Problems with my new vacuum brakes

R

Roboplex

Registered User
I got my brakes converted over to vacuum a few months ago, but I've run into a few issues.

Firstly, the brakes seem less assistive than even the aging ABS system. I feel like if someone on the highway slammed on the brakes I'd definitely rear end them. Regular slowing down and stopping is fine, but if I slam on the brakes I don't get as much power as I used to, or as I need.

Second, the car has been stalling ever since I had the brakes converted. I replaced the MAF and fuel filter, and while the new MAF sensor helped tons, it still stalls occasionally. I think it's something to do with vacuum, since when it starts to stall it's usually at a long stoplight where I'm on the brakes constantly. When this happens, the vacuum on the boost gauge drops below 12. It helps if I put the car in neutral when at a stoplight. The gas mileage has also started to fall (vacuum maybe), before the convert it was getting 19, now it's getting 14.

Third, but unrelated, I noticed my transmission fluid getting dirty, it still looks sorta red but dark. I don't have a record of it being changed, although the previous owner said a lot of the work was done by their neighbor in their yard. The car has 85k on it, and would it hurt the tranny if I replaced the fluid (just drain the pan) at this point? It's the AOD.

Sorry about the long post, but I really love your help! Thanks
 
Good evening


On the subject of ATF change I would:

- Drain the torque converter.

- Change the transmission filter.

- Add transmission pan magnet(s)

- Add a additional external filter kit such as @MAGNEFINE.

- Add some Red LUBE GARD.



Good Luck.
 
Roboplex said:
When this happens, the vacuum on the boost gauge drops below 12. It helps if I put the car in neutral when at a stoplight. The gas mileage has also started to fall (vacuum maybe), before the convert it was getting 19, now it's getting 14.
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I would suggest that your problem lies within this statement quoted above. sounds like you have a significant vacuum leak and it may be the booster. this would also explain the stalling.
 
dthompson said:
I would suggest that your problem lies within this statement quoted above. sounds like you have a significant vacuum leak and it may be the booster. this would also explain the stalling.
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Yep I'm gonna have to bring it back to the mechanic then. The booster itself definitely has a patina on it, looks like he might've got it from a junkyard or something. That's not a problem necessarily, it might just be leaky. He also mentioned that the proportioning valve he needed for the job came from a junkyard (as that's the only place he could find it) and that it leaked at first, but he had to epoxy it up. Maybe the epoxy failed. I dunno. Could this also explain my drop in gas mileage?

I opened up the hood and definitely heard a hissing sound (not loud but noticeable), so I guess that confirms the leak.
 
Dragging brakes will kill fuel mileage.

Were the brake lines to the calipers replaced?

System might be ok otherwise, and one or more of the lines is swollen inside, restricting the caliper's ability to release, and/or ballooning when the brakes are applied, making them feel spongy, etc. Might be a mis-matched proportioning valve, wrong length push rod into the master cylinder, carpet in the way of pedal travel or just a bad booster.
 
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So I did a test yesterday. I unplugged the new MAF sensor I put in a few months ago, and drove it for a little while. It was a lot better. The idle was extremely smooth, but after a short time the car realized the MAF was gone and it wouldn't hold idle at all. But it made me think maybe my new MAF sensor is either the incorrect one, or it's defective. It was working perfectly for a few weeks, but then started stalling again. Also, not sure if this is any good evidence of anything, but I unplugged the vacuum line to the brake booster and then started the car. Nothing changed. Nothing seemed different, apart from the brakes not working. Maybe that's a sign that the booster is bad? Hell I don't know. As soon as I have some free time where I don't NEED the car, I'm bringing it back to my mechanic.

Just a side note, could it be that the car's computer just isn't calculating for the extra need in vacuum from the booster? Like it's programmed a specific way and it just won't work with the extra vacuum need? I know it's a shot in the dark, but I thought I'd mention it.

Thanks,
Joseph
 
Sounds like a problem with the brake booster....leaking vacuum. Also suggest checking vacuum hose going to booster to make sure there aren't any cracks or leaks in the hose.

David
 
ThunderRoad said:
USE A WATER SPRAY AROUND BOOSTER SEE IF IT CAUSES IDLE CHANGE:eek:
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That's a good idea! I'm gonna try that tomorrow morning. The only thing is the idle isn't really off, it just stalls all of a sudden while sitting. Like it usually hovers around 600-700rpm, and while the car does idle a bit rough compared to when the MAF is unplugged, it isn't too high or low necessarily. But sitting at a stoplight for more than a minute or two and it starts to cough and stalls.
 
FYI: If the booster has an unmetered air leak, it's likely at the pedal/interior side or at the diaphragm, not at the master cylinder/engine bay side. With your head under the dash and the engine running, do you hear an air leak? How about with the pedal depressed?
 
sam jones said:
Good evening


On the subject of ATF change I would:

- Drain the torque converter.

- Change the transmission filter.

- Add transmission pan magnet(s)

- Add a additional external filter kit such as @MAGNEFINE.

