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That is so weird, my digital boost gauge in my audi has been doing similar.... might have to check the voltage like you pointed out although I noticed I crushed a small part of the vacuum line some.
Hopefully you get it sorted out, that is a little annoying for sure. I might have to go back to mechanical lol
Yeah it’s pretty weird. Even the Prosport guy was stumped but he did go over with me every test and diagnostic he could think of.
It’s got something to do with either the +12V switched source, the Ground to the battery or the signal wire itself. Once some more heat shrink tubing comes in I’ll wire in a generic 3-pin weather sealed connector to get better access to those boost sender wires and I’ll be able to narrow it down.
All I know for certain is that with the ignition key at “ON” I get a solid 1.0V boost sender signal but once I click the key to “ACC” it drops to 0.86V.
I finally found a good evening to remove the SC400 3.92 open diff and install the rebuilt Supra TT Auto 3.769 Torsen. I’ll have about 200 miles of easy break-in according to Jared Pink who rebuilt it for me last August/June (mostly for the new side carrier bearings) and then it’ll be ready for anything.
I’ll also recalibrate my Yellowbox so that the speedometer is accurate.
No test drive yet since we’re now under a statewide stay at home order but I’ll find a couple of essential trips to make sure everything is working fine.
I quadruple checked all the torque loads and gave it fresh Mobil-1 Synthetic 75W-90 GL5 (fine for Torsen LSDs) so it should be all good.
That will be such an awesome upgrade, Craig! Despite being on the the stay at home orders here too, I've managed to sneak out for a few canyon drives to avoid going absolutely insane while working and being stuck at home. Although, trying to remind myself to be thankful to still be working!
Thanks Rudy! It feels good to have the Torsen back in the car again. It was always one of my favorite upgrades. I had to have it out to get it rebuilt from 4.272 to 3.769 and now for the first time can get a feel for it with its original ratio. Now I definitely see why people like it paired with an R154 or A340E. It does feel more suited and drops the revs just a bit compared to 3.92 which does make for a nice cruising gear but without giving up anything in terms of drivability.
The 3.92 definitely feels a little more aggressive and highway revs are a bit higher (but not by all that much). 3.77 still feels aggressive enough but with slightly lower cruising and highway rpms. And the Torsen T-1 once again smooths out acceleration and turns. The SC was a little manic (in a mostly fun way) at stock boost (310whp?? I have yet to dyno it) under full acceleration with the open diff but it's smooth and controlled with the Torsen requiring less corrective steering input.
There was a little minor sound coming from what sounds like my driveshaft center bearing or the rear input shaft into the R154. It seems to have subsided mostly over about 25 miles of easy driving but if it doesn't completely go away I may put the car up again, drop the exhaust system and get to the driveshaft, undo the center bearing and re-seat it. Something about how I removed the old diff and installed the new one must have shifted the driveshaft longitudinally just a little. Although the car drives very smoothly and there was no indication of any binding from the first moment I took the car out.
I've never had this happen to me before but I will monitor it and deal with re-seating the driveshaft if I need to. If anything the initial noise has gotten softer over those 30 miles. Only a little bit of faint noise remains so if it goes away I'll know it's okay but if it doesn't I'll know it has to be dealt with.
It might also have something to do with how 1986.5-1992 Supra MKIII R154 front driveshafts do work with SC R154 swaps but are not as ideal as using a genuine Soarer R154 front driveshaft that was made for this specific chassis.
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I ran this same Torsen diff with my original NA engine, W58 (and later my R154) and with 4.272 final drive. I loved that combination. I initially ran the 4.272 Torsen diff when I first got my swap running but it was apparent the gear was just too aggressive.
It's the same as with the FR-S / GT86 / BRZ: even with only a little horsepower and torque adding an LSD changes a car
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And I have narrowed my boost gauge sender issue down to either the +12V switched power source or ground connection. But my bet is on the 12V power source wire, so I'll need to find a new circuit to hook that sender up to either from the driver's side kick panel in the footwell or by creating a totally new 12V switched and fused circuit with a relay trigger in the engine bay.
I was previously incorrect when I stated the ignition position multimeter readings from the boost sender signal wire. The correct findings for my issue are:
Ignition to "ACC" = 1.0V boost signal with engine off. IE: boost/vac gauge reading at the correct "0" PSI.
