1969 MGB GT Build Log

Tonights activity has been a bit of a tough one. I'm trying to get all the brake lines, fuel lines, exhaust and any and all remaining tabs and mounts that need to go on the subframe in the model so the final parts order can go out. This also means I need to at a minimum sketch in routing for most parts. The exhaust is the tough one. I've tried over the axle and several configurations of under the axle and I just can't find anything I'm super happy with. Snaking through the triangle on the back of the subframe is really tight to fit a 2.5" tube and going though the control arms is a no-go with suspension articulation and the axle. Any ideas or tricks to make this work?

Side exit?

I'll never vote against side exit.

I found some time this weekend to start working on the mounts and brackets for control arms. The laser cut parts arrived from sendcutsend a while ago and are very high quality. I messed a few up already and did not cut any extras so I will need another order to go out. I don't have a large sheet metal brake so I used the press and some gradually improving tooling. I ended up with some aluminum angle section and a few different press tools. It is quite time consuming but so far quite effective. 

The bolts arrived as well and fit the spherical bearings very well. The only problem found at the moment is the brake caliper bracket bolt head is too large for the counterbore provided and will need to be replaced with a SHCS or flanged 12 pt. The parts bin is getting larger and larger!

Lots of planning has been going on as well. According to my project plan I have 22.5 hr of design, ordering etc. and 62.5 hours of making things to go on the rear suspension and drivetrain. I have it planned out to complete end of September, but with some family visits and other life things that's probably not a reasonable goal. I will likely readjust that schedule for ending of October. Here is a slightly out of date, and quite behind schedule screenshot of that plan as it sits for the next few weeks. The whole plan is currently over 60 tasks for just this rear end alone. I'm trying not to think too much about the whole car.

Regarding the exhaust, would an some oval sections through the subframe give you enough space?

However, snaking it through the subframe will make building/install/removal more difficult and I don't know if I would like the proximity to the axle boots.

If you're comfortable with a little sheet metal work I think you could run it completely over the subframe by cutting in to the front corner of the space under the boot cover.

In reply to MNIMWIUTBAS :

I'll give routing it entirely over the top of the subframe a try in CAD and see how much it would need to intrude to make the turn. It's not a bad idea at all. No matter what it will have to be assembled in multiple sections, where exactly isn't super critical right now as I'm mostly trying to get hanger locations. The clearance everywhere is fairly hard to visualize though even when you can orbit around in the model, the size of the car becomes really apparent when a 2.5 inch exhaust looks like a 3+ inch exhaust. I've also thought about going out to the drivers side of the subframe between the control arms in a similar routing to what you have there, still clipping through the spare tire well.

It has been a while since my last update, some of that has been steady progress, but much of it has been weekends away from home, long days at work and generally not getting around to things. I have now nearly completed all remaining design tasks before the rear suspension and drivetrain are complete. I need to select dampers, finalize the lower control arm damper mounting, the upper damper mounting and finish designing the adjustable toe links.

The last couple weeks I put together lists of all the required brake fittings, fasteners and other hardware required to complete the rear end. The tasks are becoming less and less interesting but the list is shorter and shorter. I completed the design of the differential mounts with shotguns mated to existing tubes and laser cut brackets. For now, the differential will be hard mounted to the subframe while the subframe is isolated from the chassis. If this sound from this becomes unbearable, I will come up with a method to isolate it fully. I also finished the mounting bushings to the chassis and the notching to make everything fit as efficiently as possible. I clearance checked everything in the model and other than a couple places on the chassis nothing will have to be clearanced. The only area that required touching is where the upper control arm meets the frame rail pinch weld at full compression.

I spent a long-time researching dampers and trying to find something that I can rebuild myself and re-valve myself. Penske actually has a small damper, the 7000, targeted at the Formula-Vee and similar vehicle crowd which could support the damper forces and spring rates I need at a very affordable cost. As the MG is quite a bit heavier though I need to reach out to them and see if I am crazy. If it works out, I should be able to buy different pistons and valve shims and play around with that in the future. If I can get a non-adjustable damper, or compression only damper, valved correctly for the car that would be perfect. I could pull back the low-speed compression when driving on the street but maintain the chassis control when on the track. I also looked at the Ridetech HQ damper which I believe they can custom valve, but it is quite a bit more expensive. If anyone has any experience with either of these dampers, or the dampers from AFCO let me know. I’m looking for a damper I can rebuild which if adjustable has linear steps between damping settings and ideally a run on the damper dyno from the manufacturer.