- Add some Red LUBE GARD.



Good Luck.
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I'm a bit uneasy about draining the torque converter, since I have no record of the fluid ever being changed, and it has 85k on the clock. I'm thinking of just doing a pan drain/filter change for now. Do you think that would hurt the tranny? It shudders a little but at around 30mph, and I'm not sure if that's the tranny or something else. The fluid looks pretty brown, but it still has a red tint to it. I'm just worried I'll ruin the transmission if I do this. Thoughts?

I was planning on using Valvoline Maxlife Dex/Merc, or Castrol Dex/Merc. Are those the correct fluids?
 
Roboplex said:
I'm just worried I'll ruin the transmission if I do this. Thoughts?
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Some owners report that a significant fluid change on high mileage auto trans has resulted in an otherwise decently performing trans to give up the ghost. The logic in play is that new fluid is very much like a solvent, and in some case result in contaminated valves/pistons, etc.

I'd only change what's in the pan for a filter change, if at all. Otherwise, leave it alone, add new fluid as needed, confirm the TV cable is set right and go about my business until it begs for a rebuild.
 
KMT said:
Some owners report that a significant fluid change on high mileage auto trans has resulted in an otherwise decently performing trans to give up the ghost. The logic in play is that new fluid is very much like a solvent, and in some case result in contaminated valves/pistons, etc.

I'd only change what's in the pan for a filter change, if at all. Otherwise, leave it alone, add new fluid as needed, confirm the TV cable is set right and go about my business until it begs for a rebuild.
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Yeah there's no way I'd do more than drain the pan. I was thinking about diluting the new fluid with a little bit of the old fluid when adding it, seeing how it goes and then doing it again in a few thousand miles if it's good. But would choice of fluid make things worse? I know Maxlife is synthetic, but would this effect the tranny in the same way synthetic oil would cause an old engine to act funny? Would I be better off with plain Jane Dino tranny fluid? I know someone earlier in the post suggested Red lubeguard. Would that hurt or help the situation?

I don't want to just say it's a lost cause and not change it, because I know 85k might not be the end of the world, and I don't want it to get beyond repair. I just want to make the change as easy on the transmission as possible.

Again, thanks for the help!
 
Roboplex said:
I was thinking about diluting the new fluid with a little bit of the old fluid when adding it, seeing how it goes and then doing it again in a few thousand miles if it's good. But would choice of fluid make things worse? I know Maxlife is synthetic, but would this effect the tranny in the same way synthetic oil would cause an old engine to act funny? Would I be better off with plain Jane Dino tranny fluid? I know someone earlier in the post suggested Red lubeguard. Would that hurt or help the situation?
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I think in your example, and since I'm not familiar with the others you mention, I'd just stick w/factory spec known brand auto trans fluid. I think spending on synth (which I normally) use in my motor, isn't going to gain you anything in this case. I do like the recommendation for 10 oz of Lubegard, tho.

Good luck.
 
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KMT said:
I think in your example, and since I'm not familiar with the others you mention, I'd just stick w/factory spec known brand auto trans fluid. I think spending on synth (which I normally) use in my motor, isn't going to gain you anything in this case. I do like the recommendation for 10 oz of Lubegard, tho.

Good luck.
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Yep I just bought my fluid. Went for Valvoline (regular) Dex/Merc. None of the stores in my area sell Red Lubeguard though. Is there something else that might work just as well?
 
Roboplex said:
Yep I just bought my fluid. Went for Valvoline (regular) Dex/Merc. None of the stores in my area sell Red Lubeguard though. Is there something else that might work just as well?
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Good evening


Try TRANSTAR industries.inc. 4290 Seaboard Road
Orlando, Florida 32808
(407) 299-4400
(800) 274-5226
Fax (407) 290-6909


They supply automatic transmission parts and fluids including LUBE GARD products at whole sale prices.


Good Luck.
 
sam jones said:
Good evening


Try TRANSTAR industries.inc. 4290 Seaboard Road
Orlando, Florida 32808
(407) 299-4400
(800) 274-5226
Fax (407) 290-6909


They supply automatic transmission parts and fluids including LUBE GARD products at whole sale prices.


Good Luck.
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Just kidding, sorry xD. Didn't even occur to me that O'Reilly's had it. I'm about to do the change right now. Pray that it goes well, and that I don't get too bad of a Mercon bath xD.

Thanks so much!
 
Roboplex said:
Just kidding, sorry xD. Didn't even occur to me that O'Reilly's had it. I'm about to do the change right now. Pray that it goes well, and that I don't get too bad of a Mercon bath xD.

Thanks so much!
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Well I think it worked. Although it was a hell of a mess. I tried the "tilt the pan so it drains before removing" method, but it wouldn't come out so I just took it off, and it spilt all over me and my garage xD. I'm gonna smell like mercon for months xD. But I think it was worth it. It isn't banging into 4th anymore! The worrying part is the little plastic stopper thing was still in the pan from the factory, so that might've been the original, 26 year old fluid. Yikes.
 
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