 380 SEC, M116.963 3.8L V8, 2.47, 1.3 Liter
1984-1985, 500 SE+SEL, M117.963 5.0L V8, 2.82, from 1981-10, 2.24, 1.3 Liter
1984-1985, 500 SEC, M117.963 5.0L V8, 2.24/2.24 LSD (2.47?) 1.3 Liter
2nd Generation w126
Years, Model, Engine, Differential Ratio, Differential Case Size
1989-1991, 300 SE, M103.981 3.0L I6, 3.46 1 Liter
1988-1991, 300 SEL, M103.981 3.0L I6, 3.46, 1 Liter
1986-1987, 300 SDL, OM603.961 3.0L I6, 2.88, 1.1 Liter
1991, 350 SD, OM603.97 3.5L I6, 2.82, 1.3 Liter
1990-1991, 350 SDL, OM603.97 3.5L I6, 2.82, 1.3 Liter
1986-1991, 420 SEL, M116.965 4.2L V8, 2.47, 1.3 Liter
1986-1991, 560 SEL, M117.968 5.6L V8, 2.47 ASR/2.47, 1.3 Liter
1986-1991, 560 SEC, M117.968 5.6L V8, 2.47 ASR/2.47 LSD/2.47, 1.3 Liter
06-28-2018, 11:12 AM
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awsrock Offline
300SDL / HX30 / 90cc

Posts: 176
Joined: Oct 2009
Location: Illinois
RE: W126 short body OM606
Interesting to hear how the 2.46 did in the 617. For a while I was torn between the 722.6 and just swapping out for a different axle. Ultimately I chose the 722.6 because of all the unknowns about how much the .3 can handle. They make a clutch upgrade for the .3 but it's like $700 so kind of moot once you factor in a .6
Mine is fine right now with 240 ish hp, but ultimately I am planning on 300-330 once I get another new pump.

I want to say my IC is 3" thick. The outlets are 2.5" so it is possible that it is only 2.5" thick but I doubt it. Here is how it looks in there now. If you exclude the mounting posts on top there, there is probably another inch and a half to two inches before the top of the bumper. It is sitting on the bottom of the bumper. So even if you cut out a portion of the bottom to have it hang out a 12" tall IC should fit with little effort. It gets a little cramped if you go wider than 27" due to the curvature of the bumper but you can probably grind out more of the inside.

Attached Files Image(s)
(This post was last modified: 06-30-2018, 10:58 AM by awsrock.)
06-30-2018, 10:55 AM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
Brick  RE: W126 short body OM606
Finally had some time for work on this one, made the exhaust and started mounting up the intercooler.

What the downpipe ended up looking like, decided to dump the wastegate into the main exhaust:

[Image: 20190327123851.jpg]

Flex fitting for after transmission mount, hopefully will reduce stress on the turbo:
[Image: 20190327143903.jpg]

[Image: 20190327150155.jpg]

[Image: 20190510181638.jpg]

Added a couple bolts for adjustment on the w220 mount:

[Image: 20190327155720.jpg]

Here you can see the temporary transmission mounting, a W220 pate grafted onto a W126 pate with some support metal welded on. Someday I'll make a nicer version, but this will work for now.
[Image: 20190510181551.jpg]

[Image: 20190510181526.jpg]

I built the exhaust in three pieces with band clamps for ease of driveshaft service and rear differential/cv swap.

Don't mind the booger welds, here you can see I had a few too many and forgot to turn on the gas. Amazingly, the pipe still holds gas, not pretty though.

[Image: 20190510160006.jpg]
I used all the stock mounting points I could. I may still add a lateral brace between the old kidney bean muffler mounts once I get done under the driveshaft plates and finalize everything as there is too much side to side movement for my comfort.

[Image: 20190510181538.jpg]

[Image: 20190510155927.jpg]

Patchwork of W123 mounts grafted onto a couple pieces of metal:

[Image: 20190510155953.jpg]

Still not sure how well this W220 AMG muffler will do, hopefully will get to find out soon enough. I put one of the resonators from that car on my om642 and it seems to flow just fine, this one I'll add a resonator if it is too loud but want to try without first.

Tip alignment (she tells me this is important)

[Image: 20190511154036.jpg]

[Image: 20190511154025.jpg]

[Image: 20190511154015.jpg]

Went for the biggest intercooler I could possibly cram under the bumper:

[Image: 20190511133846.jpg]

It will work, but is going to have some mild modifications:
[Image: 20190511142812.jpg]

The front pull is in the way:

[Image: 20190511142839.jpg]

I made some cheater plates to hold the bumper out a little more. Off of these I'll build the mounts for the IC so modification of the body is minimal.

[Image: 20190511152817.jpg]

I want to keep the bumper as stock looking as possible, worst case I can take off this lower support bar and redesign the front lower radiator support, but really trying to make it work without that first:

[Image: 20190511142849.jpg]

Have a couple mm around the sides and bottom, that is the lower lip of the bumper and bottom of the IC:

[Image: 20190511142857.jpg]

Will keep updates coming, hopefully more frequently than yearly...
05-12-2019, 08:25 PM
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Tobulus Offline

Posts: 133
Joined: Jun 2015
Location: Germany
RE: W126 short body OM606
Very nice!
05-13-2019, 02:50 PM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
RE: W126 short body OM606
Had a few more hours to put into this one, got the intercooler plumbed up and mounted, and started on the fuel system. 