In the garage I tidied up the 302 block I have from the original engine plan which has been baked and crack checked and took photos in preparation for listing it. If anyone is in the LA area, I will be listing that for sale, it is a crack free, roller ready, block that just needs machining. I also had to clean up a mountain bike that will be going up as well to make room for a new bike that just came home. That bike has been some of the recent distraction catching the last evenings after work that still have light.

I bent up the remaining control arm mounts and finished welding them. I have now finished 8 of the ten mounts and just need to wait for new mounts to turn up from SendCutSend to replace the ones that were sacrificed learning how to fabricate these. I was able to put some of the hardware together and mock up the parts on the rear subframe. Next weekend will be finishing off the remaining mounts and tacking the mounts in place. I will then notch the front tubes and jig and weld the forward mounting locations. During the week I will get the remaining design tasks finished and get all the orders out. That should be all the parts I need to finish this up in theory. In practice I’m sure they will be far from the last orders. I’m hoping I can get back in the rhythm again, like always, it comes and goes in priority.

This week was productive. On the design side I have now, at least in theory, completed all the design for the rear suspension, drivetrain and brakes and I just need to compete ordering parts and finish making the parts for real. I finished design on the lower control arm damper mounts, the toe link, sent off the brake caliper bracket and lower control arm ball joint taper to get made. I also did some quick FEA analysis of the loads on the differential mounts to make sure that the stress and compliance were acceptable. It’s a obvious conclusion once you thing about it for a moment, but the farther apart longitudinally the mounts are, the lower the forces on the subframe. This helps explain the extremely long extensions Honda included on the stock S2000 differential. In my case an equal and opposite load of 1350 lbf on each pair of mounts front and rear gives a pretty good idea of peak reaction force when accelerating. The peak stress is well under the infinite-life stress level so they *shouldn’t* crack. I will have a regular crack check procedure once the car is complete to monitor the subframe and control arms for any damage. A final set of orders need to go out this week for bolts, brake fittings, some tubing for control arms and a few laser cut parts that still need to get ordered.

The plan for the weekend was to finish all the control arm mounts and brackets in preparation for fabricating the front subframe mounts, rear subframe mounts and jigging all the control arm mounts over the next few weekends. After that I will add the differential mounts and finishing touches. Following that the control arms will get made and everything will be assembled and installed on the car.

I was out of town this weekend and therefore was only able to do a limited amount of work. This was still scheduled though and therefore there is no slip to the current schedule. Many orders went out and have been gradually arriving. There are still several parts still to arrive including the brake caliper brackets hopefully tomorrow and the remaining laser cut parts including the differential mounts which should come back anodized and looking good.

I assembled both rear uprights after removing the old bearing race from one of the hubs. It took welding a bearing removal tool to the race, but it eventually came unstuck. The race was there after the first assembly attempt when the interference between the upright and the studs appeared. Both new bearings went in without too much trouble and the circlips were installed after that. I held the 2mm shim in place with a dab of grease after thoroughly measuring to ensure there would be no interference. Both hubs pressed in with no issues and the rotors fit over the hubs and have no clearance problems with the upright. One of the bearings is noticeably tighter than the other bearing after assembly and while I think the grease will loosen up it is something I will keep an eye on. The calipers will be installed this week once the brackets arrive, and I get a chance to tap the holes.

I got a head start on jigging the front mounts and made a full set of paper templates for the tubes. Unfortunately, it has been a while since I did the last tubes, and the first set of templates were made incorrectly. I made an update to the process and made the first of three templates correctly. I cut all the tubing to length and fully notched and cleaned up one of the six tubes.

I held down the two front mounts with a section of tubing and clamps to ensure they are the correct distance apart as well as colinear then working from a centerline shimmed them to the correct height. They need to be 1.200 inches below the bottom plane of the rest of the subframe so ground the front tubes of the subframe until a 1.25” tube just slipped in and supported the rear with a 1.25-inch tube. I then stacked 50 thou worth of shims under the front mounts on each side. The center crossmember is used as the datum for the subframe and it was aligned with the centerline on the table and tacked in place. I double checked all the measurements several times and will do the same thing again before I tack any tubes in place. The tube I fully ground fits in place with no issues. The two front mounts are 37 inches apart as per my measurements, the scan data and the factory service manual.