Ignition to "ON" = 0.86V boost signal with engine off. IE: boost/vac gauge reading at an incorrect number well below "0" PSI.
So the problem is that the boost sender just needs different clean 12V switched and ground connections so as not to be powered by a 12V circuit that is probably experiencing some current drop or something. That same 12V wire powers the rest of the interior gauges and 12V DC accessory port from the cigarette lighter and also serves as a 12V signal to trigger the fan controller's internal relay. So it is probably just time to move on to a new circuit.
Having the LSD is such a game changer. I don't know if I can ever go back to an open differential RWD car. The gearing sounds like it's a suitable upgrade as well! Also glad to hear that you've got the gauge sender figured out. It makes sense that you need a good clean signal since they are so precise and delicate.
Speaking of dyno numbers, I've been wanting to get mine strapped down just to get a base line for ****s and grins. I've read online guys with stock turbos, ecu, 3" turbo back, and fmic's making 330/340 whp. I'd be stoked if mine made over 300 whp/wtq on stock ecu and twins!
An LSD is definitely a good thing for any car. I don't like owning one that doesn't have one. Unless whatever electronic torque vectoring capability might be in a brand new car is 100% under my control to fine tune on its own.
I'm pretty sure that is what the issue is with my boost sender. I'll get to fixing it soon.
You should be able to hit 340whp soon with no issues. Remember that your 2JZ-GTE VVT-i engine has 440cc injectors and different ECU mapping than mine does so you have to do just a little more work initially to get it beyond what a USDM non-vvt-i puts out fully stock. That being said, you'll surpass me pretty quickly with modifications like those
MKIII R154 front driveshaft slightly too long (by 1/2" or 3/4")
I'm pretty sure I have figured out what the concerning noise is from my driveline. It's almost certainly the Supra MKIII R154 front driveshaft being slightly too long which is causing stress on itself and possibly the R154, center bearing and rear diff flex coupler.
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This is what it currently looks like at the back of my transmission. Almost exactly like it was before but apparently ever so slightly closer now. Note the missing dust shield. This is with an unmodified MKIII R154 front driveshaft.
And here is what it should look like at the back of the R154 transmission (picture is from an MKII Celica w/R154 swap but bear with me here as the way the driveshaft is sitting in this picture is the relevant part). This is how it should be sitting when at a correct length. Note that in this picture the R154 rear dust cup/shield is installed. No bottoming out at the back of the trans and ample room for minute shifting of the driveshaft without hitting the transmission.
Please be aware that the front driveshaft pictured below is NOT an MKIII R154 front driveshaft but some other Toyota R-series or A340 series front driveshaft that happened to work for the Celica MKII application.
Again, the only thing to pay attention to here is how the front driveshaft sits at the back of the R154 transmission. Regardless of what vehicle the R154 is in and regardless of what driveshaft is used, this is how it should look if the length is correct:
I've only put 45 miles on the car with the noise so far and I'm not going to drive it until I can get a solution. I just don't want to potentially hurt anything.
Since they've gone bad, some new exhaust muffler gaskets, a standby replacement R154 tail shaft seal and new Redline MT-90 fluid just in case.
And mainly I'm going to need to remove the driveshaft, take off the MKIII R154 front driveshaft and have it shortened at a driveline shop by 3/4", welded and re-balanced. I'll have to get under the car with the new rear cup/shield in hand and measure the distance the MKIII R154 driveshaft needs to be shortened, however according to my research threads it needs to be either 1/2" or 3/4" shorter.
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I had a similar issue in 2013 when I first installed the R154 with the MKIII R154 front driveshaft and encountered its joints hitting the rear trans dust cup. I had that damaged cup removed and ordered a brand new one (still haven't used it). For 7 years I have gotten away with not having to revise this driveshaft, nor did I realize it might need to be done.
But now I think I have to so as to avoid causing any issues.
Other than a Soarer R154 front driveshaft the OEM style driveshaft solutions are to get an MKIII R154 front driveshaft and have it professionally shortened and re-balanced by 1/2" or 3/4" or to take an SC300 Automatic front driveshaft (same splines as the R154) and have it professionally lengthened by 50mm / 1.96" (according to a Mighty Car Mods forum thread link below). I've even read of one instance where a Soarer R154 front driveshaft (probably an early type) was a bit too long for a late model R154 Tripod transmission and which would also need some length modification. I have no way of verifying this but it was an issue that CatManD3W (on CL) ran into some years back.