[Image: 20190608121313.jpg]

Core size is 10.5" (26.67cm)x 22" (55.88cm) x 3.5" (8.89cm) with overall length of 32" (81.28cm)

Made the mounts such that the whole assembly comes with the bumper mounts. 

I did have to trim back the lower radiator support a little:

[Image: 20190608125352.jpg]

Reinforced with thicker steel and flat supports:
[Image: 20190608132553.jpg]

A little clearance in case the bumper gets lightly tapped:

[Image: 20190608132821.jpg]

[Image: 20190612102939.jpg]

Picture of the mounting brackets:

[Image: 20190612102857.jpg]

The new front pull:

[Image: 20190612104359.jpg]

[Image: 20190612104410.jpg]

Had to make a stainless hard tube to get around the om603 oil lines and squeeze down by the AC pump:

[Image: 20190705145623.jpg]

[Image: 20190712120302.jpg]

[Image: 20190712120408.jpg]

Some IC tubes:

[Image: 20190717090628.jpg]

[Image: 20190717090646.jpg]

Even put the splash shield back on to keep water off the alternator:
[Image: 20190717101802.jpg]

Oil cooler splash shield:
[Image: 20190717101819.jpg]

And the fuel pumps. Going to try and use one of the w126 gas pumps with an aftermarket regulator to hold the 1.5 bar:

[Image: 20190717185742.jpg]

Next just need to plumb the fuel lines and see if the pumps can handle the more viscous diesel fuel...
(This post was last modified: 07-17-2019, 10:02 PM by WSchotty.)
07-17-2019, 08:53 PM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
RE: W126 short body OM606
Some more progress, the fuel system turned into a larger project than expected as the tank was full of sludge:

[Image: 20190910093750.jpg]

[Image: 20190910093728.jpg]

I decided to use the fuel tank from the other car, which means it is time to decommission the 83.

[Image: 20190910093604.jpg]

[Image: 20190918100054.jpg]

While I had the tank and differential out I had to patch up some surface rust spots:
[Image: 20190807125432.jpg]

The "audio card" from the 83, something similar may find its way onto the 91 but the music of the engine should be enough for the next year or two:
[Image: 20190912100125.jpg]

I ended up using a gas fuel strainer and intake line for the larger size, the only disadvantage to this is the strainer screen size on the gas is much finer than the diesel. This could cause no flow if the fuel gels and might clog up like a prefilter. If this becomes a problem I'll have to swap the screens between the two.

The small nipple on this elbow was filled with solder:
[Image: 20190912132757.jpg]

[Image: 20190912144527.jpg]

[Image: 20190912173212.jpg]

I made a little bracket for the firewall and mounted the regulator in the engine bay:

[Image: 20190724110217.jpg]

The single stock gas pump is plumbed through the mechanical pump, but will hold 25psi on it's own:
[Image: 20190725135303.jpg]

Once the fuel system was up and running, setup the transmission wiring and shifter:

[Image: 20190918121623.jpg]

Used a rod from a w220 or w140, it was just a little long and needed trimmed down and threaded:

[Image: 20190918195625.jpg]

The bolts didn't line up, and had to use a washer to hold one of the four in. It would be better to cut out the area and weld in a new plate but this will be fine for now.

[Image: 20190919095215.jpg]

[Image: 20190919110729.jpg]

[Image: 20190919110743.jpg]

Once I buttoned up the rear end, finalized the exhaust and added that lateral support I was talking about earlier:

[Image: 20190925145624.jpg]

Time to move up front, there was some more rust damage under the battery tray. I swapped out the sway bar mounts and sandblasted it out. The tray I had already redone in the 83, so swapped over the good parts:

[Image: 20191010115720.jpg]

You'll notice coolant lines into the washer tank, that is for heating of the fluid and battery. This is a shot inside, there is a thermostat on the end that controls flow:

[Image: 20191010115757.jpg]

For the heater core lines, the exhaust side of the engine I used a line from a 81-85 SD slightly modified, painted is the modified vs the old one from the 83:

[Image: 20191008123847.jpg]

This now runs on top of the spring perch:

[Image: 20191010121315.jpg]

[Image: 20191010121328.jpg]

[Image: 20191010155535.jpg]

I also made a steel mount to hold up the intake tube and filter.

Here you can see the short extension around the 603 oil cooler:

[Image: 20191010155742.jpg]

Found this perfect little elbow on a X5 CCV system:

[Image: 20191010170123.jpg]

Getting closer, just need to finish the throttle cable assembly, wire it all, and fill with juices.

[Image: 20191010170445.jpg]
11-06-2019, 09:00 PM
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WSchotty Offline

Posts: 15
Joined: Nov 2016
Location: USA
RE: W126 short body OM606
Here was today's progress, all fabrication is complete, now just wiring and fluids to go.

Throttle cable comes around from the front and in between the firewalls:

[Image: 20191107100124.jpg]

Then pokes out here:

[Image: 20191107090643.jpg]

Here you can see this adjustable cam lever I made from a piece of a Nissan that rides on the bearing:
[Image: 20191107090655.jpg]

Then the cable support made of steel:

[Image: 20191107090806.jpg]

[Image: 20191107100056.jpg]

Finished design, just needs the return spring on the pump and final adjustment:

[Image: 20191107100103.jpg]

This isn't the most elegant solution, but will work for now. I wish I could have used the rods and kept cruise control, maybe someday in the future.

And finally, the last weld on the car for awhile (hopefully). Installed the EGT sensor from the 83:

[Image: 20191107112123.jpg]

11-07-2019, 02:04 PM
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