Machined parts from PCBWay came in early in the week. The brake caliper brackets looked nice and fit with no issues. I only needed to tap the holes and they were ready to install. I started the tap in the drill press and finished by hand to ensure they went in straight. The LCA mounts have a very nice surface finish and will be ready for starting the LCA’s in the next few weeks once the subframe is complete.

The plan for this week was to get the front mounts and tubes cut, fit up and tacked into place. The center braces are only temporarily tacked in place to provide some structure until more of the welding is done. Once most is done, I will remove them and finish the complete weld around the tube they block. Both front mounts are now ready to test fit on the car when this comes off the table and fully weld.

In addition to the front mounts, I got 3 of the four rear mounts supports cut and fit up. I tacked together the outside joints on one side and fully welded where the other tube covers. I need to properly jig and tack in place the mount but that is for next week.

After the rear mounts only a couple remaining tasks exist on the subframe itself. I need to fabricate the diff mounts and jig the control arm mounts. Once I check it on the car I will spend a day fully welding it and capping tubes, adding the brake line tabs etc.

I still haven’t decided whether to powder-coat, or paint with steel-it. I’ve seen steel-it hold up very well on trophy truck type vehicles and being able to inspect for cracks and make repairs or changes with no trace is nice as well. On the other hand, powder-coat is strong and I never have to think about it again.

The project schedule now says 50 hours to go on the rear end and finishing somewhere around early December. Now that I have said it though it’s definitely cursed… Next I have to decide what to do next, do I pick up a transmission and get the engine and trans mounted in the car or do I get front suspension steering and brakes in the car and get a rolling chassis?

Some exciting progress this week! I got the rear subframe mounts jigged in place and pulled the subframe off the table again to be able to check the fit on the car. When I re-jig it, I will jig relative to the mounting locations to ensure the control arm mounts are in the right location with respect to the chassis.

After getting a bit sick of grinding tubes, carefully jigging and tacking in place I took some time to inspect the differential. I checked the pinion visually for any cracks, looked for debris and measured the backlash. The wear pattern on the ring gear looked mild and well patterned on the flank of each gear. I sealed that back up and pulled the studs out of the rear cover. I also installed the mounts I received from SendCutSend in preparation for jigging the differential in place in the subframe.

The remainder of the SendCutSend order contained the remaining two control arm mounts that were ruined during the learning process and control arm parts. The control arm parts will be needed in a few weeks when I start on those.

During the weekend I got to test fitting the subframe on the car. First, I had to fabricate the rear mounts and after cutting off the bump stop pads, I cut a sight hole in the wheel well to inspect the structure inside the frame rail. To my excitement there is already very good bracing inside the frame and with the load being spread significantly by the mount I am not too concerned. I will keep an eye out for any cracks developing in the area. An additional ring was added to the outside to avoid drilling into the reinforcement inside the frame. I may adjust the rear mounts on the subframe to compensate. The bolt is captured by the mount and not heat-affected by welding.

The subframe fit well on the bottom of the car and the poly mounts work well. I will add a bit more welding to the subframe in a few choice locations to lock in its geometry and pull it back off to continue with installing control arm mounts, diff mounts and tabs for brake lines. Before I continue with those items though I will fully weld what I have to control for any further distortion.

The rear subframe is done, almost… I have about a half hour of finish welding before I can fully claim that and some time to paint it when I paint control arms. Over the last two weekends I installed the remaining control arm mounts, double and triple checked their locations and installed the differential mounts. I bent up the final control arm mounts before realizing that I made two same-handed versions and got to make up a new one the old-fashioned way.

The diff mounts started with making shotgun mounts but were one of the slower parts of the projects. After installing them on the diff itself I gradually ground and fit the subframe to accept the mounts with the differential at the correct height, correct rake, correct centerline and the correct roll. It took several hours of lifting and reinstalling the differential making tiny change after tiny change.

I installed the brake line brackets and trimmed and capped all the tube ends. The differential mount tubes were shortened to their correct lengths. Finally, I put on some music and started fully welding. I stopped just short of the end when my patience was running thin, but it is 95% of the way there.