Somehow I got away with this for a VERY long time (about 7 years until now albeit with no dust shield and fairly tight clearance) but I think this was probably an underlying issue waiting to happen eventually. The MKIII R154 front driveshaft needs a slight shortening in order to not be too close to the transmission and allow for the dust cup to remain in place.
After reviewing all of these threads I'm VERY reluctant to drive my car any more until I get a revised front driveshaft in there. How this was not an issue for so many years after my initial install I really cannot say but I got away with it somehow. Now though think it needs to be dealt with.
A local engine machine shop also does driveshaft work. It's the worst timing for it but hopefully they like the turbocharger rebuild shop I just used are also an "essential" business that still operates at a minimum during this Corona virus shutdown. Fingers crossed.
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Edit: Another informative thread hits on this very issue and provides a concrete approach to custom shortening the MKIII R154 driveshaft in its last post.
^^ This poster still says the MKIII R154 front driveshaft is the closest (apart from one from a Soarer) and that it needs to be shortened by approximately 20mm (0.78in).
Last edited by KahnBB6; 04-07-20 at 04:05 AM.
Reason: Added research links
Definitely an odd issue to run into... However, I'm with you, I'd avoid driving it much more until you have it sorted. A good driveshaft shop can help you measure and get the appropriate length you need to reduce any stress on driveline components.
Definitely an odd issue to run into... However, I'm with you, I'd avoid driving it much more until you have it sorted. A good driveshaft shop can help you measure and get the appropriate length you need to reduce any stress on driveline components.
I think the reality is that the MKIII R154 front driveshaft was always slightly too long for the SC300 application and that I just got very lucky by having BARELY any extra fore-to-aft slack buffer room between the back of the transmission and slip yoke. Something I did when installing the new differential must have shifted the driveshaft(s) forward a bit and thus I got rid of that extra 1-3mm of space I probably had.
I got away with it like this for a LONG time but it was never ideal. If I had been smarter about this I'd have thought to get this shortening of the front driveshaft done while I was performing my engine swap. It just didn't occur to me at the time that it would be an issue again.
I spoke with the local driveline shop today and thankfully they are still operating as an essential business during the stay at home order. They could not confirm they'd be able to work on the Toyota slip-yoke design but hopefully they can. I know it has been done before all around the world though.
Time to get the SC up on jacks again, drop the exhaust and drop both driveshafts and take it over to them.
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Let me tell you, any trips out where people are right now have me sweating bullets between the mask, glove and sanitizer safety procedures. If this situation were not so critical to just driving the SC normally I wouldn't be trying to do it right now. I have to be extra careful not just for me but for my family members also. A very stressful time we're all currently in.
It is indeed quite stressful Craig... I've been working on my car some, and going out on short drives, but otherwise, I've really been trying to respect my fellow humans and stay home. It's getting harder some days and others I don't mind it so much. Here's hoping we don't have too much longer...
It is indeed quite stressful Craig... I've been working on my car some, and going out on short drives, but otherwise, I've really been trying to respect my fellow humans and stay home. It's getting harder some days and others I don't mind it so much. Here's hoping we don't have too much longer...
I'm with you on that hope. The biggest issue though is to get the number of infections down so that the health care system isn't totally overwhelmed to deal with it on top of every other illness and condition people come in for. It's going to take a while still. The U.S. is now one of the top three countries leading in Corona virus infections. Until that changes we have to keep doing what we're doing and survive as best we can. Easier said than done is a huge understatement.
Same as you I've been keeping my outings to an extreme minimum. It's making me stir crazy but on the other hand in addition to the few car mini projects that need to get done it has given me time to catch up on other work that can only be done in isolation.
You're doing it right, Rudy. Hang in there
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The only progress I made today with my SC is to pick up a new spare R154 transmission output seal (always good to have a new one on standby if pulling out the driveshaft). Too much other stuff going on prevented me from jacking up the SC and inspecting/removing the driveshaft to see if I have something out of alignment, a bad center bearing or simply that I just have to get that front driveshaft shortened right now.
Maybe tomorrow. Just how it goes. But still no driving of the SC until I get a look under there to assess.
I also got through de-rusting (with a concentrate called Metal Rescue-- I went through three of them) a spare USDM 2JZ-GTE stock twin cast iron collector (that mates the two turbos), priming and painting it with 1000 degree VHT paint. I don't need it right now but I wanted it freshly painted and on standby for later.
I also did a whole POR-15 de-rust metal prep, full POR-15 paint job and final protective top coat on my now removed 3.92 SC400 rear diff. It looks MUCH better now. I may keep it or I may sell it once this quarantine is behind us.
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I'll get back to solving the boost gauge sender power issue soon as well. I am either going to figure out how to wire in a new custom 12V Switched circuit direct from the engine bay or maybe (much easier I suspect) I'll just find a new circuit in the driver's side kick panel fuse area to run one of those clean fuse tap pieces from.
Looks great Craig. Keep your chin up. It's true that misery loves company and it is comforting to know that we're all in this together!! I'm trying to look on the bright side for sure. My house, yard, car, and general health seem to love this quarantine lol. However, my mental health could certainly stand to "let loose" a little once this is all over.
Thanks Rudy! Your positive attitude is infectious... (in a good way )!
We do what we can in isolation
As for the SC, I think I may have discovered why my driveline was making noise. I’m pretty sure that’s a failed original center bearing with the way it is sagging.
Thankfully I already had a new one Just in case.
I re-measured the MKIII front driveshaft length to the R154’s (removed) dust cup and it’s right about 3/4" too long if the edge of the d/s cup is to be right on the line of the R154’s cup. If it’s supposed to only have 1/2” less length then that cup on the d/s slip yoke end would sit a little deeper.
I’ve read at least one forum post in my research that suggests the Soarer R154 front driveshaft is really only 1/2” shorter than the MKIII R154 front driveshaft but another that suggests it is 3/4" too short.
I wish I had actual measurements of both factory front driveshafts to go by but I'll start making some more of my own.
Anyway, it seems I can solve my issue with a new center bearing install but long term I’d like to get a custom length adjusted OEM front d/s to solve that issue permanently since the MKIII R154 front’s clearance is still so close.
And then I could re-install a rear dust cup onto the back of the R154.
I went ahead and unbolted and pulled the entire driveshaft.
At first my old center bearing looked compressed to the bottom but then after a while it seemed to settle almost to normal(?). Well... I removed the old lock nut, used some silicone spray and put on the new bearing. But I found I could not re-use the old lock nut. So I'll have to get another one of those from my local dealer. They seem to have a LOT of COVID-19 precautions in practice all over the building so while it's a risk I'll take it just to get a new locking nut and two new washers. And then I'll wash my clothes and sanitize myself when I get home.
I'm tempted to bring this front driveshaft to the machine shop I'd looked into for getting it shortened but that may be too much potential risk right now.
What I can say is that after a lot of measurements and mocking up the replacement R154 rear input dust shield/cover this MKIII R154 front driveshaft does seem to hit right at being 3/4" too long as another one of my research threads (a few posts back) attests. 1/2" of shortening would helps a lot but 3/4" seems to be right on the money. I'll have to measure again to get the exact length adjustment in millimeters.
Right now all I know is that my center bearing's rubber seemed to be sagged down causing the driveshaft not to be totally centered inside it. However the bearings inside it actually seemed fine... but I believe this is what was making the noise nonetheless. I cannot remember if this was a brand new SC center bearing when I did my R154 install or if I had the original one swapped over.
At any rate I'll get the new locking nut and washers for the front driveshaft and make a decision on whether or not to throw it all back into the car or if I want to see about getting that part dropped off and shortened. That shop is still open for business. I'd just need to be as careful as I can be. Decisions.
I think if you're thorough with gloves, a mask, and conscious of what surfaces you do or don't touch then there isn't too much harm in going to some of those places. I've been so stir crazy that I've been to Home Depot, the car wash, etc, but have worn gloves for each visit and not sat/leaned on anything whatsoever. I throw the gloves away before I can touch anything else with them and make sure I'm very mindful of what I've touched and how I remove the gloves. I just can't manage to lock myself in my house until this is over or I think I'd have a meltdown lol. I understand your feelings and of course, feel as though you should only do what makes you feel comfortable!
Good news on the driveshaft! I suppose that no matter what, we just all have to be a little patient and let things run their course. I have to tell myself that car projects and other things of the like can wait. It doesn't mean I'm lazy or unmotivated, I'm just restricted by the conditions of the environment around me currently.
04-02-20, 03:18 AM