It is extremely exciting to have a major assembly complete after looking at versions of this part on my computer screen for nearly two years and at least 100 hours of work to get to this point.

Up next, control arm will come together over the next couple of weeks, and it can all start to become a real thing. I submitted the order with Penske for the 7000 series dampers and will get those installed once they arrive. I am very excited to see them in person.

Nice work!

Another busy week squeezed in around normal life things. Saturday was almost entirely hanging out with a friend from college who was visiting but work proceeded during the week prior and Sunday. The goal for this week was finishing the upper control arms, but significant progress was also made on the lowers. Assembled together it's looking like a real thing now. Once complete I will get a final weight for both spring and unsprung mass.

The UCA's were a fairly easy part to make. I started by cleaning up the laser cut plates and finish-sizing the hole for the outer ball joints. I cut the tubes using the normal template method and welded the outer cups in place on the table. Luckily those can be fully welded prior to and further work proceeding. 

Once those lollipops were complete I slowly enlarged the slots until the fit was perfect on a printed template. Because of the design, it was very easy to clamp down to the table to be tacked in place. Once it was tacked I checked the fit on the actual subframe which required pressing in the inner ball joints. After confirming the fit I fully welded in the tubes. Finally I tapered and capped the ends. I will paint these with the LCA's and subframe next weekend.

The LCAs went together similarly, however, I did make one design change. I changed the angle of the outer taper cup such that the bottom face was tangent to the inner cups. This required a very slight length change to the arms but significantly simplified the jigging. The suspension kinematics are completely unchanged by the modification. The tubes were cut to approximate lengths and the inner cups fully welded on. I then pressed in the inner ball joints. The first joint was a total disaster and galled significantly. I will have to order an extra when I complete the toe-links. Following that I used some grease and lightly chamfered the cup which resolved the issue on the following bearings. The wall of shame grows by 1.

To complete the LCA's I welded the outboard cup the rear arm member. This correctly sets the lateral distance as the lateral location of the pickup point is well controlled. I then installed the rear member on the subframe and measured from the datum on the table the correct longitudinal location for the outer cup. Using that location the fore-member was fit into place and tacked. This ensured that any variation in the pickup point locations would not leave stress in the members as well as ensuring the correct location in space for the pickup point. Finally, I fully welded the tubes to the outboard cup. I have completed one lower control arm to this stage and still need to fit the fore-member on the left side of the car. The gusset plates need to be bend and welded into place along with the damper mounts although I will wait for the dampers to arrive and confirm their fitment before doing that work.

Down to 20.25 hours of work in the project plan at this point and still on schedule for finishing the first week of December. Having the plan laid out with all the dates I need parts ordered by and designed by has made weekly progress much for effective. Once the rear end is completed I will take a small break in December before getting started on the engine/transmission mounting and front suspension. Step one will be getting a complete sub-project plan together but the earliest interesting things will begin shortly after that. I'm still excited about the day I get to soap box car this down the street, it will be the first time I've ever driven an MGB...

On a new topic, back to transmissions, I've been looking at both the BRZ 6 speed and miata transmissions and the BRZ transmission is starting to look appealing. It looks fairly small, although a bit heavier, is quite cheap, and can handle a bit more power. KPower has a nice adapter plate and light flywheel to pair the engine, the only big negative I have seen is the shift feel isn't great. Does anyone have any insight into how these would actually be in a full swap car like this where there isn't really a strong reason for either way? The other advantage of the BRZ transmission is it looks fairly easy to move the shifter forwards which is important with how short the trans needs to be to not be shifting in the back seat.

Wow,

I missed a few things since the last time I checked in. Amazing progress! I'll be interested in the transmission discussion. I've considered replacing the T5 behind my 302 with both of those options, but don't have first hand experience with them. Will the slave/starter location on the BRZ transmission clear your firewall?

In reply to Shavarsh :

The adapter plate from KPower has a block off plate for the starter and uses the Honda starter motor. I don't know if the slave clears, but it's not too big and making a little clearance for it isn't the end of the world I don't think. I need to do a bit more analysis on the ratios as well with the power curve I have. The 6th gear ratio is nice and long though on the BRZ transmission which makes for a ~3k 70 mph cruise with the existing ring and pinion in the rear.

In reply to DanielN :

dang son, you do nice work.